【科学课件】聚苯并咪唑的合成和表征

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A-O-34_新型可溶性聚苯并咪唑的合成与性能研究

新型可溶性聚苯并咪唑的合成与性能研究徐静，刘程，蹇锡高（大连理工大学高分子材料系，大连市中山路158号42信箱，116012）关键词: 聚苯并咪唑二氮杂萘酮耐热性溶解性聚苯并咪唑（Polybenzimidazole ）是一类重要的特种工程塑料，具有优异的热稳定性、阻燃性、耐腐蚀性和机械性能等特点[1-2]，广泛应用于航空航天、电子电气等领域。

聚苯并咪唑通常具有刚性的主链结构，导致其具有很高的熔点以及溶解性差的缺点，如商品化的聚苯并咪唑是由间苯二甲酸和3,3’-二氨基联苯二胺缩聚合成的，具有刚性结构，而且加工性差，使其应用范围受到一定的限制。

在分子主链中引入柔性基团（如醚键、砜基、烷基等）[3-5]或体积较大的基团[6]等可以改善聚苯并咪唑的溶解性，但会降低其耐热性能；也有文献报道了将咪唑环上的氢进行芳环取代可以提高聚苯并咪唑的耐热和氧化稳定性[7]；除此之外，在聚合物主链中引入芳杂环结构可以提高聚合物的耐热性能，如吡啶、三唑等[8]。

本文通过在聚苯并咪唑的分子主链中引入扭曲、非公平面二氮杂萘酮联苯结构，以改善其溶解性能，同时赋予其优异的耐热性，报道了一系列新型含二氮杂萘酮联苯结构的聚苯并咪唑均聚物和共聚物的合成、表征和性能。

PPBI NH N NN H O N N O n N H N N H N NN HH NN O N N O coPPBI m n Scheme 1 Structures of polybenzimidazole containing phthalazinone moiety (PPBI and coPPBI ) 本文采用溶液缩聚法合成聚苯并咪唑，以自制的二酸单体4-[4-（4-羧基苯氧基）苯基]-2-（4-羧基苯基）二氮杂萘-1-酮（DHPZ-DA ），为二酸单体，与3,3’-二氨基联苯胺（DAB ）进行缩聚反应，制备了含二氮杂萘酮联苯结构聚苯并咪唑均聚物（PPBI ）；并以DHPZ-DA 和间苯二酸（IPA ）为二酸单体，采用不用摩尔配比，与DAB 进行共缩聚（coPPBI ），制备了一系列具有不同二氮杂萘酮联苯结构含量的聚苯并咪唑共聚物。

聚苯并咪唑的合成及应用研究进展

V ol 36N o 8 36 化工新型材料N EW CH EM ICAL M A T ERIA L S 第36卷第8期2008年8月作者简介:马涛(1978-),男,兰州大学高分子化学与物理专业在读博士,师承李彦锋教授,从事于耐高温高分子材料的研究。

联系人:李彦锋。

聚苯并咪唑的合成及应用研究进展马涛李彦锋* 赵鑫邵瑜宫琛亮杨逢春(兰州大学化学化工学院,兰州大学生物化工及环境技术研究所,兰州730000)摘要介绍了国内外有关聚苯并咪唑高分子材料的研究状况。

论述了聚苯并咪唑的发展,二元酸和四胺单体的合成方法、聚合工艺、种类及国内外应用状况,并对聚苯并咪唑的发展方向和研究热点进行了分析。

关键词聚苯并咪唑,单体合成,聚合,应用Progress on synthesis and application of polybenzimidazolesM a Tao Li Yanfeng Zhao Xin Shao Yu Go ng Chenliang Yang Feng chun (College of Chemistr y and Chemical Eng ineering ,Institute of Biochemical Eng ineering &Environmental Technolog y,Lanzhou U niversity ,Lanzhou 730000)Abstract T he pro g ress of polybenzim idazoles was reviewed.T he char act er o f polybenzimizo les on phylog eny ,monomer,poly merization technolog y,and applicatio ns w ere detailedly descr ibed,meanwhile,the develo pments of po ly benzim izo les w ere obviously presented.Key words po ly benzimidazo le,monomer sy nthesis,polymer ization,applicat ion随着航天技术的发展,特别是航天器飞行速度和有效载荷与结构质量比的提高,耐高温先进复合材料正在成为最主要的航天结构新材料。

含有吡啶环的可溶型聚苯并咪唑共聚物的合成及表征

Ｓａｇａ２０４，Ｃｈｎ）ｈｎｈｉ０２０ｉａ
ＡｂｔａｔＣｏｌｍｅｓｃｎｔｉｎｒｄｉｅｒｎｇｓａｅｓｎｔｓｚｄｂｙｔｏｌｉｎｐｏｙｃｎｄｎｓｔｏｆ３，ｓｒｃ：ｐｏｙｒｏａｎｉｇｐｙｉｎｉｒｙｈｅｉｅｈｅｓｕｔｏｌｏｅａｉｎｏ３一
近几十年来，随着机械、电子、航空等尖端行业对耐热高分子材料需求的快速增加，杂环类聚合物材料芳的研究得到了迅猛发展，形成了聚酰亚胺（Ｉ、苯并咪唑（Ｂ）Ｐ）聚ＰＩ以及聚吡咙（Ｐ）含杂环的高分子化合Ｐｙ等物，在实际中得到了广泛的应用Ｌ。一般而言，有Ｎ、并１］含Ｏ等杂原子的芳香环结构具有优异的热稳定性、化学稳定性，的还具有良好的极性和介电性能。同时，有含有杂环和芳环的高分子材料由于分子链刚性很大且
应的基础上，入含有吡啶环的新单体 —— ２３５６四氨基吡啶（Ｐ，成了一种新型可溶性共聚型聚苯加，，，一ＴＡ）合
并咪唑。实验表明，用Ｄ使ＡＢ、Ｐ、，二羧基二苯醚（ＣＥ３种单体可以在较低温度的条件下合成ＴＡ４４＿ｒＤＤＰ）
ＰＩＢ。２年后，ｇｌ阳备了具有优异热性能的ＰＩ聚合物。上述研究中所合成的ＰＩＶｏｅ等口制Ｂ类Ｂ均具有较好的

具有烷基磺酸侧链的凝胶型聚苯并咪唑质子交换膜的制备与表征

化工进展Chemical Industry and Engineering Progress2024 年第 43 卷第 4 期具有烷基磺酸侧链的凝胶型聚苯并咪唑质子交换膜的制备与表征朱泰忠1，张良1，黄泽权1，罗伶萍1，黄菲1，薛立新1，2（1 浙江工业大学化工学院膜分离与水科学技术中心，浙江杭州 310014；2温州大学化学与材料工程学院，浙江温州 325035）摘要：磷酸（PA ）掺杂聚苯并咪唑（PBI ）以其优异的热化学稳定性和高玻璃化转变温度成为高温质子交换膜燃料电池（HT-PEMFCs ）的首选材料。

