Curable compositions comprising organopolysiloxane-polyoxyalkylene block copolymers and cured products obtained from the compositions

Claim 1

A curable composition which comprises: an organopolysiloxane-polyoxyalkylene block copolymer terminated at both ends of a molecular chain with a lower aliphatic unsaturated group and consisting essentially of organopolysiloxane units having a main chain of the formula, (R 1 R 2 SiO) m , and polyoxyalkylene units of the formula, (R 3 O) n , the organopolysiloxane units and the polyoxyalkylene units being bonded through R 1 R 2 SiR 4 groups, wherein R 1 and R 2 independently represent an unsubstituted or substituted monovalent hydrocarbon group having from 1 to 8 carbon atoms except for an aliphatic unsaturated group, R 3 and R 4 independently represent a divalent hydrocarbon group having from 2 to 4 carbon atoms, m is an integer of from 2 to 50, and n is an integer of not less than 1, provided that when n is greater than 1, the R 3 's may be the same or different; an organohydrogenpolysiloxane having at least two .tbd.SiH groups in one molecule, said organohydrogenpolysiloxane being included in an amount such that the at least two .tbd.SiH groups are present in an amount of from 0.5 to 3.0 moles per mole of the terminal lower aliphatic unsaturated group of the organopolysiloxane-polyoxyalkylene block copolymer; and a curing agent included in an amount sufficient to cause a curing hydrosilylation reaction between the block copolymer and the organohydrogenpolysiloxane.