刚性聚酰亚胺的分子堆积和热膨胀性能研究

Molecular packing and thermal expansion properties of rigid-rod polyimides

聚酰亚胺是一类高强、耐热、低介电常数特种工程材料,已在微电子领域广泛应用。因其热膨胀系数高于无机导电层,其作为集成线路板基膜材料时易与导电层剥离分层。在聚酰亚胺分子结构中引入刚性链段是降低热膨胀系数的有效方法。本文从2,5-二氨基苯基吡啶和2,5-二氨基苯基嘧啶合成了2种刚性聚酰亚胺,对其热性能和机械性能进行了表征。结果表明,此类刚性聚酰亚胺比普通聚酰亚胺具有更紧密的分子堆积,从而呈现出高密度、低热膨胀以及很好的耐热性和机械性能。另外,通过理论计算比较了聚酰亚胺堆砌系数与热膨胀系数的相关性,这些理论计算的堆砌系数可以较好的预测刚性聚酰亚胺的热膨胀性能。

Polyimides have been recognized as one of the most important inter-level dielectric materials in flexible copper clad laminates （FCCL） due to the overall balance of high temperature resistance, good mechanical strength and low dielectric constants. However, PIs had crucial drawbacks in that they were easily delaminated as a result of different coefficient of thermal expansion of each layer. The introduction of rigid-rod segmer is an effective strategy to reduce the values of CTE of PI films. Rigid-rod polyimides ware prepared via poly（amie aeid）s from the polycondensation of 2,5-diaminophenylpyridine or 2,5-diaminophenylpyrimidine with 3,3＇,4,4＇-biphenyl tetmcarboxylic dianhydride and characterized by the method of DMTA, TMA, TGA, XRD, density analyzer and mechanical test. The resulted polyimide films exhibited low coefficient of thermal expansion below 4× 10^-6 ℃ on account of increase of the molecular orientation promoted by the rigid units in polyimide chains. The CTE of the PI film containing 2,5-diaminophenylpyridine （PPD-PI） was close to that of the PI film containing 2,5-diaminophenylpyrimidine （PRM-PI）; however, the ordered molecular packing conducted by XRD was significantly different though both films containing rigid-rod segmer were high degree of order. Furthermore, the density of PPD-PI film was distinctly different from that of PRM-PI. Hence, it is difficult that the CTE of polyimide films were forecasted by characterization from XRD and density. Our research showed the theories calculating packing-coefficient was in accordance with the change of CTE of these PI films, which calculated from the intrinsic volume of the atomic groups forming the repeating unit and the molar volume calculated from the density of the polyimide film via computational approach of quantum chemistry. Therefore, the packing-coefficient can be an important structure parameter to give effective prediction of the CTE of polyimide films.