Random and block copolymers of poly(tetramethyl‐<i>p</i>‐silphenylene‐siloxane) and polydimethylsiloxane

Abstract

Abstract High molecular weight block copolymers having the structure [(CH 3 ) 2 SiO] a [(CH 3 ) 2 ‐Si‐ p ‐C 6 H 4 ‐Si(CH 3 ) 2 O]( b ) n , can be conveniently prepared from the copolymerization of hydroxy end‐blocked dimethylpolysiloxanes and p ‐bis(dimethylhydroxysilyl)benzene by use of essentially nonequilibrating catalysts, such as tetramethylguanidine di‐2‐ethylhexoate or n ‐hexylamine 2‐ethylhexoate. The values of a and b above may be altered by employing hydroxy‐ended dimethylpolysiloxane of different degrees of polymerization or by preforming tetramethyl‐ p ‐silphenylene‐siloxane units. If the length of a segment is maintained at a constant value in the copolymers decreasing the mole ratio a / b results in higher tensile strengths and higher melting points which are manifestations of increased degrees of crystallinity. If the mole ratio a / b is held constant, increasing the length of the a and b segments leads to higher melting points and higher tensile strengths again reflecting an increase in the degree of crystallinity. High molecular weight copolymers [η] ranging from 1.0 to 2.1, possessing unstressed (unvulcanized) gum tensiles of 1000–2700 psi and elongations of 500–1000% can be readily obtained by the methods described.