然而，由于低温下磷酸较弱的解离度和传递速率，导致膜的质子传导性能不佳，电池冷启动困难。

因此，研发可在宽温湿度范围内高效运行的高温质子交换膜成为当前挑战。

特别是拓宽其低温运行窗口、实现冷启动对这类质子交换膜燃料电池在新能源汽车领域的实际应用具有重要意义。

本文通过多聚磷酸溶胶凝胶工艺与内酯开环反应设计并合成了一系列磷酸掺杂的具有柔性烷基磺酸侧链的凝胶型聚苯并咪唑质子交换膜。

重点探究了烷基磺酸的引入以及侧链长度对磷酸掺杂水平、不同温湿度下的质子传导率及稳定性的影响规律。

研究结果表明，所制备的质子交换膜具有凝胶型自组装片层堆叠的多孔结构，有利于吸收大量磷酸并提供质子快速传输通道。

其中，PA/PS-PBI 展现出了在宽温域范围内均优于目前所报道的其他工作的质子传导性能。

特别是常温下，其质子传导率从原膜的0.0286S/cm 提升至0.0694S/cm 。

80℃下，其质子传导率从原膜的0.1117S/cm 提升至0.1619S/cm 。

200℃下，其质子传导率从原膜的0.2609S/cm 提升至0.3578S/cm 。

此外，该膜在80℃和0%相对湿度（RH ）条件下仍可具有与Nafion 膜在100%RH 时相当的质子传导率，为打破质子交换膜经典定义、实现宽温域（25~240℃）运行提供新的方案。

聚苯并咪唑树脂的合成与性能研究

ylmethane；polybenzimidazole；thermal stability
II
聚..............................................1
1.1 聚苯并咪唑树脂的概述.....................................................................................................1 1.2 聚苯并咪唑的发展概况.....................................................................................................1 1.3 合成聚苯并咪唑的主要单体与工艺.................................................................................3
学校代码 10530 分类号 O633.5
学号 200706020975 密级
硕士学位论文
聚苯并咪唑树脂的合成与性能研究
学位申请人指导教师学院名称学科专业研究方向
张海林原斌教授
化学学院有机化学精细有机合成
二零一零年五月二十日
Study on the Preparation and Performance of Polybenzimidazole resin
作者签名：
日期：年月日
学位论文版权使用授权书
本学位论文作者完全了解学校有关保留、使用学位论文的规定，同意学校保留并向国家有关部门或机构送交论文的复印件和电子版，允许论文被查阅和借阅。本人授权湘潭大学可以将本学位论文的全部或部分内容编入有关数据库进行检索，可以采用影印、缩印或扫描等复制手段保存和汇编本学位论文。

聚苯并咪唑纤维

学号姓名
材料性能材料制作方法材料发展历程与应用
2012-7-3
材料全称：聚2,2`-间亚苯基-5,5`-双苯并咪唑纤维抗张强度：39.7～43.2cN／tex
（短纤维为27.4cN/tex）延伸率：23％～24％（短纤维为30％）吸湿率：高达15％，高于棉花突出性能：尺寸稳定性、阻燃性；耐强酸、强碱、有机溶剂；耐高温、耐化学品腐蚀；良好的纺织性能
ห้องสมุดไป่ตู้
湿法纺丝：PBI
拉伸、热定型
乙二醇凝固浴
（高温下）水洗、干燥纤维
发展历程
聚苯并咪唑纤维于20世纪60年代初由美国空军材料实验室研制成功。1983年由美国塞拉尼斯公司正式投产，年生产能力为 460t，因生产成本高，发展缓慢。它是一种典型的杂环高分子耐热纤维，大分子主链上含有苯并咪唑撑，它主要作为宇航密封舱耐热防火材料﹐由于核纤维吸湿率高达15%﹐因此自1983年后﹐又开发了穿著舒适的高温防护服等民用产品。
可作气体、液体的耐腐蚀滤材和烟道气滤袋，可在150～ 200℃范围内使用，在酸的露点温度以下不受腐蚀。
2012-7-3
聚苯并咪唑纤维还可与聚间苯二甲酰间苯二胺纤维混织，经碳化以后的纤维可作复合材料的高强度、高模量增强材料，其中空纤维（见化学纤维）可用作反渗透膜。
聚苯并咪唑纤维
应用
制作宇宙飞船中的绳索、耐烧蚀热屏蔽材料、减速用阻力降落伞及宇航员的加压安全服等。曾经用它制作阿波罗号和空间试验室宇航员的航天服和内衣。
2012-7-3
在一般工业中可作石棉代用品，包括耐高温手套、高温防护服、传送带等，使用温度常为 250～300℃，能在500℃下短时间使用

一种聚苯并咪唑类树脂的制备方法

专利名称：一种聚苯并咪唑类树脂的制备方法专利类型：发明专利
发明人：沈晶茹,李利红
申请号：CN202111185144.5
申请日：20211012
公开号：CN114058013A
公开日：
20220218
专利内容由知识产权出版社提供
摘要：本发明公开了一种聚苯并咪唑类树脂的制备方法，是由具有式2所示化学结构的芳族四胺与具有式3所示化学结构的六氯丙酮在反应溶剂中、于45～55℃下反应得到具有式1所示化学结构的聚苯并咪唑类树脂，其化学反应式如下：其中，R为四价芳基核，化合物2中的四个氨基成对出现在R中相邻碳原子的邻位碳原子上，n选自10至100中的任一整数。

本发明提供的制备方法，芳族四胺与六氯丙酮在45～55℃下反应即可制得聚苯并咪唑类树脂，操作简单，绿色环保、反应条件温和、生产效率高，适用于工业化生产聚苯并咪唑类树脂。

申请人：上海工程技术大学
地址：201620 上海市松江区龙腾路333号
国籍：CN
代理机构：上海海颂知识产权代理事务所(普通合伙)
代理人：马云
更多信息请下载全文后查看。

