Frontally polymerizable prepreg and method and apparatus for producing fiber-reinforced polymer composite tubes

Abstract

A stable, frontally polymerizable prepreg includes a fiber preform comprising an arrangement of fibers, a frontally polymerizable resin impregnated into and coated onto the fiber preform, and encapsulated catalyst particles embedded within the frontally polymerizable resin, where the resin is in a solid phase at or below room temperature. A method of making the prepreg includes providing a fiber preform comprising an arrangement of fibers and dispersing encapsulated catalyst particles within the arrangement. The fiber preform is infiltrated and coated with a frontally polymerizable resin at a predetermined temperature where the resin is in a liquid phase. After infiltration, the fiber preform is cooled to solidify the resin, thereby forming a prepreg comprising the fiber preform, the frontally polymerizable resin in a solid phase, and encapsulated catalyst particles embedded in the frontally polymerizable resin. An apparatus and a method for making a fiber-reinforced polymer composite tube are also described.

Description

PATENT Atty. Dkt. No. 510322.5000636FRONTALLY POLYMERIZABLE PREPREG AND METHOD AND APPARATUS FOR PRODUCING FIBER-REINFORCED POLYMER COMPOSITE TUBESRELATED APPLICATION

[0001] The present patent document claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 63 / 748,556, filed on January 23, 2025, and hereby incorporated by reference in its entirety.FEDERALLY FUNDED RESEARCH AND DEVELOPMENT

[0002] This invention was made with government support under HR001122C0057 awarded by the Department of Defense. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates generally to composite materials and more particularly to a stable, frontally polymerizable prepreg and a method and apparatus for producing fiber-reinforced polymer composite tubes in terrestrial and space environments.BACKGROUND

[0004] During the past decade, access to space has become more routine for both government and commercial interests. But even with regular launches, modem rockets impose mass and volume limits on the payloads they deliver to orbit. This size constraint hinders developing and deploying large-scale, dynamic space systems. Accordingly, there is interest in developing new methods for adaptive, off-earth manufacturing, such as outside the International Space Station, to produce large space and lunar structures.

[0005] Frontal ring-opening metathesis polymerization (“FROMP” or “frontal polymerization”) catalyzed by ruthenium complexes, for example, has emerged as a promising catalytic platform for producing polymeric components. In FROMP, an initial stimulus initiates a polymerization event in a liquid-phase monomer resin. The heat released from the catalytic ring opening of typically highly strained cyclic olefin monomers triggers subsequent catalytic events ahead of the reaction zone. The net process, therefore, involves a reaction zone thatPATENT Atty. Dkt. No. 510322.5000636 traverses through the monomer resin with a measurable velocity and a well-defined monomer-to-polymer interface. Despite its promise for polymer manufacturing, frontal polymerization faces hurdles to implementation in space due to the use of a liquid-phase resin as a precursor material.SUMMARY

[0006] A prepreg comprises a fiber preform including an arrangement of fibers; a frontally polymerizable resin impregnated into and coated onto the fiber preform; and encapsulated catalyst particles embedded within the frontally polymerizable resin, wherein the frontally polymerizable resin is in a solid phase at or below room temperature (20°C).

[0007] A method of making a prepreg comprises: providing a fiber preform comprising an arrangement of fibers; dispersing encapsulated catalyst particles within the arrangement of fibers; coating and infiltrating the fiber preform with a frontally polymerizable resin at a predetermined temperature where the frontally polymerizable resin is in a liquid phase, and after infiltration, cooling the fiber preform to solidify the frontally polymerizable resin, thereby forming a prepreg comprising the fiber preform, the encapsulated catalyst particles and the frontally polymerizable resin in a solid phase.

[0008] A method of making a fiber-reinforced polymer composite tube comprises: drawing a prepreg sleeve into a reactive pultrusion apparatus, the prepreg sleeve including: a fiber sleeve comprising an arrangement of fibers; a frontally polymerizable resin impregnated into and coated onto the fiber sleeve; heating a longitudinal section of the prepreg sleeve to a temperature sufficient to transform the frontally polymerizable resin to a liquid phase and initiate a frontal polymerization reaction at a surface of the prepreg sleeve within the longitudinal section, whereby the frontal polymerizable resin is converted to a polymer and a cured tube section is formed; repeating the heating on consecutive longitudinal sections of the prepreg sleeve to form consecutive cured tube sections; and conveying the consecutive cured tube sections out of the reactive pultrusion apparatus, thereby forming a fiber-reinforced polymer composite tube

[0009] A reactive pultrusion apparatus for making a fiber-reinforced polymer composite tube includes: a roller for storing a length of prepreg sleeve in a collapsed configuration; a mandrel for receiving an open end of the prepreg sleeve, the mandrel being sized to define an inner diameter of the prepreg sleeve; a device for translating the prepreg sleeve in a downstreamPATENT Atty. Dkt. No. 510322.5000636 direction away from the roller and over the mandrel, the mandrel being configured to remain stationary as the prepreg sleeve moves over the mandrel; a curing oven downstream of the mandrel for heating consecutive longitudinal sections of the prepreg sleeve; and a conveyor mechanism downstream of the curing oven to convey cured tube sections out of the apparatus.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The embodiments may be better understood with reference to the following drawing(s) and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views.

[0011] FIG. 1 shows a longitudinal cross-sectional view of a portion of a stable prepreg undergoing frontal polymerization during reactive pultrusion to form a fiber-reinforced polymer composite tube, where the motion of the prepreg and a longitudinal direction of the tube coincide with the arrow, and the polymerization front moves in a radial direction through the thickness of the prepreg.

[0012] FIG. 2 shows a transverse cross-sectional schematic of an exemplary fiber-reinforced polymer composite tube.

[0013] FIG. 3 is a flow chart showing steps in a method to produce a stable, frontally polymerizable prepreg.

[0014] FIG. 4 is a flow chart showing steps in a method to form a fiber-reinforced polymer composite tube by reactive pultrusion.

[0015] FIGS. 5A-5E illustrate assembly and vacuum sealing of a prepreg sleeve within impermeable films, where FIGS. 5D and 5E are cross-sectional views of the regions indicated in FIG. 5C.

[0016] FIGS. 6A-6E illustrate assembly and vacuum sealing of a prepreg sleeve within impermeable films that further enclose a puncture control layer, where FIG. 6E is a cross-sectional view of the region indicated in FIG. 6D.

[0017] FIGS. 7A-7D show schematics conceptually illustrating a method to form a fiber-reinforced polymer composite tube.

[0018] FIGS. 8 A and 8B show an exemplary implementation for a curing over that can be open and closed, where FIG. 8B provides an exploded view.

[0019] FIGS. 9 A and 9B show an exemplary implementation of a reactive pultrusionPATENT Atty. Dkt. No. 510322.5000636 apparatus for fabrication of a fiber-reinforced polymer composite tube.

[0020] FIGS. 10A and 10B show an exploded view and a perspective view, respectively, of part of an exemplary pultrusion apparatus, and FIG. 10C shows a transverse cross-section at the location of the curing oven (or heated mold).

[0021] FIG. 10D shows a longitudinal cross-sectional view of a prepreg sleeve moving over a mandrel and into position over a radially-expandable collet adjacent to a curing oven for frontal polymerization.

[0022] FIG. 10E shows a partial cross-sectional view of a mechanical collet design that may be used to support the prepreg sleeve during heating / curing.

[0023] FIG. 11 shows a prior art pultrusion process.

[0024] FIGS. 12A and 12B show how a kinematically constrained arrangement of opposing internal and external rollers may be employed to stabilize the mandrel during translation of the prepreg sleeve.

[0025] FIGS. 13A-13C show alternative embodiments of a kinematically constrained mandrel support for keeping the mandrel stationary during reactive pultrusion.

[0026] FIG. 14 shows an exemplary housing for the reactive pultrusion apparatus.

[0027] FIG. 15 is a scanning electron microscope (SEM) image of carbon fibers functionalized with encapsulated catalyst particles after dip coating.

