Characterization of Thermoplastic Polyurethanes Prepared Using Different Macroglycols

Three polyurethane elastomers (PU_s) were prepared using macroglycols of different nature (varepsilon-polycaprolactone, polyadipate of 1,6-hexanediol) and length of the hydrocarbon chain (polyadipate of 1,4-butanediol, polyadipate of 1,6-hexanediol). The PU_s were characterized using Gel Permeation Chromatography, Differential Scanning Calorimetry, Wide X-ray angle Diffraction, Dynamic Thermal Mechanical Analysis, stress-controlled rheometry and stress-strain experiments. The surface properties were evaluated from contact angle measurements. The PU_s were used as raw materials for solvent-based adhesives, whose adhesion properties were measured from T-peel strength of plasticized poly(vinyl chloride) (PVC)/polyurethane adhesive joints. The use of polyadipate of 1,6-hexanediol produced a polyurethane with high crystallinity (i.e. poor rheological and mechanical properties) and enhanced interactions between soft segments. Low adhesion was obtained in joints produced with this polyurethane and a cohesive failure of the adhesive was produced. The decrease in the polyadipate hydrocarbon chain length decreased the degree of crystallinity between polymer chains, therefore, no reduction in rheological and mechanical properties was obtained; a higher joint strength was also obtained. In this study the best performance was obtained with the polyurethane based on varepsilon-polycaprolactone, presumably because of its higher surface energy and reduced crystallinity. The properties of the polyurethanes prepared in this study were more affected by the characteristics of the macroglycol, and the crystallinity of the polyurethane had a more marked effect on the properties than the degree of phase separation.