RU2550364C1 - Method of modifying polydimethylsiloxane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of modifying polydimethylsiloxane by methods of radiation polymerisation. Claimed is a method of modifying polydimethylsiloxane by the action of ionising radiation on a polymer under the pressure not higher than 10^-4 mm Hg, with the application for the modification of an octamethylcyclotetrasiloxane admixture, contained in the polymer. For this purpose used is X-ray radiation of the average energy ~30 keV in the interval of doses from 5 to 20 kGy or gamma-radiation Co⁶⁰ in the interval of doses from 5 to 20 kGy.

EFFECT: possibility of obtaining polydimethylsiloxane with improved physical-chemical characteristics by the technological method, which does not require the application of organic solvents.

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Description

The invention relates to the field of high energy chemistry, in particular to a method for modifying polydimethylsiloxane, and can be used to obtain new silicon-containing materials with a wide range of applications, including biologically inert polymers, as well as materials resistant to radiation.

It is known that the modification of polymers, including polymethylsiloxane, methods of radiation polymerization and radiation grafting polymerization is an effective way to change their physico-chemical characteristics. However, the search for modification possibilities without additional introduction of modifiers made it necessary to study the mechanism of radiolysis of polydimethylsiloxane and impurities inevitably formed during synthesis.

A known method of modifying polydimethylsiloxane rubber by irradiation with ultraviolet light in the presence of a photoinitiator, which is used as organic carbonyl-containing compounds of a number of aromatic ketones and quinones (RF Patent No. 2196784, CL C08G 77/38).

However, this method uses carbonyl-containing quinones and ketones, which not only modify polymethylsiloxane rubbers, but also introduce photosensitive groups into the composition of the material, which can stimulate the destruction of the material, especially in the presence of atmospheric oxygen.

Known photochemical oxidation of polydimethylsiloxane (Israeli Y. etc. Photooxidation of PDMS oils. Effect of dimetylene groops // Polym. Degrad. & Stab. 1993. V.42. No. 3. P.267-279) due to the disclosure of the existing double bonds.

The closest is the method of direct modification of polydimethylsiloxane by the action of ionizing radiation on a mixture of polyorganosiloxane powder with a modifying additive, i.e. a polymer containing double bonds and allowing grafting to low molecular weight PDMS rubbers of unsaturated compounds (AC 176069, BI 1965, No. 21).

However, this method does not allow to obtain materials based on polydimethylsiloxane that do not contain double bonds, as is obvious from the above prototype.

The technical result of the invention is to improve the physicochemical properties of the material, simplify the process and improve the environment due to the fact that organic solvents are not used additionally.

This technical result is achieved by the method of modifying polydimethylsiloxane by the action of ionizing radiation on the polymer at a pressure of not more than 10 ^-4 mm Hg, and when irradiated, the admixture of octamethylcyclotetrasiloxane contained in the polymer reacts.

For irradiation using x-ray tube 5BHV-Wt average energy of ~ 30 keV in the dose range from 5 to 20 kGy or gamma radiation Co ⁶⁰ in the dose range from 5 to 20 kGy.

A method for modifying polydimethylsiloxane (PDMS) without additional reagents is proposed, which involves irradiation in a vacuum in the presence of a crosslinking agent, which uses octamethylcyclotetrasiloxane (D ₄ ), which is contained in the PDMS matrix of block copolymers as an impurity in an unbound state in the amount of ~ 8%, in the temperature range of 150-300K and doses of ionizing radiation of 5-20 kGy. This modification leads to the sewing of D ₄ to the PDMS matrix and to prevent sweating or evaporation of unbound impurities from the material. In addition, the modification leads to an improvement in the mechanical properties of the material: an increase in dynamic viscosity and elongation (FIGS. 2 and 3). Figure 2 shows the dependence of the dynamic viscosity of the film samples of the BSP 20: 5 block copolymer on shear rate (1 - before irradiation, 2-10 kGy, 3-30 kGy, 4-70 kGy). The dynamic viscosity was measured on a Rheostress instrument with a controlled shear rate with a plane-plane measuring cell (d = 20 mm, a gap of 0.5 mm at T = 90 ± 0.1 ° C). It has been shown that at doses of 0-30 kGy, the dynamic viscosity changes slightly with an increase in the shear rate by two orders of magnitude. However, for reasons of economic feasibility, we settled on doses of 5-20 kGy. This is due to the formation of crosslinks with octamethylcyclotetrasiloxane. When the absorbed dose is increased to 70 kGy, the dynamic viscosity changes significantly.

