轻度交联PMMA的结构转变及自由体积特性

STRUCTURAL TRANSITIONS AND FREE VOLUME CHARACTERISTICS OF LIGHTLY CROSSLINKED PMMA

用正电子湮没技术（ＰＡＴ）研究了具有两种交联度的轻度交联ＰＭＭＡ试样的结构转变，包括玻璃化转变及次级弛豫过程（β转变），交联度对轻度交联ＰＭＭＡ的β转变无影响，交联度较大试样的Ｔｇ较高，用ＰＡＴ测得的Ｔｇ比用动态力学分析（ＤＭＡ）法得到的Ｔｇ低７℃。交联度较高的试样中自由体积孔穴数目较多。讨论了正电子湮没平均寿命（τｍ）与聚合物总自由体积的关系。此外，还从ｏ－Ｐｓ寿命大小计算了轻度交联ＰＭＭＡ中的自由体积孔穴半径，并研究了其随温度变化的规律。

Structural transitions, glass and sub transition, of lightly crosslinked PMMA with two different corsslinking density were studied by positron annihilation technique (PAT). The cross linking density has no influence on T β, T g of the PMMA increases with an increase of cross linking density. T g obtained from danymic mechanical analysis (DMA) is 7 ℃ higher than that measured by PAT. There are much more free volume voids in the PMMA with higher crosslinking density. The relationship between average positron annihilation lifetime ( τ m) and free volume was analyzed. Sizes of free volume voids were calculated from o Ps lifetime and their temperature dependence was also studied.