Effect of crosslinking on mechanical and viscoelastic properties of semiinterpenetrating polymer networks composed of poly(vinyl chloride) and isocyanate crosslinked networks

Abstract

Semiinterpenetrating polymer networks (SIPNs) of PVC/isocyanate/poly-triol were prepared by premixing small (150 μm dia.) porous (30% voids) unplasticized PVC particles, 10% by weight of isocyanate, and a triol at different OH/NCO mol ratios. Three types of isocyanates (methylene bis-phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), and toluene diisocyanate (TDI) prepolymer/polytriol) were used. Two-roll milling was followed by hot-press curing. The tensile, flexural, and impact strengths increased when small amounts of crosslinked isocyanate networks were created in PVC. The isocyanate/polyol hydroxyl stoichiometry was varied, and the effects of crosslinking on the tensile, impact, and flexural strengths of PVC/isocyanate/triol SIPNs were examined. The strength increments were greater when the OH/NCO mole ratio went from 0 to 0.25, than when it went from 0.25 to 1.0. In many cases, increasing OH/NCO mol ratio from 0.5 to 1.0 decreased tensile, impact, and flexural strengths. Both PAPI and MDI (30% NCO content) gave bigger improvements in the these mechanical strengths than the TDI (only 9.7% NCO). These SIPN blends exhibited lower tan δ peak temperatures and a single distinct loss modulus, E″, peak values at lower temperatures than those of PVC that had been exposed to the same processing temperatures. Substantial amounts of isocyanate networks exist in SIPN phases according to DMTA studies. The OH/NCO ratio did not generally correlate with the decreases in the glass transition temperatures in these three sets of blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1402–1411, 2000