RU2441039C2 - Method of obtaining heat- and frost-resistant siloxane rubber - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing modified high-molecular siloxane rubber involves modification thereof with diphenyloxy links while carrying out anionic copolymerisation of dimethylsiloxanes, methyl vinyl cyclosiloxanes and diphenyl silane diol at high temperature and stirring in the presence of an anionic polymerisation catalyst - sodium polydimethylsiloxane diolate. The invention is also characterised by use, during anionic copolymerisation, of an aromatic hydrocarbon selected from toluene or xylene as a solvent, as well as azeotropic distillation of water released during anionic copolymerisation.

EFFECT: high frost resistance and heat resistance.

3 cl, 4 ex

Description

The invention relates to the field of organosilicon elastomers, in particular to a process for producing modified high molecular weight siloxane rubbers with high thermal and frost resistance, which are used in many fields of machine and instrument making, in the cable and electrical industry. The currently used siloxane rubbers have frost resistance in the range of - 70 ° C.

Known [Karlin A.V. et al. Collection of Organosilicon Materials, Moscow, Chemistry, 1971, p. 170] a method for producing organosilicon rubber SKTFV-2 by polymerizing a mixture of dimethylcyclosiloxanes and octaphenylcyclotetrasiloxane (or other diphenyl-containing cycles) under the influence of anionic polymerization catalyst (polydimethylsilioxandi at a temperature of 150 ° C. The resulting rubber has frost resistance within minus 70 ° C.

The disadvantages of the process are the need for special purification of diphenyl-containing cycles from mono- and trifunctional impurities, which are respectively molecular weight regulators or three-crosslinking agents, as well as the risk of phenyl groups being cleaved off by the action of a strongly nucleophilic PDSK catalyst. Another disadvantage of this process is the impossibility of obtaining an optimal, close to statistical, distribution of modifying diphenylsiloxyl units along the macromolecule chain.

The closest in technical essence is the method [Goldovsky EA et al., Collection "Research in the field of physics and chemistry of rubbers and rubbers", Leningrad, LTI im. Lensoveta, 1975, p. 140] for the production of rubbers SKTFV 2103 and SKTFV 2101 containing 8-10% molar diphenylsiloxane units by anionic copolymerization of dimethyl-, methylvinylcyclosiloxanes with octaphenylcyclotetrasiloxane in the presence of a PDSK catalyst at a temperature of 150 ± 3 ° С. Rubbers are obtained with a molecular weight of 450,000 to 1,000,000 and frost resistance within minus 70 ° C.

The disadvantages of the process are the need for special purification of diphenyl-containing cycles from mono- and trifunctional impurities, which are respectively molecular weight regulators or three-crosslinking agents, as well as the risk of phenyl groups being cleaved off by the action of a strongly nucleophilic PDSK catalyst. Another disadvantage of this process is the impossibility of obtaining an optimal, close to statistical, distribution of modifying diphenylsiloxyl units along the macromolecule chain and, accordingly, with insufficiently high molecular weight. As a result, the thermostability and frost resistance of these rubbers is insufficient for operation in some climatic zones.

The aim of the present invention is to provide modified high molecular weight siloxane rubbers with high heat and frost resistance.

The proposed method for producing a particularly heat- and frost-resistant high molecular weight siloxane rubber involves modifying it with diphenylsiloxyl compounds. The specified method involves conducting anionic copolymerization of dimethylcyclosiloxanes, methylvinylcyclosiloxanes and diphenylsilanediol at an elevated temperature of 150-170 ° C and stirring in the presence of an anionic polymerization catalyst. At the same time, a commercially pure product, diphenylsilanediol (DFSD) of the general formula (C ₆ H ₅ ) ₂ Si (OH) ₂ , practically containing no trifunctional crosslinking microimpurities, as well as an undesirable growth-regulating microimpurity of tetraphenyldisiloxanediol, is used as a modifying diphenylsiloxane component. In addition, in order to exclude the removal of phenyl groups from DFSD, sodium polydimethylsiloxane diolate (PDSN) less nucleophilic than PDSK, which does not cause noticeable cleavage of benzene during anionic copolymerization and formed in situ upon interaction with NaOH, is used as an anionic polymerization catalyst. Distinctive features of the invention are the use of an aromatic hydrocarbon in the anionic copolymerization as a solvent — toluene or xylene, as well as azeotropic distillation of the water released during the anionic copolymerization. The use of such techniques in the process of anionic polymerization of siloxane rubbers, apparently, ensures the homogeneity of the mixture of siloxane cycles (octamethylcyclotetrasiloxane, methylvinylcyclosiloxanes) and diphenylsilanediol, as well as a shift in the equilibrium of the copolymerization reaction towards high molecular weight products due to azeotropic distillation of water anionotropically.

The following are examples of specific embodiments of the invention, illustrating, but not limiting it.