聚苯并咪唑的合成_性能及在燃料电池膜材料中的应用_浦鸿汀

与熔融聚合相比溶液聚合的优点有[12] : (1) 一步法代替二步法 ; (2) 对控温要求不严 ; (3) 溶剂中的极性化基团可以使过渡状态的产物溶剂化 ,从而降低活化能 ,使得反应可以在较低的温度和较短的时间内完成 ,从而降低了交联的可能性 ; (4) 在整个反应过程中都可以保证反应物充分混合 ,从而使活性端基可以很好地接触 ,而在熔融缩聚反应中端基有可能被包埋而不能接触 ; (5) 反应的副产物 ,如水、酚等可以通过沸腾的溶剂被带出反应体系 ,而在熔融缩聚中则被包含在体系中 ,影响聚合物分子量的提高 ; (6) 溶液状态或悬浮状态中的单体比在熔融状态中更容易脱除。 113 母体法
表 2 各种 PBI 的结构 Table 2 Different structures of PBI
R1 为以下结构 :
参考文献 R1 为杂环结构 : [2]
参考文献 R1 含杂原子结构 : [ 15 ]
[ 15 ] [2]
[2] [ 16 ]
[2]
R1 为其他结构 : [ 21 ]
[ 17 ]
1 PBI 的制备方法
PBI 的制备方法按反应种类分 ,大致有 4 种 :熔融缩聚法 (包括二步法和一步法) 、溶液缩聚法、母体
法、亲核取代法 , 其中对熔融缩聚和溶液缩聚的研究较多。PBI 的合成方法按反应单体分大致有 5 种[1 ,2 ,4 ,5] :四胺与二酸、四胺与二酯、四胺与二醛、四胺与二酰胺、四胺与二腈。其中 ,四胺与二酯的反应最
表 1 熔融一步法与二步法聚合的主要区别 Table 1 Differences between one2stage and two2stage polymerizations
一步法聚合

含苯并咪唑分子的合成及表征

含苯并咪唑分子的合成及表征亓昭鹏;程兴;李佩玉【摘要】A novel benzimidazole-containing compound, i.e. 3-（2-benzimidazolylmethyl）-1, 5-diamino- 3-azapentane is synthesized by a four-step reaction of protection, cyclization, substitution and hydrolysis, using chemical materials like diethylenetriamine, 1,2-diaminobenzene, and chloroacetic acid, etc. And then the structure of the compound is characterized by IR and 1H NMR.%以二乙烯三胺、邻苯二胺、氯乙酸等为原材料，经过保护，环化，取代，水解等步骤，得到了一个新颖的苯并咪唑的衍生物3-（2-甲基苯并咪唑）-1，5-二胺-3-氮杂戊烷，并通过红外光谱、核磁共振确定其结构。

【期刊名称】《黄山学院学报》【年(卷),期】2012(040)003【总页数】2页(P48-49)【关键词】3-（2-甲基苯并咪唑）-1;5-二胺-3-氮杂戊烷;合成;二乙烯三胺;邻苯二胺【作者】亓昭鹏;程兴;李佩玉【作者单位】黄山学院化学化工学院,安徽黄山245041;黄山学院化学化工学院,安徽黄山245041;黄山学院化学化工学院,安徽黄山245041【正文语种】中文【中图分类】O614.241苯并咪唑类化合物是一类具有良好生物活性的杂环化合物，广泛用于药物中间体、杀菌剂、驱虫剂等，在抗癌、镇痛、抗风湿、抗病毒等方面都有重要的药用价值。

[1-3]而且，含苯并咪唑类化合物具有较强的配位能力，也是配位化学领域中一个十分活跃的课题，常被用作超氧化物歧化酶活性中心的模拟物等。

聚苯并咪唑胶粘剂的合成

聚苯并咪唑胶粘剂的合成一、聚苯并咪唑的合成及性能聚苯并咪唑是杂环高分子中第一个被考虑作为耐高温结构胶粘剂的，它是从3，3’-二氨基联苯胺（DAB）和间苯二甲酸二苯酯进行熔融缩聚反应制得。

合成聚苯并咪唑的方法除熔融缩聚以外，还可以用溶液缩聚方法合成，而不同方法制备的聚苯并咪唑，其粘度也不相同。

聚苯并咪唑的特点是瞬时耐高温性优良，在538℃不分解，而聚酰亚胺的分解温度比它低。

到目前为止，研究得比较多的是聚[2，2’-间苯基-5，5’-二苯并咪唑]。

它的预聚物能溶于二甲基甲酰胺（DMF）、二甲基乙酰胺（DMAc）、二甲基亚砜（DMSO），N-甲基吡咯酮（NMP）、六次甲基磷酰胺（HMPA）、甲酸、硫酸等强极性溶剂中。

在70%硫酸或25%氢氧化钾溶液中不分解，在浓盐酸中加热也不溶解。

但预聚物再400℃处理一段时间待固化完全后，分子量增大，溶解度降低，就成为不溶不熔的树脂而难以加工成型。

因此在应用过程中先制成低分子量的预聚物。

这种低分子量的预聚物，具有比较好的流动性和对基材的浸润性。

作为胶粘剂和复合材料所需的树脂，一般是二聚体和三聚体，不过这就意味着在进一步缩合中会产生挥发分（水与苯酚），致使胶层及界面上出现针孔。

若大面积胶接则必须在高温（399℃）和加压0.686MPa下固化。

研究表明聚苯并咪唑核上NH的H原子是氧化破坏的活性中心，如用苯基C6H5-或甲基CH3-来取代该H原子，则高聚物的性能发生一定的变化。

当R=C6H5-时，热稳定性比未取代的略佳，但高聚物是热塑性的，应力受到了限制。

研究还表明甲基的取代位置对高聚物的性能有很大的影响，此外，在聚苯并咪唑的主链中引入氧、硫、亚甲基或其他基团可以改变聚苯并咪唑的性能。

比如引入醚键可以增加聚苯并咪唑的溶解性和分子链的柔性，改进成膜性能，还有良好的耐热性，但醚键的位置对热稳定性有一定的影响。

间苯二乙酸和间苯二甲酸混合物与DAB起反应制得的高聚物性能较好，溶解性也有改进，所有聚合反应都是在170℃多聚磷酸（PPA）中进行的。

聚苯并咪唑PBI

聚苯并咪唑(polybenzimidazoles)主链含重复苯并咪唑环的一类聚合物。

英文缩写PBI托基纶（Togylen）。

由芳族四胺和脂族或芳族二羧酸酯制备的聚苯并咪唑结构为：式中R为烷基碳链，Ar为芳香环结构。

聚烷基苯并咪唑的密度1.2克/厘米3，玻璃化温度234～275℃；全芳族聚苯并咪唑的密度1.3～1.4克/厘米3，玻璃化温度比前者高100～250℃。

聚苯并咪唑最突出的优点是瞬间耐高温性，烷基PBI在465～475℃才完全分解，芳基PBI 在538℃尚不分解，900℃失重仅30% ，常期使用温度300～370℃。