[0028] FIG. 16 illustrates an exemplary set-up for prepreg fabrication.

[0029] FIG. 17 shows the effect of the dip-coating solution concentration on the ply mass increase for encapsulated catalyst particles with varying amounts of the catalyst.

[0030] FIG. 18 shows the effect of the dip-coating solution concentration on the molar ratio (ppm) of the catalyst to the DCPD resin in the resulting prepreg. Note, the G2:DCPD ratio for 4.2 wt.% G2 in poly sulfone is not plotted in FIG. 18.DETAILED DESCRIPTION

[0031] Described in this disclosure is a stable, frontally polymerizable prepreg and a method of making the prepreg. Also described is a method of making a fiber-reinforced polymer composite that may utilize the prepreg, as well as an apparatus for making fiber-reinforced polymer composites. These technologies are designed for manufacturing large components in space, for example, on-orbit outside the International Space Station (ISS) but may also have application for on-earth manufacturing.PATENT Atty. Dkt. No. 510322.5000636

[0032] Referring to FIG. 1, the stable prepreg 100 includes a fiber preform 102 comprising an arrangement of fibers 104, a frontally polymerizable resin 108 impregnated into and coated onto the fiber preform 102, and encapsulated catalyst particles 106 embedded within the resin 108. The frontally polymerizable resin may comprise a cyclic olefin monomer, such as a dicyclopentadiene (DCPD) resin, a tricyclopentadiene resin, or another frontally polymerizable monomer, such as a frontally polymerizable epoxy resin. In this disclosure, the description and figures focus on the DCPD resin, but it is understood that the term “DCPD resin” may be replaced with “frontally polymerizable resin” in some or all instances to refer to alternative resins.

[0033] The DCPD resin is a solid phase at or below room temperature (20°C). Solid DCPD, which may have the consistency of wax, is beneficial for forming a stable prepreg that can be transported to and used in a space environment. In traditional prepregs, the resin formulation is partially cured or gelled to ensure retention in the fiber preform. The solid-phase DCPD resin 108 utilized in this disclosure is uncured but stable against spontaneous polymerization and able to be retained in the fiber preform during storage and transport, prior to use. It is noted that, in this disclosure, the DCPD resin 108 may alternatively be referred to as a DCPD monomer or simply as DCPD.

[0034] The inventors have developed a method and apparatus to fabricate a fiber-reinforced polymer composite 200 from the stable prepreg 100 at a desired time via frontal polymerization (FP), as illustrated in FIG. 1 and described below. In traditional frontal polymerization, in contrast to the present method, a liquid-phase resin is employed as a precursor material. The stable prepreg 100 comprising the solid-phase DCPD resin 108 may have the form of a prepreg sleeve 510, and the resulting fiber-reinforced polymer composite 200 may have the form of a hollow tube 220, as illustrated in the transverse cross-section of FIG. 2. Alternatively, the stable prepreg may have another shape and size determined by the intended application, as discussed below.

[0035] The solid-phase DCPD resin 108 may consist essentially of the endo-dicyclopentadiene isomer. That is, the DCPD resin 108 may contain at least about 99% endo-dicyclopentadiene and up to 100% tw / -dicyclopentadiene. Lower purity DCPD may contain the exo-dicyclopentadiene isomer or cyclopentadiene, the precursor material, both of which are in the liquid phase at room temperature. The stable prepreg 100 is preferably devoid of any monomers other than the cw / -DCPD monomer 108. For example, ethylidene norbomenePATENT Atty. Dkt. No. 510322.5000636 (ENB), which is a monomer typically added to DCPD in small amounts to ensure that the DCPD is in the liquid phase at room temperature, is absent from the stable prepreg 100. The DCPD resin 108 can remain stable in the solid phase for long time durations, such as six months or more. Notably, the stability of the prepreg 100 may be achieved without use of a polymerization inhibitor. Furthermore, it is not necessary to keep the prepreg 100 at low temperatures, such as in a freezer, to avoid premature polymerization. The long-term stability of the prepreg 100 is particularly beneficial for space applications, since the time duration between preparation of the prepreg and its use in space may be several months, given the current cadence of payload launches to the ISS.

[0036] Typically, the fibers 104 comprise carbon fibers, which are strong and lightweight, although the technology is not limited to carbon fibers. The arrangement of fibers 104 may be, for example, a woven, braided or unidirectional arrangement of tows 110. Individual tows 110 may include from 1,000 to 50,000 fibers 104, and each fiber 104 may have a microscale diameter in a range from 2 pm to 20 pm, typically. For some applications, such as when the prepreg 100 is employed to form a composite tube as shown in FIGS. 1 and 2, the fiber preform 102 may take the form of a fiber sleeve, and thus the prepreg 100 may be referred to as a prepreg sleeve. In such an example, the fibers may be oriented in a longitudinal, transverse, or oblique (helical) direction with respect to an axis of the hollow composite tube to control the mechanical stiffness and strength.

[0037] The encapsulated catalyst particles 106 may comprise a ruthenium-based catalyst with an overlying polymer coating, such as a polysulfone coating or another thermoplastic polymer coating. The polymer coating is designed to inhibit or prevent polymerization by separating the DCPD monomer from the ruthenium-based catalyst, which may be a Grubb’s catalyst, e.g., a second-generation Grubb’s catalyst (G2). The encapsulated catalyst particles 106 typically have a nominal linear size (width or diameter) in a range from 0.5 micron to 5 microns. The polymer coating may take the form of an assembly of polysulfone particles that encapsulate the ruthenium-based catalyst. The encapsulated catalyst particles 106 typically contain the ruthenium-based catalyst in an amount from 2 wt.% to 8 wt.%. A molar ratio of the the frontally polymerizable resin to the ruthenium-based catalyst may be in a range from 1000:1 to 15000:1.

[0038] A method of making the stable prepreg 100 is now described in reference to the flow chart of FIG. 3. The method entails providing 302 a fiber preform comprising anPATENT Atty. Dkt. No. 510322.5000636 arrangement of fibers, such as a unidirectional, braided or woven arrangement. The fiber preform may be obtained from commercial suppliers; for example, fiber sleeves constructed from carbon fibers may be commercially available from Fibre Glast Developments Corp, of Brookville, OH, or Rock West Composites of San Diego, CA, among other companies. Alternatively, the fiber preform 102 may be prepared using fiber assembly and / or weaving methods known in the art.

[0039] The method of making the stable prepreg 100 further includes dispersing 304 encapsulated catalyst particles within the arrangement of fibers. In one implementation, this may entail immersing (or dipping) the fiber preform in a suspension containing the encapsulated catalyst particles and a liquid such as water, and then removing the fiber preform once the suspension has penetrated interstices of the fiber preform. This approach may be referred to as dip coating. After removal of the preform from the suspension, the liquid can evaporate from the fibers while the encapsulated catalyst particles remain attached to the fibers by a mechanism such as van der Waals forces. After this process, the fibers or fiber preform may be described as being functionalized with the encapsulated catalyst particles.

[0040] The method further includes coating and infiltrating 306 the fiber preform with a frontally polymerizable resin, which may be a DCPD resin, for example, at a temperature at which the resin is in liquid form. More specifically, the temperature is selected to be at or above a melting temperature of the frontally polymerizable resin, so that the resin can readily flow for infiltration, and below an activation or onset temperature of the frontally polymerizable resin, to avoid prematurely initiating frontal polymerization. The melting temperature of DCPD resin is about 33°C (e.g., 32-34°C) for cw / -DCPD. As described above, the DCPD resin may be highly pure, consisting essentially of the enr / -dicyclopentadiene isomer (e.g., at least about 99% endo-dicyclopentadiene). At or above the onset temperature, which may be in range from 60°C to 100°C, frontal polymerization may be initiated. Additionally, at temperatures sufficient to induce polymerization, the encapsulated catalyst particles are believed to swell or otherwise lose integrity such that the catalyst is released or otherwise comes into direct contact with the frontally polymerizable resin. Accordingly, coating and infiltration of the stable prepreg may take place at a temperature in a range from 33°C to less than 60°C, such as 35°C to 50°C.

