The molecular‐weight dependence of the glass‐transition 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 (dl · g−1), which corresponds to a viscosity‐averaged molecular weight (Mv) of 1 590 000–3 000. 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 chain‐transfer mechanism in an aqueous medium.Molecular‐weight dependence of the Tg for PAN (WA). An error bar is given by a short vertical arrow.magnified imageMolecular‐weight dependence of the Tg for PAN (WA). An error bar is given by a short vertical arrow.

The glass‐transition temperature (Tg) of several atactic monodisperse polystyrenes (PSt)s was studied by an inverse gas chromatographic (IGC) analysis, as a preliminary study for the detection of the Tg of polyacrylonitrile. The Tg of PSt with different molecular weights was clearly obtained by this method. The agreement in the Tg values obtained by IGC and by differential scanning calorimetry (DSC) was quite good within the molecular‐weight range Mp = 7 600–2 430 000 (where, Mp = (Mn × Mw)1/2). This method has a wide universality for the detection of the Tg of polymers. Several essential factors were extracted for the establishment of the optimum conditions for IGC measurements, such as the concentration of polymer toward a clay matrix (10 wt.‐%), and the type of lower probe, decane. The best probe was determined empirically from the most effective detection in the IGC measurements of PSt.Molecular‐weight dependence of the Tg of PSt. Experimental data obtained here are indicated by an arrow. Other data was taken from ref.21magnified imageMolecular‐weight dependence of the Tg of PSt. Experimental data obtained here are indicated by an arrow. Other data was taken from ref.21