RU2178424C2 - Method of preparing modified polymeric materials with controllable brittleness and based on epoxy resins - Google Patents

Abstract

FIELD: chemistry of polymers. SUBSTANCE: modified polymeric materials based on epoxy resins are prepared by mixing epoxydiane resin, hardener such as primary or secondary amine or catalyst such as tertiary amine and modifier in amount of 2-30 wt. % of composition. Modifier includes alkyl acrylates containing volume alkyl substituents of formula:

Description

 The invention relates to the field of technology for the production of polymeric materials based on thermosetting synthetic resins, namely epoxy resins (ES).

 ES is a large-tonnage industrial product with very good technological properties when processed into materials and products due to the development of ES curing methods for a wide variety of conditions (low, moderate and high temperatures, juice components - hardeners of various chemical nature: polyfunctional amines, acids, etc.) . In addition, cured ES have a high level of useful properties, of which the most valuable is the combination of high strength with very high adhesive ability. Therefore, the field of application of ES in a wide variety of technical fields is constantly expanding, and this trend stimulates efforts towards the modification of ES in order to improve individual properties.

 The most developed direction of such a modification is the use of additives of modifier substances (BM), mixed into the initial ES composition before curing begins. Further, during curing, the modifiers, depending on their nature, variously evolve in the forming matrix of a networked ES polymer.

 VMs of the type of polymers, due to thermodynamic incompatibility with the matrix-forming polymer, ES, as a rule, undergo phase separation and stand out as a dispersion. Modifiers of this type are usually opaque, and the initial compositions at the optimum (from the point of view of influence on the properties) content of VMs of 15 - 20% are quite highly viscous, which limits their technological capabilities. For example, the cost of molding products increases significantly due to the need for injection molding instead of free casting.

 The use of low molecular weight compounds as VMs from this point of view has undoubted advantages. More than 2000 patents over the past 15 years that have appeared in this direction are a vivid confirmation of this. As low molecular weight VMs, monomers and oligomers of the acrylic series — acrylates and methacrylates — are widely used. Their use allows you to implement the following options.

 1. The formulation of ES compositions is formed in such a way that it lacks components capable of chemically interacting with VMs of the type of (meth) acrylates during curing. In this case, the initiator of the radical polymerization of (meth) acrylates is added to the formulation, which triggers when heated at a certain temperature and converts (meth) acrylate into the corresponding polymer at a given stage of ES curing. If this occurs at the initial stage and the polymerization process develops in parallel with the process of forming a networked ES polymer, then phase separation is observed and the BM polymer forms a dispersion phase in the medium of the matrix polymer. In this case, the modification effect is the same as if, instead of low molecular weight (meth) acrylate, but its polymer was used as the initial VM. But on the other hand, technological limitations during molding associated with the high viscosity of the initial ES compositions are eliminated.

 If a sufficiently high-temperature initiator is selected that is triggered already after the formation of the matrix-forming ES polymer is completed, the polymerization of (meth) acrylate in a densely-mesh polymer matrix is not necessarily accompanied by phase separation with the formation of a dispersion - this process may turn out to be diffusion-frozen. In this case, the modifier is transparent and has the structure of either a “snake in a cell” (if the VM molecule contains only one double bond and a linear polymer “snake” is formed during polymerization), or a “network in a network” (“interpenetrating networks”, “interpenetrating networks” ") if (meth) acrylate is an oligoester acrylate (OEA) containing two or more double bonds in the molecule and forming a densely-linked polymer during polymerization.