[0041] The encapsulated catalyst particles may be dispersed in the fiber preform prior to coating and infiltration with the DCPD, as described above (e.g., via dip coating) or during DCPD infiltration. In the latter implementation, the encapsulated catalyst particles may bePATENT Atty. Dkt. No. 510322.5000636 mixed with the DCPD resin while the DCPD resin is in the liquid phase to form a mixture, and the mixture may be coated onto and infiltrated into the preform. Thus, the dispersing and coating / infiltrating steps 304 and 306 illustrated in the flow chart of FIG. 3 may in some implementations occur at the same time. More specifically, the encapsulated catalyst particles may be dispersed among and coated onto the fibers as the mixture penetrates interstices of the fiber preform.

[0042] After infiltration, the fiber preform is cooled 308 to solidify the DCPD resin. Since the DCPD is solid at or below room temperature, the cooling may comprise active or passive cooling to room temperature, or lower if desired. Thus, a prepreg 100 including a fiber preform 102 impregnated with a solid-phase DCPD resin 108 and including encapsulated catalyst particles 106 is formed, as illustrated in FIG. 1. The prepreg 100 may optionally be cut to a size and shape suitable for the intended application. Prior to use, the prepreg 100 may be encapsulated within impermeable film layers or stored in a sealed impermeable bag or package, e.g., a nylon bagging film, to prevent evaporation of the DCPD and / or to reduce background reactions. The prepreg encapsulating films or bag may be compliant and space capable e.g., low outgassing). Also or alternatively, the prepreg encapsulating films or bag may facilitate infusion, enable compact stowage and prepreg freezing, contain both liquid and gas from resin, extend storage life, enable pressurization, allow thermal transport, and / or achieve high burst strength when allowed to expand to burst. One example is a multilayer bagging film such as a Dahlar® release film, which includes ethylene tetrafluoroethylene (ETFE) (space capable) on one side and nylon (good for thermal sealing) on the other. Other polymers that are impermeable to DCPD up to temperatures of about 200°C with sufficient elongation, such as polyether ether ketone (PEEK), may be employed for the bagging films

[0043] For example, referring to FIGS. 5A to 5C, a prepreg sleeve 510 may be assembled between outer and inner impermeable films 520, 530 where the outer impermeable film 520 may be, for example, an outer multilayer film (e.g., a Dahlar® film) including a nylon layer facing an outer surface of the prepreg sleeve 510, and the inner impermeable film 530 may be an inner multilayer (e.g., Dahlar®) film including a nylon layer facing an inner surface of the prepreg sleeve 510, forming the assembly 540 shown in FIG. 5B. Lengths of the films 520,530 extending beyond the prepreg sleeve 510 may be sealed together to encapsulate the prepreg sleeve 510, forming a vacuum sealed assembly 550, where the seals 560 are illustrated in FIG.5C. The sealing may entail vacuum sealing using suction to remove air from the assembly priorPATENT Atty. Dkt. No. 510322.5000636 to heating to seal the films together. FIGS. 5D and 5E show cross-sectional schematics of the vacuum sealed assembly 550. In some examples, it may be advantageous to incorporate one or more puncture control layers into the assembly. For example, referring to FIGS. 6A and 6B, a first puncture control layer 610 may be assembled between two outer impermeable films 520a, 520b, forming a first assembly 630, and a second puncture control layer 620 may be assembled between two inner impermeable films 530a, 530b, forming a second assembly 640 (FIG. 6C). The outer and inner films 520a, 520b, 530a, 530b may then be sealed (e.g., vacuum sealed) to provide two levels of containment for the prepreg sleeve 510, as shown in FIG. 6D, and form a final sealed assembly 650. A cross-sectional view of the prepreg sleeve within the final sealed assembly 650 is illustrated in FIG. 6E. Materials suitable for use as the puncture control layer are sufficiently mechanically tough to provide puncture resistance up to a temperature of about 200°C, such as, for example, a woven or knitted textile comprising aramid fibers (e.g., poly-para-phenylene terephthalamide (PPTA) or Kevlar®).

[0044] The thermally stable prepreg may be used to fabricate a fiber-reinforced polymer composite of any size or shape via new or existing earth-based or space-based manufacturing methods. One targeted use of the prepregs is for the on-orbit construction of longerons, which are large structural components of spacecraft or aircraft. For this application and / or to produce other tubular composite parts, such as structural members for bicycles, e-bikes, and e-scooters, a reactive pultrusion apparatus and process have been developed that may utilize the stable prepregs described above in the form of prepreg sleeves. In other examples, the stable prepregs may have the form of plies that can be laid up onto a substrate or mold to prepare a fiber-reinforced polymer composite having a complex shape and / or large size. After lay-up of the prepregs, frontal polymerization may be initiated to induce curing to form the composite.

[0045] Referring now to the flow chart of FIG. 4 and the schematics of FIGS. 7A-7D, a method of making a fiber-reinforced polymer composite tube is described. The method may include drawing 402 a prepreg sleeve 710 into a reactive pultrusion apparatus, which is shown according to one embodiment in FIGS. 9A and 9B, and conceptually in FIGS. 7A-7D. The prepreg sleeve 710 comprises a fiber sleeve comprising an arrangement of fibers and a dicyclopentadiene (DCPD) resin impregnated into and coated onto the fiber sleeve. The prepreg sleeve 710 may have a length at least as long as a length of the desired fiber-reinforced composite tube. The prepreg sleeve 710 may be formed by rolling up a flat prepreg, or the prepreg sleeve 710 may take the form of a continuous, seamless sleeve. A longitudinal sectionPATENT Atty. Dkt. No. 510322.5000636 of the prepreg sleeve 710 is then heated 404 (e.g., by a retractable heating element or curing oven 720) to a temperature sufficient to transform the DCPD resin to a liquid phase and initiate a frontal polymerization reaction within the longitudinal section, as illustrated in FIG. 7A. During heating, an outward radial pressure may be applied to an inner surface of the prepreg sleeve 710 at the location of the longitudinal section, which may be referred to as the curing zone 740. The longitudinal section undergoing curing may be thermally isolated from upstream portions of the prepreg sleeve 710, e.g., by cooling element(s) 730, as discussed below. Consequently, the DCPD resin is converted to polydicyclopentadiene (pDCPD) and a cured tube section 750 is formed within the curing zone 740.

[0046] In some examples, the prepreg sleeve 710 is a stable prepreg sleeve as described above, where the prepreg sleeve further comprises encapsulated catalyst particles embedded in the DCPD resin, and the DCPD resin is in a solid phase at or below room temperature (20°C). Upon heating the longitudinal section of the prepreg sleeve, the catalyst contained within the encapsulated catalyst particles is released or otherwise brought into direct contact with the DCPD resin. In other examples, the prepreg sleeve 710 may further include ethylidene norbornene (ENB) dispersed in the DCPD resin and the DCPD resin may thus be in a liquid phase at room temperature (20°C), such that freezing is beneficial or necessary prior to pultrusion. Accordingly, in such examples, prior to drawing the prepreg sleeve into the reactive pultrusion apparatus, the DCPD resin containing the ENB (e.g., up to 5 wt.%) may be maintained at a reduced temperature sufficient to keep the DCPD resin in a solid phase (e.g., 0°C or below). Prior to use, the frozen prepreg sleeve may be contained in a sealed impermeable bagging material to improve stability.

