Composite Interfaces, Vol.6, No.4, 297-304, 1999
Effects of confinement on the glass transition temperature of macromolecules
The glass transition temperatures, T(g)s of oligopropylene glycol (OPG), oligoethylene glycol (OEG) of molecular weights M-W = 1000 g/mol and poly(ethylene oxide) of molecular weight M-W = 40 000 g/mol confined to small pores of the controlled pore glass with pore diameter similar to 102 Angstrom 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 T(g)s of both oligomers in pores are lower than those in the bulk, and the depression of T-g increases with pore surface treatment and with increase of molecular weight of macromolecules. The depression of the glass transition temperature, Delta T-g in the unmodified glass was 1.5 K for OEG and 2.0 K for OPG, whereas in the silanized glass Delta T(g)s were 11.0 K and 8.3 K, respectively and for PEO Delta T-g = 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.
Keywords:glass transition;controlled pore glass;poly(ethylene oxide);oligoethylene glycol;oligopropylene glycol;differential scanning calorimetry;confinement effect