此外耐酸碱介质、耐焰和有自灭性、良好的机械和电绝缘性，热收缩极小。

制备方法由多胺与二酸或二酯在高温下熔融缩聚，先生成可溶性的聚氨基酰胺，然后通过脱水环化反应生成咪唑环聚合物。

高温（ 400℃）处理到完全固化后，聚合物变为不溶不熔。

典型的聚合物由 3，3′-二氨基联苯和间苯二甲酸二苯酯缩合而成，其纤维称PBI纤维。

工业上可采用熔融本体缩聚工艺制备PBI，即在惰性气体保护下按照一定比例是单体TAB和DPIP熔融本体缩聚反应合成PBI：上述的缩聚反应分两个阶段进行。

第一阶段为预缩聚，反应温度270~300℃，反应时间1~2h，除去副产物苯酚和水得到泡沫状预聚体，将其冷却和粉碎后再在真空下与375~400℃固相聚合2~3h，制成黄棕色粒状PBI树脂。

制备工艺——纺丝成型聚2,2`-间亚苯基-5,5`-双苯并咪唑（PBI）的纺丝溶剂主要有硫酸—水溶液、二甲基甲酰胺（DMF）、二甲基亚砜（DMSO）和二甲基甲酰胺（DMAC）等，其中DMAC较理想，是适宜的纺丝溶剂。

制备纺丝原液时，将粒状PBI加入DMAC 中，边搅拌边加热到250℃左右，聚合物全部溶解，配制成重量浓度约25%、室温下粘度约150Pa·s(1500P)的纺丝原液。

为防止纺丝原液因氧化交联而出现凝胶现象，需要在溶解及纺丝过程中保持非氧化条件。

一种硼酸取代的聚苯并咪唑聚合物及其制备方法

一种硼酸取代的聚苯并咪唑聚合物及其制备方法嘿，朋友们！今天咱要来聊聊一种特别有意思的东西，那就是硼酸取代的聚苯并咪唑聚合物。

这玩意儿可神奇啦！你想想看啊，聚合物就像是一个大家庭，里面有各种不同的成员。

而硼酸取代的聚苯并咪唑聚合物呢，就是这个大家庭中很独特的一位。

它有着自己独特的性格和本领。

先来说说它的制备方法吧。

这就好比是做菜，得有合适的食材和步骤。

首先呢，得准备好各种原料，就像做菜要准备好蔬菜、肉类啥的。

然后呢，通过一系列巧妙的操作，让这些原料发生反应，就像把菜在锅里翻炒一样。

最后，神奇的事情发生了，就得到了我们想要的硼酸取代的聚苯并咪唑聚合物。

这过程可不简单啊！就像你要盖一座漂亮的房子，得精心设计、仔细施工。

要是有一个环节出了差错，那可就麻烦啦！但一旦成功了，那可真是让人兴奋不已。

你说这硼酸取代的聚苯并咪唑聚合物有啥用呢？嘿，用处可大了去了！它就像是一把万能钥匙，可以打开很多神奇的大门。

比如说，在一些高科技领域，它能发挥重要作用呢。

它可以让一些材料变得更坚固、更耐用，就像给它们穿上了一层坚固的铠甲。

而且哦，它还可能在未来给我们带来更多的惊喜呢！说不定哪天，你就会发现身边到处都有它的身影。

也许你的手机变得更轻薄、更耐用了，也许一些新的高科技产品因为它而诞生了。

咱再回过头来想想，这一切是多么神奇啊！从一些普通的原料，经过一系列复杂的过程，最后变成了这么厉害的硼酸取代的聚苯并咪唑聚合物。

这难道不像是一场奇妙的魔法吗？真的，朋友们，科技的力量就是这么强大。

它能让我们看到以前想都不敢想的事情。

这硼酸取代的聚苯并咪唑聚合物就是一个很好的例子。

所以说啊，大家可别小看了这些看似普通的东西，它们背后可能隐藏着巨大的潜力和惊喜呢！让我们一起期待着硼酸取代的聚苯并咪唑聚合物在未来能给我们带来更多的精彩吧！。

PBI聚苯并咪唑

侨氏达塑胶材料：PBI（聚苯并咪唑）是当今最为高档的工程热塑性塑料，具有最耐高温和最好的机械性能优点.因其优越的性能，在其他塑料无法实现的领域，PBI都可能找到最佳解决方案。

特征：空气中最大允许使用温度极高(可以310度下持续工作，短时间最高使用温度可达500度).出色的机械强度和刚度保持力,出色的耐磨和摩擦性能,极低的线性热膨胀系数,固有的低可燃性，离子污染环境下的高纯度,低排气性(干性材料)。

应用：通常用来制造要求极严的元器件以降低维护维修费用，并且使用寿命最长。

已建立的应用领域有半导体和航空工业，白炽灯或荧光灯高温接触件，如真空杯、推指和保持架，电气接触器等.规格：板材：厚*宽*长=12.7～31.75mm x 620mm x 1000mm;棒材：25.4 - 120.65 x1000mm 颜色：黑色产地：瑞士分子式：CAS号：聚苯并噻唑;polybenzothiazole性质：又称聚苯并双噻唑。

