Preparation Of Polyacrylates And Their Block Copolymers By Single Electron Transfer-Degenerative Chain Transfer Iving Radical Miniemulsion Polymerizations

Living radical polymerization(LRP)is an alternative to living anion polymerization to synthesize living polymers and block copolymers,due to its mild polymerization conditions and the ability to control the polymer structure.Single electron transfer(SET)and single electron transfer-degenerative transfer(SET-DT)LRPs are effective approaches for LRP of acrylate monomers,styrene(St)and vinyl chloride,using iodoform as the initiator,copper/ligand or sodium dithionite/sodium bicarbonate as the catalyst system.In order to solve the disadvantages of acryalte monomer SET-DT LRP using suspension or emulsion process,such as the lower polymerization rate,greater usage of initiator,and lower molecular weight of the resulted polymer,the miniemulsion process was employed to conduct butyl acrylate(BA)and ethyl acrylate(EA)SET-DT LRP.SET-DT LRP of St was also carried out in the miniemulison form to prepare polystyrene-b-poly(butyl acrylate)-b-polystyrene(PS-b-PBA-b-PS)block copolymers,using idoine-terminated PBA as the macro-initiator.The effects of polymerization conditions on the kinetics of acrylate monomers and St polymerizations were investigated.The phase structure,thermal and mechanical properties of PS-b-PBA-b-PS copolymers,and structures and properties of PEA containing crosslinking sites were studied,to explore their application as thermal plastics elastomer and acrylate rubber,respectively.Firstly,PBA terminated with iodine(I-PBA-I)and PEA terminated with iodine(I-PEA-I)were synthesized through SET-DT miniemulsion living polymerization,using iodoform as the initiator,sodium dithionite/sodium bicarbonate as the catalytic system and sodium dodecyl sulfate/hexadecane as complex emulsifiers.Influences of initiator,emulsifier concentrations on the polymerization kinetics of acrylate monomers were investigated.It was found that the SET-DT miniemulsion living polymerizations exhibited greater polymerization rate than SET-DT solution and suspension living polymerizations.Thus,the usage of iodoform initiator could be decreased,favoring to formation of polyacrylates with greater molecular weights,i.e.,the polymerization conversions were greater than 90%after 2h,and PBA with a number average molecular weight(Mn)of 630K and PEA with Mn of 610K were obtained when[CHI3]0/[BA]0=1/5000 and[CHI3]0/[EA]0=1/80 00,respectively.Mn of polyacrylates was increased with the increase of conversion.The molecular weight distributions of PBA were wider than that of PBA prepared by solution and suspension polymerization,due to the absorption-desorption of radicals and hetergeneous nature in the miniemulsion system.FI-IR and 1H-NMR analysis of PBA and PEA also confirmed the living nature of acrylate polymerzaitons.Secondly,I-PBA-I was further employed as a macro-initiator to initiate St SET-DT seeded miniemulsion polymerization to prepare PS-b-PBA-b-PS block copolymers.The structure and properties of PS-b-PBA-b-PS copolymers were characterized.St miniemulsion polymerizations also exhibit great polymerization rates.Using of I-PBA-I with Mn=220K and Mn=320K as the macro-initiators,PS-b-PBA-b-PS copolymer with Mn of 730K were prepared.PS-b-PBA-b-PS copolymers exhibited characteristics of micro-phase separation and thermoplastic elastomer.For PS-b-PBA-b-PS copolymer with PS mass fraction of 50%,the ultimate tensile strength and the elongation at break reach 9.8 MPa and 600%,respectively.Finally,ethyl acrylate-vinyl chloroacetate(EA-VCA)and ethyl acrylate-glycidyl methylacrylate(EA-GMA)copolymers were synthesized through SET-DT miniemulsion LRPs,compounded and chemically crosslinked to obtain acrylate monomer rubbers(ACM).The properties of self-made ACMs were determined and compared with commercial ACM with trade-names of AR72LS and AR840.The tensile strength of ACM prepared from VC-VCA copolymer(48.75/1.25 in mass)was slightly greater than that of ACM prepared from AR72LS and AR840,while the elongation at break of self-made ACM was 510%,which is 2.2 and 2.1 times of that of ACM prepared from AR72LS and AR840,respectively.In conclusion,this thesis provides base for preparation of polyacrylates and their block copolymers by a environmentally friendly LRP method.The resulted polymers would find use in preparing thermal plastics elastomer and crosslinked rubbers.