JPH0432087B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to liquid copolymers of mercaptan-terminated polymers, such as polysulfides, and epoxy-terminated polymers, such as epoxy resins, which can be stored as prepolymers before final curing to form a fixed product. The production of resins by co-reaction of polyfluorides and polyepoxides in the presence of catalysts is well known. The reaction between the mercaptan groups of polysulfides and the oxirane groups of polyepoxides proceeds readily, and US Pat.
-A-2789958. US-A-
All but one of the examples presented in No. 2,789,958 describe the reaction between a liquid polysulfide and a so-called polyepoxide curing agent in the presence of an amine catalyst. The cured product was a hard, tough, sometimes rubbery material. In another example, a polysulfide polymer was prepared at 70°C in the absence of an amine catalyst.
and a polyepoxide curing agent for 6 hours at 25°C and 2 days at 25°C. The product was a tough rubbery polymer. The invention described in US-A-2,789,958 formed the basis for the use of polysulfide polymers as softeners for polyepoxy resins. In these systems, a liquid polysulfide polymer is mechanically mixed with a polyepoxide resin along with a catalyst, usually a tertiary amine. The resulting product is a tough, impact-resistant solid that can be attached to a wide variety of supports if necessary. The products of such processes have been used in the production of adhesives, paints, electronic encapsulation systems and moldings. GB-A-787022 describes self-curing resins prepared by mixing liquid or semi-solid epoxide resins with liquid aliphatic saturated polythiopolymercaptans. These resins are generally
Cure to a hard rubbery state within 24 hours, or in some cases 48 hours. According to the present invention, there is provided a curable liquid polymer composition having a stable viscosity before curing, said composition comprising epoxy groups of an epoxy-terminated polymer having at least two epoxy groups per molecule; a copolymer formed by an addition reaction between the mercaptan groups of a mercaptan-terminated polymer having at least two mercaptan groups per polymer; The substance has free mercaptan groups. The present invention also provides a method for preparing said composition, comprising reacting an epoxy-terminated polymer having at least two epoxy groups per molecule with a mercaptan-terminated polymer having at least two mercaptan groups per molecule. wherein the mercaptan-terminated polymer is in stoichiometric excess such that the final product has free mercaptan groups.
The composition so produced can be stored for subsequent curing with a curing agent reactive with said mercaptan groups to give a fixed copolymer. The basis of the invention is that stable liquid prepolymers can be produced by direct, non-catalytic reaction between liquid polymers with terminal or pendant mercaptan groups and solid or liquid polymers with terminal oxirane groups. In the present invention, mercaptan groups are in stoichiometric excess over oxirane groups. This limits the amount of chain extension and thus 2
Ensures that viscosity increases resulting from polymer binding are kept to a minimum. The product of the invention represents a new class of liquid polymer compositions containing alternating blocks of polysulfide and polyepoxide, depending on the relative proportions of the two components in the initial reaction mixture, containing block copolymers with mercaptan end groups. These liquid copolymers can be stored until needed for final curing, at which time the residual reactive groups of the copolymers can further participate in chain extension reactions and have useful commercial applications using conventional epoxide curing agents. A series of solid polymers can be produced. The products of the invention preferably have a viscosity at 25° C. not higher than 100 Pas, more preferably lower than 60 Pas. Their molecular weight usually ranges from 1600 to 5000, preferably not exceeding 3000. The reactions of the invention are preferably carried out at temperatures between 10 and 120°C, conveniently at relatively lower temperatures, e.g.
It can be carried out at 50°C, typically 20°C. High reaction temperatures and low viscosities can be obtained using relatively high temperatures, for example 60°C. The reaction can be carried out by simply combining the two components in the desired proportions, and the mixture is then allowed to stand until the reaction is complete.
