Glass-transition temperature (Tg) of free-radically prepared polyacrylonitrile by inverse gas chromatography, 2a -: Molecular-weight dependence of Tg of two different types of aqueous polymers

The molecular-weight dependence of the glasstransition temperature (Tg) of a series of atactic polyacrylonitriles (PAN)s was studied by inverse gas chromatographic (IGC) analysis. PANs having different molecular weights were prepared by either; (i) the addition of isopropyl alcohol as a chain-transfer agent, or (ii) a scission reaction induced by the addition of alkali (NaOH) to a solution (N,N-dimethylformamide solution, at 25 °C) of the resulting polymer. The intrinsic viscosity [η] was in the range of 10-9-0.1 (d-· g-1), which corresponds to a viscosity-averaged molecular weight (M̄v) of 1590 000-3 000. As part of the results, a side reaction, which saw the conversion of the nitrile (CN) groups of PAN into amide (CONH2) and/or carboxylic acids (COOH) groups by alkali, was found to occur. The typical molecular-weight dependence of the Tg in free-radically prepared PAN was discussed in connection with a chaintransfer mechanism in an aqueous medium.