Crystallinity and morphology of segmented polyurethanes with different soft-segment length

✍ Scribed by Fengkui Li; Jianan Hou; Wei Zhu; Xian Zhang; Mao Xu; Xiaolie Luo; Dezhu Ma; Byung Kyu Kim

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 795 KB
• Volume: 62
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19961024)62:4<631::aid-app6>3.0.co;2-u

✦ Synopsis

A series of polycaprolactone/4,4'-diphenylmethane diisocyanate/l,4-butanediol (PCL/MDI/ BDO) segmented polyurethanes of different compositions was synthesized by solution po- lymerization. The molecular weight of PCL diols used was in the range of 1600-7000. The crystallinity and morphology of these polymers were studied by using DSC, dynamic mechanical analysis, WAXD, and polarizing microscopy methods. It was found that the crystallinity of PCL prepolymers was depressed in segmented polyurethanes. A lower limit of PCL molecular weight was found, below which the PCL segments were not able to crystallize a t the usual processing conditions. This limit of molecular weight is in the range of 2000- 3000 and exhibits a slight increase with increasing hard-segment content of polyurethanes.

The glass transition temperature related to the PCL segment regions in polyurethane specimens deviated from that of pure amorphous PCL prepolymer to a higher temperature. The deviation resulted from the crystallization of PCL segments and also the influence of hard segments. The formation of hard-segment domains becomes very difficult for polyurethanes having low hard-segment content and short hard-segment length. There is a lower limit of hard-segment content and segment length. Only above that limit do the polyurethanes have enough hard-segment domains acting as physical crosslinks at temperatures above the melting point of the PCL crystals. The structural characteristics of segmented polyurethanes which may exhibit a shape memory effect are also discussed.