大変形市販PMMAガラスにおける構造緩和の分子量依存性

概要

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Effect of molecular weight on structural evolution in compressively strained commercial poly(methyl methacrylate)(PMMA) was studied using low and high molecular weight samples abbreviated here as L-PMMA and H-PMMA, respectively. The weight-averaged molecular weight of L-PMMA was 8×104, whereas that of H-PMMA was 338×104. The polydispersity indices MW/Mn were 2.8 for L-PMMA and 4.7 for H-PMMA. Structural evolution under various amounts of compressive strain in L-PMMA and H-PMMA was monitored at an arbitrarily selected temperature 20 °C less than their glass transition temperature Tg in a time range of 0 to 105 s by constant-rate mechanical compression test and differential scanning calorimetry(DSC) technique. Well-defined structural evolution was observed in a manner qualitatively quite similar in both PMMA samples as progressive developments of the yield stress in constant rate compression test and the endothermic peak at temperatures less than Tg in DSC measurement. The structural evolution was dependent on time period passed under strain and the amount of strain, yet apparently independent of molecular weight. Such quite similar behaviors of the structural time evolution in L-PMMA and H-PMMA are likely to be attributed to relatively wide molecular weight distribution of each sample tailing off in a lower molecular weight range.