The elongation was measured on a Tinius Olsen H5KS universal tensile testing machine with a load sensor of up to 250 N. Figure 3 shows the dependence of the elongation of the films of the BSP block copolymer 10: 5 in the range of radiation doses of 0-40 kGy. It can be seen that in the indicated dose range, the relative elongation increases by 1.5–2 times. The elastic modulus in this case varied within the measurement error.

The invention relates to a method for radiation grafting polymerization of polydimethylsiloxane, which does not contain active groups, but contains an admixture of octamethylcyclotetrasiloxane, which forms radical cations capable of forming bonds (crosslinking) with radicals of the PDMS matrix under the action of ionizing radiation.

It is as a result of studying the mechanism of radiation-chemical reactions, as well as studying the dose dependence of the formation of stable radiolysis products, we propose this method of modifying materials from polydimethylsiloxane. As sources of ionizing radiation, we used X-rays of the 5BXB6-W (30 keV) tube and Co ⁶⁰ gamma radiation at the K-120000 source, dose rate of 0.1 kGy / h.

Irradiation is carried out in evacuated glass ampoules. All modified samples are transparent films with a thickness of ~ 100 μm and 200 μm, evacuated to a residual pressure of 10 Pa. The radiation dose was 0-70 kGy (the dose dependence of the formation of the gel fraction is presented in figure 1). It is seen that an increase in the fraction of the gel fraction goes up to a dose of ~ 30 kGy.

The proposed mechanism for the modification of polydimethylsiloxane including in the composition of block copolymers includes the following stages:

- The formation of the radical Si-CH ₂ matrix PDMS

- The formation of a dystonic cation radical D ₄ and the opening of the cycle

- Crosslinking

The method is as follows:

Example 1. A 30% solution of the polymer in toluene is applied to a glass substrate and dried for 2 hours at room temperature. After drying, the film thickness is ~ 100 μm. After preparation of the films, they are placed in ampoules, vacuum to a residual pressure of 10 Pa (10 ^-4 mm Hg) and irradiated at a source of Co ⁶⁰ with a dose of 5 kGy at a temperature of 300 K. Relative elongation at break of 20%. Dynamic viscosity 10 ⁵ Pa · s

Example 2. A 30% solution of the polymer in toluene is applied to a glass substrate and dried for 2 hours at room temperature. After drying, the coating thickness is ~ 100 μm. After preparation of the films, they are placed in an ampoule of SK-4B glass, evacuated to a residual pressure of 10 Pa and irradiated with X-rays of a 5BXB6-Wt tube (~ 30 keV) with a dose of 15 kGy at a temperature of 300 K. Relative elongation at break of 30%. Dynamic viscosity 5 · 10 ⁵ Pa · s.

Example 3. A 30% polymer solution is applied to a cellophane film stretched on a glass ring with a diameter of 90 mm and dried for a day, the thickness of the resulting film is 200 ± 5% μm. After preparation of the films, they are placed in an ampoule of SK-4B glass, evacuated to a residual pressure of 10 Pa and irradiated at a Co ⁶⁰ source with a dose of 20 kGy at a temperature of 300 K. Elongation at break of 25%. Dynamic viscosity 5 · 10 ⁵ Pa · s.

The advantages of this method of modifying polydimethylsiloxane are:

no need for introducing any reagent into the matrix of the block copolymer, polydimethylsiloxane, i.e. simplification of the modification method;

lack of solvents i.e. lack of environmental pollution;

used to modify the radiation dose (5-20 kGy) is 100 times less than in the case of the prototype;

lack of the possibility of leakage, evaporation or sweating of an impurity of octamethylcyclotetrasiloxane from the material during its operation;

improving the mechanical properties and elasticity (i.e., the ability to elongate, rather than tear or crack) of the material during its operation in the fields of ionizing radiation, a sharp change in temperature.

Within the proposed doses (5-20 kGy), this modification is selective and leads to improved material properties.

Claims (2)

1. The method of modifying polydimethylsiloxane by the action of ionizing radiation on a polymer, characterized in that the irradiation is carried out at a pressure of not more than 10 ^-4 mm Hg, and the admixture of octamethylcyclotetrasiloxane contained in the polymer is used for modification. 2. The method of modifying polydimethylsiloxane according to claim 1, characterized in that for irradiation using x-rays of an average energy of ~ 30 keV in the dose range from 5 to 20 kGy or gamma radiation Co ⁶⁰ in the range from 5 to 20 kGy.

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