The Glass Transition of Oligomers Confined to Small Pores of a Controlled Pore Glass

The glass-transition temperatures, Tg of oligopropylene glycol (OPG) and oligoethylene glycol (OEG) of molecular weights Mw = 1000 g/mol confined to the small pores of a controlled pore glass with pore diameter ∼ 102 Å were studied by differential scanning calorimetry. In several cases the surface of the porous glass was modified with trimethyl-chlorosilane to make it more hydrophobic. We find that the Tgs of both oligomers in the pores are lower than those in the bulk, the depression of Tg increasing with surface treatment. For example, the depression of the glass-transition temperature, ΔTg , in the unmodified glass was 1.5 K for OEG and 2.0 for OPG, whereas in the silanized glass ΔTgs 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.