The effect of the use of an unsaturated reactive plasticizer trimethylopropane trimethacrylate, TMPTMA, on the structure and the creep behavior of poly(vinyl chloride), WC, plastisols has been investigated as part of a program to develop a high-temperature creep-resistant Liner material. The crosslinking reaction was initiated with a peroxide. The effect on the network structure of using a free radical scavenger in the formulation has also been studied. Gel yield and grafted WC content in the gel increase with increased TMPTMA content in the plastisol. However, the residual unsaturation of TMPTMA decreases with increase of TMPTMA content. Introduction of TMPTMA into the plastisol promotes the creep resistance at high temperatures, and the effectiveness increases when there are WC molecules grafted onto TMPTMA networks.