The influence of molecular weight (900 to 1.8 × 106) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimetry at heating rates of 5 to 80 °C min−1. Over the range of molecular_weight studied, and at an extrapolated heating rate of 1 °C min−1,[Formula: see text] A thermally prepared polystyrene sample ([Formula: see text]and Pd = 3.2) showed a Tge value of 93 °C, some 10° below the value predicted by the above equation. Low molecular weight species in the highly polydisperse sample are believed to be responsible for the discrepancy. The changes in heat capacity brought about by the glass transitions are accompanied in all cases on heating by an endothermic peak and this regardless of the heating rate (even extrapolated to 1 °C min−1) or the molecular weight of the sample, suggesting that the glass transition phenomenon encountered with polystyrene is a process involving a positive heat effect.

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The influence of the nature of exchangeable cations on the tacticity of poly(methyl methacrylate) (PMMA) prepared from montmorillonite–MMA adsorption complexes was investigated. The strength of ion‐dipole interactions was estimated either by the value of the electrostatic interaction potential or by the value of the carbonyl‐stretching frequency shift. It was shown that Pi, the percentage of isotactic triads in the polymer, increases with increasing strength of the ion‐dipole interactions, while the persistence ratio and the mean length of closed isotactic (or syndiotactic) sequences remain essentially unchanged regardless of the nature of the cation. It was shown that values of Pi may vary from 0.15 for weakly interacting ions to 0.5 for strongly interacting ones, reaching at the upper limit the value calculated from the model proposed in a previous paper, thus confirming its validity.

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