A thermally stable, high molecular weight copolymer of vinyl chloride and trimethylolpropane monoallylether (PVC-co-TMPME) has been synthesized via the suspension polymerization process. Proton nuclear magnetic resonance (NMR) characterization of the copolymer shows the presence of TMPME in the saturated form, indicative of the TMPME reaction. Characterization by differential scanning calorimetry (DSC) shows that the glass transition temperature of the TMPME copolymer is similar to that of the homopolymer, and to that of a 5% vinyl acetate (PVC-co-VA) copolymer. Characterization of plasticized polymers by dynamic mechanical analysis (DMA) shows that both PVC-co-TMPME and PVC-co-VA have lower modulae than the corresponding homopolymer, as well as lower distortion temperatures, as shown by creep compliance master curves. These data indicate that PVC-co-TMPME should share similar process and end-use property characteristics with conventional PVC copolymers without adversely affecting thermal stability.