Elastic parylene

Abstract

Elastic parylene films produced on substrates via chemical vapor deposition polymerization (CVDP) are disclosed.

Description

Technical Field

[0001] Aspects generally relate to parylene films, and more particularly to elastic parylene films for use as coatings on flexible substrates and methods of their attachment.

Background Art

[0002] Poly(para-xylylene) (PPX) (trade name Parylene) is a polymer commercially used as a coating material. PPX provides a unique set of properties related to biocompatibility, insolubility, high temperature stability, excellent electrical insulation, and barrier properties, which are interesting for practical applications related to medical devices, electronics, MEMS, preservation of human remains, and barrier coatings.

[0003] PPX can be produced by chemical vapor deposition polymerization (CVDP), resulting in a pinhole-free conformal (insulating protection) film. The precursor [2,2] paracyclophane generally evaporates under reduced pressure and then thermally decomposes at high temperature to become the corresponding 1,4-quinodimethane, which is the actual monomer. This condenses on the substrate below 30°C and spontaneously polymerizes while simultaneously forming a PPX film. This film can be stretched to some extent without breaking depending on the specific PPX composition, but it is not elastic enough for use in connection with flexible substrates. This lack of elasticity can result in peeling and / or damage of the PPX coating.

Summary of the Invention

Means for Solving the Problems

[0004] According to one or more aspects, chemically crosslinked elastic parylene or poly(para-xylylene) (PPX) polymer films are disclosed. According to one or more aspects, a method of preparing a chemically crosslinked elastomeric parylene or poly(para-xylylene) (PPX) polymer film is disclosed. The method can include mixing a substituted p - cyclophane and a vinyl-functionalized p - cyclophane to form a mixture and copolymerizing the mixture on a substrate via a chemical vapor deposition polymerization (CVDP) process to form a chemically crosslinked elastomeric polymer film.

[0005] According to one or more aspects, a chemically crosslinked elastomeric parylene or poly(para-xylylene) (PPX) polymer film is prepared by any of the methods disclosed herein.

[0006] According to one or more aspects, an apparatus including a flexible substrate is disclosed. The flexible substrate is coated with any of the parylene polymer films disclosed herein. These and still other aspects, embodiments, and advantages of these exemplary aspects and embodiments are discussed in detail below. Embodiments disclosed herein may be combined with other embodiments in any manner consistent with at least one of the principles disclosed herein, and references to "one embodiment," "some embodiments," "alternative embodiments," "various embodiments," "one aspect," or the like are not necessarily mutually exclusive and are intended to indicate that the particular features, structures, or characteristics described may be included in at least one embodiment. The appearance of such terms herein is not necessarily all referring to the same embodiment.

[0007] Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide examples and further understanding of the various aspects and embodiments, are incorporated into and constitute a part of this specification, but are not intended to limit the scope of the invention. When reference numerals follow technical features, the reference numerals are included for the sole purpose of increasing the clarity of the figures and the description. In the figures, each identical or substantially identical component shown in the various figures is represented by a similar number. For clarity, not all components are labeled in every figure.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] According to one or more embodiments, an elastic parylene or PPX coating is disclosed. According to various embodiments, the elastic parylene or PPX coating can be produced via chemical vapor deposition polymerization (CVDP).

[0010] The imparting of elasticity generally includes the softening of the solid polymer below the use temperature in combination with the crosslinking of the individual polymers. However, the production of PPX via CVDP typically involves the reagent passing through a pyrolysis zone of about 500°C to about 700°C, which degrades the functional groups usually used for crosslinking.

[0011] According to one or more embodiments, the elastic parylene coating is generally made of any of the common parylene polymer series or a variant thereof. The selection of the parylene polymer can be based mostly on the desired properties considering the intended use.

[0012] According to one or more embodiments, a substituted p - cyclophane, as well as a mixture of p - cyclophanes having reactive and / or crosslinkable groups such as vinyl or ethynyl, can be used to produce an elastic PPX film via CVDP.

[0013] According to one or more embodiments, a mixture of a substituted p - cyclophane and vinyl p - cyclophane can be used to produce an elastic PPX film via CVDP. The amount of vinyl p - cyclophane can be considered important with respect to the degree of elasticity obtained. An excess of vinyl p - cyclophane can result in a brittle coating, while too little may not result in crosslinking.

