Influence of the prepolymerization on the properties of thermoplastic polyurethane elastomers. Part II. Relationship between the prepolymer and polyurethane properties

Abstract

The synthesis of thermoplastic polyurethane elastomers (TPUs) is generally carried out using the prepolymer method. To study the influence that the properties of the prepolymer may have in the final TPUs, four TPUs were prepared by using different NCO/OH ratios. The prepolymers and the macroglycol used in their synthesis were characterized in the first part of this article. TPUs were characterized by using gel permeation chromatography, strain–stress measurements, differential scanning calorimetry, and contact-angle measurements. To test their adhesion properties, the T-peel strength of PVC/TPU/PVC adhesive joints was determined. It was found that the properties of the prepolymers determine the properties of the TPUs when the amount of hard segments (related to the soft-segments size) is small. In contrast, when the amount of hard segments (related to the soft-segments size) is high, it is the chain extension step that determines the TPUs structure and properties. On the other hand, it was observed that a high amount of ever hard or soft segments gives TPUs with similar properties. This behavior is explained by the structure of the prepolymer (related to the degree of polymerization) and the TPUs. Finally, it was found that the adhesive properties of the finished TPUs are comparable to those of blocked prepolymers prepared with low NCO/OH ratio. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1602–1607, 2000