Здесь R₃ = H (для акрилата) или R₃ = CH₃ (для метакрилата). Эта реакция, известная как реакция Михаэля, позволяет использовать (мет)акрилаты для модификации аминоотверждаемых композиций ЭС на молекулярном уровне, то есть как компоненты, химически встраивающиеся в структуру сетчатой макромолекулы матричного полимера. При этом (мет)акрилаты, содержащие одну двойную связь в молекуле, M₁, и две и более двойных связей, M_n (n ≥ 2), будут по-разному влиять на топологию образующейся матричной сетки. Молекулы M₁, замещая в узлообразующих аминных атомах азота валентности, предназначенные для образования межузловых цепей сетки, на подвески >N-CH₂CH(R₃)R₂, уменьшают тем самым густоту результирующей матричной сетки, формируя число топологических дефектов типа "свободных концов", равное числу молекул добавки M₁. В отличие от M₁ молекулы M_n (n ≥ 2) химически встраиваются в сетчатую макромолекулу матричного полимера не в виде "свободных концов", а в качестве межузловых цепей, точно также как это свойственно и самим молекулам ЭС. Если при этом n > 2, то такие межузловые цепи окажутся носителями дополнительных центров разветвления (узлов сетки).2. The formulation of the ES composition is formed in such a way that it contains components capable of chemically interacting with (meth) acrylates. Such a chemically active component is the most common amine type ES hardeners (diamines, polyamines). The latter have extremely high reactivity with respect to (meth) acrylates, entering into a reaction with them of the addition of primary and secondary amine groups to a double bond with the formation of the corresponding amino adduct:

Here, R ₃ = H (for acrylate) or R ₃ = CH ₃ (for methacrylate). This reaction, known as the Michael reaction, allows the use of (meth) acrylates to modify the amino-curable ES compositions at the molecular level, that is, as components chemically incorporating into the structure of the network macromolecule of the matrix polymer. In this case, (meth) acrylates containing one double bond in the molecule, M ₁ , and two or more double bonds, M _n (n ≥ 2), will have different effects on the topology of the formed matrix network. Molecules M ₁ , replacing valencies in knot-forming amine nitrogen atoms, intended for the formation of interstitial network chains, with> N-CH ₂ CH (R ₃ ) R ₂ pendants, thereby reducing the density of the resulting matrix network, forming the number of topological defects of the type of "free ends "equal to the number of molecules of the additive M ₁ . Unlike M _1, M _n molecules (n ≥ 2) chemically integrate into the network macromolecule of the matrix polymer not in the form of "free ends", but as interstitial chains, just like the ES molecules themselves. If in this case n> 2, then such inter-nodal chains will prove to be carriers of additional branching centers (mesh nodes).

Both variants of the modification of ES with additives of (meth) acrylates are reflected in the patent literature. Moreover, the first option — the radical polymerization of (meth) acrylates in ES media that do not contain hardeners of the type of primary and secondary amines — was even the subject of a detailed discussion in the monograph [P. Sperling. Interpenetrating polymer nets and similar materials. M.: World. 1984.]. The second option is the application of the Michael reaction to the process of modifying the ES with (meth) acrylate additives (patent US 4675374. Solventless polymeric composition reaction product of (1) adduct of amine and acrylate with (2) polyacrylate. June 23. 1997. (July 18. 1985). Nichols, Gus. ]: as components of ES compositions, the amine - (meth) acrylate pairs are listed in combinations covering almost all known amine hardeners and monomers (oligomers) from the series of (meth) acrylates, including both M ₁ and M _n (for n from 2 to 6). However, the effect of the modification is claimed in the patent only in relation to improving the specific properties of coatings based on ES compositions. In particular, in the patent [US Pat. No. 4,675,374. Solventless polymeric composition reaction product of (1) adduct of amine and acrylate with (2) polyacrylate. June 23. 1997. (July 18. 1985). Nichols, Gus. ] does not contain information allowing, by applying this invention, to regulate one of the most important properties of materials based on ES - their fragility.

 In the patent [patent GB 1247116. Process for producing high-impact thermosetting compositions. Sept. 22.1971. Lee Marion Porter at al. ], where the ES composition is cured with a stepwise increase in temperature in the presence of amine hardeners, brittleness is controlled by mixing ES compositions with modifiers, which use insoluble crosslinked elastomers in an amount of 3-30 wt. %, forming a dispersion in the environment of the ES. In this case, it is possible to double the value of the Izod impact strength, chosen as the characteristic of brittleness.