[0014] According to one or more embodiments, a method for preparing a chemically crosslinked PPX polymer film includes mixing a substituted p - cyclophane and a vinyl - functionalized p - cyclophane to form a mixture. The mixture can be copolymerized on a substrate via a chemical vapor deposition polymerization (CVDP) process to form a chemically crosslinked PPX polymer film. The substituted p - cyclophane and the vinyl - functionalized p - cyclophane can generally be mixed before or during the CVDP process.

[0015] According to one or more embodiments, an optimized weight fraction of vinyl p - cyclophane relative to other p - cyclophanes can result in optimized elasticity of the PPX film. In some embodiments, the substituted p - cyclophane can have a low glass transition temperature. In some specific embodiments, the substituted p - cyclophane can be a dialkyl - functionalized p - cyclophane, such as a dibutyl - functionalized p - cyclophane. In some specific non - limiting embodiments, the substituted p - cyclophane is 4,12 - dibutyl[2,2]p - cyclophane. Other p - cyclophanes, such as those having 2, 3, 5, or 6 carbon atoms, for example, having alkyl chains that are side - chain, straight - chain, or branched - chain, can be used. In some embodiments, a mono - substituted p - cyclophane can be used.

[0016] In some specific non-limiting embodiments, the vinyl-functionalized paracyclophane can be 4-vinyl[2.2]paracyclophane. The ratio of vinyl paracyclophane to substituted paracyclophane can be between approximately 1:500 and 1:10, preferably between about 1:200 and 1:100.

[0017] With respect to the various substituents, various isomers or mixtures thereof can be used. According to one or more embodiments, the crosslinking can be a physical or chemical process. The crosslinking can result from an intermolecular reaction of reactive groups of the polymer initiated by an external stimulus, i.e., heat, irradiation, light, such as UV light, or plasma. In some embodiments, an additional initiator can be implemented.

[0018] In at least some embodiments, the PPX polymer film can be produced in a parylene deposition system commercially available from Specialty Coating Systems. Various CVDP methods commonly known to those skilled in the art can be implemented. In some embodiments, simultaneous pyrolysis and deposition can result in the PPX polymer film of the present disclosure. In some non-limiting embodiments, a mixture of precursors can be placed into the sublimation chamber of a CVDP apparatus. A mixture of substituted paracyclophane and vinyl-functionalized paracyclophane can be introduced into the CVDP apparatus for deposition.

[0019] According to one or more embodiments, the parylene coating can be formed from a gaseous monomer. The parylene coating can be formed without an intermediate liquid stage. The parylene coating can be applied at ambient temperature using a vacuum deposition apparatus. The film can grow over time as the parylene polymer adheres at the molecular level. The parylene coating can generally be applied via a vapor deposition polymerization process in a room temperature vacuum chamber. The substrate to be coated can be placed within the coating chamber. The solid, granular dimer feedstock can be heated under vacuum and evaporated into a dimer gas. A mixture of substituted parylene and vinyl-functionalized parylene can be introduced into a CVDP apparatus as a dimer. In some non-limiting embodiments, evaporation can be performed at about 150 °C and about 1.0 torr. The gas can then be pyrolyzed to cleave the dimer into its monomer form. In some non-limiting embodiments, pyrolysis can be performed at about 680 °C and about 0.5 torr. The monomer gas can be deposited as a polymer film onto the substrate at ambient temperature in the deposition chamber. The monomers can strike the surface of the desired substrate and spontaneously polymerize into a continuous film on the substrate. The film can be of a desired thickness or thickness range based on the intended application and can be substantially transparent. In some embodiments, the thickness can range from hundreds of angstroms to several millimeters. In at least some embodiments, typical thicknesses can be in the micron range.

[0020] Standard parylene deposition process conditions, including temperature and pressure, can be implemented by one or more embodiments. In at least some embodiments, the CVDP apparatus can include multiple heating zones. According to one or more particular non-limiting embodiments, the CVDP process can be characterized by a pyrolysis temperature of about 500 °C. The CVDP process can be characterized by a transport temperature of about 300 °C. The CVDP process can be characterized by a deposition temperature of about 10 °C. The CVDP process can be characterized by a sublimation temperature of about 125 °C. Any one or more of the process temperatures or other process parameters can be controlled for process optimization. Strategic control of the deposition temperature can beneficially result in less monomer residue and an optimized crosslink content.

