Inner layer of vehicle air-conditioning hose

Abstract

The refrigerant hose has an innermost tube in which an inner cavity is defined, and the innermost tube is based on hydrogenated nitrile rubber (HNBR), a polymer blend containing HNBR, or one of its copolymers, which is cured with phenol-formaldehyde resin. The refrigerant hose may further include an optional permeation inhibition layer that surrounds the innermost tube when included, and when this layer is used, a reinforcing layer arranged outward from the innermost tube and the optional permeation inhibition layer, and a covering layer arranged outward from the reinforcing layer. When exposed to polyol ester oil or polyalkylene glycol oil for 168 hours at 125°C, the innermost tube has a volume expansion percentage of 10% or less. In addition, the innermost tube does not contain peroxides and may further contain no added elemental sulfur, sulfur donors, and / or additives containing sulfur in its molecular structure.

Description

Technical Field

[0001] The present disclosure generally relates to the field of hoses suitable for use in refrigerant systems such as vehicular, industrial, and residential refrigerant systems, such as automotive air conditioning systems. The hoses have an inner layer with improved properties for use in air conditioning systems. Background Art

[0002] This section provides background information to facilitate a better understanding of various aspects of the present disclosure. It should be understood that the statements in this section of this document are to be read in this light and not as admissions of prior art.

[0003] Hoses are used to transport refrigerants in vehicle air conditioning (AC) systems, as well as industrial and residential refrigerant systems. These hoses serve the purpose of connecting the main operating components of a refrigeration unit. Hoses are typically designed to have good flexibility, high strength, the ability to bend to a tight radius without kinking, and to remain impermeable to the fluids present within them.

[0004] Recent changes in vehicle air conditioning systems have necessitated changes to the traditional compounds used to form certain layers of vehicle air conditioning hoses, particularly the layers on the hose's inner surface (which come into contact with the refrigerant and compressor oil present and contained within the hose). In one example, the move toward refrigerants with low global warming potential (GWP), such as 2,3,3,3-tetrafluoropropene (commercially known as R1234yf), presents challenges in selecting materials for hose layers. Some traditional hose inner layers may reduce the effectiveness of these new refrigerants. Rubber materials with certain polymerization initiators, including peroxides, may cause 2,3,3,3-tetrafluoropropene to polymerize.

[0005] Furthermore, with the hybridization and electrification of vehicles, there has been a shift away from traditional polyalkylene glycol (PAG) AC system compressor oils toward polyol ester (POE) compressor oils, coupled with the need for higher operating temperatures. However, POE oils can cause increased swelling and softening of traditional automotive AC hose layer compounds (such as butyl, halobutyl, and chloroprene). Furthermore, these traditional AC hose layer compounds may not be designed for use at high operating temperatures.

[0006] Another consideration is the emerging use of nickel in automotive AC compressors. Due to nickel corrosion, this necessitates avoiding sulfur-curing systems, sulfur donors, and other sulfur-containing accelerators and additives. Elemental sulfur can provide crosslinks containing 3 to 8 sulfur atoms. These crosslinks have lower bond energies than carbon-to-carbon bonds, and those with the highest number of sulfur atoms provide the weakest bond strength. These weaker sulfur-to-sulfur bonds create opportunities for bond breakage when exposed to heat or stress. Any unreacted sulfur, along with this bond breakage, can contribute to sulfur corrosion in AC compressors when using nickel and other materials with lower corrosion resistance. To reduce the number of sulfur crosslinks, the amount of elemental sulfur can be reduced or eliminated, and sulfur-containing accelerators can be used. While the number of sulfur atoms in the crosslinks will be reduced compared to rubbers conventionally cured with elemental sulfur, any sulfur-to-carbon or sulfur-to-sulfur bonds will be more susceptible to rupture than carbon-to-carbon bonds when exposed to heat or stress. Any unreacted portion of the sulfur accelerator or sulfur donor will also be available to corrode susceptible AC compressor components, such as nickel. Typically, the need to avoid sulfur or the requirement for elevated operating temperatures will drive material selection toward peroxide cured elastomers, which present the aforementioned problems.

