以二級丁基鋰起始聚己烷噻吩之起始機制研究

Abstract

近年來導電高分子材料的演進日新月異，其中又以共軛導電硬桿端與絕緣柔曲端之嵌段共聚物(block copolymers)藉由改變其共聚成分比例而造成各種形態的功能應用最受注目。其中以聚烷基噻吩(poly(alkylthiophenes))以低能階、低氧化電位與穩定的導電性質在發光二極體、場發射電晶體、高分子太陽能電池、顯示器等應用。為了近一步討論硬桿柔曲嵌段共聚物在不同特性上的相關性，有效控制的共聚反應將是一大關鍵，因此我們以聚烷基噻吩為主之共聚起始機制為主要研究目標。 目前以原子轉移自由基聚合反應(Atom Transfer Radical Polymerization)為主，此方法以高分子之末端官能基改質起始自由基共聚反應。考慮連鎖聚合機制(chain addition polymerization)對聚合物平均分子量之有效控制，因此本研究採用陰離子聚合機制(anionic polymerization)起始聚己烷噻吩之共聚合反應。 以二級丁基鋰(sec-butyllithium)起始聚己烷噻吩poly(3-hexylthiophenes)後觀察到紫外光可見光吸收光譜出現較長波長之吸收峰，推斷出與過量二級丁基鋰起始劑反應下將聚己烷噻吩兩端氫去質子化(deprotonation)之後近一步氧化產生鏈段內極子(polaron)。其中自由電子也由電子順磁共振光譜(ESR)得到自由基訊號。進一步研究發現在起始後聚己烷噻吩分子量降低，此一斷鏈反應推論由自由電子受到共平面結構之牽制導致高分子主鏈斷鍵。此一斷鍵反應對共聚反應之控制造成極大影響。 因此提出常溫滴定反應以有效控制起始劑二級丁基鋰的反應量。在常溫下二級丁基鋰活性高因此加速反應並以顏色橘至深棕色判定滴定當量點，有效起始聚己烷噻吩，並避免過量氧化造成分子鏈斷鏈，成功合成聚己烷噻吩聚二吡啶乙烯之低分散性(polydispersity)共聚合物。

The new class of conducting-rod and insulating-coil copolymers is widely studied for morphologies and advanced applications. Yet the correlations of chemical compositions, morphologies and properties of copolymers require further exploration. In this research, regioregular poly(3-hexylthiophenes), P3HT, was initiated by sec-butyllithium as block copolymerization macroinitiator. Anionic polymerization is known for the kinetic control of chain growth mechanism with low polydispersities. sec-Butyllithium initiated P3HT induced a chemical doped radical anion model, which is responsible for the fragmentation of conjugated chain bond breaking effect. The molecular weight decrement of P3HT macroinitiator was observed in GPC traces. Further investigation with ESR showed free radical signal within macroinitiator, along with the transition observed in optical energy absorption. Fragmented macroinitiator exhibit radical reactivity caused high polydispersities of copolymers. To eliminate the fragmentation reaction, the amount of excess s-BuLi was controlled by titration in room temperature. Further control of copolymerization temperature of macroinitiator, conversion of 2VP monomer was improved. In optimized condition, P2VP-P3HT-P2VP copolymers with low polydispersities can be synthesized and purified by extraction.