[0047] Returning to the flow chart of FIG. 4, the heating is repeated 406 on consecutive longitudinal sections of the prepreg sleeve to form consecutive cured tube sections, where the first longitudinal section to undergo polymerization is typically a downstream end of the prepreg sleeve. After the heating is carried out as illustrated in FIG. 7 A, the curing oven 720 may be retracted or opened, as shown in FIG. 7B, to allow for translation of the cured tube section 750 in a downstream direction (FIG. 7C) and for conveyance of a second longitudinal section of the prepreg sleeve 710 into the curing zone 740, such that another heating step 406 may take place (FIG. 7D), aided by closing of the curing oven 720. An exemplary implementation for opening and closing the curing oven 720 that includes a motor and worm gear mechanism to actuate motion of the oven 720 is illustrated in FIGS. 8 A and 8B (explodedPATENT Atty. Dkt. No. 510322.5000636 view). The consecutive cured tube sections are conveyed 408 out of the reactive pultrusion apparatus, such that a fiber-reinforced polymer composite tube is formed. The composite tube may have any desired length (e.g, up to hundreds of meters), and the (inner) diameter of the composite tube may be determined by the mandrel and collet employed for fabrication. Advantageously, the fiber-reinforced pDCPD composite tube produced by frontal polymerization has mechanical properties comparable to commercially available fiber-reinforced epoxy composite tubes.

[0048] The frontal polymerization reaction may be triggered at an outer surface of the prepreg sleeve, such that a polymerization front travels from the outer surface through the thickness of the prepreg sleeve to the inner surface, as illustrated in FIG. 1. Accordingly, the polymerization front may move in a radial direction. In other examples, the polymerization or curing front may move in a longitudinal direction with respect to the axis of the prepreg sleeve. A longitudinal curing front may take the form of a flat plane or a curved surface oriented normal to the axis of the sleeve / tube and propagating longitudinally along the length of the sleeve. A through-thickness or radial curing front may take the form of a thin cylindrical (curved) plane propagating either outwards from the inner surface to the outer surface of the sleeve / tube, or inwards from the outer surface to the inner surface of the sleeve / tube, as in the example here. As described below, the longitudinal section of the prepreg sleeve may be positioned within a curing oven for heating. In some examples, the heating may be carried out by rotatable heating elements in rolling contact with the prepreg sleeve. Preferably, the polymerization front travels only within the longitudinal section to avoid premature polymerization of upstream portions of the prepreg sleeve. The reactive pultrusion apparatus described below may be configured to contain the polymerization front to within the longitudinal section.

[0049] The reactive pultrusion apparatus is illustrated according to one embodiment in FIGS. 9 A and 9B. Set-up and operation of the apparatus are engineered to be simple and rapid, which may be especially advantageous for space manufacturing.

[0050] The apparatus 900 may include a roller or other material storage system 910 as shown in FIG. 9A for storing a length of prepreg sleeve 710 in a collapsed configuration, and a mandrel 1010 (visible in FIG. 10A) for receiving an open end of the prepreg sleeve 710. The mandrel 1010 is sized to accommodate the open end and define an inner diameter of the prepreg sleeve 710. As shown in FIG. 9A, a lock mechanism 920 may be positioned between the roller 910 and the mandrel 1010 for holding the open end of the prepreg 710 in place on the mandrelPATENT Atty. Dkt. No. 510322.5000636 1010 prior to use of the apparatus 900. The lock mechanism 900 may be raised to an unlocked position so that the reactive pultrusion process may commence. In some examples, the apparatus 900 may include a gripper for drawing the prepreg sleeve 710 axially downstream away from the roller 900 and over the mandrel 1010. The apparatus 900 may include a kinematically constrained mandrel support 930 configured to allow the mandrel 1010 to remain stationary during translation of the prepreg sleeve, as described below according to various embodiments in reference to FIGS. 12A, 12B and 13A-13C.

[0051] Returning to FIGS. 9A and 9B, the curing oven 720 is positioned downstream of and / or radially adjacent to the mandrel for heating consecutive longitudinal sections of the prepreg sleeve 710 brought into position, e.g., by a gripper or other conveyance device. The heat may be restricted to a single longitudinal section at a time to prevent premature curing of the prepreg sleeve 710. For example, the apparatus 900 may further include a cooling clamp, ring, and / or thermal spacer (cooling element(s)) 730 immediately upstream of the curing oven 720, as shown in FIGS. 9A and 7A, for example. The cooling clamp, ring and / or other cooling element 730 may function as a heat sink to prevent upstream propagation of the curing front initiated during heating of each longitudinal section of the prepreg sleeve 710. Accordingly, the cooling clamp and / or ring may comprise a material exhibiting a high thermal conductivity and a high heat capacity. As shown in FIG. 9A, the curing oven 720 may be designed to partially or fully enclose each longitudinal section of the prepreg sleeve 710 during heating and may be configured to retract away from the sleeve, e.g., in an outward radial direction, as shown in FIG. 9B, as the next longitudinal section is brought into position. A conveyor mechanism (e.g., a roller guide) 940 may be positioned downstream of the curing oven 720 to convey cured tube sections 750 out of the apparatus 900, as illustrated in FIG. 9B. In some examples, the curing oven 720 may comprise rotatable heating elements that are configured to generate heat while in rolling contact with the prepreg sleeve. The rotating heater elements may allow for continuous translation of the prepreg sleeve during heating.

[0052] During curing, the longitudinal section of the prepreg sleeve 710 undergoing heating is also preferably exposed to an applied pressure. More specifically, as illustrated in FIGS. 10A and 10B, a device capable of exerting an outward radial pressure on an inner surface of the prepreg sleeve (such as a mechanical collet or an expandable bladder 1020) may be used to support the consecutive longitudinal sections of the prepreg sleeve 710 during curing. A suitable outward radial pressure may lie in a range from greater than 0 to 20 psi, for example.PATENT Atty. Dkt. No. 510322.5000636 The combination of heat and pressure may be beneficial to achieve the desired tube shape and properties during curing. FIGS. IOC and 10D illustrate radial expansion of a collet 1020 that is axially connected to the mandrel 1010 and positioned downstream of the mandrel 1010 at a location of the curing oven 720 (curing zone 740), where each longitudinal section of the prepreg sleeve 710 undergoes heating. The collet 1020 may be configured to expand radially prior to and / or during heating of each longitudinal section, such that the consecutive longitudinal sections of the prepreg 710 are supported and compacted while in position for curing. The collet 1020 may be expanded mechanically with the expansion driven by a motor; accordingly, gas inflation of the consecutive longitudinal sections of the prepreg sleeve 710 during heating may not be required. In other examples, an expandable (e.g., elastomeric) bladder may be inflated with a fluid (e.g., a gas or liquid) to provide radial support to and promote compaction of each longitudinal section during curing. However, for space applications and given the heating involved in the pultrusion apparatus, gas inflation using a an expandable bladder may not be desirable.

[0053] FIG. 10E illustrates a possible implementation of a mechanical collet 1020 for support of the prepreg sleeve during heating. Only an upper half of the collet 1020 is illustrated in the drawings, which show a retracted (top) and expanded (bottom) position of the collet 1020; the views on the left are longitudinal cross-sections and the views on the right are transverse cross-sections from the sections indicated. The outer surface of the collet 1020, which contacts an inner surface of the prepreg sleeve when the collet 1020 is expanded, may comprise silicone or another compliant material to ensure a uniform pressure distribution over the surface of the prepreg sleeve.

[0054] As indicated above, the mandrel 1010 may be configured to remain stationary during translation of the prepreg sleeve by an axial and radial constraining device 930, as illustrated in FIGS. 12A and 12B and according to various alternative embodiments in FIGS.13A-13C. In some examples, the constraining device 930 may be described as a kinematically constrained arrangement where a minimal number of components are employed to stabilize the mandrel, and the stabilization is done without constraining the mandrel from the upstream side. This innovation is significant, since conventional approaches to constraining the mandrel during pultrusion require access to the mandrel from the feeding side of the pultrusion die (see FIG. 11). Such access is not available in the reactive pultrusion apparatus due to the continuous or step-wise feeding of the prepreg sleeve.PATENT Atty. Dkt. No. 510322.5000636

[0055] The axial and radial constraining device 930 may take the form of a kinematically constrained arrangement of opposing internal and external rollers, as shown for example in FIGS. 12A and 12B. Here, the internal rollers 1220 are rotatably attached to the mandrel 1010 and configured to contact an inner surface of the prepreg sleeve, and the external rollers 1230 are rotatably attached to an external structure 1240 and configured contact an outer surface of the prepreg sleeve. The internal rollers 1220 are spaced apart from the external rollers 1230 by a predetermined gap through which the prepreg sleeve travels. In space, friction between the rollers and the prepreg sleeve may be kept extremely low with an appropriately sized gap, such that the mandrel is effectively floating. Rotation of the rollers 1220, 1230, e.g., driven by a motor in the motor housing 1250, allows for sliding motion of the prepreg sleeve.