一类由苯并噻唑稠杂环重复单元构成的溶致液晶棒状聚合物。

可由2,5-二氨基-1,4-苯二巯基二盐酸盐和对苯二甲酸，在多聚磷酸中经缩聚和环化而制得。

PBT不熔不燃，热氧稳定性高，空气中560℃时失重10％，316℃老化200h仅失重2％。

溶于多聚磷酸、甲磺酸等强酸，耐有机溶剂和有机碱。

可由液晶溶液进行纺丝和浇铸薄膜。

由挤出流延法制得的单轴拉伸薄膜的拉伸强度和拉伸模量分别为3.5GPa和255GPa。

纤维的密度为1.5g/cm3，拉伸强度和拉伸模量达4.2GPa和365GPa，具有高耐热、超高强度、超高模量特征。

PBT纤维、薄膜和分子复合材料主要用作飞机、宇宙飞船、导弹的结构材料及电子电器部件。

聚苯并噻唑;polybenzothiazole性质：一种耐高温树脂。

有很好的耐热性。

在370℃以下对氧化有突出的稳定性。

在高温和载荷下蠕变破裂性、烧蚀性和水解稳定性均极好。

用于制薄板、结构材料、烧蚀材料和胶粘剂，如火箭前锥体的结构材料和宇宙飞船的部件。

聚苯并咪唑PBI的制备及性能研究

N-alkyl polybenzimidazole:Effect of alkyl chainlengthSudhangshu Maity,Arindam Sannigrahi,Sandip Ghosh,Tushar Jana ⇑School of Chemistry,University of Hyderabad,Hyderabad,Indiaa r t i c l e i n f o Article history:Received 10December 2012Received in revised form 26March 2013Accepted 13May 2013Available online 6June 2013Keywords:PolybenzimidazoleProton exchange membrane Fuel cell Membrane Polyelectrolytea b s t r a c tDespite the presence of bulk literature on polybenzimidazole (PBI),unavailability of readily soluble and processable PBI remains as the tallest challenge for the end-use.N-alkyl PBIs (N-PBIs)were synthesized by grafting the alkyl chain in the imidazole backbone to resolve this key constrain.The chain length of substituted alkyl groups was varied to evaluate the inﬂuence of chain size on the structures and properties of N-PBIs.Signiﬁcant enhancement of solubility of N-PBIs compared to parent PBI in formic acid offered the opportunity to fab-ricate the homogeneous mechanically tough membranes with minimal efforts.The substi-tuted long alkyl chains pushes apart the PBI chains and hence increases the face-to-face packing distance by breaking the self-association between the chains;resulted into less rigid highly soluble N-PBIs.Alkyl chain length dependent weight loss at $300°C,presence of two glass transition temperatures and peculiar deep rubbery modulus in storage mod-ulus vs.temperature plots resembled the copolymer molecular structure of N-PBIs.Hydro-phobic character of alkyl chains and loosely packed structure of N-PBIs facilitated decrease in water uptake and swelling of the N-PBI membranes compared to parent PBI membrane.The temperature dependent proton conductivity of PA loaded N-PBIs membranes were found to be satisfactory.Ó2013Elsevier Ltd.All rights reserved.1.IntroductionDue to large demand of efﬁcient,powerful and eco-friendly source of energy devices,polymer electrolyte membrane fuel cell (PEMFC)has become the one of the most promising candidate for mobile and as well as sta-tionary applications.Although varieties of PEMs are known to the literature,till today the perﬂuoro sulfonic acid based membrane (Naﬁon)[1]is mostly used despite of many drawbacks like its high cost and relatively low stability at high temperature etc.As an alternative of Naﬁon,recently phosphoric acid (PA)doped polybenzimidazole (PBI)mem-brane [2]has been used and found to be the best alterna-tive because of unique properties such as excellent thermo-chemical and mechanical stability [3],high proton conductivity up to 180°C,zero water osmotic drag coefﬁ-cient etc.[4–6].However,one of the major drawbacks of PBI is its poor solubility in common organic solvents.It is soluble in only highly polar solvents like N ,N -dimethyl acetamide (DMAc),N ,N -dimethyl formamide (DMF),1-methyl-2-pyrrolidone (NMP),dimethyl sulfoxide (DMSO)at higher temperature [7–9].Hence,structural modiﬁca-tion of the PBI polymer to increase the solubility and pro-cessability in common organic solvents and low boiling solvents is one of the key challenge to be addressed for the development of PBI based PEMFC.Till today many research groups made efforts to produce different types of PBI structure like poly(2,5-benzimidazole)(AB-PBI)[10],sulfonated PBI [11–13],hyperbranched poly-benzimidazole [14],crosslinked polybenzimidazole [15],pyridine based polybenzimidazole [16],N-substituted poly-benzimidazole [17–31]etc.Unfortunately,the solubility and processability of PBI as discussed above were not re-solved very satisfactorily.Among various efforts,it has been noticed that substitution on the A N atoms of the imidazole rings of the PBI backbone by appropriate functionalities re-sulted better solubility and processability of PBI in common organic solvents.Synthetically,PBI can be modiﬁed in two ways either by modiﬁcation of monomers or substitution0014-3057/$-see front matter Ó2013Elsevier Ltd.All rights reserved./10.1016/j.eurpolymj.2013.05.011⇑Corresponding author.Tel.:+914023134808;fax:+914023012460.E-mail addresses:tjsc@uohyd.ernet.in ,tjscuoh@ (T.Jana).(grafting)to the A N atoms of mother PBI.PBI backbone has highly rigid rod aromatic structure which inﬂuences and controls the crucial physical properties of PBI.Upon grafting the PBI chain rigid structure might get affected which in turn may alters the mechanical strength,thermal stability and other physical properties.The chainﬂexibility which en-hances the solubility of polymer can be adjusted by intro-ducing theﬂexible group[32,33]in the polymer backbone or by substitution in the A N atoms with alkyl[30],alkyl sul-fonate[34]or benzene sulfonate[24]groups.However,a careful optimization has to be made between the chainﬂex-ibility and thermo-mechanical stability.Imidazolium hydrogens are acidic in nature;in each repeat unit backbone has two substitutable hydrogen atoms.So,when DMAc solution of PBI treated with alkali hydride like NaH at higher temperature,it forms a polyanion and then one can do sub-stitution reaction with electrophile like R A CH2A X.Earlier,it has been reported that the degree of substitu-tion does not depend on the concentration of alkali hydride and electrophile[23].However,the effect of electrophile molecular size or other words the effect of alkyl chain length in case the electrophile is alkyl halide on the degree of substitution has not been studied.PBI has very high glass transition temperature(T g>400°C)attributing the rigid structure which resulting poor solubility.The very small free volume because of intra and inter hydrogen bonding in PBI are found to be the main reason for high T g and less solubility.It can be hypothesized that grafting of long alkyl chain in the PBI backbone may decrease the packing density and thereby increase the free volume by disrupting the hydrogen bonding which in turns decrease the T g and increase theﬂexibility of PBI.Earlier,in few re-ports it was observed that T g can be decrease with grafting [25],unfortunately no systematic study has been carried out to understand the effect alkyl chain length size on the T g and other physical properties.Also it will be inter-esting to analyze the effect of alkyl chain length on the properties of PA doped N-PBI.In this paper,we have synthesized a series of N-alkyl grafted(ethyl,pentyl,hexyl,heptyl,octyl,decyl,dodecyl, tetradecyl and hexadecyl)polybenzimidazoles.The chem-ical modiﬁcation of polybenzimidazole established by1H NMR and FT-IR technique.The thermal stability,mechani-cal property and the glass