 Closest to the claimed technical solution is the "Method of producing a binder for coatings" described in the patent SU 679150. The prototype has a wide coverage of the nature of the starting components, the technical solution of the invention is aimed at eliminating the stickiness of the coatings. According to the invention, SU 679150, a method for producing a binder comprises curing an epoxy compound with (meth) acrylic derivatives and a hardener, a primary or secondary amine, as well as a catalyst. The disadvantage of the prototype is that the proposed solutions cannot be applied to a block, non-solvent technology for producing materials based on ES-compositions. In addition, the disadvantages of the prototype include the multicomponent binder and multi-stage process, as well as the need for curing with ultraviolet or electron rays.

 The objective of the invention is to simplify the process if it is possible to obtain materials based on ES compositions with reduced brittleness without the use of solvents.

The problem is solved by the claimed method of producing modified polymeric materials with controlled brittleness based on epoxy resins, including mixing epoxy resin, hardener, modifier and curing with a stepwise increase in temperature, in which (meth) acrylates containing bulk alkyl substituents in the molecules are taken C _n H _{2n + 1} , n = 6-12 (preferably n = 8-10), and / or (meth) acrylates containing -OC (O) O- carbonate atomic groups, and / or amino adducts of these alkyl acrylates and (meth ) acrylates at the content of modifiers in ES compositions 2 - 30 wt. %, and curing is carried out with a stepwise increase in temperature. In addition, in the inventive method, the curing of ES compositions is carried out in the presence of a catalyst (tertiary amines), and a radical polymerization initiator selected from the group comprising organic peroxides, hydroperoxides, azodinitriles, etc. in an amount of 0.1 - 3% by weight is introduced compositions providing complete polymerization of modifiers. In addition, primary or secondary amines selected from the group of aliphatic, cycloaliphatic, aromatic di and polyamines are used as hardeners, while the composition is balanced in such a way that the molar concentration of amine groups is equal to the sum of the molar concentrations of epoxy groups of the epoxy resin and double bonds of the modifier .

The synthesis of amino adducts is carried out by the interaction of primary or secondary amines with alkyl acrylates or (meth) acrylates containing carbonate groups, with their isolation, analytical control and the subsequent introduction of the amino adduct as a modifier. In this case, curing is carried out at a temperature of the first stage of curing 20 - 50 ^o C, providing the reaction of the hardener - the primary or secondary amine with the modifier to form an amino adduct at a higher rate compared to the main curing reaction - by attaching the epoxy groups of the epoxy resin to the amine groups of the hardener . It is also proposed that the temperature of the first stage of curing is maintained in the range of 50 - 120 ^o C, while the reaction of the hardener, the primary or secondary amine, with the modifier will be ensured until the formation of the amine adduct at a rate commensurate with the rate of the main curing reaction by the addition of epoxy groups of epoxy resins to amine groups of the hardener. Modifiers are taken in an amount of 2 to 30 wt. % based on the composition. As modifiers, a mixture of alkyl acrylates, (meth) acrylate containing carbonate groups, with each other and with their amino adducts can be used.

 The proposed method for modifying ES with additives of (meth) acrylates in order to reduce brittleness is intended for use in any ES-based compositions cured both without the use of primary (or secondary) amines (for example, catalytic curing with tertiary amines) or with primary (or secondary) ) di- (or poly-) amines as ES hardeners. The essence of the invention lies in the fact that we were able, from the variety of monomers and oligomers of the acrylic series, (meth) acrylates, to select representatives (alkyl acrylates with bulky alkyl substituents and oligocarbonate (meth) acrylates), which are characterized by unpredictably high efficiency as modifiers that reduce the fragility of materials based on ES. In this case, the following additional advantages arise.