The reaction mixture can include a solvent. The compositions of the present invention usually contain as major components a block copolymer of epoxy and mercaptan-terminated polymers. The ideal structure for a block copolymer is a polyepoxide molecule capped by two polysulfide molecules: HS with polysulfide

[Formula] Po epoxy

[Formula] Polysulfide - ABA structure containing SH. A typical adduct of this type has a molecular weight of about 1700. Typical polymer compositions of the invention also contain excess polymer in unreacted form. A slightly undesirable structure for a copolymer is: HS-Polysulfide-Polyepoxy-Polysulfide-Polyepoxy-Polysulfide-SH
as well as higher-grade analogues with a molecular weight of 3000 or greater. The viscosity of the latter analog is greater than that achieved in the ideal structure. The copolymers of the invention do not necessarily have an exclusively ideal structure, but preferred formulations according to the invention provide a predominantly ideal structure in the final product. The invention is not limited to the use of difunctional polysulfide polymers and difunctional polyepoxide polymers, ie, polymers having two functional groups per polymer molecule. Polymers with functionality greater than 2 can also be used to make liquid products. However, polymers with functionality much greater than 2 will yield solid products or liquid products with high viscosities that are difficult to handle. Copolymers produced by the chemistry described in this invention are designated as adducts. Basically, it is of the following type. Formed from mercaptan groups in stoichiometric excess over oxirane groups. The resulting liquid polymer product has no residual oxirane groups, may retain a mercaptan odor, has free mercaptan groups, and is treated with hardeners commonly used in polysulfide polymer technology, such as manganese dioxide. can be reacted. This product is known as permercaptan adduct. Permercaptan adducts can be used in technologies where mercaptan polysulfide polymers are currently used. Curing and crosslinking can be carried out by the use of reagents capable of oxidizing mercaptan groups to disulfide bonds, such as inorganic peroxides, dichromates and permanganates or organic hydroperoxides. It is customary, although not necessary, to form a compound of the liquid polysulfide polymer with powder fillers, plasticizers, thixotropic agents, adhesion promoters, and the like. Similar compounding principles apply to permercaptan adducts. The permercaptan adduct can also be mixed with other liquid polymers, such as polysulfide and polyepoxide polymers, in which case the mercaptan groups in the adduct will co-react with the mercaptan and oxirane groups of the other polymers, respectively. Permercaptan group adducts can also be blended with high molecular weight solid polysulfide polymers containing co-reacting free mercaptan groups. The addition of adducts to one of these polymers improves one or more properties in the cured product, such as tear strength, adhesion,
It is expected to enhance elastic recovery and abrasion resistance. In order for the theory of adduct production to be understood, certain terminology related to epoxy resins and liquid polysulfide polymers must be explained. Epoxy Group Content This term is used to mean the number of molecules of epoxide groups in one kilogram of epoxy-terminated polymer. Unit=mol/Kg LP Mercaptan Content The -SH mercaptan content of the liquid mercaptan-terminated polymer is usually expressed as a percentage. For co-reaction with epoxy-terminated polymers, the mercaptan content should be expressed in the same units as the epoxy group content, i.e. mol/Kg;
It is more useful to express it as For example, LP-33 (described in more detail later)
Has a mercaptan content of 5.76%, i.e. LP
-33 There are 0.0576 kg of mercaptan groups in 1 kg. Number of moles of mercaptan per kg = Weight of mercaptan group in 1Kg of polysulfide / Molecular weight of mercaptan group Molecular weight of mercaptan group = 0.033Kg Therefore, Number of moles of -SH in 1Kg of LP-33 = 0.