transition temperature(T g)are measured by thermogravimetric analyzer(TGA),dynamic mechanical analyzer(DMA),respectively.Efforts have been made to prepare PA doped membranes and all types of essential characterization were carried out to evaluate the potential of these acid doped membranes for their use as PEM in fuel cell.In this present work,our goal is to improve theﬂexibility and solubility of PBI by grafting alkyl chain in the backbone.2.Experimental section2.1.Materials3,30,4,40-Tetraaminobiphenyl(TAB)and polyphosphoric acid(PPA,115%)were purchased from Sigma–Aldrich.Iso-phthalic acid(IPA),1-bromoheptane,1-bromodecane,1-bromododecane,1-bromotetradecane,1-bromohexadec-ane were received from SRL,India.1-bromopentane,1-bro-mohexane,1-bromooctane,1-iodoethane were received from Avra Synthesis Pvt.Ltd.,India.NaH was received from Finar Chemicals India Pvt.Ltd.Dimethylacetamide(HPLC grade)and deuterated dimethyl sulfoxides(DMSO-d6) were procured from Qualigens,India.Sulfuric acid(98%) and phosphoric acid(PA)(85%)were received from Merck, India.All the chemicals were used without further puriﬁcation.2.2.PBI synthesisThe synthetic procedure for PBI was similar to our ear-lier reports[35,36].Brieﬂy the process was as follows: equal moles of TAB and IPA were taken into a three neck ﬂask with PPA(115%)and the reaction mixture continu-ously stirred by mechanical stirrer in nitrogen atmosphere at190–210°C for24h.After completion of the reaction PBI was poured into water,then neutralized by sodium hydro-gen carbonate and thoroughly washed with water.The PBI was dried in vacuum oven at120°C for24h.The inherent viscosity(IV)of polymer was measured to evaluate the molecular weight of the synthesized polymer.The mea-sured IV of PBI was1.02dL/g at30°C in H2SO4(98%).2.3.Synthesis of N-alkyl substituted PBIThe different chain lengths(from C2to C16)alkyl groups were substituted to the imidazole A NH functional group of the PBI backbone(Scheme1).The reactions were carried out as follows:ﬁrstly250ml0.5%(w/v)PBI(4.06mmol) solution in DMAc solvent was prepared and the solution wasﬁltered through0.5l m PTFE membrane.This PBI solution in DMAc was stirred in500ml three neckﬂask for1h at30°C in nitrogen atmosphere.Then0.195g (8.12mmol)NaH was added and then stirring was contin-ued for another12h.The PBI in DMAc solution became red in color after addition of NaH.Then alkyl halide (8.12mmol)was added to this solution and reﬂux at 100°C for overnight(12h).Then this solution was poured into ice-water mixture andﬁltered.The residue was thor-oughly washed with water which was light brown color. The N-substituted PBIs(N-PBIs)were kept in vacuum at 120°C for48h to remove the moisture and other solvents.2.4.Preparation of membraneThe parent PBI and N-PBIs were dissolved in DMAc sol-vent at2%(w/v)concentration by continuous stirring for 12h.Then solutions wereﬁltered through0.5l m PTFEﬁl-ter paper,poured intoﬂat glass petridis and kept at120°C for12h.Homogeneousﬁlms were obtained,taken out from glass petridis,soaked in water and then boiled for three days to remove trace amount of DMAc.Theseﬁlms wereﬁnally kept in vacuum oven at120°C for2days for complete removing of solvent.The thickness of theseﬁlms was approximately from30to40l m.Theseﬁlms were stored in the desiccator for further studying.S.Maity et al./European Polymer Journal49(2013)2280–229222812.5.Characterization2.5.1.Solubility testThe solubility of parent PBI and N-PBIs were measured in various solvents in room temperature,under sonication and as well as in reﬂux condition.The solubility was tested up to3%(w/v)polymer concentration.2.5.2.Spectroscopic studyFT-IR spectra were recorded from the membranes made from DMAc(2wt%)solutions.The IR spectra were recorded using Nicolet5700FT-IR spectrometer.The NMR spectra were recorded from Bruker AV400-MHz NMR spectrome-ter with DMSO-d6as a NMR solvent at room temperature. The1H NMR peaks integral ratio was used to evaluate the% of n-alkylation.2.5.3.Thermal studyThe thermal stability of N-PBIs was carried out using thermogravimetric and differential thermal analysis(TG-DTA,Netzsch STA409PC)instrument.The data was re-corded using TG-DTA instrument with the scanning rate 10°C/min from30to800°C with continuous nitrogen purging.2.5.4.X-ray diffraction studyThe X-ray diffraction(XRD)patterns of dry powder samples were collected from a Philips powder diffraction instrument(model No.PW1830).The powder was taken in a glass slide and the diffractograms were recorded using nickel-ﬁltered Cu K a radiation at a scanning rate of0.6°2h/ min from2h=5–50°.Temperature dependent XRD pat-terns from50to400°C with50°C intervals were collected by keeping the samples inside the temperature control chamber of the instrument.Samples were equilibrated for30min at each temperature prior to the collection of XRD pattern.2.5.5.Thermo-mechanical studyThe mechanical properties of N-PBIs were measured by using a dynamic mechanical analyzer(DMA)(TA Instru-ment,model Q-800).The N-PBI membranes which were casted from DMAc solvent were cut into25mmÂ5mmÂ0.05mm dimension and then clamped on the ten-sion clamp of the instrument.The samples were scanned separately in the DMA in sub-ambient temperature(À120 to100°C)range and as well as from100to450°C.Two dif-ferent pieces of same samples were used separately for scanning in two different temperature ranges.The scanning rate for both the temperature ranges was4°C/min.The membranes were annealed at100°C for30min before scan-ning from100to450°C.The storage modulus(E0),loss mod-ulus(E00)and tan d values were recorded at a constant linear frequency10Hz and preload force0.01N.2.5.6.Water uptake and swellingPBI and N-PBIs membranes of similar dimension (2cmÂ1cmÂ40l m)were dipped into deionized water at room temperature for7days for the measurement of water uptake,swelling ratio and swelling volume of the membranes.The weight and dimensions of membranes were measured before and after immersed into the water. The water uptake was measured gravimetrically.The data presented in the manuscript are the average of three equal dimension samples.The percentage of water uptake,swell-ing ratio and swelling volume were calculated using the following equations.