Using ellipsometry, it is found the glass transition temperature of the spin-coated polyacrylamide （PAL） thin films on the supported silicon （Si） substrates with an oxide layer decreases with decreasing the film thickness. But Tgs of the as- prepared thin films are much higher than that of the bulk sample. Such observations can be attributed to the combined result of the ＂surface effect＂ and increased hydrogen bonding interaction between PAL chains due to spin coating/thin film confinement.
