RO115735B1 - Process of producing liquid silicone rubber - Google Patents

Abstract

According to the invention, the process consists in cross-linking by addition, such as by hydrosylylating, the linear polymethylvinyl, dimethylsiloxane copolymer blocked with dimethylsiloxy groups with a polysiloxane with reactive groups Si-H in the chain, wherein the molar ratio of the reactive groups Si-CH=CH 2/Si-H ranges from 005 to 05, in admixture with a SiO 2 filling material and silicone oil, in the presence of hexachloroplatinic acid as hydrosylylation catalyst, for 5 10 hours, at the room temperature, or 30 60 min at the temperature of 80 110 degrees C The obtained silicone rubber has reduced consistency, high purity and turns less to yellow with aging It does not require post -vulcanization

Description

The present invention relates to a process for obtaining liquid silicone rubber, which can be used for medical and pharmaceutical purposes, as a matrix for incorporating controlled release drugs.

It is known that silicone rubber elastomers of type α, (o-poly (dimethylsiloxanes) diols, which vulcanize, at high temperature, in the presence of peroxides, with the elimination of harmful substances, are used in the processes for obtaining silicone rubbers. I know silicone rubbers, which contain silicone elastomer and a hydrolysable cross-linking agent, vulcanizing at room temperature (RTV), eliminating volatile substances.

The known processes have the disadvantage that post heat treatments are necessary, for the removal of the volatile toxic substances, resulting in vulcanization or maturation over time, for the RTV tires. The silicone rubbers, as a result, are not of high purity and cannot be used as such for medical and pharmaceutical purposes.

The problem solved by the invention consists in determining the composition of the reactive components, choosing the catalyst and verifying the parameters of the hydrosilylation and crosslinking reaction so as to work at room temperature, and the silicone rubber obtained has a reduced consistency and high purity.

The process of obtaining a liquid silicone rubber, according to the invention, removes said disadvantages, by subjecting it to cross-linking by addition, such as, by hydrosilylation, the linear copolymer po // (methylvinyl, dimethylsiloxane blocked with dimethylsiloxyl groups of 50 molecular mass) ... 200,000, with a polysiloxane having Si-H reactive groups on the chain, of average molecular weight 1,000 ... 50,000, in which the molar ratio of the reactive groups Si-CH = CH ₂ / Si-H, varies from 0, 05 to 0.5, in combination with Si0 ₂ filler, in an amount of 5 ... 10% and a silicone oil with a viscosity of 1,000 ... 10,000 cSt, in a proportion of 5 ... 20%, in the presence hexachloroplatinic acid as a hydrosilylation catalyst, taken in an amount of 50 ... 100 ppm, 2% solution, in isopropyl alcohol, which vulcanises at room temperature for 5 ... 10 h or at 80 ... 110 ° C, for 30 ... 60 min.

The addition crosslinking reaction occurs according to the following scheme:

ch ₃ I ch ₃ I ^d 'ch ₃ ch ₃ ch ₃ ch ₃ ch ₃ ch ₃ And 0 | And 0 I - And 0 - Yes-CH ₃ + CH ₃ -Si -0 - And 0 - And 0 - Yes - CH ₃ ch ₃ CH II | ch ₃ CH ₃ ch ₃ I H ch ₃ ch ₃ ch ₂ n m P q

ch ₃ ch ₃ CH ch ₃ —► CH ₃ - Yes -0 - And 0 - And 0 - Yes-CH ₃ ch ₃ j ch ₂ | ch ₃ m CH ₃ ch ₃ ch ₂ ch ₃ CH ₃ CH ₃ - If -0 - If-0 | - If-0 | - Yes-CH ₃ ch ₃ ch ₃ n + p CH ₃ q CH ₃

where: n, m, p, q are variable.

n: m = 1: 500 and p: q = 1: 50

RO 115735 Bl

Physical-mechanical properties (Shore A hardness, elongation and breaking strength) vary, depending on the number of crosslinking centers, expressed by the molar ratio of the reactive groups CH ₂ = CH / Si-H.

Liquid silicone rubber, of small consistency, obtained according to the invention, are two-component systems, intended for injection into the mold, obtaining semipermeable membranes 50 and incorporating drugs.

