Heterogeneous Polymerization Based On The Difference Of RAFT Polymerization Regulation

Reversible addition-fragmentation chain transfer(RAFT)polymerization has been widely used in many fields due to its wide monomer applicability,no metal catalysts and mild reaction conditions.Therefore,it has attracted much attention and has rapidly developed into a hot research field.According to the difference in solubility of polymers in solution,it can be divided into homogeneous RAFT polymerization and heterogeneous RAFT polymerization.Among them,heterogeneous RAFT polymerization has the following advantages:it can easily prepare polymer materials of different sizes and structures;the polymerization system has low viscosity,allows effective heat transfer of exothermic polymerization;can prepare multi-component block copolymers and ultra-high molecular weight polymers and other advantages,showing considerable prospects in the synthesis of polymers and colloids.The research of heterogeneous RAFT polymerization basically revolves around strong RAFT polymerization controllability(such as narrow molecular weight distribution,high block rate,and linear relationship between polymer molecular weight and conversion rate).And the research based on weak RAFT polymerization regulation is rarely reported.In this paper,RAFT reagents with low chain transfer coefficient are used in the research of heterogeneous RAFT polymerization,which expands the field of heterogeneous RAFT polymerization.1.In heterogeneous RAFT polymerization,the poor macromolecular RAFT reagent m PEG₁₁₃-BTPA was used to regulate the polymerization of monomer HPMA,led to the formation of samples contain high-molecular-weight block copolymers,uncontrolled homopolymers,and the unreacted macro-RAFT agent.Remarkably,uniform polymer spheres with precise size could be obtained via heterogenous RAFT polymerization,although molecular weight distributions of the obtained polymers were broad.It was found that the particle size of the prepared microspheres changed linearly with the degree of polymerization of HPMA by adding HPMA through a two-step method.In depth studies of heterogenous RAFT polymerization mediated by a binary mixture of RAFT agents with different controllability,the RAFT agent with good controllability dominated the polymerization while the RAFT agent with poor controllability was mainly inactivated or unreacted.2.On the basis of the unique mechanism provided,we have been able to prepare block copolymer assemblies with rich pendant RAFT groups on the surface by one-step heterogenous RAFT polymerization using a macro-RAFT agent with divergent RAFT end-groups.A small amount of BTPA groups will regulate the polymerization of HPMA and subsequently assemble into the polymer nanomaterials,and most of them still remain on the surface due to inactivation.The reactivity of pendant RAFT groups on the surface provides a landscape for further functionalization of block copolymer assemblies.Using NIPAM and t BA as monomers for seed emulsion polymerization,functional polymer nanomaterials with temperature responsiveness and surface containing nanoscale structure regions ware successfully prepared.These proof-of-concept experiments demonstrate that the utilization of poor RAFT control in heterogenous RAFT polymerization is a promising strategy to a variety of polymer particles that are challenging to be prepared by traditional heterogenous RAFT polymerizations.3.The bifunctional macromolecular RAFT agents BTPA-DEG-POEGMA_n-CEPA was used to initiate the polymerization of HPMA on the CEPA side under the condition of green light irradiation without initiator to prepare diblock copolymer nanomaterials,and all BTPA remains on the surface of the polymer nanomaterials.Control the number of BTPA groups on the surface by mixing single/dual functional macromolecular RAFT agents.The diblock polymers with worm morphology were used for the seed emulsion polymerization of t BA to prepare worm nanomaterials with nanoscale structure regions on the surface.By mixing BTPA-DEG-POEGMA_n-PHPMA-CEPA vesicles and PDMA-DDMAT to control DAAM for seed emulsion polymerization,a new multi-component polymer nanomaterial with small spheres connected to the surface of the vesicle was successfully obtained.