[0056] Alternatively, referring to FIG. 13 A, the mandrel may be configured to remain stationary during translation of the prepreg sleeve by an opposing arrangement of low-friction internal and external die parts. The internal die parts are attached to the mandrel and configured to contact an inner surface of the prepreg sleeve, and the external die parts are part of an external die and configured to contact an outer surface of the prepreg sleeve, where the internal die parts are spaced apart from the external die parts by a predetermined gap through which the prepreg sleeve travels. In space, friction between the die parts and the prepreg sleeve may be kept extremely low with an appropriately sized gap, such that the mandrel is effectively floating.

[0057] In another example, the mandrel may be configured to remain stationary during translation of the prepreg sleeve by an opposing arrangement of internal and external magnets, as shown in FIG. 13B, where the external magnets may be fixed on an external frame and the internal magnets may be constrained by the opposing arrangement. The internal magnets are spaced apart from the external magnets by a predetermined gap that is sufficient to allow translation of the sleeve therein, as discussed above. Finally, referring to FIG. 13C, the mandrel may be configured to remain stationary during translation of the prepreg sleeve by a support cable. A pre-installed wire inside the prepreg sleeve may be configured to exert a tension force on the mandrel to keep the mandrel stationary as the prepreg sleeve advances. Extra length accumulated of this tension wire may be collected and stored on an internal roller using a spring-loaded rotary device. External rollers fixed on an external frame may be configured to constrain the motion in the radial direction.

[0058] For delivery and use in space, the reactive pultrusion apparatus may be contained within a housing that may also hold a power supply, electronics and / or monitoring cameras,PATENT Atty. Dkt. No. 510322.5000636 for example, with an opening in the housing for extraction of the composite tube. The opening may be covered by an end cap connected to an expandable coiled structure attached to a mylar film, as shown in FIG. 14, that expands during pultrusion to contain and protect the composite tube. The housing may have a compact size, e.g., less than 20 cm in height, less than 10 cm in width, and less than 30 cm in length.

[0059] Example: Preform Fabrication and Testing

[0060] Dicyclopentadiene (DCPD) was purchased from Cymtech Corporation (Ultrene99, CAS: 77-73-6, >99%). Grubb’s second-generation catalyst (G2) was purchased from Chemscene Corporation (CAS: 246047-72-3, >98%). Polysulfone (PSU) was purchased from Sigma Aldrich Corporation (428302, CAS: 25135-51-7). Poly(ethylene-alt-maleic anhydride) (EMA) was purchased from Aurorium (Zemac E400, CAS: 9006-26-2). Dichloromethane was purchased from Fischer Scientific. All chemicals were used as received without further purification.

[0061] The encapsulated catalyst particles in this example comprise PSU-coated G2 microparticles (PSU-G2) manufactured using an oil-in-water emulsion technique. The oil phase was prepared using dichloromethane (56mL), PSU (5g), and G2 (0.7g). The aqueous phase (200mL) contains the EMA (7.6g) surfactant. After emulsification using a homogenizer, the solvent is removed by evaporation. The microparticle-containing emulsion is centrifuged, and the supernatant is decanted. After two subsequent aqueous washing steps to remove EMA, the encapsulated catalyst particles are freeze-dried to yield a free-flowing light pink powder (~4g, -70% yield). The composition of the encapsulated catalyst particles determined using NMR is typically 4-8 wt.% G2.

[0062] The reinforcing phase or fiber preform of the prepreg produced in this example includes 5 plies of T300 2x2 twill weave carbon fiber fabric from Rockwest Composites (1300D, 3K tow, 204 g / m2). The fabric is cut to size (100 mm x 125 mm) and dried in an oven at 110°C for at least 2 hours to remove residual moisture. The plies are cooled and stored in a desiccator. The plies are functionalized with the PSU-G2 microparticles by dip-coating each ply individually in a suspension of PSU-G2 microparticles in deionized water. FIG. 15 shows a scanning electron microscope (SEM) image of carbon fibers functionalized with encapsulated catalyst particles by dip-coating in water or MeOH suspension (5 wt%). The plies are then oven-dried at 110°C for 2 h-4 h to remove moisture and stored in a desiccator.

[0063] The prepreg is prepared using vacuum-assisted resin transfer molding (VARTM) toPATENT Atty. Dkt. No. 510322.5000636 infuse the functionalized fabric plies with liquid-phase DCPD resin. The Ultrene99 DCPD used in this work is solid at room temperature. This is typical for high purity cw / -DCPD which has a melting point of 32-34°C. Critically, the infusion temperature is greater than the melting point of the monomer (32°C) but lower than the onset temperature of the reaction (~65°C by DSC) or it will spontaneously cure. This limits the monomer selection to compositions that have a window between melting point and onset temperature. For example, tricyclopentadiene transitions directly from melting to polymerization at 65 °C.

[0064] An exemplary set-up for prepreg fabrication is shown in FIG. 16. Heat is applied to the inlet tube and preform using silicone rubber heating blankets and tapes with built-in controllers preprogrammed to maintain 49 °C. The tool plate is thermally conductive to ensure uniform heating of the reinforcement. After infusion, the inlet and outlet lines are clamped, and the heaters are removed to allow the preform to air-cool to ambient temperatures. The prepreg is then cut and stored in a sealed nylon bagging film to prevent evaporation of the DCPD.

[0065] The molar ratio of G2 to DCPD impacts many properties of the resin (e.g., front speed, degree of cure) and is thus an important parameter to control in prepreg manufacturing. The mass gain of the fabric plies during functionalization is found to be linearly proportional to the concentration of the dip coating solution and independent of the composition of the encapsulated catalyst particles (FIG. 17). Consequently, a desired resin formulation may be achieved by precisely selecting the concentration of the dip coating solution based on the composition of the encapsulated catalyst particles with careful control of the infusion process to maintain a consistent infusion of DCPD (FIG. 18). Moreover, drying the plies before and after dip-coating may be critical as the presence of water will obfuscate the ratio of initiator to monomer.

[0066] This disclosure also encompasses the following aspects:

[0067] A first aspect relates to a prepreg comprising: a fiber preform comprising an arrangement of fibers; a frontally polymerizable resin impregnated into and coated onto the fiber preform; and encapsulated catalyst particles embedded within the frontally polymerizable resin, wherein the frontally polymerizable resin is in a solid phase at or below room temperature (20°C).

[0068] A second aspect relates to the prepreg of the first aspect, wherein the frontally polymerizable resin is selected from the group consisting of a dicyclopentadiene (DCPD) resin, a tricyclopentadiene resin, and a frontally polymerizable epoxy resin.PATENT Atty. Dkt. No. 510322.5000636

[0069] A third aspect relates to the prepreg of the first or second aspect, wherein the encapsulated catalyst particles comprise a ruthenium-based catalyst and a polymer coating on the ruthenium-based catalyst.

[0070] A fourth aspect relates to the prepreg of the third aspect, wherein the ruthenium-based catalyst comprises a Grubb's catalyst and the polymer coating comprises a polysulfone coating.

[0071] A fifth aspect relates to the prepreg of the fourth aspect, wherein the polysulfone coating has a form of an assembly of polysulfone particles.

[0072] A sixth aspect relates to the prepreg of any of the first to fifth aspects, wherein a molar ratio of the frontally polymerizable resin to the ruthenium-based catalyst is in a range from 1000:1 to 15000:1.

[0073] A seventh aspect relates to the prepreg of any of the first to sixth aspects, wherein the fibers comprise carbon fibers.

[0074] A eighth aspect relates to the prepreg of any of the first to seventh aspects, wherein the arrangement of fibers comprises a braided, woven or unidirectional arrangement.

