Synthesis And Properties Of Crosslinkable Dielectric Polynorbornene Derivatives An Novel Vanadium(V) Complex For Metathesis Polymerization

Ring-opening metathesis polymerization (ROMP) develops with the research of functional materials and catalysts. When ROMP of cycloolefine occurs, the polymer possesses a variety of microstructures, such as cis/trans ratio of the unsaturated carbon-carbon double bond in the main chain and the tacticity of the side chain. Crosslinking is a convenient method to improve physical performance. The metathesis polymers with high performance, for instance, high dielectric materials, can be obtained by combining the advantages of microstructure and crosslinking, which are accompanied with the development of catalysts. Nowadays, the study of vanadium complex for ROMP is not mature. Therefore, it is an important subject for metathesis polymerization to design and synthetize novel vanadium catalysts with high catalytic efficiency, remarkable stability, and polymerization controllability.In the second chapter, the dielectric block copolymers poly(endo-N-3,5-bis(trifluoromethyl)biphenyl-norboornene-pyrrolidine)-block-poly(ex o-N-(cinnamoyloxyethyl)-7-oxanorbom-5-ene-2,3-dicarboximide)(endo-PTNP-b-exo-PCONBI)and poly(exo-N-3,5-bis(trifluoromethyl)biphenyl-norbornene-pyrrolidine)-block-poly(exo-N-(cinnamoyloxyethyl)-7-oxanorborn-5-ene-2,3-dicarboximide)(exo-PTNP-b-exo-PCONBI) were synthesized by ROMP. endo-PTNP or exo-PTNP served as high dielectric functional chain, and exo-PCONBI acted as crosslinking segment. endo-PTNP-b-exo-PCONBI, in which endo-PTNP shows a trans double bond of 88% and adopts isotactic configuration, has a dielectric constant (ε) of 15.6, whereas exo-PTNP-b-exo-PCONBI, in which exo-PTNP has a trans double bond of 67%and atactic microstructure, displays relatively low ε of 7.1. The results show that polymer with relatively more double bond and better tacticity has higher dielectric constant. The cinnamate groups in exo-PCONBI were crosslinked to form network by cycloaddition reaction under UV irradiation. The dielectric constant of endo-PTNP-b-exo-PCONBI has been increased by 7%after irradiation, likely due to decreasing the free volume of the polymers and thus increasing the number of polarizable groups per unit volume. So high dielectric polymer can be achieved by controlling microstructure and crosslinking.In the third chapter, a novel vanadium(V) complex containing methylimidazolinium ligand shows good catalytic activity for ROMP. The catalytic efficiency or stability can be evaluated by yield and TON (turnover number). Polymerization controllability is confirmed by the molecular weight and polydispersity index using NMR spectroscopy. The ROMP of NBE by the vanadium complex at 80 ℃ with high yield indicated that the vanadium complex had high efficiency and stability, because it was easier to form vanadium(V)-alkylidene complex with bulky ligand to promote a-hydrogen elimination by steric crowding upon addition of PMe3. Aromatic ring with extensive conjugation of the associated π-orbital was recognized as a particularly suitable ligand for stabilization of transition metal complex in high oxidation state. The control of olefinic double bonds with relatively higher rans-olefinic double bonds and tacticity in the resultant polymer would be explained as a result of the coordination mode of norbornene into the vanadium metal center.