低分子量的熔融態聚苯乙烯及聚苯乙烯溶液內核磁共振T1及T2鬆弛的 研究

Abstract

本論文對低分子量的熔融態聚苯乙烯和聚苯乙烯溶液內核磁共振T1鬆弛和 T2鬆弛提出研究報告,前者(A1000)的分子量(Mw=1051)很接近估計的勞斯 或柯恩鏈節分子量,沒有勞斯協同動力效應和因鏈的糾纏引起的局限.後 者(F1)的分子量(Mw=9830)因低於糾纏分子量,所以也沒有上述的局限.熔 融態聚苯乙烯T2鬆弛的依溫性和小分子有很大的不同是因為前者存在著玻 璃橡膠轉變現象.單一指數函數無法解釋高分子系統的T2鬆弛,固體模型卻 可成功地說明A1000的T2鬆弛.此模型建立在將高分子鏈視為高斯鏈的統計 基礎上,在靠盡Tg的溫度,高分子鏈可保有一定程度的殘留偶極交互作用. 利用固體模型分析A1000的T2鬆弛,可由其唯一參數得到包含各種運動的平 均活化能79-109 kj/mol,這些值介於由T1和黏度實驗值分析得來的活化 能31 kj/mol和161 kj/mol之間,顯示高分子系統的運動模式從地區性快速 鏈節運動到高分子鏈領域的緩慢運動都有,由 T2鬆弛分析得來的活化能是 將這些運動模式的活化能加以平均的結果.高濃度F1溶液的T2鬆弛可用半 固體模型合配得很好,雖其T2鬆弛的曲線極為特殊,但半固體模型只用三到 五個參數合配,足見其成功之處.由於 涉的參數本身是某種統計上的平均, 故參數的依溫性及依濃度性尚難 與明確的物理意義. The NMR T1 and T2 relaxations of nearly monodisperse low molecular weight liquids have been studied . In the case of the melt system of the sample A1000 ( Mw=1051 ; Mn=930 ) , the T1 relaxation data measured at different temperatures are analyzed in terms of the Redfield theory with a local field fluctuation process . It is shown that the T1 relax- ations deviate greatly from a theoretical prediction based on treating the system as one of small molecules and calcu- lated using the parameter values obtained from the T1 data analysis . The deviation and the non-exponential decaying function of the T2 relaxation are explained in terms of the the solid model , which has a fundamental physical basis similar to the motional narrowing phenomenon occurring to a solid benzene . From the only parameter ( delta , residual dipolar interaction ) involved in the T2 relaxation curve fitting , weighed average activation energy values ranging from 79 to 109 kj/mol have been obtained for the modes of motions participating in the averaging the dipolar inter- actions . These activation energy values are between that determined from the analysis of the T1 relaxation data and the value obtained from the viscosity data . This result supports that the modes of motions involved in averaging the dipolar interactions range from the local segmental motions to that involving the whole molecule . In another case , the T2 relaxations of the solutions of the sample F1 ( Mw=9830 ; Mn=9610 ) are studied at different temper- atures and concentrations . It is shown that the unique T2 relaxation curves can be well described in terms of the semi-solid model , which has a basic picture similar to that of the solid model and contains the partial fluidity imposed on the system by the solvent .