[0075] A ninth aspect relates to the prepreg of any of the first to eighth aspects, wherein the fiber preform has a form of a fiber sleeve, and wherein the prepreg has a form of a prepreg sleeve.

[0076] A tenth aspect relates to the prepreg of any of the first to ninth aspects, wherein the frontally polymerizable resin comprises a DCPD resin consisting essentially of an endo-dicyclopentadiene isomer.

[0077] An eleventh aspect relates to the prepreg of any of the first to tenth aspects, wherein the frontally polymerizable resin comprises a DCPD resin containing at least about 99% endo-dicyclopentadiene isomer.

[0078] A twelfth aspect relates to the prepreg of any of the first to eleventh aspects, wherein the prepreg is devoid of any monomers other than the DCPD resin.

[0079] A thirteenth aspect relates to the prepreg of any of the first to twelfth aspects, wherein the prepreg is devoid of a polymerization inhibitor.

[0080] A fourteenth aspect relates to the prepreg of any of the first to thirteenth aspects having a stability against spontaneous frontal polymerization of at least about six months while at or below room temperature.

[0081] A fifteenth aspect relates to the prepreg of any of the first to fourteenth aspects beingPATENT Atty. Dkt. No. 510322.5000636 encapsulated between impermeable films or sealed within an impermeable bag or package.

[0082] A sixteenth aspect relates to a method of making a prepreg, the method comprising: providing a fiber preform comprising an arrangement of fibers; dispersing encapsulated catalyst particles within the arrangement of fibers; coating and infiltrating the fiber preform with a frontally polymerizable resin at a predetermined temperature where the frontally polymerizable resin is in a liquid phase, and after infiltration, cooling the fiber preform to solidify the frontally polymerizable resin, thereby forming a prepreg comprising the fiber preform, the encapsulated catalyst particles and the frontally polymerizable resin in a solid phase.

[0083] A seventeenth aspect relates to the method of the sixteenth aspect, wherein the frontally polymerizable resin is selected from the group consisting of a dicyclopentadiene (DCPD) resin, a tricyclopentadiene resin, and a frontally polymerizable epoxy resin.

[0084] An eighteenth aspect relates to the method of the sixteenth or seventeenth aspect, wherein the predetermined temperature is at or above a melting temperature and below an activation or onset temperature of the frontally polymerizable resin.

[0085] A nineteenth aspect relates to the method of any of the sixteenth to eighteenth aspects, wherein the frontally polymerizable resin comprises a DCPD resin, and wherein the melting temperature of the DCPD resin is in a range from 32OOC to 34°C.

[0086] A twentieth aspect relates to the method of any of the sixteenth to nineteenth aspects, wherein the cooling comprises active or passive cooling.

[0087] A twenty-first aspect relates to the method of any of the sixteenth to twentieth aspects, wherein the frontally polymerizable resin comprises a DCPD resin consisting essentially of an endo -dicyclopentadiene isomer.

[0088] A twenty-second aspect relates to the method of any of the sixteenth to twenty-first aspects, wherein the frontally polymerizable resin comprises a DCPD resin containing at least about 99% endo-dicyclopentadiene isomer.

[0089] A twenty-third aspect relates to the method of any of the sixteenth to twenty- second aspects, wherein no other monomers other than the DCPD resin are coated on and infiltrated into the fiber preform.

[0090] A twenty-fourth aspect relates to the method of any of the sixteenth to twenty-third aspects, wherein the prepreg is devoid of a polymerization inhibitor.

[0091] A twenty-fifth aspect relates to the method of any of the sixteenth to twenty-fourthPATENT Atty. Dkt. No. 510322.5000636 aspects, wherein dispersing the encapsulated catalyst particles within the arrangement of fibers comprises: dipping the fiber preform into a suspension comprising the encapsulated catalyst particles and a liquid; and after the suspension penetrates interstices of the fiber preform, removing the fiber preform from the suspension, whereby the liquid evaporates and the encapsulated catalyst particles attach to the fibers.

[0092] A twenty-sixth aspect relates to the method of any of the sixteenth to twenty-fourth aspects, wherein dispersing the encapsulated catalyst particles within the arrangement of fibers comprises: mixing the encapsulated catalyst particles into the frontally polymerizable resin while the frontally polymerizable resin is in the liquid phase, whereby, upon coating and infiltrating the fiber preform with the frontally polymerizable resin at the predetermined temperature, the encapsulated catalyst particles are dispersed within the arrangement of fibers.

[0093] A twenty-seventh aspect relates to the method of any of the sixteenth to twentysixth aspects, further comprising forming a vacuum sealed assembly including the prepreg encapsulated between impermeable films, and wherein the vacuum sealed assembly optionally includes one or more puncture control layers.

[0094] A twenty-eighth aspect relates to a method of making a fiber-reinforced polymer composite tube, the method comprising: drawing a prepreg sleeve into a reactive pultrusion apparatus, the prepreg sleeve comprising: a fiber sleeve comprising an arrangement of fibers; a frontally polymerizable resin impregnated into and coated onto the fiber sleeve; heating a longitudinal section of the prepreg sleeve to a temperature sufficient to transform the frontally polymerizable resin to a liquid phase and initiate a frontal polymerization reaction at a surface of the prepreg sleeve within the longitudinal section, whereby the frontal polymerizable resin is converted to a polymer and a cured tube section is formed; repeating the heating on consecutive longitudinal sections of the prepreg sleeve to form consecutive cured tube sections; and conveying the consecutive cured tube sections out of the reactive pultrusion apparatus, thereby forming a fiber-reinforced polymer composite tube.

[0095] A twenty-ninth aspect relates to the method of the twenty-eighth aspect, wherein the heating is carried out by a retractable curing oven or by rotatable heating elements in rolling contact with the prepreg sleeve.

[0096] A thirtieth aspect relates to the method of the twenty-eighth or twenty-ninth aspect, further comprising, during the heating, applying an outward radial pressure to an inner surface of the prepreg sleeve at a location of the longitudinal section.PATENT Atty. Dkt. No. 510322.5000636

[0097] A thirty-first aspect relates to the method of any of the twenty-eighth to thirtieth aspects, wherein the outward radial pressure is applied by a mechanical collet, an expandable bladder, or another radial pressurization device.

[0098] A thirty- second aspect relates to the method of any of the twenty-eighth to thirty-first aspects, wherein the longitudinal section undergoing heating is thermally isolated from upstream portions of the prepreg sleeve.

[0099] A thirty-third aspect relates to the method of any of the twenty-eighth to thirty-second aspects, wherein, upon initiating the frontal polymerization reaction at the surface, a polymerization front travels in a radial direction through the longitudinal section.

[0100] A thirty-fourth aspect relates to the method of any of the twenty-eighth to thirty-third aspects, wherein the frontally polymerizable resin is in a solid phase at or below room temperature (20°C), and wherein the prepreg sleeve further comprises encapsulated catalyst particles embedded in the frontally polymerizable resin, and wherein, upon heating the longitudinal section of the prepreg sleeve, the catalyst contained within the encapsulated catalyst particles is released or otherwise brought into direct contact with the frontally polymerizable resin.

[0101] A thirty-fifth aspect relates to the method of any of the twenty-eighth to thirty-third aspects, wherein the frontally polymerizable resin is in a liquid phase at room temperature (20°C), and wherein the prepreg sleeve further comprises ethylidene norbornene (ENB) dispersed in the frontally polymerizable resin, and wherein, prior to drawing the prepreg sleeve into the reactive pultrusion apparatus, the frontally polymerizable resin is maintained at a reduced temperature at which the frontally polymerizable resin is in a solid phase.

[0102] A thirty-sixth aspect relates to the method of any of the twenty-eighth to thirty-fifth aspects, wherein the prepreg sleeve is formed by rolling up a flat prepreg.

[0103] A thirty-seventh aspect relates to the method of any of the twenty-eighth to thirtyfifth aspects, wherein the prepreg sleeve has a form of a continuous, seamless sleeve.

