含酰胺结构超低膨胀聚酰亚胺薄膜的热膨胀行为

采用联苯二酐与3种含酰胺结构二胺制备了具有不同取代基团的聚酰胺-酰亚胺薄膜, 考察了酰胺结构对薄膜力学、 耐热及尺寸稳定性的影响, 研究了聚集态结构与薄膜热膨胀行为的关系和规律. 该系列薄膜具有超高强度和优异的耐热性能, 拉伸强度高达280.5 MPa, 玻璃化转变温度在389~409 ℃, 并在30~300 ℃温度范围内表现出超低负膨胀, 热膨胀系数(CTE, ppm/℃, 即10 ⁶ cm·cm ^-1·℃ ^-1)在-3.05~-1.74 ppm/℃之间. 聚集态分析结果表明, 酰胺结构使分子链间形成了强氢键相互作用, 分子链在薄膜面内方向高度有序取向, 并在膜厚方向堆积更为紧密, 使薄膜表现出热收缩现象. 通过不同体积大小的取代基团进一步调控分子链间相互作用及排列堆积, 可实现薄膜在高温下近乎零尺寸形变, 为设计制备超低膨胀聚合物基板材料提供了新思路.

Thermal Expansion Behavior of Amide-containing Polyimide Films with Ultralow Thermal Expansion Coefficient

A series of amide-containing polyimide i.e.poly(amide-imide)films was prepared from biphenyl tetracarboxylic dianhydride and three diamines comprising diamide groups via two-step thermal imidization method.The effect of amide structure and different substituents on mechanical properties,water absorption,thermal properties and thermal expansion behavior of poly(amide-imide)films were investigated.The results showed that these films exhibited ultrahigh tensile strength up to 280.5 MPa and excellen theat resistance with T g above 389℃.Moreover,these films showed ultralow thermal expansion coefficient(CTE)from-3.05 to-1.74 ppm/℃in the wide temperature range of 30-300℃.The correlation of their thermal expansion behavior with aggregation structures including molecular chain interactions,orientation and packing was systematically studied.It was found that the molecular chains of poly(amide-imide)s were highly oriented along the in-plane direction while densely packed in the out-of-plane direction,because of the hydrogen bonding interactions between amide structures and the rigid linear backbone.That was the main reason for the thermal contraction of films and contributed to their outstanding dimensional stabilities.The aggregation structures of poly(amide-imide)s could be further affected by the substituents in the backbones with different volume and steric effect,resulting in the regulation of CTE values close to zero.It provids a new design thought for the heat-resistant polymer substrates with ultralow CTE for optoelectronic application.