0576/0.033 = 1.75 mol/Kg Mercaptan content of LP-33 = 1.75 mol/Kg A low molar excess of mercaptan groups is generally preferred in perpolysulfide adducts, typically in the range of 1.5:1 to 3:1. Polysulfide/
Polyepoxide weight ratio. The preferred range is 3:1 to 6:1. The mercaptan-terminated polymers usually have an average molecular weight of 500 to 12,000, preferably not exceeding 2,000. The viscosity is preferably between 0.5 and 2.5 Pas and the mercaptan content is preferably between 1.5 and 2.5 mol/Kg. Mercaptan-terminated polysulfide polymers which are particularly suitable for the purposes of the present invention are characterized by the fact that they have repeating polysulfides between organic groups having at least two primary carbon atoms connected to disulfide bonds. Typical examples of disulfide polymers are those corresponding to the general formula HS-(-RSS-)P _x -RSH, where R is an organic polyvalent group, preferably primarily a divalent alkyleneoxahydrocarbon or thia hydrocarbon group, an example of which is shown in U.S. Patent No.
No. 2789958, where x is a number greater than 1,
A relatively low molecular weight for liquid polymers with a molecular weight of about 500 to 12,000, e.g. from 3 to 100 to about 100,000 to several million when R is -(C- _CH2 - _CH2 -)-. can vary up to a relatively large number in the case of solid polymers that can have . The low molecular _weight polysulfide polymers, _e.g.
(wherein y is usually larger than 2). A solid organic polysulfide polymer can be produced and split to give a liquid polythiol polymer by the method of US Pat. No. 2,466,963. The preferred liquid polysulfide used in making the liquid products of the present invention is manufactured by Morton Thiokol Incorporated and is known as LP. Three brands in particular are exemplified:

Table: In the production of adducts, the use of LP-33 results in adducts with lower and more stable viscosities than those based on LP-3. This is probably due to the low proportion of trifunctional components present in LP-33 (0.5
%, 2% in LP-3). Trifunctionality provides more sites for chain extension and polymer crosslinking by mercaptan-epoxy co-reaction. Cross-linking and chain extension lead to higher adduct molecular weights and therefore higher viscosities. It has been shown that the use of liquid polysulfides without trifunctionality results in adducts with lower and more stable viscosities than those based on LP-3 and LP-=3. ZL-1400C is one viable "zero-crosslinked" form of LP. A variety of commercially available epoxy resins can be used as the polyepoxy polymer to make the liquid polymer products of the present invention. Although the polyepoxide polymers used are usually liquid, the chemical principles also relate to solid polyepoxide polymers. Preferred polymers have an average molecular weight of 250-600. The preferred epoxy group content is in the range 2-6 mol/Kg. When liquid polymers are used, their viscosity is preferably between 0.5 and 20 Pas. Liquid epoxy resins formed from epichlorohydrin and bisphenol A and sold under the trade names "Epikote" and "Araldite" are particularly suitable. The properties of some of these epoxides are as follows:

Table It is also possible to use low molecular weight polyfunctional glycidyl compounds. These are often referred to as reactive diluents by manufacturers of polyepoxide polymers. One example is Anchar Chemicals' Heloxy 68.
, it has an epoxy molar mass of 135-155 g, a viscosity of 1-16 mPas at 25° C. and an average epoxide content of 6.89 mol/Kg (Heloxy is a registered trademark). The following examples are presented to more fully illustrate the features of the invention, but are merely illustrative and should not be construed as a limitation on the scope of the invention as defined in the claims. Example 1 250 g of Epicote 828 was mixed with 1000 g of LP-3. The mixture was kept at room temperature and after 24 weeks the oxirane concentration decreased to zero. First LP-3
and Epicote 828 means a 1.62 to 1 molar ratio of mercaptan groups to oxirane groups. The viscosity of the product was 66.0 Pas (25°C). product 100
g was mixed with 34.5 g of a paste consisting of 10 g of activated manganese dioxide, 12.5 g of liquid chlorinated paraffin and 0.5 g of tetramethylthiuram disulfide.