[0007] Therefore, there is a continuing need for an air conditioning hose having certain layers comprised of material layers that overcome the aforementioned problems, and this need is at least partially satisfied by embodiments according to the following disclosure. Summary of the Invention

[0008] This section provides a general summary of the disclosure, and is not necessarily a comprehensive disclosure of its full scope or all of its features.

[0009] In a first aspect of the present disclosure, a refrigerant hose has an innermost tube defining an inner lumen, and the innermost tube is one of hydrogenated nitrile rubber (HNBR), a polymer blend containing HNBR, or a copolymer thereof, cured with a phenol-formaldehyde resin. The refrigerant hose may further include an optional permeation-inhibiting layer, which, when included, surrounds the innermost tube and, when used, a reinforcing layer disposed outwardly from the innermost tube and the optional permeation-inhibiting layer, and a cover layer disposed outwardly from the reinforcing layer. When exposed to polyol ester oil or polyalkylene glycol oil at 125°C for 168 hours, the innermost tube has a volume expansion percentage of 10% or less. In addition, the innermost tube does not contain peroxides and may further contain no added elemental sulfur, sulfur donors, and / or additives containing sulfur within its molecular structure. When a permeation barrier layer is included, the refrigerant hose may further include a connecting layer disposed between the permeation-inhibiting layer and the reinforcing layer.

[0010] In some aspects of the present disclosure, molecules of 2,3,3,3-tetrafluoropropene or 1,1,1,2-tetrafluoroethane refrigerant are present in the inner cavity, and the inner cavity can be free of polymerized 2,3,3,3-tetrafluoropropene molecules.

[0011] The cover layer can be based on any suitable material, such as, but not limited to, butyl (IIR), halogenated butyl (CIIR / BIIR), HNBR (HNBR), brominated isobutylene-p-methyl-styrene (BIMS), ethylene-propylene-diene monomer rubber, etc. In some aspects, the reinforcement layer can be based on a polyester material, such as polyethylene terephthalate, or other suitable polyesters. The reinforcement layer can be a material including glass fiber, cotton fiber, polyester fiber, polyaramid fiber, aramid fiber, or a suitable mixture thereof.

[0012] According to some aspects of the present disclosure, the phenol-formaldehyde resin can be a brominated octylphenol-formaldehyde resin, an octylphenol-formaldehyde resin and a Lewis acid activator (halogen) added to the composition in the form of a halogenated organic compound, an octylphenol-formaldehyde resin and a Lewis acid activator (halogen) added to the composition in the form of a metal halide, or phenol-formaldehyde and a halogenated organic compound added to provide a Lewis acid activator. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Certain embodiments of the present disclosure will be described below with reference to the accompanying drawings, wherein like reference numerals represent like elements. However, it should be understood that the accompanying drawings illustrate various embodiments described herein and are not intended to limit the scope of the various techniques described herein, and:

[0014] According to this disclosure, Figure 1 The barrier braided hose is shown in a cutaway perspective;

[0015] According to this disclosure, Figure 2 An all-rubber braided hose is depicted in cutaway perspective;

[0016] According to this disclosure, Figure 3 The spiral barrier hose is shown in a cutaway perspective;

[0017] Figure 4 A cross section of a hose containing refrigerant and oil is shown.

