| Polymers produced by polar monomers contain a large number of polar groups,so they possess many excellent physical and chemical properties.In recent years,the research of polar monomer polymerization is very hot.The existing studies show that the polymers formed from vinyl pyridine have great application value.The methods that can achieve vinyl pyridine polymerization mainly include free radical polymerization,anionic polymerization,frustrated Lewis acid-base pair(FLP)polymerization and coordination polymerization.However,factors such as initiation efficiency,degree of polymerization,and stereochemical control can not taken into consideration at the same time by the reported polymerization of vinylpyridine.In view of the above problems,the main goal of this thesis is to achieve the living polymerization and stereospecific polymerization of vinylpyridine by means of coordination polymerization using neutral rare earth metal complexes as catalysts,and finally to prepare functionalized poly vinylpyridine.The main work includes the following parts:(1)A series of new rare earth metal complexes based on phenol ether bidentate ligands were designed,synthesized and accurately characterized.The polymerization of 2-vinylpyridine(2-VP)was studied using this series of complexes as catalysts.A series of characterizations such as 13C NMR and gel permeation chromatography(GPC)were performed on the obtained poly 2-vinylpyridine[P(2-VP)],and it was found that the metal ion radius,the size and type of the ligand all affected the polymerization result.(2)A series of trivalent rare earth metal tetrahydrofuran alkyl complexes were synthesized.2-VP was polymerized using the in-situ reaction products of the series of complexes and 2-VP as catalysts.The relationship between the polymerization effect and the ion radius was explored.When the metal center was lutetium,the isotacticity of the prepared P(2-VP)was the highest(mm=95%),the molecular weight distribution(D)was 1.29,and the initiation efficiency was 100%.In addition,the TOF value is up to 12000 h-1.It can be seen that the polymerization reaction meets the standards of living polymerization:the molecular weight of the polymer is controllable,the conversion rate of the monomer is linear with the molecular weight,and the active species can maintain activity for a period of time after complete transformation of monomer.The effect of Lewis base(LB)on the stereochemical control of the polymerization reaction was explored.A pyridyl alkyl complex based on trivalent lutetium was synthesized for the first time.It was used as a catalyst and B(C6F5)3 as a cocatalyst to prepare P(2-VP)with almost perfect isotacticity(mmmm>99%),and differential scanning calorimetry(DSC)test results show that the melting temperature of the polymer is as high as 217℃.Based on the influence law of LB on stereochemical control,a method for synthesizing stereoblock P(2-VP)was proposed.Finally,the mechanism of polymerization was explored,a possible polymerization mechanism is proposed,and its rationality is verified by DFT calculation.(3)The chemoselective polymerization of 2,5-divinylpyridine(2,5-DVP)was carried out for the first time using tetrahydrofuran alkyl complexes of trivalent rare earth metals(scandium,yttrium,dysprosium,holmium and lutetium)as catalysts.According to the mechanism of coordination polymerization,the 2-position vinyl group of 2,5-DVP participated in the polymerization,while the 5-position vinyl group was selectively retained.Using alkyl complex of lutetium as catalyst,poly(2,5-divinylpyridine)[P(2,5-DVP)]with different isotacticity can also be obtained by means of LB controlling,and the maximum mmmm value was over 99%.Finally,multiblock polymers of 2-VP and 2,5-DVP with controlled isotacticity,molecular weight and side chain vinyl distribution were successfully prepared.The resulting polymers were functionalized by means of crosslinking and click reaction. |
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