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Abstract
The glass transition temperatures, Tgs of oligopropylene glycol (OPG), oligoethylene glycol (OEG) of molecular weights Mw = 1000 g/mol and poly(ethylene oxide) of molecular weight Mw = 40000 g/mol confined to small pores of the controlled pore glass with pore diameter ~ 102 Å were studied by differential scanning calorimetry. In several cases (OPG and OEG), the surface of the porous glass was modified with trimethylchlorosilane to make it more hydrophobic. It has been established that the Tgs of both oligomers in pores are lower than those in the bulk, and the depression of Tg increases with pore surface treatment and with increase of molecular weight of macromolecules. The depression of the glass transition temperature, ΔTg, in the unmodified glass was 1.5 K for OEG and 2.0 K for OPG, whereas in the silanized glass ΔTgs were 11.0 K and 8.3 K, respectively and for PEO ΔTg = 10.2 K and 9.7 K. The last effect can be explained by increasing spatial limitations as the surface of pores becomes more hydrophobic or effective size of the macromolecules becomes larger.