Synthesis and characterization of unsaturated thermotropic polyesters prepared via acyclic diene metathesis polymerization
Synthesis and characterization of unsaturated thermotropic polyesters prepared via acyclic diene metathesis polymerization
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DOI：
10.1021/ma0497456
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发表时间：
2004-07-13
期刊：
影响因子：
5.5
通讯作者：
Coughlin, EB
中科院分区：
文献类型：
--
作者：
Qin, HH;Chakulski, BJ;Coughlin, EB
采用无环二烯复分解（ADMET）聚合方法制备了柔性间隔基含双键的热致液晶聚合物（TLCPs）。以双烯单体2-叔丁基-1，4-苯基双（4-戊烯基氧基苯甲酸酯）（5 tB）为原料，通过ADMET聚合，成功地合成了不饱和液晶低聚物和聚合物P5 tBn。开发此类不饱和TLCPs以允许制备定制的、热交联的、液晶热固性材料作为粘合剂和复合基质树脂。实现了高聚合度，并且所得聚合物显示出完全不存在结晶的清楚的介晶行为。不同的合成条件下制备的聚合物的热分析表明，使用不同的钌复分解催化剂制备的TLCPs具有显着不同的转变温度，这意味着所得到的TLCP链的微观结构的催化剂的影响。根据这些观察结果，进行NMR研究（1D H-1和C-13，以及2D COSY和HMQC），允许测定催化剂对聚合物链中单元的反式/顺式键联和偶联/异构化的选择性。通过对聚合反应动力学和异构化反应动力学的研究，揭示了异构化反应的原因。结果发现，Grubbs催化剂的降解产物涉及异构化催化，与1-辛烯复分解的报道一致。相反，第二代Grubbs催化剂本身（不是降解产物）显然会引起异构化。对于由Nolan开发的相关催化剂，催化剂及其降解产物都被认为是异构化反应的原因。
Acyclic diene metathesis (ADMET) polymerization was employed to prepare thermotropic liquid crystalline polymers (TLCPs) bearing double bonds within flexible spacers. Starting from a diene monomer, 2-tert-butyl-1,4-phenyl bis(4-pentenyloxybenzoate) (5tB), we successfully synthesized unsaturated liquid crystalline oligomers and polymers, P5tBn, via ADMET polymerization. Such unsaturated TLCPs were developed to allow the preparation of tailored, thermally cross-linkable, liquid crystalline thermosets as adhesives and composite matrix resins. High degrees of polymerization were achieved and the resulting polymers showed clear mesomorphic behavior with complete absence of crystallization. Thermal analysis of polymers prepared with varying synthetic conditions showed that TLCPs prepared using different ruthenium metathesis catalysts featured substantially different transition temperatures, implying an influence of the catalyst on the resulting TLCP chain microstructure. In light of these observations, NMR studies (1D H-1 and C-13, and 2D COSY and HMQC) were carried out, allowing determination of the selectivity of the catalysts toward trans/cis linkage and coupling/isomerization of units in the polymer chain. Furthermore, by studying the polymerization and isomerization kinetics, we shed light on the cause of isomerization. It was found that the degradation product of Grubbs catalyst is implicated in isomerization catalysis, in agreement with reports on the metathesis of 1-octene. In contrast, second-generation Grubbs catalyst itself (not a degradation product) apparently causes isomerization. For a related catalyst, developed by Nolan, both the catalyst and its degradation product are concluded to be responsible for the isomerization reaction.