| Aliphatic polyester, especially polylactide and polycaprolactone, is widely usedin medical, pharmaceutical and material field, due to their biodegradability andbiocompatibility. And it has be one of biodegradable polymer. Metal catalyst activityhas an important impact on polymerization, and designing of the ligand is the key ofmetal catalyst.In this paper, we chooses catalytic system of low-toxic and accessible zinccomplexes, designed and synthesis of pyridineimine, ɑ-diimine zinc complexes andSalen zinc complexes with sidearm, also studied the catalyst performance ofε-caprolactone polymerization. Inspected the steric hindrance and electronic effect onthe catalytic properties of the ε-caprolactone polymerization, polymerizationmechanism of the catalyst are discussed.24zinc ligand and its complexes bothcharacterized by1HNMR,13CNMR, and the catalytic polymer characterized by GPC.1〠Seven pyridineimine zinc complexes was synthesized, and investigatedpolymerization catalytic properties. Substituted pyridine aldehyde, aromatic amineand zinc chloride as raw materials, through "one pot method" reaction, got sevenpyridine imine zinc complexes C1-C7, and catalyted ε-caprolactone polymerization.The experiments showed that the steric on the aromatic ring ortho-position had mucheffect on the catalytic activity, small resistance resulted high activity. But the steric onmeso-position(C4) increase the thermal stability of the catalyst, which protected theactivity center. When the meso-position introduce strong electron-withdrawing group (C5), its activity increased significantly; The obtained polymer PDI isnarrower(1.06-1.19), of which a moderate resistance of C4and C5whose molecularweight were close to the theoretical value. 2〠Eleven ɑ-biimine zinc complexes was synthesized, and investigatedpolymerization catalytic properties. butanedione or acenaphthenequinone, aromaticamine and zinc chloride as raw materials, got elevenɑ-biimine zinc complexes, andcatalyted ε-caprolactone polymerization. Small steric hindrance andelectron-withdrawing substituent increase the catalytic activity. By contrast, theactivity of backbone with butanedione are higher than the acenaphthenequinone. Withbenzyl alcohol initiator, its catalytic activity is higher. Thus speculated that thepolymerization mechanism is monomer activation mechanism.Its catalyst activity is higher than pyridineimine zinc catalysts, but the molecular weight distribution werebroad(1.31-2.2).3〠Six salen type zinc complexes was synthesized, and investigatedpolymerization catalytic properties. With ethylenediamine, substituted salicylaldehydeas raw material, through condensation reaction, zinc acetate got six Salen type zinccomplexes, and catalyted ε-caprolactone polymerization. This catalysts can catalyticbulk polymerization of ε-caprolactone with highly activity, compared with thecorresponding Salen complexes. Research results show that the structure of alkylamine have a significant influence on the catalytic performance, more Steric withlower activity. When ligand introducing highly alkaline groups such as piperidine(C23), its activity increased significantly. It speculated that the polymerizationmechanism may be bifunctional activation mechanism because of that alkyl aminecan activate the initiator.In this paper, the study found three kinds of zinc complexes show catalyticactivity for ε-caprolactone bulk polymerization. In pyridineimine and ɑ-biimine zinccatalysts, the experiment shows that the catalytic activity has relationship with ligandsteric hindrance and electronic effect, high catalytic activity withelectron-withdrawing groups and small steric, but the polymer molecular weightdeviated from the theoretical value. And in Salen type catalysts, introduced suitablealkaline groups can significantly improve the catalytic activity. |