[0104] A thirty-eighth aspect relates to the method of any of the twenty-eighth to thirtyfifth aspects, wherein, prior to being drawn into the reactive pultrusion apparatus, the prepreg sleeve is encapsulated between impermeable films in a vacuum sealed assembly, and wherein the vacuum sealed assembly optionally includes one or more puncture control layers.

[0105] A thirty-ninth aspect relates to a reactive pultrusion apparatus for making a fiber-reinforced polymer composite tube, the apparatus comprising: a roller for storing a length ofPATENT Atty. Dkt. No. 510322.5000636 prepreg sleeve in a collapsed configuration; a mandrel for receiving an open end of the prepreg sleeve, the mandrel being sized to define an inner diameter of the prepreg sleeve; a device for translating the prepreg sleeve in a downstream direction away from the roller and over the mandrel, the mandrel being configured to remain stationary as the prepreg sleeve moves over the mandrel; a curing oven downstream of the mandrel for heating consecutive longitudinal sections of the prepreg sleeve; and a conveyor mechanism downstream of the curing oven to convey cured tube sections out of the apparatus.

[0106] A fortieth aspect relates to the apparatus of the thirty-ninth aspect, wherein the curing oven comprises rotatable heating elements configured to generate heat while in rolling contact with the prepreg sleeve.

[0107] A forty-first aspect relates to the apparatus of the thirty-ninth or fortieth aspect, further comprising: a radial pressurization device positioned downstream of the mandrel at a location of the curing oven, the radial pressurization device being axially connected to the mandrel and configured to expand radially prior to and / or during heating, whereby the consecutive longitudinal sections of the prepreg sleeve are supported and compacted.

[0108] A forty- second aspect relates to the apparatus of the forty-first aspect, wherein the radial pressurization device comprises a mechanical collet or an expandable bladder.

[0109] A forty-third aspect relates to the apparatus of any of the thirty-ninth to forty-second aspects, further comprising: a lock mechanism between the roller and the mandrel for holding the open end of the prepreg sleeve on the mandrel prior to use of the apparatus.

[0110] A forty-fourth aspect relates to the apparatus of any of the thirty-ninth to forty-third aspects, further comprising a cooling clamp or ring immediately upstream of the curing oven, wherein the cooling clamp or ring is configured to prevent propagation of a curing front in the prepreg sleeve outside of the longitudinal section.

[0111] A forty-fifth aspect relates to the apparatus of any of the thirty-ninth to forty-fourth aspects, wherein the device comprises an axial and radial constraining device.

[0112] A forty- sixth aspect relates to the apparatus of the forty-fifth aspect, wherein the axial and radial constraining device comprises: a kinematically constrained arrangement of opposing internal and external rollers, the internal rollers being rotatably attached to the mandrel and configured to contact an inner surface of the prepreg sleeve, and the external rollers being rotatably attached to an external structure and configured contact an outer surface of the prepreg sleeve, wherein the internal rollers are spaced apart from the external rollers byPATENT Atty. Dkt. No. 510322.5000636 a predetermined gap sufficient to allow translation of the sleeve therein.

[0113] A forty-seventh aspect relates to the apparatus of the forty-fifth aspect, wherein the axial and radial constraining device comprises: an opposing arrangement of internal and external die parts, the internal die parts being attached to the mandrel and configured to contact an inner surface of the prepreg sleeve, and the external die parts being part of an external die and configured to contact an outer surface of the prepreg sleeve, wherein the internal die parts are spaced apart from the external die parts by a predetermined gap sufficient to allow translation of the sleeve therein.

[0114] A forty-eighth aspect relates to the apparatus of the forty-fifth aspect, wherein the axial and radial constraining device comprises: an opposing arrangement of internal and external magnets, the external magnets being fixed on an external frame and the internal magnets being constrained by the opposing arrangement, wherein the internal magnets are spaced apart from the external magnets by a predetermined gap sufficient to allow translation of the sleeve therein.

[0115] A forty-ninth aspect relates to the apparatus of the forty-fifth aspect, wherein the axial and radial constraining device comprises: a pre-installed wire inside the prepreg sleeve configured to exert a tension force on the mandrel as the prepreg sleeve advances to keep the mandrel stationary, wherein extra length of the tension wire is collected and stored on an internal roller using a spring-loaded rotary device, and external rollers configured to constrain the motion in the radial direction, where the external rollers are fixed on an external frame.

[0116] To clarify the use of and to hereby provide notice to the public, the phrases "at least one of , , ... and <N>" or "at least one of , , ... <N>, or combinations thereof" or ", , ... and / or <N>" are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, ... and N. In other words, the phrases mean any combination of one or more of the elements A, B, ... or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, "a" or "an" means "at least one" or "one or more."

[0117] While various embodiments have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible.PATENT Atty. Dkt. No. 510322.5000636 Accordingly, the embodiments described herein are examples, not the only possible embodiments and implementations.

Claims

PATENT Atty. Dkt. No. 510322.5000636 CLAIMSWhat is claimed is:

1. A prepreg comprising:a fiber preform comprising an arrangement of fibers;a frontally polymerizable resin impregnated into and coated onto the fiber preform; andencapsulated catalyst particles embedded within the frontally polymerizable resin, wherein the frontally polymerizable resin is in a solid phase at or below room temperature (20°C).

2. The prepreg of claim 1, wherein the frontally polymerizable resin is selected from the group consisting of a dicyclopentadiene (DCPD) resin, a tricyclopentadiene resin, and a frontally polymerizable epoxy resin.

3. The prepreg of claim 1, wherein the encapsulated catalyst particles comprise a ruthenium-based catalyst and a polymer coating on the ruthenium-based catalyst.

4. The prepreg of claim 3, wherein the ruthenium-based catalyst comprises a Grubb’s catalyst and the polymer coating comprises a polysulfone coating.

5. The prepreg of claim 4, wherein the poly sulfone coating has a form of an assembly of polysulfone particles.

6. The prepreg of claim 1, wherein a molar ratio of the frontally polymerizable resin to the ruthenium-based catalyst is in a range from 1000:1 to 15000:1.

7. The prepreg of claim 1, wherein the fibers comprise carbon fibers.

8. The prepreg of claim 1, wherein the arrangement of fibers comprises a braided, woven or unidirectional arrangement.PATENT Atty. Dkt. No. 510322.50006369. The prepreg of claim 1, wherein the fiber preform has a form of a fiber sleeve, and wherein the prepreg has a form of a prepreg sleeve.

10. The prepreg of claim 1, wherein the frontally polymerizable resin comprises a DCPD resin consisting essentially of an tw / -dicyclopentadiene isomer.

11. The prepreg of claim 1, wherein the frontally polymerizable resin comprises a DCPD resin containing at least about 99% tw / -dicyclopentadiene isomer.

12. The prepreg of claim 1, wherein the prepreg is devoid of any monomers other than the DCPD resin.

13. The prepreg of claim 1, wherein the prepreg is devoid of a polymerization inhibitor.

14. The prepreg of claim 1 having a stability against spontaneous frontal polymerization of at least about six months while at or below room temperature.

15. The prepreg of claim Ibeing encapsulated between impermeable films or sealed within an impermeable bag or package.

16. A method of making a prepreg, the method comprising:providing a fiber preform comprising an arrangement of fibers;dispersing encapsulated catalyst particles within the arrangement of fibers; coating and infiltrating the fiber preform with a frontally polymerizable resin at a predetermined temperature where the frontally polymerizable resin is in a liquid phase, and after infiltration, cooling the fiber preform to solidify the frontally polymerizable resin, thereby forming a prepreg comprising the fiber preform, the encapsulated catalyst particles and the frontally polymerizable resin in a solid phase.PATENT Atty. Dkt. No. 510322.5000636 17. The method of claim 16, wherein the frontally polymerizable resin is selected from the group consisting of a dicyclopentadiene (DCPD) resin, a tricyclopentadiene resin, and a frontally polymerizable epoxy resin.

18. The method of claim 16, wherein the predetermined temperature is at or above a melting temperature and below an activation or onset temperature of the frontally polymerizable resin.

