Segmented polyurethane elastomers - with good low temp. mechanical properties having a low urethane and urea gp. content

摘要

Segmented polyurethanes are based on polyisocyanates, polyhydroxy cpds. with a mol. wt. of 500-25000, and opt. low mol. wt. chain lengthening agents. The prods. contain 60-99.8 wt.%, based on polyurethane, of the following segments: (a) 10-90 wt.% on (a)+(b) of segments of formula (I):- in which A is a k-valent residue obtd. by removing k OH gps. from a polyol with n OH gps., with an av. mol. wt. of 500-5000 and a m.pt. of 130 degrees C; n = 2 or 3, and k has an av. value of 0 - n, (b) 10-90 wt.% (on (a)+(b)) segments of formula (II):- in which B is an 1-valent residue obtd. by removing 1 OH and/or SH gp. from a polyol or polythiol with m OH and/or SH gps., with an av. mol. wt. of 500-2500 and a m..pt. of 60 degrees C; m is a whole number 2-8; 1 has an av. value of 0-m and X is O or S. The high molecular segments (a) and (b) are linked by lower mol. bridge units of formula (III) or (IV) R -(NHCO)-p (III) R' -(CO)-q (IV) in which R is a p-valent gp. obtd. by removing p NCO gps. from a 2-50 C polyisocyanate which opt. contains urethane, urea, allophanate, biuret, isocyanurate, uretedione or carbodiimide gps.,; R' is a q-valent residue obtd. by removing q COOH gps. from a 2-20C aliphatic, cycloaliphatic or aromatic polycarboxylic acid, and p and q (same or different) = 2 or 3. The polyurethane contain a low content of urethane-and urea gps. They are block copolymers built up from relative high molecular segments derivs. from high- and low melting polyols, coupled by ester- and/or urethane and/or urea gps. Compared with prior art polyurethane elastomers, the present segmented materials have excellent mechanical properties at low temps. and are not brittle at room temp. They may be made in the form of solid or foamed materials.