[0021] According to one or more embodiments, the chemically crosslinked PPX polymer film can be subjected to further processing. The further processing can generally involve one or more applications of temperature, UV irradiation, e-beam crosslinking, and plasma conditioning. The mechanical properties of the elastomeric parylene film can be further improved by additional temperature treatments that can affect the crystallinity, further promote crosslinking, and / or remove low molecular weight impurities. In some embodiments, the crystallinity can be reduced via further heat treatment, UV irradiation, plasma conditioning, and / or e-beam crosslinking. In some embodiments, the parylene film can be annealed at an elevated temperature. For example, the further heat treatment can be characterized by an application at an annealing temperature of about 100 °C to about 350 °C, such as about 300 °C, for about 1 to about 30 minutes, such as 5 minutes.

[0022] According to one or more embodiments, one or more precursor materials can be synthesized. For example, vinyl-functionalized parylene can be synthesized. According to one or more embodiments, the chemically cross-linked PPX polymer film may have a vinyl content of about 5% or less. In some embodiments, the chemically cross-linked PPX polymer film may have a vinyl content of about 2.5% or less. For example, the chemically cross-linked PPX polymer film may have a vinyl content of about 0.5% to about 1.25%. In some specific embodiments, the cross-linked PPX polymer film may have a vinyl content of about 1%.

[0023] According to one or more embodiments, the elastomeric parylene film may be characterized by a low softening point, enhanced solvent resistance, and / or thermal dimensional stability. In some embodiments, the PPX film may be characterized by improved resistance to solvents, such as organic solvents, such as THF or chloroform. In at least some embodiments, the PPX film may be characterized by a thermal dimensional stability of at least about 350 °C or less.

[0024] According to one or more embodiments, the PPX film is substantially insoluble. According to one or more embodiments, the PPX film may have a low glass transition temperature.

[0025] According to one or more embodiments, the PPX film may have a Young's modulus between about 0.01 GPa and about 0.05 GPa. In some non-limiting embodiments, the PPX film may have a Young's modulus between about 0.02 GPa and about 0.04 GPa.

[0026] According to one or more embodiments, the PPX film may be characterized by a break elongation value of about 100%, 150%, 200%, 300%, or 350% or less. The PPX film may be characterized by a cyclic strain test value of at least about 100% elongation per cycle. The PPX film may not show significant damage after the cyclic strain test, but may not return to its original shape. The PPX film may be characterized by a shape shift value of the cyclic strain test between about 20% and 30%.

[0027] According to one or more embodiments, the parylene coating can be a thin film coating. The coating can be continuous and substantially uniform across the substrate. In some non-limiting embodiments, a parylene coating with a controlled thickness of at least about several thousand angstroms or more can be achieved. A parylene coating with a controlled thickness of at least about several millimeters or less can also be achieved. The thickness can generally be controlled to within at least plus or minus about 10%. In some non-limiting embodiments, the PPX film can have a thickness of greater than about 0.5 μm.

[0028] The parylene coating can be conformal with respect to the surface, edges, and gaps of the substrate and can be substantially pinhole-free. Multilayer penetration can be achieved. In some embodiments, the parylene coating can add a minimal dimension or mass to critical and weight-sensitive components. The parylene coating can be optically transparent or a labeling compound such as a fluorescent agent can be incorporated to facilitate identification. The parylene coating can be associated with a preferred water vapor transmission rate.

[0029] In some embodiments, the parylene coating can be substantially biostable and biocompatible. The coating can comply with the biological test requirements of ISO-10993. The coating can comply with the biological test requirements of USP Class VI plastics. The coating can promote the growth of human cell types. In some embodiments, the parylene coating can exhibit barrier properties, such as protecting the substrate from, for example, fluids, moisture, chemicals, and common gases. Protection from biological fluids and biological gases can be provided. The parylene coating can exhibit high dielectric strength and / or can impart dry film lubricity to the substrate. The parylene coating can protect against corrosion, discoloration, and contaminant uptake. The parylene coating can contribute as a dielectric barrier. In some embodiments, the parylene coating can be flexible, prevent surface adhesion, and reduce the coefficient of friction. The parylene coating can have various favorable coefficients of friction, as measured by ASTM D1894 for static observations. In some embodiments, the parylene coating can exhibit thermal stability and / or UV stability.

