Influence of the prepolymerization on the properties of thermoplastic polyurethane elastomers. Part I. Prepolymer characterization

Abstract

Thermoplastic polyurethane elastomers (TPUs) are generally synthesized by using the two-step, so-called prepolymer, method. To study the influence of the prepolymer on the properties of the final TPUs, four polyurethane prepolymers were prepared from a diisocyanate and a macroglycol by using different NCO/OH ratios. The prepolymers and the macroglycol used in their synthesis were characterized by using gel permeation chromatography, differential scanning calorimetry, and strain–stress measurements. Additionally, to test the adhesion properties of the prepolymers and the macroglycol, adhesive solutions were prepared, and the T-peel strength of plasticized poly(vinyl chloride)/prepolymer solution joints was determined. It was found that the properties of the prepolymers depend on those of the macroglycol used in their synthesis in such a way that the lower the relative amount of macroglycol units in the prepolymer molecules (higher NCO/OH ratio), the closer the properties of the prepolymer and macroglycol. The maximal theoretical degree of polymerization (DPn) determines the relationship between the macroglycol and prepolymer properties. Finally, the possibility of obtaining good adhesives from prepolymers, using low NCO/OH ratio in the synthesis, is evidenced. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1596–1601, 2000