[0018] List of Reference Numerals

[0019] 100 Barrier Braided Hose

[0020] 200 full rubber hose

[0021] 300 Spiral Barrier Hose

[0022] 400 hose

[0023] 102, 202, 302, 402 innermost tube

[0024] 104, 304, 404 penetration inhibition layer

[0025] 106, 306, 312, 406 connection layers

[0026] 108, 208, 408 braided reinforcement layer

[0027] 308, 314 spiral reinforcement layer

[0028] 110, 210, 310, 410 covering layers

[0029] 412 Lumen

[0030] 420 2,3,3,3-tetrafluoropropylene refrigerant

[0031] or the molecule of 1,1,1,2-tetrafluoroethane refrigerant

[0032] 422 POE or PAG oil beads

[0033] 424 Polymerized 2,3,3,3-tetrafluoropropene DETAILED DESCRIPTION

[0034] The following description of variants is essentially merely illustrative and is in no way intended to limit the scope of the present disclosure, the application of the present disclosure or the purposes. Presenting description herein is only for the purpose of illustrating the different embodiments of the present disclosure and should not be interpreted as limiting the scope and applicability of the present disclosure. In the present disclosure and in this embodiment, each numerical value should be read as modified by the term "about" (unless it has been explicitly modified), and then read again as if it has not been modified, unless otherwise specified in the context. In addition, in the present disclosure and in this embodiment, it should be understood that the value ranges listed or described as useful, suitable, etc. are intended to be all values (including endpoints) within the range that are considered to have been stated. For example, "a range of 1 to 10" will be read as indicating every possible number along the continuum between about 1 and about 10. Therefore, even at a specific data point within the range, or even without the data point within the range being explicitly specified or merely referring to a few specific points, it should be understood that the inventors appreciate and understand that any and all data points within the range are considered to have been specified, and the inventors have the entire range and all points within the range.

[0035] Unless expressly stated to the contrary, "or" refers to an inclusive or and not an exclusive or. For example, condition A or B can be satisfied by any of the following: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist).

[0036] In addition, the use of "a / an" is used to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general meaning to the concepts according to the present disclosure. This description should be read to include one or at least one, and the singular also includes the plural, unless otherwise specified.

[0037] The terms and phrases used herein are for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving" and variations thereof are intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter that is not listed.

[0038] Furthermore, as used herein, any reference to "one embodiment" or "an embodiment" means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in different places in the specification are not necessarily referring to the same embodiment.

[0039] Hose embodiments according to the present disclosure generally include a rubber hose having an innermost tube, at least one reinforcement layer, and an outer cover layer. Hose embodiments also include barrier hoses, which generally include a barrier layer, at least one reinforcement layer, optionally one or more reinforcement layers, optionally one or more tie layers, an outer cover layer, and an innermost tube.

[0040] The innermost tube is formed by an elastomeric material, which is formed by HNBR or its copolymer in the hydrogenated nitrile rubber (HNBR) of resin curing, polymer blend. The resin curing system is based on the use of phenol formaldehyde resin, which reacts with a small amount of unsaturated points remaining in the HNBR slightly less than fully saturated to form a crosslinked structure. These phenol formaldehyde resins can be directly added to the composition, or can be formed by phenol and phenol derivatives and various aldehyde reaction in situ. The example of phenol derivatives includes but is not limited to bisphenol, phenol, cresol, resorcinol and hexamethylenetetramine (HMT). The phenol-formaldehyde resin produced by the alkylation of phenol or resol and resorcinol novolac resin or resorcinol phenol novolac resin is some non-limiting examples suitable for crosslinked elastomers. Commercial example is the brominated octylphenol formaldehyde resin SP-1055 available from Saint-LeCoultre International Group (SIGroup).

[0041] In order to catalyze the curing reaction of phenol formaldehyde resin, the presence of Lewis acid activators such as halogenated substances is used. This halogenated substance can be a part of the resin itself, as is the case with the aforementioned brominated octylphenol formaldehyde resin. Halogen is also commonly added to the composition containing non-halogenated phenol formaldehyde resin in the form of a small amount of halogenated organic compounds such as, but not limited to, chloroprene or halobutyl. Halogen can also be added as one of many suitable metal halide materials, including but not limited to stannous chloride (i.e., SnCl ).

[0042] The inventors have observed that by using such a resin-cured HNBR innermost tube, the effectiveness of the refrigerant is improved by avoiding the use of peroxide cure systems for the innermost tube, as residual peroxide may cause crosslinking of the refrigerant. The inventors have observed that by using such a resin-cured HNBR innermost tube, the compressor integrity is improved by avoiding the use of sulfur, which is known to corrode nickel in AC compressors.

[0043] Regarding the barrier layer, any suitable material may be used to form this layer when constructing the barrier hose. In all-rubber constructions, no barrier layer is used. Some suitable, but non-limiting, examples of barrier materials include polyamides such as PA11, PA46, PA6, PA66, PA6,66, PA66,6, PA69, PA610, PA612, PA1010, PA1212, PA4T, PA6T, PA9T, and PA10T; thermoplastic polyester elastomers based on polyether-ester block copolymers, such as those sold under the trade names or thermoplastic elastomers consisting of polyamide and polyether backbone blocks, such as those sold under the trade name Those that are supplied.

