合成具有benzimidazole側基之PBI共聚物，其固有黏度範圍在 0.91~1.58dL/g之間，均可塗佈成具有韌性之薄膜，這些共聚物隨著側基比例的提升，共聚物的溶解度也增加，且有好的熱安定性，於氮氣下10%熱重量損失溫度高於540℃、以及高玻璃轉換溫度(Tg約在 300℃左右)，它的抗張強度大於80MPa，但是當摻雜磷酸後，薄膜因為吸磷酸的膨潤，體積增加，使機械強度會明顯下降，所以我們導入甲基側基的單體，形成交聯PBI共聚物，交聯後PBI共聚物因受交聯鍵結，形成高分子鏈緊密堆積，抑制吸附磷酸量，雖然質子傳導度有稍微降低，但機械性質比起原先未交聯之PBI共聚物，其抗張強度增加了1~2倍。
質子傳導度隨溫度與磷酸摻雜量增加而增加，其中在相似吸附磷酸量下mBI30F70在160℃無水環境下，磷酸摻雜量為212wt%，質子傳導度為51.3 mS/cm高於m-PBI(35.5 mS/cm)，至於交聯後之PBI薄膜C-10-mBI30F70在160℃無水環境下，磷酸摻雜量為181 wt%，質子傳導度為40.3 mS/cm。
這些含benzimidazole側基之PBI薄膜具有高磷酸摻雜量、高質子傳導度和好的熱安定性，與耐氧化安定性，經由交聯結構的形成，使PB薄膜在高的磷酸摻雜量下，仍保有良好的機械性質，與高的質子傳導度，是很有潛力成為中溫型燃料電池中質子交換膜材料。

A series of polybenzimidazoles (PBIs) with pendant benzimidazole had been synthesized. The resulting polymers showed good solubility in aprotic solvents. They had inherent viscosities in the range of 0.91~1.58 dLg-1, and they could form tough and flexible films.The PBIs exhibited high thermal stability with 10% decomposition temperature more than 540℃ in nitrogen, and their glass transition temperature around 300℃. These films also exhibited good mechanical properties with tensile stress exceeded 80 MPa. Phosphoric acid (PA) doped PBI was swollen result in the volume of PBI showed a larger volume swelling. The mechanical properties of phosphoric acid doped PBI significantly decreased.The mechanical properties of PBIs were improved using crosslinking in methyl pendent PBIs. Mechanical strength of cross-linked PBI is twice as strong as noncross-linked PBI.
The proton conductivity of phosphoric acid doped PBI was dependent on doping PA level and temperatures.At the approximate doping PA level,the proton conductivity of mBI30F70 was 51.3 mS/cm at 160℃, compared with 35.5 mS/cm of m-PBI membrane. The proton conductivity of C-10-mBI30F70 was approximately 40.3 mS/cm at 160℃.
Thus, these polybenzimidazoles (PBIs) with pendant benzimidazole membranes could be the promising materials alternative to m-PBI membrane for medium-temperature fuel cells applications because they had high phosphoric acid doped, good thermal stability, and higher proton conductivity.

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