Prepn. of vulcanisable elastomers with low compression set and Shore hardness - by mixing high-viscosity vinyl-terminated polysiloxane with filler and water, heating to remove water and adding more polysiloxane

摘要

A process is claimed for the prodn. of materials (I) which can be cured to give elastomers, from high-viscosity diorganopolysiloxanes (1) and fillers (2). The process comprises mixing (1) with 40-500 wt.% (2) and 5-50 wt.% water (3) (w.r.t. amt. of 1), heating to remove volatiles and then adding a further 40-200 wt.% (1) (w.r.t. total wt. of first mixt.). Pref. polysiloxane (1) has the formula (R1)xR3-xSiO(SiR2O)m (SiRR1O)nSiR3-x(R1)x and viscosity (0.1-10) x 10 power 6 mPa.s; wherein R = opt. substd. 1-18C hydrocarbyl; R1 = 1-6C unsatd. hydrocarbyl; m = 100-20,000; n = 0 or 1-200; x = 0 or 1. Filler (2) is SiO2 with specific surface (BET) at least 50 m2/g. The first mixt. also contains 0-10 wt.% low-viscosity organosilicon cpd. (4), pref. with formula R2OSiR2O(SiR2O)pR2 (with R2 = H or 1-4C hydrocarbyl (opt. with in-chain -O-); p = 0 or 1-50). The first mixt. is heated for 0.5-5 hrs. at 20-200 deg.C, and the curable prod. (I) is crosslinked with organic peroxide. USE/ADVANTAGE - Used for the prodn. of seals, coatings for photocopier rollers, etc.. The process enables the prodn. of silicone elastomers with low compression set and low Shore hardness. Prior-art materials either have a high Shore hardness or liberate hydrogen from the vulcanisation reaction.