%Water uptake¼W wÀW dW dÂ100%ð1Þ%Swelling volume¼V wÀV ddÂ100%ð2Þ%Swelling ratio¼L wÀL dL dÂ100%ð3Þwhere W w,V w,L w are wet membranes weight,volume, length,respectively and W d,V d,L d are dry membranes weight,volume,length,respectively.2.5.7.Acid loadingPreviously dried mother and N-PBIs membranes were dipped in different concentration of phosphoric acid solu-tion for seven days at room temperature.The dimensions of dipped membranes were3cmÂ2cmÂ40l m.The membranes were taken out from phosphoric acidafter Scheme1.Synthesis of N-substituted PBI(N-PBI).seven days,blotted byﬁlter paper and titrated by pre-stan-dardized0.1N NaOH solution using an Autotitrator(Metr-ohm Titrino Titrator).The acid loading was calculated from average of three membranes for each type samples as the number of mol per PBI repeat unit.The number of acid loading per repeat unit of polymer was calculated by the following equation:Acid doping level¼W21where W2,W1arebrane,respectively.weight of PBI,N-PBIF N-PBI is the fraction2.5.8.ConductivityThe protonsured by using a fourin a Zahnerwith a frequencyzero humidityfor its superiorityeliminates thebrane surface as wellsize(3cmÂ1.5cmÂa homemadewires.The inner twolon plates apart fromthe potential drop ofwere measured inand second heating.theﬁrst heating dataity calculation.Aftera desiccator and thenperature secondity of acid doped160°C at20°intervaleach temperature thereach themeasured atintercept of theplot).The protonlowing equation:r¼Dwhere D is the(0.5cm),L and B arebranes,respectively,value.3.Results and3.1.Synthesis ofThe linear alkyl(C2A C16)are grafted conditions as presented in Scheme1.FT-IR and1H NMRspectroscopy are used to characterize the grafting of alkyl chains in the backbone.The FT-IR spectra of parent PBI and alkyl grafted PBI(N-PBI)membranes are shown in Fig.1.PBI is hygroscopic in nature and can absorb mois-ture up to5–15%of its weight[37].The presence of O A H stretching frequency at3620cmÀ1is conﬁrmed the hygro-scopic nature of parent PBI and N-PBIs.Fig.1shows that with increasing alkyl chain length,the intensity of O A H stretching frequency gradually decreases which indicates1.FT-IR spectra of N-substituted Polybenzimidazoles.All spectra recorded from the thinﬁlms($40l m).S.Maity et al./European Polymer Journal49(2013)2280–22922283imidazole A NH group and long alkyl chain in the N-PBIs indicates that 100%alkyl substitution did not take place and therefore the molecular structure of the N-PBIs is as shown in Scheme 1.Hence it becomes necessary to esti-mate the %of N-alkylation in N-PBIs and we have utilized NMR spectroscopy as described in the following section.The representative 1H NMR spectra of N-PBIs along with peak assignments and chemical structures are shown in Fig.2.The NMR signal matches perfectly as expected from the chemical structure.The characteristic aromatic C A H THF,formic acid (FA),chloroform etc.and the solubility chart is shown in Table 1.It is clearly evident from the sol-ubility chart (Table 1)that the PBI and N-PBIs are highly soluble in DMAc and NMP.Interestingly,N-PBIs show very high solubility in formic acid (FA)whereas parent PBI is partially soluble.This enhanced solubility of N-PBI is be-cause after alkyl substitution the PBI backbone becomes less rigid (as seen from the T g data in the later section)by increasing their face-to face packing distances (dis-cussed in the XRD section)which helps to decrease the self-association between the chains.FA is a low boiling sol-vent and hence one can readily remove the solvents to cast the ﬁlm from the polymer solution.Earlier,we have ob-served that certain type of PBI structure like [poly(4,40diphenylether-5,50-bibenzimidazole)],an ether linkage present in the polymer backbone,forms very transparent homogeneous ﬁlms when ﬁlms were made from FA solu-tion [39].Therefore the solubility in FA helps easy process-ability.Table 1clearly shows that N-PBIs have very high solubility compared to parent PBI which makes these mod-iﬁed PBI as easily processable material when FA is used as2.1H NMR spectra of few representative N-substituted PBI along parent PBI.DMSO-d 6is used as NMR solvent.Table 1Solubility of N-substituted PBI in different organic solvents and %of N-alkylation.Polymer %of N-alkylation a DMAc NMP FA CH 2Cl 2CHCl 3THF PBI À+++++ÀÀÀPBI-C 242.25++++++ÀÀÀPBI-C 546.25++++++ÀÀÀPBI-C 650.25++++++ÀÀÀPBI-C 757.75++++++ÀÀÀPBI-C 1060.75++++++ÀÀÀFig.3.TGA curves of N-PBI under N 2atmosphere.2284S.Maity et al./European Polymer Journal 49(2013)2280–2292processing medium.Supplementary data Fig.1compares the photographs of PBI and N-PBI membranes obtained from DMAc and FA.It is very clear from photographs that the N-PBI membranes obtained from FA are very much homogeneous and transparent compared to all other membranes.Also,parent PBI membrane from FAis120to 100°C)plots of mechanical properties obtained from DMA of few representative and (C)tan d .mechanically weak owing to its low solubility as evident from the photographs.Therefore it can be summarized that N-substitution with alkyl group in the PBI backbone en-hances the processability and solubility of rigid PBI.3.3.Structural prediction of N-PBIsThe thermal stability of N-PBI samples obtained from TG-DTA studies under nitrogen atmosphere are presented in Fig.3.It is known that approximately 5–15%weight loss occurs for PBI due to its hygroscopic nature at 100°C.We observed here from TGA that with increasing alkyl chain length the initial weight loss due to hygroscopic nature de-creases indicating that N-PBIs are less hydrophilic than PBI,which is also observed from FT-IR studies presented in ear-lier section.Although N-PBIs are found to be less thermally stable compared to parent PBI,however all the samples show ﬁrst major degradation above $300°C,indicating good and enough thermal stability for the use as thermally stable processable materials.All the N-PBIs samples display weight losses in three stages;ﬁrst one is at $100°C due to absorb moisture,the second weight loss is at $300°C followed by third weight loss at $510°C owing to the degradation of PBI backbone (Fig.3and Supplementary data Fig.2).Parent PBI does not exhibit second weight loss at $300°C.This attributes that at $300°C,the grafted alkyl chains are knocked out form the PBI backbone.The extent of this weight loss for N-PBI samples increases with increasing alkyl chain length attributing the fact that this weight loss is associated with N-substituted PBI backbone.Hence the second weight loss is due to degradation of grafted alkyl chains.The degrada-tion behavior of N-PBIs also predicts the partial grafting of alkyl group in the polymer backbone and copolymer type molecular structure as discussed in the previous section from NMR results.The effect of alkyl substitution on the glass transition temperature (T g )and the mechanical properties of the PBI are studied using DMA both in the sub-ambient tem-perature (À120°C to 100°C)as well as in the higher tem-perature (100–450°C).DMA data for both the temperature ranges are shown in Fig.4and 5and Supplementary data Figs.3and 4.It is known that the peaks appeared in the loss modulus (E 00)and tan d plot corresponds to the thermal transitions of the polymer.Parent PBI exhibits a transition at À78°C (from E 00plot)[À71°C from tan d plot]which cor-responds to the rotation of the m-phenylene ring [40]This transition can be called as d transition and it shifts towards higher temperature with increasing size of alkyl chain length in case of N-PBIs (Fig.4,Supplementary data Fig.3Fig.5.Temperature dependent (100–450°C)plots of mechanical prop-erties obtained from DMA of few representative N-PBI samples;(A)storage modulus (E 0),(B)loss modulus (E 00),and (C)tan d .Inset of (C)is the magniﬁed tan d plot of parent PBI.Table 2Various thermal transition data of N-PBI ﬁlms obtained from DMA study.Polymer T g (°C)from E 00T g (°C)from tan d d (°C)from E 00d (°C)from tan d PBI 327350À78À71C 5320341––C 6297324À62À58C 7275309À54À55C 8279,361315À57À55C 10240,366278,343À55À54C 12225,353264,340À41À32C 14215,359258,335––C 16220,359270,330À36À27Journal 49(2013)2280–2292and Table2).This indicates that the substituted alkyl group interferes the m-phenylene ring rotation resulting the d-transition shift.Parent PBI also displays a transition at $30°C which is known as c transition[40]but this transi-tion is absent in N-PBI(Fig.4).The d transition and T g values obtained from loss modulus(E00)and tan d plots are listed in Table2.The parent PBI shows only one T g at 350°C(tan d,inset of Fig.5)which is in agreement with previous results[36].DMA studies exhibit peculiar thermo-mechanical prop-erties for N-PBI samples.The decrease in T g valueFig.6.Temperature dependent(ﬁrst and second heating scans)plots of mechanical properties obtained from DMA of C14and C16N-PBI samples;(A)storage modulus(E0),(B)loss modulus(E00),and(C)tan d.Inset of(C)is the magniﬁed second heating scan plot of C14and C16samples.7.FT-IR spectra of PBI,C14and C16samples after DMA scan and annealing at400°C.Fig.8.WAXD patterns of N-PBI samples at room temperature.Powder samples are used to record the WAXD pattern.compared to parent PBI is expected asﬂexible alkyl groups are incorporated in the PBI backbone;T g value of N-PBI de-creases with increasing alkyl chain length up to C7(Ta-ble2).We observed two distinct T g’s from C8substitution onwards for all N-PBI(Table2,Fig.5and Supplementary data Fig.4);in which one T g(T g1<300°C)appears much below than the parent PBI T g($350°C)and other T g(T g2) appears quite close to T g of parent PBI.It also must be noted that T g1decreases with increasing alkyl chain length; however T g2remains almost unaltered with size of alkyl chain length.The presence of two T g’s and variation of one T g with altering the chemical structures clearly attri-butes the copolymer structure of the N-PBI backbone. The lower T g(T g1)is the segmental motion of the PBI back-bone in which N-substitution has taken place with the al-kyl chain and the higher T g(T g2)is the segmental motion of the unsubstituted PBI backbone.The alteration in T g1with increasing alkyl chain length is due to the increase alkyl is crossed the rubber modulus increases sharply with increasing temperature.This deep rubbery modulus is quite uncommon and very interesting.This kind of obser-vation was observed earlier in case of PVDF/PMMA blend where deep rubbery modulus is explained as the result of non-equilibrium crystalline states of PVDF[41].But in the current system,no crystallization is observed since all PBI and N-PBI are amorphous in nature(discussed in la-ter section).It is also noticed that(Fig.5)the deepness of rubbery modulus increases with increasing size of the alkyl chain length.We believe this deep may be the result of fol-lowing;as we increase the temperature the N-PBI shows the T g1(N-substituted chains)at$<300°C(onset of deep is<300°C),after that with increasing temperature the N-substituted part degrades;as seen in TGA studies where at$300°C a major weight loss is observed and which var-ies with alkyl chain length size;and then only unsubstitut-ed PBI exists which has T g beyond350°C(T g2).To displayFig.9.Variable temperature WAXD patterns;(A)PBI,and(B)C14N-PBI sample. 2288S.Maity et al./European Polymer Journal49(2013)2280–2292results are shown in Fig.7.It is clear that the parent PBI does not show any signiﬁcant changes in the spectrum; however N-PBI spectra after annealing display a peak around$2235cmÀ1which corresponds to A C…N vibra-tion resulting from the degradation of imidazole group; attributing that N-substituted part are degrading after heating at400°C.The wide angle X-ray diffraction(WAXD)patterns of the parent PBI and representative N-PBI samples are pre-sented in Fig.8.Absence of any sharp peak in all the sam-ples suggests the amorphous nature of all N-PBIs.It is known in the literature that PBI is amorphous in nature and our results indicate that substitution did not alter the amorphous nature of the PBI.Earlier several authors [42–44]pointed out two broad peaks at around$25and 11°2h for the PBI.These peaks correspondence to d-spac-ing 3.64and7.29Å,respectively.Theﬁrst d-spacing is the characteristic of the planes formed by face to face pack-ing of PBI chain and the later is due to the length of one re-peat unit.Fig.8clearly shows that in case of N-PBI samples the peak corresponding to7.29Åd-spacing does not alter with increasing alkyl length size.However d-spacing for face to face packing increases with increasing alkyl chain length size and reaches to maximum value at 4.38Å(2h=20.25°)for C16sample.These observations clearly attributes that with increasing alkyl chain length size the distance between the PBI chains are increasing and as a re-sult the self-association between the PBI chains decreases with increasing alkyl length.Therefore,substituted alkyl chains in the PBI backbone pushes the PBI chains apart and hence decrease the self association between the Fig.9.Both the cases the d-spacing increase(2h decreases) with increasing temperature indicating the increase in dis-tance between the PBI chains.However in case of parent PBI a signiﬁcant peak broadening is observed which is not observed in case of C14N-PBI.This attributes that in case of N-PBI,part of the polymer chain has already been separated apart by the long alkyl chain.In earlier section,we have concluded that the N-PBI samples have copolymer structure,in which one part is N-PBI and other part is unsubstituted PBI,and the N-PBI part degrades upon annealing at400°C.Fig.10data recon-ﬁrms our claims.The XRD pattern of N-PBI(C14)samples recorded at room temperature after annealing at400°C for30min is similar with the parent PBI,indicating that the N-PBI structure is indeed a copolymer in nature and degradable at400°C.3.4.Studies of crucial PEM membrane properties of N-PBIsIt is well known that PBI is hydrophilic and moisture sensitive.Even at room temperature PBI can absorb water up to15wt%when dipped into deionized water for several days.This may be due to hydrogen bonding formation be-tween two nitrogen atoms of amine and imine groups [45,46].In the imidazole moiety there are two nitrogen atoms one is proton accepter and one is proton donor and these nitrogen atoms undergo hydrogen bonding read-ily with H2O molecule.Fig.11displays that the water absorption capacity gradually decreases with increasing size of the alkyl chain length.In our earlier sections(FTIR and TGA study),we have seen the exactly similar observa-Fig.10.WAXD patterns of PBI,C14samples and C14sample afterannealing at400°C for30min.Fig.11.Water uptake of N-PBI samples.S.Maity et al./European Polymer Journal49(2013)2280–22922289。