19. The method of claim 16, wherein the frontally polymerizable resin comprises a DCPD resin, and wherein the melting temperature of the DCPD resin is in a range from 32°C to 34°C.

20. The method of claim 16, wherein the cooling comprises active or passive cooling.

21. The method of claim 16, wherein the frontally polymerizable resin comprises a DCPD resin consisting essentially of an tw / -dicyclopentadiene isomer.

22. The method of claim 16, wherein the frontally polymerizable resin comprises a DCPD resin containing at least about 99% tw / -dicyclopentadiene isomer.

23. The method of claim 16, wherein no other monomers other than the DCPD resin are coated on and infiltrated into the fiber preform.

24. The method of claim 16, wherein the prepreg is devoid of a polymerization inhibitor.

25. The method of claim 16, wherein dispersing the encapsulated catalyst particles within the arrangement of fibers comprises:dipping the fiber preform into a suspension comprising the encapsulated catalyst particles and a liquid; andPATENT Atty. Dkt. No. 510322.5000636 after the suspension penetrates interstices of the fiber preform, removing the fiber preform from the suspension, whereby the liquid evaporates and the encapsulated catalyst particles attach to the fibers.

26. The method of claim 16, wherein dispersing the encapsulated catalyst particles within the arrangement of fibers comprises:mixing the encapsulated catalyst particles into the frontally polymerizable resin while the frontally polymerizable resin is in the liquid phase,whereby, upon coating and infiltrating the fiber preform with the frontally polymerizable resin at the predetermined temperature, the encapsulated catalyst particles are dispersed within the arrangement of fibers.

27. The method of claim 16, further comprising forming a vacuum sealed assembly including the prepreg encapsulated between impermeable films, andwherein the vacuum sealed assembly optionally includes one or more puncture control layers.

28. A method of making a fiber-reinforced polymer composite tube, the method comprising:drawing a prepreg sleeve into a reactive pultrusion apparatus, the prepreg sleeve comprising:a fiber sleeve comprising an arrangement of fibers;a frontally polymerizable resin impregnated into and coated onto the fiber sleeve;heating a longitudinal section of the prepreg sleeve to a temperature sufficient to transform the frontally polymerizable resin to a liquid phase and initiate a frontal polymerization reaction at a surface of the prepreg sleeve within the longitudinal section, whereby the frontal polymerizable resin is converted to a polymer and a cured tube section is formed;repeating the heating on consecutive longitudinal sections of the prepreg sleeve to form consecutive cured tube sections; andPATENT Atty. Dkt. No. 510322.5000636 conveying the consecutive cured tube sections out of the reactive pultrusion apparatus, thereby forming a fiber-reinforced polymer composite tube.

29. The method of claim 28, wherein the heating is carried out by a retractable curing oven or by rotatable heating elements in rolling contact with the prepreg sleeve.

30. The method of claim 28, further comprising, during the heating, applying an outward radial pressure to an inner surface of the prepreg sleeve at a location of the longitudinal section.

31. The method of claim 28, wherein the outward radial pressure is applied by a mechanical collet, an expandable bladder, or another radial pressurization device.

32. The method of claim 28, wherein the longitudinal section undergoing heating is thermally isolated from upstream portions of the prepreg sleeve.

33. The method of claim 28, wherein, upon initiating the frontal polymerization reaction at the surface, a polymerization front travels in a radial direction through the longitudinal section.

34. The method of claim 28, wherein the frontally polymerizable resin is in a solid phase at or below room temperature (20°C), and wherein the prepreg sleeve further comprises encapsulated catalyst particles embedded in the frontally polymerizable resin, and wherein, upon heating the longitudinal section of the prepreg sleeve, the catalyst contained within the encapsulated catalyst particles is released or otherwise brought into direct contact with the frontally polymerizable resin.

35. The method of claim 28, wherein the frontally polymerizable resin is in a liquid phase at room temperature (20°C), and wherein the prepreg sleeve further comprises ethylidene norbomene (ENB) dispersed in the frontally polymerizable resin, andPATENT Atty. Dkt. No. 510322.5000636 wherein, prior to drawing the prepreg sleeve into the reactive pultrusion apparatus, the frontally polymerizable resin is maintained at a reduced temperature at which the frontally polymerizable resin is in a solid phase.

36. The method of claim 28, wherein the prepreg sleeve is formed by rolling up a flat prepreg.

37. The method of claim 28, wherein the prepreg sleeve has a form of a continuous, seamless sleeve.

38. The method of claim 28, wherein, prior to being drawn into the reactive pultrusion apparatus, the prepreg sleeve is encapsulated between impermeable films in a vacuum sealed assembly, andwherein the vacuum sealed assembly optionally includes one or more puncture control layers.

39. A reactive pultrusion apparatus for making a fiber-reinforced polymer composite tube, the apparatus comprising:a roller for storing a length of prepreg sleeve in a collapsed configuration;a mandrel for receiving an open end of the prepreg sleeve, the mandrel being sized to define an inner diameter of the prepreg sleeve;a device for translating the prepreg sleeve in a downstream direction away from the roller and over the mandrel, the mandrel being configured to remain stationary as the prepreg sleeve translates over the mandrel;a curing oven downstream of the mandrel for heating consecutive longitudinal sections of the prepreg sleeve; anda conveyor mechanism downstream of the curing oven to convey cured tube sections out of the apparatus.

40. The apparatus of claim 39, wherein the curing oven comprises rotatable heating elements configured to generate heat while in rolling contact with the prepreg sleeve.PATENT Atty. Dkt. No. 510322.5000636 41. The apparatus of claim 39, further comprising:a radial pressurization device positioned downstream of the mandrel at a location of the curing oven, the radial pressurization device being axially connected to the mandrel and configured to expand radially prior to and / or during heating, whereby the consecutive longitudinal sections of the prepreg sleeve are supported and compacted.

42. The apparatus of claim 41, wherein the radial pressurization device comprises a mechanical collet or an expandable bladder.

43. The apparatus of claim 39, further comprising:a lock mechanism between the roller and the mandrel for holding the open end of the prepreg sleeve on the mandrel prior to use of the apparatus.

44. The apparatus of claim 39, further comprising a cooling clamp or ring immediately upstream of the curing oven,wherein the cooling clamp or ring is configured to prevent propagation of a curing front in the prepreg sleeve outside of the longitudinal section.

45. The apparatus of claim 39, wherein the device comprises an axial and radial constraining device.

46. The apparatus of claim 45, wherein the axial and radial constraining device comprises:a kinematically constrained arrangement of opposing internal and external rollers, the internal rollers being rotatably attached to the mandrel and configured to contact an inner surface of the prepreg sleeve, and the external rollers being rotatably attached to an external structure and configured contact an outer surface of the prepreg sleeve,wherein the internal rollers are spaced apart from the external rollers by a predetermined gap sufficient to allow translation of the sleeve therein.

47. The apparatus of claim 45, wherein the axial and radial constraining device comprises:PATENT Atty. Dkt. No. 510322.5000636 an opposing arrangement of internal and external die parts, the internal die parts being attached to the mandrel and configured to contact an inner surface of the prepreg sleeve, and the external die parts being part of an external die and configured to contact an outer surface of the prepreg sleeve,wherein the internal die parts are spaced apart from the external die parts by a predetermined gap sufficient to allow translation of the sleeve therein.

48. The apparatus of claim 45, wherein the axial and radial constraining device comprises:an opposing arrangement of internal and external magnets, the external magnets being fixed on an external frame and the internal magnets being constrained by the opposing arrangement,wherein the internal magnets are spaced apart from the external magnets by a predetermined gap sufficient to allow translation of the sleeve therein.

49. The apparatus of claim 45, wherein the axial and radial constraining device comprises:a pre-installed wire inside the prepreg sleeve configured to exert a tension force on the mandrel as the prepreg sleeve advances to keep the mandrel stationary, wherein extra length of the tension wire is collected and stored on an internal roller using a spring-loaded rotary device, andexternal rollers configured to constrain the motion in the radial direction, where the external rollers are fixed on an external frame.

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