[0030] According to one or more embodiments, the parylene coating can be applied to a substrate. Adhesion promotion techniques can be used in conjunction with the deposition method. The substrate can generally be any material, device, or component for which it may be desirable to apply a coating, such as a barrier or functional layer. The parylene coating can be applied to virtually any surface material, including metals, elastomers, plastics, glass, ceramics, and paper. The parylene coating can find use in a variety of industries, including medical devices, electronics, automotive, military, aerospace, LEDs, and elastomers.

[0031] In some embodiments, the substrate can be a flexible substrate. In some non-limiting embodiments, the flexible substrate can be attached to a printed circuit board (PCB) or a medical device. In some embodiments, the substrate may be related to electronics, printed circuit boards, printed circuit assemblies, sensors, detectors, LEDs, MEMS, capacitors, wafers, ferrite cores, fuel cells, digital displays, metal parts. In other embodiments, the substrate may be a gasket or a seal. In still other embodiments, the substrate may be a medical device. The substrate may be pretreated prior to parylene deposition. Fixing techniques and masking techniques may be used to minimize contact points and avoid leaving areas of the coating uncoated.

[0032] According to one or more embodiments, a parylene coating may be applied to implantable or non-implantable medical devices. Medical devices, including but not limited to, for example, heart valves, coronary stents, cerebral stents, cardiac assist devices including defibrillators and pacemakers, electrosurgical tools, artificial ears, eye implants, mandrels, molds, catheters, elastomeric seals, needles, epidural probes, artificial joints, discs, screws, other orthopedic instruments, or medical electronics, such as flexible medical electronics, may be coated with parylene. The parylene coating may also be used as a release agent for molds and shaping devices such as wire mandrels. The parylene coating may provide an acceptable surface for tissue contact and protect medical devices and related components. In some embodiments, the parylene coating may function as a surface primer on, for example, a drug-eluting stent where a drug-containing copolymer is applied to a parylene-coated metallic coronary stent for human implantation. The parylene coating may enable the integration of various combinations of drugs and polymers.

[0033] In at least some embodiments, the elastic parylene coating is halogen-free or substantially halogen-free. For example, the elastic parylene coating of the present disclosure may be characterized as chlorine-free.

[0034] According to one or more embodiments, an antibacterial parylene coating may be provided. In some embodiments, the method may introduce an antibacterial material into the parylene film during the parylene deposition process. According to one or more embodiments, the coating may include a parylene material and an antibacterial agent immobilized on the parylene material.

[0035] The functions and advantages of these and other embodiments will be more fully understood from the following non-limiting examples. The examples are intended to be illustrative in nature and should not be regarded as limiting the scope of the embodiments discussed herein.

Examples

[0036] Using the simultaneous thermal decomposition and deposition of 4-vinyl[2.2]paracyclophane and 4,12-dibutyl[2.2]paracyclophane, a set of crosslinked PPX copolymers having a varying vinyl content between 0 and 2.5% was synthesized, respectively.

[0037] Comparison of the IR spectra showed no significant differences. The TGA measurements of the copolymers also varied only slightly. All copolymers showed a first decomposition step at about 200 °C and a second major step at about 465 °C where the polymer decomposed.

[0038] Comparison of the elongation at break values showed a maximum of 195% for the copolymer with a vinyl content of 1%. Only the copolymer with 1.25% vinyl achieved a value equivalent to 190%. The lowest elongation was obtained for the copolymer with a 2.5% vinyl moiety. The determined Young's modulus for all samples was low, with values between 0.025 and 0.037 GPa, but no trend between vinyl content and Young's modulus could be observed. The cyclic strain test showed a shape shift between 25 and 30% after the first elongation for all samples. In the next cycle, the shape was maintained almost the same.

