Poly (vinylpyrrolidone) (PVP) immobilized zinc halides

ZnX2(PVP) (X=Cl

Br and I)

were prepared by reaction of ZnX2 with PVP and used as catalyst for one-pot melt transesterification of diphenyl carbonate (DPC) with diols to synthesize high-molecular-weight aliphatic polycarbonates (APCs).The relationship of structure and catalytic performance was investigated using elemental analysis

FTIR

TGA and XPS for these catalysts.It was found that Zn2+ can be chelated with PVP through two ways

i.e. (a) Zn2+ ions anchored to oxygen and nitrogen in one amide moiety; (b) Zn2+ ions coordinated to two carbonyl oxygen atoms to from two neighboring amide ligands.The Mw

yield and PDI of obtained PBC were influenced by the halogen anions because the interaction of halogen anions

PVP and Zn2+ could obviously affect the varieties of Lewis acidity and steric hindrance of Zn2+.Lewis acidity was found to be dominant for the polymerization rate at lower temperature

and increasing steric hindrance seemed to give a positive effect on the improvement of yield.Polymerization and its reverse reaction

decomposition processes

were both promoted by increasing Lewis acidity

and the side reactions would be restrained by increasing the steric hindrance of Zn2+.Therefore

the increase of Mw and yield for ZnBr2(PVP) compared with ZnBr2 and ZnCl2 at a high temperature was mainly resulted from the conflicting factors of Lewis acidity and steric hindrance of Zn2+ compensated each other

thus generating the best activity for ZnBr2(PVP) at higher temperature

where the highest Mw of 1.59×105 with yield of 84.5% was obtained under suitable reaction conditions.The main reasons for ZnBr2(PVP) catalyst displaying the higher yield and Mw than other plain zinc halide catalysts should be ascribed to the presence of the interaction between ZnBr2 and PVP

which provided this melt transesterification reaction with appropriate Lewis acidity as well as the steric hindrance.In addition

the electronic density of O atom in diols also played a crucial role in this reaction.