| Aliphatic polyesters are a class of biorenewable,biodegradable,biocompatible materials that are widely used in the biomedical and food packaging fields.At present,aliphatic polyesters are mainly obtained by ring-opening polymerization of lactones.However,the polyester obtained by the ring-opening polymerization of lactones with a simple structure limits its further application due to lack of functional groups.One common method currently used for the modification of polyester structures is the ring-opening polymerization of functional lactones containing substituents in the alpha,beta or gamma positions.Based on this,starting from the common lactone monomer ?-valerolactone(?-VL),?-methylene-?-valerolactone(?-MVL)with its alpha position introduced double bond was synthesized.By its regioselective polymerization,cyclic lactone-containing polyolefins and unsaturated polyesters were prepared.And unsaturated polyesters can be further functionalized by the thiol-ene click reaction.In addition,unsaturated polyesters can also be chemically degraded to ?-MVL to achieve a cyclic process from monomer to polymer and then polymer to monomer.In this paper,?-MVL polymerization was firstly catalyzed by N-heterocyclic carbines.Through the screening of solvents,catalysts and alcohol initiators,the regioselective control of ?-MVL polymerization was achieved.Vinyl addition polymers and ring-opening polymers were obtained,respectively.This article also explores the influence of solvents on the regioselective polymerization of ?-MVL.When N,N-dimethylformamide is used as a solvent in the presence of benzyl alcohol,the hydrogen bond between benzyl alcohol and N,N-dimethylformamide will destroy the activation of benzyl alcohol to the monomer,which will cause the initiator to preferentially attack the double bond and only obtain the double bond polymerization product.When toluene,dichloromethane or tetrahydrofuran was used as solvent,the activation of benzyl alcohol to the monomer would not be destroyed,resulting in the initiator preferentially attacking the carbonyl group on the ring,and only the ring-opening polymer was obtained.In the following,urea/thiourea and different bases were used as bifunctional catalysts to catalyze ?-MVL polymerization.It was found that it can catalyze ?-MVL polymerization regioselectively.And only ring-opening polymer was obtained.Among them,N-[3,5-bis(trifluoromethyl)phenyl]-N'-cyclohexylthiourea/1,8-diazabicyclo[5.4.0]undec-7-ene performed the highest catalytic activity.Besides,it performed well controlled toward molecular weight distribution of the polymer.The molecular weight of the polymer is distributed from 1.20 to 1.30. |
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