[0039] Figure 1 shows a graphical summary of the elongation at break values and Young's modulus of a PPX butyl copolymer having a vinyl content between 0% and 2.5%. The as - attached samples showed unreacted vinyl groups and low - molecular - weight compounds. These low - weight compounds were considered to act as plasticizers. The semi - crystalline copolymers were then heat - treated to increase the cross - link density and decrease their crystallinity. In particular, the PPX butyl copolymer was annealed at 350 °C for 5 minutes under vacuum. In addition to cross - linking after attachment, this treatment led to the removal of low - molecular - weight compounds and a decrease in crystallinity.

[0040] Accordingly, harder copolymers were obtained, and thus the elongation at break values and Young's modulus increased. The insoluble copolymer (copolymer having a vinyl content of 1%) showed an elongation at break value of 340% or less. The cyclic strain test showed that at a cyclic elongation of 100%, the sample was not significantly damaged. The initial shape of the sample was affected by the cyclic strain, and thus a certain degree of elongation was maintained.

[0041] Figure 2 shows a graphical summary of the elongation at break measurements after the annealing step of a PPX butyl copolymer having a vinyl content between 0% and 2.5%. Table 1 (below) shows a summary of the mechanical properties after the annealing step of a PPX butyl copolymer having a vinyl content between 0% and 2.5%.

[0042]

Table 1

[0043] The improved stability was further demonstrated by the coating and expansion of the stent. A copolymer coating having a vinyl content of 1% was selected, and after further temperature treatment, the coated stent was expanded and compressed three times. For comparison, another stent was coated with PPX - C and treated in the same way three times. The coating on the stent showed the stability of the copolymer after expansion compared to PPX - C.

[0044] The SEM images of the two stents showed a smoother surface that could be observed for the PPX butyl copolymer coating. At the junction of the stents, the PPX-C layer showed damage through mechanical stress, so that the metal surface of the stent appeared. In the stents coated with the copolymer, these damages could not be observed, and therefore, this coating minimizes the risk of cell adhesion.

[0045] The results indicate that the chemically cross-linked PPX polymer is a promising coating material for demanding applications. Those skilled in the art will readily recognize that the various parameters and configurations described herein are meant to be exemplary and that the actual parameters and configurations will depend on the particular application for which this disclosure is used. Those skilled in the art will be able to recognize or confirm many equivalents to the specific embodiments described herein using only routine experimentation. Accordingly, the foregoing embodiments are presented by way of example only, and it should be understood that within the scope of the appended claims and their equivalents, the coating and attachment methods of this disclosure may be practiced in ways other than as specifically described. This coating and this technology are directed to each individual feature or method described herein. Additionally, any combination of two or more of such features, devices or methods, provided such features, devices or methods are not mutually inconsistent, is included within the scope of this disclosure.

[0046] While exemplary embodiments of the present disclosure have been disclosed, many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the present disclosure and its equivalents as defined in the following claims. It should be recognized that various changes, modifications, and improvements will readily occur to those skilled in the art. Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to be within the spirit and scope of this disclosure. For example, existing coatings, deposition apparatuses, or deposition methods can be modified to utilize or incorporate any one or more aspects of the present disclosure. Thus, in some cases, embodiments can involve configuring existing processes or apparatuses to provide elasticity. Accordingly, the foregoing description is merely an example.

Claims

1. A chemically crosslinked elastic poly(para-xylylene) (PPX) polymer film having a Young's modulus between 0.01 GPa and 0.05 GPa.

2. The poly(para-xylylene) polymer film according to claim 1, wherein the vinyl content of the polymer film is 5% or less.

3. The poly(para-xylylene) polymer film according to claim 1 or 2, wherein the vinyl content of the polymer film is 2.5% or less.

4. The poly(para-xylylene) polymer film according to any one of claims 1 to 3, wherein the polymer film has a Young's modulus between 0.02 GPa and 0.04 GPa.

5. The poly(para-xylylene) polymer film according to any one of claims 1 to 4, wherein the polymer film has an elongation at break value of 350% or less.

6. The poly(para-xylylene) polymer film according to any one of claims 1 to 5, wherein the polymer film has a cyclic strain test value of at least 100% elongation per cycle.