[0044] When used, the one or more tie layers are typically composed of any suitable thermosetting material, including but not limited to polybutadiene (BR), copolymers of butadiene and acrylonitrile (NBR), butyl rubber (IIR), chloroprene rubber (CIIR), bromobutyl rubber (BIIR), copolymers of butadiene and styrene (SBR), polychloroprene (CR), ethylene propylene rubber (EPM), or ethylene propylene diene (EPDM). In one embodiment, the base material of the layer is EPDM.

[0045] The reinforcement layer can be based on a material formed by braiding, twisting, knitting, or spiral knitting of yarns. The reinforcement layer can be based on a woven or non-woven material. The material can be selected from conventional hose reinforcement yarns such as glass, cotton, polyester, or aramid fibers, or blends of any of these fibers. In some aspects, the reinforcement layer in the hose is a polyester or aramid fabric, or even a blend of polyethylene terephthalate yarn and polyethylene naphthalate yarn to form a fabric.

[0046] The cover layer used in the embodiments of the present disclosure is selected from rubber, including but not limited to the following rubbers and blends or copolymers thereof, selected from ethylene propylene diene rubber (EPDM), ethylene propylene rubber (EPR), butyl rubber (IIR), chloroprene rubber (CIIR), bromobutyl rubber (BIIR), chloroprene rubber (CR), nitrile rubber (NBR), chlorosulfonated polyethylene rubber (CSM), epichlorohydrin rubber (ECO), acrylic rubber (ACM), chloroprene rubber (CR), ethylene-acrylic acid elastomer (AEM), or chlorinated polyethylene (CPE), etc. In one embodiment, the basic material of the cover layer is EPDM.

[0047] With the exception of the innermost tubular layer, the various material components used in the hose embodiments of the present disclosure can be cured with conventional curing agents, including but not limited to peroxides, sulfur, sulfur donor curing agents, amine curing agents, resin curing systems, metal oxide curing agents, and the like. For example, peroxides such as dicumyl peroxide, α-α-bis(tert-butylperoxide)diisopropylbenzene, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 1,1-bis(tert-butylperoxy)3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexyne-3, and 4,4-bis(tert-butylperoxy)n-butyl valerate can be used to cure the rubber component of the hose. Typically, 1 to about 10 parts peroxide is used per 100 parts base polymer. Peroxides are preferred as curing agents because they are less susceptible to premature crosslinking (scorch). Sulfur / sulfur donor curing agents are also commonly used. A few examples of the many sulfur-containing accelerators and sulfur donors that can be used in rubber cure systems include tetramethylthiuram disulfide, 4,4'-dimorpholine disulfide, dipentamethylenethiuram tetrasulfide, thiocarbamoylsulfenamide, mercaptobenzothiazole, zinc dimethylcarbamate, dibenzothiazole disulfide, and N-cyclohexyl-2-benzothiazolesulfonamide.

[0048] The rubber component used in the hose of the present invention may also contain various additives in conventional or appropriate amounts. Such additives may include, but are not limited to, retarders to prevent excessively rapid curing, antioxidants, processing aids, reinforcing agents, and fillers such as carbon black, silica, coupling agents, dispersants, and adhesion promoters.

[0049] Now refer to Figures 1 to 4 , which depicts some hose embodiments according to the present disclosure. Figure 1 The barrier braided hose 100 is shown in a cutaway perspective view. The hose 100 includes an innermost tube 102 surrounded by a permeation inhibiting layer 104. Disposed adjacent to the permeation inhibiting layer 104 is a tie layer 106 having a reinforcement layer 108 disposed outwardly therefrom. The cover layer 110 is the outermost layer of the hose 100.

[0050] refer to Figure 2 , which depicts an all-rubber braided hose 200 , in a cutaway perspective view, the hose 200 includes an innermost layer 202 surrounded by a reinforcement layer 208 , and a cover layer 210 is the outermost layer of the hose 200 .