Example 1

In a 1 L four-necked glass reactor equipped with a stirrer, thermometer, direct Liebig cooler and nitrogen bubbler, 250 g of octamethylcyclotetrasiloxane, 0.5 g of methyl vinylcyclosiloxane, 10 g of crystalline diphenylsilanediol (DPSD), 0.01 g of NaOH are charged to form an in situ catalyst anionic polymerization - PDSN and pour 150 ml of toluene. The mixture is then heated with stirring to a temperature of 150-155 ° C for 1.5 hours with a nitrogen purge, collecting 159 g of the toluene-water azeotrope in the receiver. Get the copolymerizate with a refractive index at 20 ° C p _d = 1.4280 and a molecular weight of 240 thousand. After neutralizing the PDSN in a paddle mixer 20 ml of a 1% aqueous solution of MgSO ₄ for 2 hours, as well as de-volatilization for 24 hours in a vacuum oven at a temperature of 150 ° C to give 215 g of the modified rubber SKTFV with a refractive index n _d ²⁰ = 1.4292, a molecular weight of 380 thousand. (determined by viscometry) and _a glass transition temperature T = -98 ° C, which corresponds to degrees of frost resistance -98 ° C. Such rubber is suitable for the production of universal thermofreeze-resistant siloxane rubbers. Thermostability at a temperature of 280 ° C is 4.17%.

Example 2

250 g of cyclodimethicone (a mixture of dimethyl cyclosiloxanes), 0.5 g of methyl vinylcyclosiloxanes, 10 g of crystalline DFSD, 0.01 g of NaOH to form an in situ anionic polymerization catalyst, PDSN, are charged into a 1 liter glass four-necked reactor and 150 ml of toluene are added. The mixture is heated with stirring to a temperature of 150-160 ° C for 1 hour with a nitrogen purge, collecting 159 g of a toluene-water azeotrope in the receiver. A copolymerizate is obtained with a refractive index at 20 ° С p _d ²⁰ = 1.4275 and a molecular weight of 285000. After neutralizing the PDS in a paddle mixer, 20 ml of a 1% aqueous solution of MgSO ₄ , as well as after 24 hours of volatilization at a temperature of 150 ° C, vacuum oven, get 218 g of rubber SKTFV with a refractive index of n _d ²⁰ = 1,4288, a molecular weight of 390000 (determined by the method of viscometry) and a glass transition temperature T _c = -100 ° C, which corresponds to a degree of frost resistance of -100 ° C. Such rubber is suitable for the production of universal thermofreeze-resistant siloxane rubbers. Thermostability at a temperature of 280 ° C is 3.08%.

Example 3

250 g of cyclodimethicone (a mixture of dimethyl cyclosiloxanes), 0.5 g of methyl vinylcyclosiloxanes, 25 g of crystalline DFSD, 0.01 g of NaOH to form an in situ anionic polymerization catalyst, PDSN, are charged into a 1 liter glass four-necked reactor and 150 ml of o-xylene are added. The mixture is heated with stirring at a temperature of 170 ± 3 ° C for 1 hour with a nitrogen purge, collecting 163 g of the xylene-water azeotrope in the receiver. Obtained copolymer with a refractive index at 20 ° C n _d ²⁰ = 1,4300-1,4305 and molecular weight above 260000. After neutralization PDSN in a paddle mixer with 20 ml of a 1% aqueous solution of MgSO _4, as well as after 24 hours at obezletuchivaniya temperature of 150 ° C in a vacuum oven to give 225 g SKTFV rubber with a refractive index n _d ²⁰ = 1.4312, a molecular weight of more than 340,000 (determined by viscometry) and a glass transition temperature T _c below -107 ° C, suitable for producing versatile heat- and frost-resistant siloxane rubbers. Thermostability at a temperature of 280 ° C is 4.75%.

Example 4 (comparative)

400 g of octamethylcyclotetrasiloxane, 28 g of previously double-recrystallized (from heptane) octaphenylcyclotetrasiloxane, 0.05 g of 20% potassium polymethylsiloxane diolate (PDSK) and 0.15 g of methylvinylcyclosiloxane are charged into a 1 L glass reactor. The mixture is heated with stirring to a temperature of 155 ° C and copolymerization is carried out under nitrogen for 3.5-4.5 hours. Depending on the quality of octaphenylcyclotetrasiloxane receive either a low molecular weight rubber type SKTNF different marks (D, E, F) or structured strongly smelling benzene copolymer with a refractive index n _d ²⁰ = 1.4255, a molecular weight of about 40000 (determined by viscometry) and glass transition temperature T _c = -70 ° C, which corresponds to a degree of frost resistance of -70 ° C. Such rubber is not suitable for universal thermo-frost-resistant siloxane rubbers. Only the use of reactively pure “bpm” grade octaphenylcyclotetrasiloxane allows one to obtain a copolymerizate with a molecular weight of 310,000 (determined by the method of viscometry) and a glass transition temperature T _c = -85 ° C, p _d ²⁰ = 1.4260, which after neutralization is 20 ml 1% aqueous solution of MgSO ₄ for 2 hours and obezletuchivaniya vacuum for 24 hours at a temperature of 150 ° C gives a rubber SKTFV n _d ²⁰ = 1.4280 and a molecular weight of 390,000 (determined by viscometry), suitable for the manufacture of rubbers.

Claims (3)

1. A method of producing a modified high molecular weight siloxane rubber by anionic copolymerization of dimethylcyclosiloxanes, methylvinylcyclosiloxanes and modifying diphenylsiloxane diol and units in the presence of an anionic copolymerization catalyst at elevated temperature, characterized in that the process of anionic copolymerization is carried out at a temperature of 150-170 ° C with a solvent in the presence of azeotropic distillation of water, and use as anionic copolymerization catalyst sodium olidimetil-siloksandiolyat (PDSN) as well as modifying difenilsiloksi-units using diphenylsilanediol. 2. The method according to claim 1, characterized in that toluene is used as a solvent. 3. The method according to claim 1, characterized in that xylene is used as a solvent.