The formulation cured to an elastomeric solid in 90 minutes. Example 2 150g of Epicote 828 was mixed with 1000g of LP-3. When the mixture was kept at 60 °C for 14 weeks, the viscosity of the mixture increased from the initial value of 1.9 Pas to 2.0-2.5 Pasn. Infrared analysis of the product showed the presence of hydroxyl groups at 3500 cm ^-1 indicating that an adduct was formed. When this adduct was further stored at 60°C for 6 weeks, the viscosity increased to 3.75 Pas. After further storage at 25°C for 60 weeks, the final viscosity was 2.60 Pas, indicating the storage stability of the adduct. The original LP-3 to Epicote 828 ratio corresponds to a 2.7:1 ratio of mercaptan groups to oxirane groups. Example 3 150g of Epicote 828 was mixed with 1000g of LP-33. When the mixture was kept at 60°C for 14 weeks, the viscosity of the mixture increased from the initial value of 2.6 Pas to 3.4-3.7 Pas. Infrared analysis of the product showed the presence of hydroxyl groups at 3500 cm ^-1 indicating that an adduct was formed. When this adduct was further stored at 60°C for 6 weeks, the viscosity increased to 4.7 Pas. After further storage at 25°C for 60 weeks, the final viscosity was 3.60 Pas, indicating the storage stability of the adduct. The original LP-33 to Epicote 828 ratio corresponds to a 2.8:1 ratio of mercaptan groups to oxirane groups.

Claims (1)

[Scope of Claims] 1. A curable liquid polymer having a stable viscosity before curing, which has the following formula: HABDAH or HABDABDAH (where A is (-SC ₂ H ₄ OCH ₂ OC ₂ H ₄ S)- _a and B is and D is a mercaptan-terminated block copolymer represented by the following formula: H is a hydrogen atom, a is an integer from 3 to 7, and b is 1 or 2. 2. A copolymer according to claim 1 having a viscosity of 100 Pas or less at 25°C. 3. A copolymer according to claim 2 having a viscosity of 60 Pas or less at 25°C. 4. The copolymer according to claim 1, having a molecular weight of 1,600 to 5,000. 5. The copolymer according to claim 4, having a molecular weight not exceeding 3000. 6 A curable liquid polymer having a stable viscosity before curing, which has the following formula: HABDAH or HABDABDAH (where A is (-SC ₂ H ₄ OCH ₂ OC ₂ H ₄ S) - _a , and B is , D is [Formula], H is a hydrogen atom, a is an integer from 3 to 7, and b is 1 or 2). It's hot, (However, b is 1 or 2) An epoxy-terminated polymer represented by the following formula: H (-SC ₂ H ₄ OCH ₂ OC ₂ H ₄ S) - _a H (However, a is 3 to 7) A method characterized by reacting a mercaptan-terminated polymer represented by the following formula with a ratio of epoxy groups in the epoxy-terminated polymer to mercaptan groups in the mercaptan-terminated polymer that is less than 1. 7. The method of claim 6, wherein the reaction is carried out in the absence of a catalyst. 8. The method of claim 6, wherein the epoxy-terminated polymer has an epoxy content of 2 to 6 mol/Kg. 9. The method of claim 6, wherein the epoxy terminated polymer has a viscosity of 0.5 to 20 Pas. 10 The average molecular weight of the epoxy-terminated polymer is
7. The method according to claim 6, wherein the molecular weight is between 250 and 600. 11. The method of claim 6, wherein the mercaptan-terminated polymer is a liquid. 12 The mercaptan-terminated polymer is 0.5 to
7. The method of claim 6, having a viscosity of 2.5 Pas. 13. The method according to claim 6, wherein the mercaptan-terminated polymer has an average molecular weight of 500 to 12,000. 14 The mercaptan-terminated polymer has a molecular weight of 500 to 2000
14. The method of claim 13, having an average molecular weight of. 15. The method according to claim 6, wherein the reaction is carried out at 10 to 120°C. 16. The method of claim 6, wherein the molar ratio of mercaptan groups in the mercaptan-terminated polymer to epoxide groups in the epoxy-terminated polymer is from 1.5:1 to 3:1. 17. The method of claim 6, wherein the copolymer is stored as an uncured liquid and then cured with a curing agent to form a solid product.