THE GLASS-TRANSITION OF OLIGOMERS CONFINED TO SMALL PORES OF A CONTROLLED-PORE GLASS

The glass-transition temperatures, T-g, of oligopropylene glycol (OPG) and oligoethylene glycol (OEG) of molecular weights M-w = 1000 g/mol confined to the small pores of a controlled pore glass with pore diame ter similar to 102 Angstrom were studied by differential scanning calo rimetry. In several cases the surface of the porous glass was modified with trimethylchlorosilane to make it more hydrophobic. We find that the T(g)s of both oligomers in the pores are lower than those in the b ulk, the depression of T-g increasing with surface treatment. For exam ple, the depression of the glass-transition temperature, Delta T-g, in the unmodified glass was 1.5 K for OEG and 20 for OPG, whereas in the silanized glass Delta T(g)s were 11.0 K and 8.3 K, respectively. The last effect can be explained by increasing spatial limitations as the surface of the pores becomes more hydrophobic.