High molecular wt. polyurethane resins - contg. alternating segments from high and low melting poly:ol(s), linked by ester, urethane or urea gps.

摘要

Polyurethane resins based on polyisocyanates polyhydroxy cpds. of mol. wt. 500-25000 and opt. low mol. wt. chain extenders, contain a total of 60-99.8 wt % of following segments: (a) 40-85 wt % (based on a+b) segments of formula (I) and (b) 15-60 wt % segments of formula (II): In (I) A is a residue of valency k obtd. by eliminating k OH gps. from a polyol contg n OH gps. having a mol. wt. of 500-1000 and m. pt. 80 degrees C, n is 2 or 3 and k is o-n. In (II) B is a residue of valence l obtd. by eliminating l OH and/or SH gps. from a polyol or polythiol contg. m OH and/or SH gps. having a mol. wt. 500-25000 and m. pt. 60 degrees C, m is 2-4 and l is o-m, X is O or S. The segments (a) and (b) are linked by low mol. wt. units of formula R- NH.CO -p and opt. R1- CO -q where R is a residue of valency p obtd. by eliminating p NCO gps. from a 2-50C polyisocyanate which opt. contains urethane, urea, allophanate biuret, isocyanurate, uretedione or carbodiimide gps. R1 is a residue of valency q obtd. by eliminating q COOH gps. from a 2-20C (cycloealiphatic or polycarboxylic acid, and p and q are independently 2 or 3. The polyurethanes have excellent mechanical properties and the amt. of polyisocyanate reqd. for their prepn. is low.