[0051] Now refer to Figure 3 , which illustrates a spiral barrier hose 300 in a cutaway perspective view. Hose 300 includes an innermost elastomeric tube 302 surrounded by a permeation-inhibiting layer 304. Adjacent to permeation-inhibiting layer 304 is a tie layer 306 having a spiral reinforcement layer 308 disposed outward therefrom. Surrounding spiral reinforcement layer 308 is a second tie layer 312 having a second spiral reinforcement layer 314 disposed thereon. Cover layer 310 is the outermost layer of hose 300.

[0052] Now refer to Figure 4 , which illustrates a cross-section of an isolation hose according to one embodiment of the present disclosure, wherein refrigerant and oil are present and contained. The cross-section is taken in a plane parallel to the longitudinal centerline of the hose, which centerline is indicated by a +. Additionally, for purposes of illustrating the concepts presented, this description is presented as linear and dimensionless. Hose 400 includes an innermost tube 402, which in some aspects is surrounded by an optional permeation inhibition layer 404, and disposed adjacent to permeation inhibition layer 404 is an optional connecting layer 406. Outwardly therefrom is disposed a reinforcement layer 408. Cover layer 410 is the outermost layer of hose 400. Present within an inner cavity 412 defined within innermost tube 402 are molecules 420 of 2,3,3,3-tetrafluoropropylene refrigerant and POE oil droplets 422. Because innermost tube 402 is formed from hydrogenated nitrile rubber (HNBR) cured with a reactive phenol-formaldehyde resin, the 2,3,3,3-tetrafluoropropylene refrigerant is stabilized, expansion caused by contact of the inner wall of innermost tube 402 with POE oil is minimized or substantially eliminated, and the formation of polymerized 2,3,3,3-tetrafluoropropylene molecules 424 is avoided. Consequently, innermost tube 402 is free of peroxides and any added sulfur or sulfur-containing materials, and inner lumen 412 is also free of polymerized 2,3,3,3-tetrafluoropropylene molecules 424.

[0053] Examples

[0054] The following examples illustrate some embodiments of the present disclosure, which are provided for illustrative purposes only and are not to be considered as limiting the scope of the present disclosure or the manner in which it may be practiced. Unless otherwise specified, parts (phr) are given by weight based on the amount of HNBR resin. In this experiment, a rubber formulation for the innermost layer of an AC hose was prepared, cured, and tested for the indicated physical properties.

[0055] Table 1:

[0056]

[0057] The cured rubber formulations were determined to have the physical properties provided in Table 2.

[0058] Table 2:

[0059]

[0060]

[0061] The above examples demonstrate that the rubber material forming the innermost tube has sufficient properties for this layer and has a volume expansion percentage of 10% or less and a hardness change of less than 10 Shore A durometer points when exposed to polyol ester oil at 125°C for 168 hours.

[0062] For the purpose of illustration and description, the foregoing description of the embodiments has been provided. Exemplary embodiments are provided so that this disclosure will be fully thorough and the scope will be conveyed to those skilled in the art. Many specific details, such as examples of specific parts, devices and methods, are set forth to provide a thorough understanding of the embodiments of this disclosure, but are not intended to be exhaustive or limit this disclosure. It should be understood that within the scope of this disclosure that the individual elements or features of a specific embodiment are generally not limited to this specific embodiment, but are interchangeable where applicable and can be used in the selected embodiment (even if not explicitly shown or described). This disclosure also can change in many ways. Such changes are not considered to depart from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

[0063] In addition, in some exemplary embodiments, well-known methods, well-known device structures, and well-known technologies are not described in detail. Furthermore, it will be apparent to those skilled in the art that in the design, manufacture, and operation of devices used to implement the contents described in this disclosure, there may be variations in device design, construction, condition, corrosion of components, and gaps between components.