By applying the invention, the following advantages are obtained:

- post-vulcanisation is not necessary and therefore the costs are reduced;

- there are no volatile or toxic secondary products;

- the tires become less yellow due to aging. 55

The following are examples of embodiments of the invention:

Example 1. To a mixing vessel, mixer type, add 15 g ~ α, ω-trimethylsilyloxy copolymer (methylvinyl, dimethyljsiloxane of M = 104,000, 15 g of polyfmethylH, dimethyl) copolymer of siloxane of M = 1O.528 , to a molar ratio CH ₂ -CH / Si-H of 0.067, to which is added 3 g polydimethylsiloxane oil (I / O IOLDOSIL UMD), as a plasticizer and 2 g material 60 filling, Si0 ₂ (Cabosil EH-S) . The components are mixed, until a homogeneous paste is obtained, which flows.

Before use, add the catalyst, acid H ₂ PtCl ₆ .6H ₂ 0, 2% solution in isopropyl alcohol, 0.3 ml (75 ppm), then pour into the mold. The cross-linking is performed at room temperature for 10 hours. 65

The rubber obtained has the following physico-mechanical properties:

- breaking strength, Kgf / cm ² : 2,18

- elongation at break,%: 332.5

- hardness, ° Sh A: 20

Example 2. Work under the conditions described in Example 1, with the exception that 70 g of the copolymer of p / [methyl-H, dimethylsiloxane of M = 12,000 and 12 g of the copolymer of α, ω-trimethylsilyloxy of p [[methylvinyl, dimethyl] are used. ) siloxane with an average molecular weight of 77,740 and a CH molar ratio _of -CH / Si-H equal to 0.22. To this composition are added 2 g MOLDOSIL UMD and 2 g Cabosil EH-S.

The mixture obtained, homogenized, is mixed with H ₂ PtCl ₆ .6H ₂ 0 acid, 2% solution 75 in isopropyl alcohol, 0.2 ml (68 ppm), poured into the mold. The cross-linking takes place at room temperature for 10 hours.

The rubber obtained has the following physico-mechanical properties:

- breaking strength, Kgf / cm ² : 3,58

- elongation at break,%: 5080

- hardness, ° Sh A: 38

Example 3. Work under the conditions described in Example 1, with the exception of using 14 g ~ α, ω-trimethylsilyloxy copolymer / methylvinyl, dimethylsiloxane with M = 73,850, and g copolymer poly (methyl-H, dimethyl) siloxane. M = 12,000 and a molar ratio CH ₂ -CH / Si-H equal to 0.279. To this mixture is added 0.2 MOLDOSIL UMD and 1.5 g Cabosil EH-S. 85

To the mixture, homogenized, add H ₂ PtCl ₆ .6H ₂ D acid, 2% solution in isopropyl alcohol, 0.2 ml (68 ppm), then pour into the mold. The cross-linking takes place at a temperature of 100 ... 110 ° C for one hour.

RO 115735 Bl

The rubber obtained has the following physico-mechanical properties:

- breaking strength, Kgf / cm ² : 2,89

- elongation at break,%: 85

- hardness, ° Sh A: 25

Claims (1)

Claim Process for obtaining liquid silicone rubber, usable for medical and pharmaceutical purposes as a matrix for incorporation of controlled release drugs, characterized in that it is subjected to crosslinking by addition, such as, by hydrosilylation, the linear copolymer po // [methylvinyl, dimethyljsiloxane blocked. with dimethylsiloxy groups of average molecular weight 50,000 ... 200,000, with polysiloxane with Si-H reactive groups on the chain, of average molecular weight 1.0 (30 ... 50.0 (30, in which the molar ratio of Si-CH reactive groups = CH ₂ / Si-H, ranging from 0.05 to 0.5, in combination with Si0 ₂ filler, in an amount of 5 ... 10% and a silicone oil with a viscosity of 1,000 ... 10,000 cSt, in the proportion of 5 ... 20%. in the presence of hexachloroplatinic acid as a hydrosilylation catalyst, taken in an amount of 50 ... 100 ppm, 2% solution, in isopropyl alcohol, which cures at room temperature for 5 ... 10 h, or at 80 ... 110 ° C, for 30 ... 60 min.