 For the case of catalytic curing of ES, the effect of modification is also manifested in the absence of phase separation with the formation of a dispersion, which makes it possible to obtain transparent materials with reduced brittleness. Usually, the reduction of fragility for such systems is achieved only if phase-separating modifiers are used, forming dispersions that cloud the resulting material [P. Sperling. Interpenetrating polymer nets and similar materials. M.: Mir, 1984].

 In the proposed method, in most cases, the addition of a modifier that provides a significant reduction in brittleness (while brittleness in terms of the energy of viscous fracture is reduced by 7-8 times compared with non-modifiable material) practically does not affect the elastic modulus (E) of the cured ES (and in some cases even increases it). The patent literature cites data from which it follows that usually the value of E decreases with increasing concentration of the additive that controls the fragility, for example, according to the patent [US patent 5362799. Unsaturated polyester-flexible polymer network composition. Nov. 8. 1994. Frederic J. Ms. Carry at al. ] a decrease in brittleness by a factor of 5–10 (in terms of fracture toughness G) leads to a drop in E by almost the same amount.

As a result of experimental testing of representative sets of monomers and oligomers from the series of (meth) acrylates, R ₂ (R ₃ ) C = CH ₂ , with a systematically varying structure of the substituents R ₂ and R ₃ , regularities were established that allowed the selection of compounds with the highest efficiency as fragility modifiers. Experimental testing was carried out using a special express method for measuring the physicomechanical characteristics of cured modified ES compositions on mini-samples weighing ~ 0.1 g. Additional testing of promising samples selected by the express method was carried out in accordance with ASTM standard D1708-66 and ASTM D5045-91.

 Based on the data obtained, the following modifier substances are proposed as highly effective ES modifiers that control brittleness, which simultaneously fulfill the role of technological additives that reduce the viscosity of modified ES compositions.

1. Alkyl acrylates of the formula CH ₂ = CHCOOC _n H _{2n + 1} with a bulky alkyl substituent C _n H _{2n + 1} , the value of which satisfies the condition 6 ≤ n ≤ 12 (preferably n = 9 for unbranched C _n H _{2n + 1} and n = 8-10 for branched isomers).

,
где R₁= H (олигокарбонатакрилат) или CH₃ (олигокарбонатметакрилат), R₂ - гетероцепь, содержащая в качестве звеньев карбонатные группы

,
например

или

Вещества ОКМ-2 и ОКМ-5 были синтезированы, очищены и охарактеризованы по методике [А. А. Берлин, Г. В. Королев, Т. Я. Кефели, Ю. М. Сивергин. Акриловые олигомеры и материалы на их основе. М. : Химия, 1983, с. 232] .2. Oligocarbonate (meth) acrylates of the formula

,
where R ₁ = H (oligocarbonate acrylate) or CH ₃ (oligocarbonate methacrylate), R ₂ is a hetero chain containing carbonate groups as units

,
eg

or

Substances OKM-2 and OKM-5 were synthesized, purified and characterized according to the method [A. A. Berlin, G.V. Korolev, T. Ya. Kefeli, Yu. M. Sivergin. Acrylic oligomers and materials based on them. M.: Chemistry, 1983, p. 232].

 Amino-adducts of alkyl acrylates (p. 1) and oligocarbonate (meth) acrylates (p. 2) are the products of the addition of these (meth) acrylates to amines - hardeners of ES according to the Michael reaction. Aliphatic (e.g. diamine dicyclohexylmethane) and aromatic (e.g. metaphenylenediamine) diamines were used as amines.

The synthesis of amino adducts is carried out in a reactor with or without stirring in an air-insulated atmosphere, with the exception of high-temperature (T> 120 ^o C) syntheses, when an inert atmosphere (nitrogen, argon) is used to avoid oxidation by atmospheric oxygen.

 Nonilacrylate (HA), hexyl acrylate (HA), decyl acrylate (DA), OKA-2, OKM-2, OKM-5, 2-ethylhexyl acrylate (EGA), triethylene glycol dimethacrylate (TGM-3), and the adduct NA with hexamethylenediamine (HMDA), HA adduct with diaminodicyclohexylmethane (DADCM), OKA-2 adduct with DADCM, OKM-2 adduct with 4,4'-diamino-3,3'-dichlorodiphenylmethane (DADCHFM), Na adduct (metafenedi).