[0064] Although can use term first, second, third etc. to describe various element, component, region, layer and / or part at this, these element, component, region, layer and / or part should not be restricted by these terms.These terms can only be used for an element, component, region, layer or part and another region, layer or part are distinguished.Unless context clearly points out, otherwise term such as " first ", " second " and other numerical terms do not imply order or sequence when used here.Therefore, when not departing from the teaching content of exemplary embodiment, the first element, component, region, layer or part discussed below can be referred to as second element, component, region, layer or part.

[0065] For ease of description, spatially relative terms, such as "inside," "adjacent," "outside," "below," "beneath," "lower," "above," "upper," etc., may be used herein to describe the relationship of one element or feature to another element or features, as shown in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if the device in the figures were turned over, elements described as "below" or "beneath" other elements or features would be oriented "above" the other elements or features. Thus, the example term "below" can encompass both above and below orientations. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein interpreted accordingly.

[0066] Although several embodiments of the present disclosure have been described in detail above, it will be readily understood by those skilled in the art that many modifications are possible without departing substantially from the teachings of the present disclosure. Therefore, such modifications are intended to be included within the scope of the present disclosure as defined in the claims.

Claims

1. A refrigerant hose (400), comprising: (a) an innermost tube (402) defining an inner lumen (412) therein, the innermost tube (402) comprising hydrogenated nitrile rubber (HNBR), a polymer blend containing HNBR, or a copolymer thereof, cured with a phenol-formaldehyde resin; (b) an optional permeation-inhibiting layer (404) surrounding the innermost tube (402); (c) a reinforcement layer (408) disposed outwardly from the innermost tube (402) and the optional permeation inhibiting layer (404); and, (d) a cover layer (410) disposed outwardly from the reinforcement layer (408); wherein the innermost tube (402) has a volume expansion percentage of 10% or less when exposed to polyol ester oil or polyalkylene glycol oil at 125°C for 168 hours; and, The innermost tube (402) is free of peroxides and contains no added elemental sulfur, sulfur donors, or additives containing sulfur within the additive's molecular structure.

2. The refrigerant hose (400) according to claim 1, further comprising a connecting layer (406) disposed between the optional permeation inhibiting layer (404) and the reinforcing layer (408) when the optional permeation inhibiting layer (404) is included in the refrigerant hose (400).

3. The refrigerant hose (400) of claim 1, further comprising 2,3,3,3-tetrafluoropropylene molecules (420) in the inner cavity (412).

4. The refrigerant hose (400) according to claim 3, wherein The inner cavity (412) is free of polymerized 2,3,3,3-tetrafluoropropylene molecules (420).

5. The refrigerant hose (400) according to claim 1, wherein The cover layer (410) is made of butyl (IIR), halogenated butyl (CIIR / BIIR), HNBR (HNBR), brominated isobutylene methyl-styrene (BIMS) or ethylene-propylene-diene monomer rubber (EPDM).

6. The refrigerant hose (400) according to claim 1, wherein The reinforcement layer (408) is a woven polyester fabric.

7. The refrigerant hose (400) according to claim 6, wherein The woven polyester fabric is a woven polyethylene terephthalate fabric.

8. The refrigerant hose (400) according to claim 1, wherein The reinforcement layer (408) is a woven fabric composed of glass fiber, cotton fiber, polyester fiber, polyaramid fiber or aramid fiber.

9. The refrigerant hose (400) according to claim 1, wherein The reinforcement layer (408) is a spiral reinforcement layer (408), and the refrigerant hose (400) further includes a second connection layer (312) surrounding the spiral reinforcement layer (408), and a second spiral reinforcement layer (314) arranged between the cover layer (410) and the second connection layer.

10. The refrigerant hose (400) according to claim 1, wherein The phenol-formaldehyde resin is brominated octylphenol-formaldehyde resin.

11. The refrigerant hose (400) according to claim 1, wherein The phenol-formaldehyde resin is an octylphenol-formaldehyde resin with a Lewis acid activator (halogen) added in the form of a halogenated organic compound.

12. The refrigerant hose (400) according to claim 1, wherein The phenol-formaldehyde resin is an octylphenol-formaldehyde resin with a Lewis acid activator (halogen) added in the form of a metal halide.

13. The refrigerant hose (400) according to claim 1, wherein A halogenated organic compound is added to provide a Lewis acid activator.

Images