Maity Sudhangshu, Jana Tushar
School of Chemistry University of Hyderabad Hyderabad 500046, India.
ACS Appl Mater Interfaces. 2014 May 14;6(9):6851-64. doi: 10.1021/am500668c. Epub 2014 Apr 21.
A series of meta-polybenzimidazole-block-para-polybenzimidazole (m-PBI-b-p-PBI), segmented block copolymers of PBI, were synthesized with various structural motifs and block lengths by condensing the diamine terminated meta-PBI (m-PBI-Am) and acid terminated para-PBI (p-PBI-Ac) oligomers. NMR studies and existence of two distinct glass transition temperatures (Tg), obtained from dynamical mechanical analysis (DMA) results, unequivocally confirmed the formation of block copolymer structure through the current polymerization methodology. Appropriate and careful selection of oligomers chain length enabled us to tailor the block length of block copolymers and also to make varieties of structural motifs. Increasingly distinct Tg peaks with higher block length of segmented block structure attributed the decrease in phase mixing between the meta-PBI and para-PBI blocks, which in turn resulted into nanophase segregated domains. The proton conductivities of proton exchange membrane (PEM) developed from phosphoric acid (PA) doped block copolymer membranes were found to be increasing substantially with increasing block length of copolymers even though PA loading of these membranes did not alter appreciably with varying block length. For example when molecular weight (Mn) of blocks were increased from 1000 to 5500 then the proton conductivities at 160 °C of resulting copolymers increased from 0.05 to 0.11 S/cm. Higher block length induced nanophase separation between the blocks by creating less morphological barrier within the block which facilitated the movement of the proton in the block and hence resulting higher proton conductivity of the PEM. The structural varieties also influenced the phase separation and proton conductivity. In comparison to meta-para random copolymers reported earlier, the current meta-para segmented block copolymers were found to be more suitable for PBI-based PEM.
通过缩合二胺封端的间位聚苯并咪唑（m-PBI-Am）和酸封端的对位聚苯并咪唑（p-PBI-Ac）低聚物，合成了一系列聚苯并咪唑嵌段-对位聚苯并咪唑（m-PBI-b-p-PBI），这是聚苯并咪唑的嵌段共聚物，具有各种结构单元和嵌段长度。核磁共振研究以及从动态力学分析（DMA）结果获得的两个不同的玻璃化转变温度（Tg）明确证实了通过当前聚合方法形成了嵌段共聚物结构。对低聚物链长进行适当且仔细的选择，使我们能够调整嵌段共聚物的嵌段长度，并生成各种结构单元。随着嵌段共聚物嵌段长度的增加，Tg峰越来越明显，这归因于间位聚苯并咪唑和对位聚苯并咪唑嵌段之间的相混合减少，进而导致纳米相分离域的形成。由磷酸（PA）掺杂的嵌段共聚物膜制备的质子交换膜（PEM）的质子电导率随着共聚物嵌段长度的增加而大幅提高，尽管这些膜的PA负载量并未随嵌段长度的变化而明显改变。例如，当嵌段的分子量（Mn）从1000增加到5500时，所得共聚物在160°C下的质子电导率从0.05增加到0.11 S/cm。更高的嵌段长度通过在嵌段内形成更少的形态学屏障，诱导了嵌段之间的纳米相分离，这有利于质子在嵌段内移动，从而使PEM具有更高的质子电导率。结构的多样性也影响相分离和质子电导率。与先前报道的间位-对位无规共聚物相比，发现当前的间位-对位嵌段共聚物更适合用于基于聚苯并咪唑的质子交换膜。
