Class transition of ultra-thin films of modified PVC

Ultra-thin layers (h = 50-150 nm) of PVC, functionalised in solution by thi ophenol (t-PVC) and 4-aminothiophenol (am-PVC), were prepared by spin-coati ng an silicon wafers. The glass transition temperature of these thin films was investigated by kinetic scan ellipsometry.. The Tg of the am-PVC and t- PVC modified PVC is found to increase more strongly with the degree of modi fication in thin layer geometry than in the hulk Also, Tg(h) of t-PVC exhib its a larger increase in the confined state as compared to am-PVC. This res ult is unexpected since no specific interactions are assumed between thioph enyl group and the surface indicating that other driving forces for the alt eration of Tg(h) should be taken into account. In a second step, the supported PVC thin films are chemically cross-linked in solution by terephthaloyl chloride. The Tg(h) of the polymer layer incre ases with the cross-linking time more severely at a higher degree of modifi cation but independently of the thickness of the layer indicating that the diffusion process is not altered in thin layers. Above Tg, the thermal expa nsion coefficient cu of the thin films is not modified after cross-linking, whereas, it was found to decrease strongly between 4 and 8% of modificatio n in the uncured state. (C) 2001 Elsevier Science Ltd. Ah rights reserved.