Abstract: Provided is an elastic polyurethane fiber comprising a polyurethane obtained by copolymerizing a polymer diol (A), an organic diisocyanate (B) and a chain extender (C);said polymer diol (A) that constitutes the polyurethane being a polyester diol and/or polyesterpolycarbonate diol having an average molecular weight of 1,000 to 6,000, and satisfying the following condition (I); ##EQU1## wherein the total number of carbon atoms means the number of the carbon atoms contained in the polymer diol and excluding those contained in the ester bonds and carbonate bonds thereof;the diol units that constitute said polymer diol containing branched diols in an amount of at least 10 mol %;said polyurethane constituting said elastic fiber satisfying the following conditions (II) and (III)45%.ltoreq.long chain hard segment content.ltoreq.

Abstract: Novel polyamide copolymers having skeletons of a specific structure are disclosed. The polyamide copolymers have excellent resistance to hydrolysis, low temperature characteristics (low temperature softness), heat aging resistance and mechanical properties as compared to conventional polyamide copolymers. The polyamide copolymers also show excellent efficiencies in fabrication properties and transparency. In particular, the polyamide copolymers having a branched structure in the molecule thereof provide good results.

Abstract: The present invention is directed to an elastic polyurethane obtained by copolymerization of a polymer diol of a polyesterpolycarbonate diol utilizing a long-chain diol having methyl branches or a mixed diol of a polyester diol and a polycarbonate diol, with an organic diisocyanate and a chain extender. Elastic fibers obtained by spinning said polyurethane have low tensile stress at low tensile strain zone and high tensile stress at high tensile strain zone.

Abstract: Provided is an elastic polyurethane fiber having excellent hot water resistance, elastic recovery at low temperatures and elongation, prepared from a polyurethane obtained by copolymerization of a high polymer diol obtained from 3-methyl-1,5-pentanediol and an aliphatic dicarboxylic acid, an organic diisocyanate and a chain extender.

Abstract: Novel polyamide copolymers having skeletons of a specific structure are disclosed. The polyamide copolymers have excellent resistance to hydrolysis, low temperature characteristics (low temperature softness), heat aging resistance and mechanical properties as compared to conventional polyamide copolymers. The polyamide copolymers also show excellent efficiencies in fabrication properties and transparency. In particular, the polyamide copolymers having a branched structure in the molecule thereof provide good results.