Abstract: The main aim of the present invention is a method of preparing photochromic or non-photochromic organic pieces of optical quality and especially organic lenses, by radical polymerisation of a mixture of radically polymerisable monomers, characterised in that it comprises: a) adjusting, by pre-polymerisation, the viscosity of said mixture, to a value between 0.4 and 2 Pa.s; b) pouring said pre-polymerised mixture into a mould; c) photogelifying, in said mould, said pre-polymerised mixture until its gel point; d) completing the polymerisation of said pre-polymerised and gelified mixture in said mould, by heat treatment; adding effective amounts of at least one thermal catalyst and of at least one photoinitiator intervening in said mixture of monomers for the implementation of said pre-polymerisation, photogelification and polymerisation; said photoinitiator(s) intervening in an amount less than or equal to 0.009 parts by weight per 100 parts by weight of said mixture of monomers.

Abstract: A dual master cylinder (10) for the braking system of a motor vehicle comprising a primary portion and a secondary portion (14) in which the high pressure chamber (56) of the secondary portion includes a check valve (62) mounted within a piston bore (64) in the secondary piston (44), the piston bore providing a fluid passage (70,96,66) between the high pressure chamber and the low pressure chamber (48) of the secondary portion, the check valve allowing hydraulic fluid to flow through the fluid passage during a rest mode or a release mode of the dual master cylinder, but preventing such flow during an apply mode. Prevents damage to elastomeric cup seal (52) when back-pressure is generated by ABS dus to the absence of a dilation port in the secondary portion, which is no longer required due to the presence of the check valve.