INFLUENCE OF THE LENGTH OF THE CHAIN EXTENDER ON THE PROPERTIES OF THERMOPLASTIC POLYURETHANES

Three polyurethane elastomers (PUs) were prepared using MDI (diphenylm ethane-4,4'-diisocyanate), polyadipate of 1,4-butanediol, and three li near chain extenders with different lengths (ethylene glycol, 1,4-buta nediol, and 1,6-hexanediol). The prepolymer procedure was used to prep are the PUs. The PUs were characterized using gel permeation chromatog raphy, differential scanning calorimetry, wide angle X-ray diffraction , dynamic mechanical thermal analysis, and stress-controlled rheometry . The surface properties were evaluated from contact angle measurement s. The PUs were used as raw materials for solvent-based adhesives, the adhesion properties of which were assessed from T-peel tests of solve nt-wiped poly(vinyl chloride) (PVC)/polyurethane adhesive joints. The use of a short-chain extender produced phase separation, high crystall inity, and adequate rheological properties in the PUs. The length of t he chain extender used in this study did not affect the surface proper ties of the PUs nor the T-peel strength of PVC/polyurethane adhesive j oints but a change in the locus of failure was obtained: the decrease in the length of the chain extender, i.e. the improved crystallinity a nd the high degree of phase separation in the PUs, favoured the interf acial failure.