7. The poly(para-xylylene) polymer film according to any one of claims 1 to 6, copolymerized on a substrate and comprising a dialkyl-substituted parylene and a vinyl-functionalized parylene.

8. The poly(para-xylylene) polymer film according to claim 7, wherein the dialkyl-substituted parylene is dibutyl-functionalized parylene.

9. The poly(para-xylylene) polymer film according to claim 8, wherein the dialkyl-substituted parylene is 4,12-dibutyl[2,2]parylene.

10. The poly(para-xylylene) polymer film according to any one of claims 7 to 9, wherein the vinyl-functionalized parylene is 4-vinyl[2.2]parylene.

11. The poly(para-xylylene) polymer film according to any one of claims 1 to 10, wherein the polymer film is treated with UV, plasma, e-beam crosslinking, or temperature.

12. The poly(para-xylylene) polymer film according to any one of claims 1 to 11, wherein the polymer film has a thickness greater than 0.5 μm.

13. A method for preparing a chemically crosslinked elastic poly(para-xylylene) (PPX) polymer film, comprising: mixing a dialkyl-substituted parylene and a vinyl-functionalized parylene to form a mixture, and Copolymerizing a mixture on a substrate via a chemical vapor deposition polymerization (CVDP) process to form a chemically crosslinked elastic polymer film A method comprising.

14. The method according to claim 13, wherein the dialkyl-substituted p-cyclophane is dibutyl-functionalized p-cyclophane.

15. The method according to claim 13 or 14, wherein the dialkyl-substituted p-cyclophane is 4,12-dibutyl[2,2]p-cyclophane.

16. The method according to any one of claims 13 to 15, wherein the vinyl-functionalized p-cyclophane is 4-vinyl[2.2]p-cyclophane.

17. The method according to any one of claims 13 to 16, wherein the ratio of the vinyl-functionalized p-cyclophane to the dialkyl-substituted p-cyclophane is between 1:500 and 1:

10.

18. The method according to any one of claims 13 to 17, wherein the chemically crosslinked elastic poly(para-xylylene) polymer film has a vinyl content of 5% or less.

19. The method according to any one of claims 13 to 18, wherein the chemically crosslinked elastic poly(para-xylylene) polymer film has a vinyl content of 2.5% or less.

20. The method according to any one of claims 13 to 19, wherein the chemically crosslinked elastic poly(para-xylylene) polymer film has a vinyl content of 0.5% to 1.25%.

21. The method according to any one of claims 13 to 20, wherein the CVDP process includes a pyrolysis temperature of 500°C.

22. The method according to any one of claims 13 to 21, wherein the CVDP process includes a transport temperature of 300°C.

23. The method according to any one of claims 13 to 22, wherein the CVDP process includes a deposition temperature of 10°C.

24. The method according to any one of claims 13 to 23, wherein the CVDP process includes a sublimation temperature of 125°C.

25. The method according to any one of claims 13 to 24, further comprising synthesizing a vinyl-functionalized p-cyclophane.

26. The method according to any one of claims 13 to 25, further comprising subjecting the chemically crosslinked elastic polymer film to further heat treatment, UV irradiation, plasma conditioning, or e-beam crosslinking.

27. The method according to claim 26, wherein the further heat treatment includes applying an annealing temperature of 100°C to 350°C for a period of 1 minute to 30 minutes.

28. The method according to any one of claims 13 to 27, wherein the substrate is a flexible substrate. **Claim 29** The method according to claim 28, wherein the flexible substrate is attached to a printed circuit board (PCB) or a medical device. **Claim 30** An apparatus comprising a flexible substrate coated with a chemically crosslinked elastic poly(para-xylylene) polymer film according to any one of claims 1 to 12. **Claim 31** The apparatus according to claim 30, wherein the flexible substrate is attached to a printed circuit board (PCB). **Claim 32** The apparatus according to claim 30 or 31, wherein the flexible substrate is attached to a medical device. **Claim 33** The apparatus according to claim 32, wherein the medical device comprises a heart valve, a stent, a defibrillator, or a pacemaker. **Claim 34** The medical device according to claim 32, wherein the medical device comprises an artificial joint, a disc, a screw, or other orthopedic instruments. The apparatus according to claim 32.

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