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

Abstract

SYNOPSISA series of polycaprolactone/4,4'-diphenylmethane diisocyanate/l,4-butanediol (PCL/MDI/ BDO) segmented polyurethanes of different compositions was synthesized by solution polymerization. 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.

Segmented linear shape memory polyurethanes with thermoreversible Diels-Alder coupling: Effects of polycaprolactone molecular weight and diisocyanate type

“…The latter, might be hidden by the PCL melting. Furthermore, the crystallinity of polyurethanes can be influenced by the length of the soft segment and the amount of hard segment [34]. Considering PUs 1 and 2 the higher BMI amount seems to reduce the crystallinity thereby lowering T m , as well.…”

A Novel Approach for the Utilization of Biocellulose Nanofibres in Polyurethane Nanocomposites for Potential Applications in Bone Tissue Implants

“…This is observed in another study that shows that, in a polycaprolactone (PCL) and MDI PU, PCL crystallinity dominates for low HS/SS values and MDI crystallinity dominates for high HS/SS values [34]. It should be noted that crystallinity is also dependent on the types of HS applied [35,36].…”

Segmented shape memory polyurethane and its water vapor transport properties

“…The other interactions are thermally reversible and used for maintaining the transient shapes. Li et al [43,44] stated that high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical cross-links in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented PU co-polymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals.…”