Based on the results of studying the kinetics of the synthesis of amino adducts by the calorimetric method, temperature conditions were optimized in which, in a modified ES composition with alkyl acrylates or methacrylates containing carbonate groups, the rate of the synthesis reaction of the amino adduct is significantly higher than the cure rate - the addition of epoxy groups to amine hydrogens in the temperature range 20-50 ^o C. At temperatures of 50 - 120 ^o C, the cure rate for epoxy groups and the rate of synthesis of amino adducts are comparable.

 The samples presented in the examples were studied by standard methods: strength σ, elastic modulus E and fracture strain ε under uniaxial tension in accordance with ASTM standard D1708-66, and viscous fracture energy G in accordance with ASTM standard D5045-91. Alkyl acrylates with an alkyl substituent length n = 6 to 12 units, oligocarbonate (meth) acrylates and / or their adducts with amines added to ES compositions in concentrations up to 30 wt. %, significantly increase the parameter G (reduce fragility), without decreasing E, which significantly distinguishes them from all the previously patented modifiers. In some cases (for moderate modifier concentrations, up to 10%), E even increases in parallel with G.

 For the amine curing of the ES composition, their composition must be balanced in such a way that the amino adducts of (meth) acrylates are first synthesized according to the well-known Michael reaction with their isolation, analytical control and then introduced as a modifier into the original ES composition.

 The invention is illustrated by the following examples.

 Example 1

To obtain a modified epoxy resin, a bisphenol A diglycidyl ether (DMEBA) with MM ~ 378 and (meth) acrylate are placed in an mixer equipped with a device for controlled heating, a thermometer, a device for evacuating and filling the mixer chamber with inert gas, and stirred under vacuum P ~ 0.8 mmHg. Art. at a temperature of T ≅ 50 ^o C for 15 min, fill the chamber with an inert gas and add diaminodicyclohexylmethane (DADCM) in an amount corresponding to the equation [EG] + [DS] = [AB] ([EG], [DS], [AB] - molar concentrations, respectively, of epoxy groups, double bonds, amine hydrogens). The ratios of all components for the compositions of the example are given in table. 1. The composition is stirred under vacuum P ~ 0.8 mm RT. Art. for 10 min at T = 40 ^o C and poured into molds heated to 50 ^o C. The molds are placed in a heating cabinet where curing is carried out according to the following regime: at T = 30 ^o C - 29 hours, 90 ^o C - 19.5 hours, 162 ^o C - 10 hours; then cool the form at a rate of not more than 0.8 ^o C / min. The physicomechanical properties of the samples were investigated according to ASTM D1708-66 and ASTM D5045-91. The results are shown in table. 7.

 Example 2

 A modified ES is obtained under the conditions of Example 1, but instead of diamine, a dimethylbenzylamine catalyst (DMBA) is added in an amount of 3% with respect to the mass of DHEBA and the initiator of radical polymerization is dicumyl peroxide (MPC). The ratio of all components for the compositions of example 2 are given in table. 2.

Curing is carried out according to the following mode: 70 ^o C - 21 hours, 120 ^o C - 10 hours, 150 ^o C - 28 hours; after which the molds are cooled at a speed of not more than 0.8 ^o C / min. The results of physical and mechanical tests of the samples are given in table. 7.

 The Michael reaction synthesized the adducts of (meth) acrylates with amines described in [US Pat. No. 4,675,374. Solventless polymeric composition reaction product of (1) adduct of amine and acrylate with (2) polyacrylate. June 23. 1997. (July 18. 1985). Nichols, Gus. ]. The molecular weights of the isolated and purified products were measured by the cryoscopic method. Functional groups were quantitatively analyzed by chemical and spectral methods. The composition and characteristics of the adducts used in the following examples are given in table. 3.

