Applications Of Recyclable Polystyrene Supported Phosphazene Base In The Ring-opening Polymerization Of Cyclic Esters

Aliphatic polyesters such as polycaprolactone（PCL）,polylactide（PLA）and polyvalerolactone（PVL）have received extensive research interests and been widely used in biomedical,food-packing and other fields due to their biocompatible and biodegradable properties.Generally,aliphatic polyesters is prepared by ring-opening polymerization of cyclic esters.Compared to traditional condensation polymerization of diacids and diols,ROP is more convenient and controlled for synthesis of well-defined polymers under wild conditions without small molecule byproducts.The catalysts play an important role in the polymers synthesis.It is no doubt that the metal catalysts are dominant in ROP considering the countless species and high catalytic activity.However,the metal residues in polyesters may prevent their application in biomedical and microelectronics fields.In contrast,organocatalysts start to be attractive considering their mild reaction conditions,catalytic efficiency and metal-free properties.Phosphazene bases,a new series of organocatalysts,have drawn much interests in ROP because of their easy synthesis and high activity.However,recent reports suggested that the residual organocatalysts in polyesters were also cytotoxic because of the difficulty of the removal of homogeneous catalysts from polymers.In response to these problems,we decided to figure out the catalytic activity of heterogeneous catalysts in ROP of cyclic esters and successfully designed a heterogeneous catalyst PS-CTPB which displayed high efficiency for the ROP of a varity of cyclic esters and finally obtained nontoxic polyester materials.The main works are as follows:1)It was found that polystyrene supported phosphazene base PS-t-BuP₂ could efficiently catalyze the ROP ofδ-VL in the presence of benzyl alcohol as initiator and finally obtained the PVL with different molecular weights as well as narrow distributions.Moreover,the catalyst exhibited good recoverability for at least five consecutive cycles without obvious deactivation.2)We successfully desighed and synthesized a novel heterogeneous catalyst PS-CTPB.It proved that PS-CTPB can sufficiently catalyze the ROP of various cyclic esters such asε-caprolactone,δ-valerolactone,γ-butyrolactone and rac-lactide with alcohols as initiators.The obtained polyesters is not only with certain molecular weights as well as narrow distributions,but also nontoxic.The recovered catalysts PS-CTPB via filtration exhibited excellent reusability for at least six consecutive cycles without obvious deactivation.