運用全原子分子動力學模擬具剛直鏈段及柔軟接點之聚醇酯共軛高分子並擬合而得相對應之粗粒化分子動力學模擬參數

Abstract

本研究利用分子動力學模擬方法探討共軛高分子Poly(p-biphenylene terephthalate)-O9 之分子鏈構形與聚集形態，其分子鏈結構於主鏈為聯苯之剛硬鏈段與酯基之柔軟分子基團交替組合而成，且又於苯環上連接各九個碳之對稱柔軟烷基側鏈。我們利用波茲曼迭代反轉方法擬合全原子與粗粒化分子動力學模擬，並建構粗粒化力場。其中包括以徑向分佈函數曲線分析分子間作用力與以機率分佈函數曲線描述鍵長、鍵角和兩面角之分子鏈內結構參數。初期取得單條鏈擬合之分子內作用力參數進行粗粒化模擬只能獲得無序聚集形態，然而，經四條鏈擬合之分子內作用力參數之粗粒化模擬結果比較後發現，四條鏈擬合參數之設計可獲得局部規整排列形態，由結果得知兩面角之控制為重要影響要素。此外，若能於擬合參數下反應真實系統之主側鏈間不相容性於粗粒化分子間作用力參數設計上，可更容易獲得有序聚集形態。本研究即以擬合真實狀態為前提，獲得上述重要影響要素，用以分析剛直鏈段與柔軟接點之分子鏈構形變化和聚集形態的關聯性。

We developed a coarse-grained force field for the Poly(p-biphenylene terephthalate)-O9 alternating copolymer which consist of biphenyl group and ester group in main-chain and lateral alkyl chain in side chain, respectively. We adopted iterative Bozeman inversion method to develop a coarse-grained force field connecting with all-atom molecular dynamics. The force field contains intra- and inter-molecular interactions including bonds, angles, dihedral angles, and nonbonded terms. Through comparison of RDF, bond length distribution, angle distribution, and dihedral angle distribution are fitted between all-atom and coarse-grained molecular dynamics to comprehend the mapping results. The results indicated the disordered and locally ordered packing are revealed in mapping of single chain and 4 chains, respectively. Otherwise, the dihedral angle parameter is the most important parameter to affect the chain conformation and packing behavior. Besides, the incompatibility between main-chain and side-chain help the PBpT-O9 to pack into ordered morphology. Finally, the effective coarse-grained force field parameters are obtained to describe the realistic polymer chain.