 Example 3

The modified resin is obtained under the conditions of example 1, but together with (meth) acrylate or instead of (meth) acrylate, an adduct is introduced, and curing is carried out according to the following regime: 70 ^o C - 10 h, 100 ^o C - 20 h, 160 ^o C -10 h, after which the molds are cooled at a speed of not more than 0.8 ^o C / min The ratio of all components for the compositions of example 3 are given in table. 4. The results of physical and mechanical tests of cured samples are given in table. 7.

 Example 4

The modified resin is obtained under the conditions of Example 3, but in addition to (meth) acrylates, mixtures of them with adducts are used as modifiers, and instead of cycloaliphatic diamine, aromatic - 4,4'-diamine-3,3'-dichlorodiphenylmethane (DADXDM) is introduced and the curing mode is changed : 120 ^o C - 17 h, increase the temperature to 170 ^o C at a speed of 10 ^o C / h and at 170 ^o C they withstand 170 h. The molds are cooled at a speed of not more than 0.8 ^o C / min. The ratio of all components for the compositions of example 4 are given in table. 5. The results of physical and mechanical tests of the samples are given in table. 7.

 Example 5

 The modified resin is obtained under the conditions of Example 2, but instead of (meth) acrylate, adducts and mixtures thereof with (meth) acrylates are introduced, and cumyl hydroperoxide (CCP) is taken as the initiator of radical polymerization. The ratio of components for the compositions of example 5 are given in table. 6. The test results of the cured samples are shown in table. 7.

 Thus, the claimed technical solution allows to obtain modified polymer transparent materials based on epoxy resins with reduced brittleness.

Claims (7)

1. A method of producing modified polymeric materials with controlled brittleness based on epoxydian resins by mixing an epoxydian resin, a hardener - a primary or secondary amine or a catalyst - a tertiary amine, a modifier, followed by curing of the resulting composition, characterized in that alkyl acrylates containing molecules volumetric alkyl substituents of general formula C _n H _{2n + 1} where n = 6-12 and / or (meth) acrylates containing carbonate atomic group -OC (O) O-, and / or at aminoaddukty those indicated acrylates or (meth) acrylates, wherein the modifier content of 2-30% by weight of the composition, and curing is carried out at stepwise increasing temperature.  2. The method according to p. 1, characterized in that the curing is carried out in the presence of a tertiary amine catalyst and an initiator of radical polymerization selected from the group comprising organic peroxides, hydroperoxides, azodinitriles, etc. in an amount of 0.1-3% of the mass of the composition, providing complete polymerization of the modifier.  3. The method according to p. 1, characterized in that as the hardener use primary or secondary amines selected from the group of aliphatic, cycloaliphatic, aromatic di and polyamines, while the composition is balanced so that the molar concentration of amine groups is equal to the sum of molar concentrations of the epoxy groups of the epoxy resin and double bonds of the modifier.  4. The method according to p. 1, characterized in that the synthesis of amino adducts is preliminarily carried out by reacting primary or secondary amines with alkyl acrylates or (meth) acrylates containing carbonate groups with their evolution, analytical control followed by the introduction of the amino adduct as a modifier. 5. The method according to PP. 1, 3, characterized in that the curing is carried out at a temperature of the first stage of curing 20-50 ^o With, this ensures the reaction of the hardener - the primary or secondary amine with the modifier to the formation of the amino adduct with a higher speed compared with the main curing reaction - by joining epoxy groups of epoxy resin to hardener amine groups. 6. The method according to PP. 1, 3, characterized in that the curing is carried out at a temperature of the first curing step of 50-120 ^o C, while the reaction of the hardener - the primary or secondary amine with the modifier is ensured until the formation of the amino adduct at a rate commensurate with the speed of the main curing reaction - the addition of epoxy epoxydioxide resin groups to hardener amine groups.  7. The method according to p. 1, characterized in that as a modifier use a mixture of alkyl acrylate, (meth) acrylate containing carbonate groups, with each other and with their amino adducts.

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