PMDA-BPDA-HAB聚苯并噁唑的合成及耐热性

Preparation and Heat-Resistance of PMDA-BPDA-HAB Polybenzoxazoles

用廉价的均苯四甲酸二酐（PMDA）代替部分或全部3，3′，4，4′-联苯四羧酸二酐（BPDA），与3，3′-二羟基联苯胺（HAB）进行缩聚，然后脱水酰亚胺化，制备了5种聚酰亚胺（PI）。TGA分析显示，这些PI的DTG曲线为2个峰，可分为生成聚苯并曙唑（PBO）再发生PBO分解的2个阶段。PI膜在500℃通N2气1h，所得聚合物膜的DTG曲线仅为1个峰，表明这些PI可充分转变成PBO。用FTIR表征了PI和PBO膜的结构。PBO的耐热性（用失重5％时的温度L表示）比PI高100～170℃。PMDA-HAB PBO的耐热性高于BPDA-HAB PBO。HAB-BPDA-PMDA PBO的耐热性优于二元PBO。当PMDA在二酐单体中所占的摩尔分数为75％时，PBO的Td高达643℃。

Five Polyimides （PIs） were prepared from 3,3＇-dihydroxy-4,4＇-diamino-biphenyl（HAB） and 3, 3＇ ,4,4＇-biphenyltetra-earboxylie dianhydride （ BPDA）, pyromellitie dianhydride （ PMDA）, or their mixtures by condensation, and then dehydration-imidization. The derivative thermogravimetry （DTG） of the thermogravimetrie analysis（TGA） showed 2 heat decomposition peaks, upon which the heat decomposition process can be considered as two-staged the formation of Polybenzoxazoles （PBOs） and then the decomposition of PBOs. The DTG curves of the PI films treated at 500℃ for 1 h under nitrogen showed only one peak, which indicated that PIs can be sufficiently converted into PBO. The structures of the PIs and the PBOs were characterized by FTIR. The heat resistance （HR） of PBOs, indicated by the decomposition onset temperature Td, was better than that of PIs by 100 - 170℃. HR of PMDA-HAB PBO was better than that of BPDA-HAB PBO. HR of HAB-BPDA-PMDA PBOs with different BPDA/PMDA molar ratios was better than that of BPDA- HAB PBO or PMDA-HAB PBO. The HAB-BPDA-PMDA PBO with molar ratio of 1：0. 25：0. 75 showed the best HR.