環狀共軛高分子排列與開環聚合反應之觀察

此研究透過掃描穿隧顯微镜(STM)及原子力顯微鏡(AFM)觀察環狀共軛單體及其高分子於高定向熱解石墨(HOPG)自主排列之現象。藉由McMurry反應合成帶有6碳、12碳、18碳與6碳支鏈的環狀單體，STM圖顯示單體在1-苯基辛烷溶液中可自主於石墨表面上形成排列。由於支鏈會影響環狀主分子排列，支鏈較短的單體排列較穩定而延展，而支鏈較長的單體較易捲曲不易排列。除此之外，我們也藉由STM觀察到開環聚合後的產物(順式與反式高分子)會沉積於由單體排列而成的平面上方(非連續觀察狀態)以及透過AFM觀察其反應過程(連續觀察狀態)，並可藉由催化劑含量濃度控制其高分子的覆蓋面積。此研究可貢獻於有機光電元件之表面製成優化，並顯示順式與反式高分子型態的直接觀察，更提供了開環聚合反應之現象觀察

關鍵字

開環聚合；共軛高分子；掃描穿隧顯微镜；原子力顯微鏡

並列摘要

This study presents direct observation of self-assembled cyclic conjugated monomers and polymers on a highly ordered pyrolytic graphite (HOPG) surface using scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The cyclic monomers comprising of trimer of cyclopentadithiophene-vinylene (CPDTV) with various side chains of -C6H13, -C12H25, -C18H37, and 2-ethylhexyl are synthesized by McMurry coupling using TiCl4/Zn. STM images of the monomers indicate that the molecules spontaneously form a “face on” ordered monolayer at an interface between 1-phenyloctane and HOPG. The molecular alignment is varied by the side chains, indicating that the cyclic molecules with shorter alkyl chains have stretched planar structures on HOPG, whereas the molecules with -C18H37 chain has a shrunk structure. In addition, ring-opening metathesis polymerization (ROMP) of the monomers is performed in solution or on HOPG to observe a single molecular chain of the resulting conjugated polymers by STM or polymerization process by AFM. After the ROMP of the monomer, the polymer is spontaneously deposited on the top of unreacted monomers on HOPG (i.e. ex situ polymerization). STM images of the deposited surface show the presence of a mixture of cis- and trans- vinylene microstructures of the polymer single chains. Furthermore, ROMP of the cyclic conjugated molecules on the HOPG (in situ polymerization) as well as in solution (ex situ polymerization) are carried out and their surface morphology is observed by AFM. The AFM images show a partially covered surface with polymer fibers at lower catalyst concentration and a fully covered surface with polymer clusters at higher catalyst concentration. Consequently, drastic manipulation of the surface coverage and morphology of the polymer is achieved by varying the concentration of the ROMP catalyst. The self-assembly of the unique cyclic conjugated molecules is potentially useful for surface modification using such conjugated monolayers for use in organic opto-electronic devices. Furthermore, direct molecular structural analysis for the conjugated polymers using STM provides important information of cis-trans microstructural configurations of poly(arylene-vinylene)s and intermolecular interaction between the unique cyclic conjugated molecules and polymers. In situ AFM observation of ROMP also affords information for the unique reaction mechanism of ROMP.