DE1117873B - Process for the preparation of organopolysiloxane elastomers by curing organopolysiloxanes containing vinyl groups in the presence of diorganoperoxides - Google Patents

Description

For organopolysiloxanes, which can be hardened to elastomers with the help of peroxide catalysts in the heat have recently found particular interest in those peroxides which do not contain acyl groups wear, e.g. B. Di-tert-butyl peroxide and dicumyl peroxide. These two peroxides only cure organopolysiloxanes containing vinyl groups and their elastomers are characterized by a particularly small compression set. One would therefore be inclined to the two peroxides mentioned in all cases instead of the peroxides used up to now, such as. B. Benzoyl peroxide, 2,4-dichlorobenzoyl peroxide and tertiary butyl perbenzoate to be used. A general one However, the use of these alkyl or aryl peroxides is out of the question because of the following disadvantages:

a) The di-tert-butyl peroxide is too volatile for practical use, so that it is mixed with it Organopolysiloxane mixtures lose peroxide during storage and processing and are therefore accurate Dosing becomes impossible. It is true that this disadvantage can be compensated for by using the di-tert-butyl peroxide absorbed in a so-called molecular sieve. In this case, however, it is no more possible to manufacture transparent products, since the molecular sieves give the elastomers a white-gray Impart opacity; Furthermore, this process is cumbersome and uneconomical because the adduct Peroxide molecular sieve is difficult to manufacture. In addition, it is not possible to use di-tert-butyl peroxide to harden without pressure.

b) The solid dicumyl peroxide, on the other hand, is not volatile, but prepares its distribution in the organopolysiloxane mixture greater difficulty. It must either be in powder form, based on calcium carbonate deposited, are used, whereby no transparent products can be achieved either, or it must be worked in on hot rollers in the molten state, with the distribution even in this case it is very difficult.

In the case of pressureless curing, the di-tert-butyl peroxide reacts very slowly, so that the production of Profiles or cables can only take place at an uneconomically slow pace.

It has now surprisingly been found that the disadvantages of these two peroxides are avoided and their advantages, namely low compression set and good hardening in a thick layer, are retained if the mixed peroxide is used when curing organopolysiloxanes containing vinyl groups, namely the tertiary-butyl-cumyl peroxide used. This peroxide is liquid and can therefore be used properly without carrier substance evenly in the organo-process of manufacture

of organopolysiloxane elastomers

by hardening vinyl group-containing

Organopolysiloxanes in the presence

of diorganoperoxides

ίο applicant:

Wacker-Chemie G. mb H.,
Munich 22, Prinzregentenstr. 22nd

Dr. Siegfried Nitzsche and Dr. Manfred Wick,

Burghausen (Obb.),
have been named as inventors

distribute the polysiloxane compound. It is so reactive that pressureless curing is about the same The speed is the same as with 2,4-dichlorobenzoyl peroxide. In addition, it is so little fleeting that suction in molecular sieves is not required. Mixtures containing carbon black can also be used with the new peroxide are cured and thus electrically conductive organopolysiloxane elastomers are produced will.

example

1000 g of a dimethylpolysiloxane with a molecular weight of 500,000, which is found on every thousandth silicon atom carries a vinyl group, are on a rubber mill with 400 g one on the flame path recovered silica and 20 g of tertiary butylcumyl peroxide were added. This mixture is then pulled out on a calender to a 40 mm thick and 50 mm wide plate. This record is then heated to 250 ° C for 10 minutes in an electric oven, leaving a bubble-free Hardening takes place. The compression set of the elastomer was after 22 hours at 175 ° C and a compression of the test specimen to 70% of its original height only 9.7% · The elastomers were completely transparent. The same result was obtained when using the above mixture had been left open for 14 days after curing in the heating cabinet.

109 740/587

Claims (1)

Claim: Catalyst tertiary-butyl-cumyl peroxide used Process for the production of organopoly- is, siloxane elastomers by curing vinyl group-containing organopolysiloxanes in counter- Considered publications: wart of diorganoperoxides as catalysts 5 U.S. Patent No. 2,816,089; in the heat, characterized in that as Rubber-World, 137 (1958), No. 5, p. 758. When the application was announced, comparative tests were carried out. © 109 740/587 11.61