Synthesis Of RAFT Type Polyacrylate Dispersants And Polymer Polyether Polyols

Reversible addition-fragmentation chain transfer(RAFT)polymerization offers a powerful means for controlling the polymerization processes and the structures of the polymerization products by introducing a reversible chain transfer process to impart the function of living polymerization to conventional radical polymerization.The polymers prepared by RAFT polymerization have narrow molecular weight distribution and chain extension ability to synthesize block polymers.In this paper,the combination of RAFT polymerization and gradient polymer elution chromatography(GPEC)was used to study the head addition incidences of different monomers in radical polymerization and RAFT polymerization block efficiency.And a new type of poly(acrylate polyether)s was synthesized by RAFT polymerization and as a dispersant to produce polymer polyether polyol(POP)with high solids content.In free radical polymerization,the regioselectivity of addition is a basic problem,but often neglected for more active monomers.In this article,RAFT polymerization of three acrylate monomers(ethyl,butyl and 2-ethylhexanyl acrylate),two methacrylates(ethyl and butyl methacrylate)and styrene were studied by a combination of RAFT block polymerization derivation and GPEC.Dead dormant species(DDS)content of these monomers were determined,and head addition incidences of these monomers at60°C were estimated based on a kinetic model of RAFT polymerization,and the influence of monomer structures on head addition incidence was discussed.The results showed that the number or type of side groups both had significant influence on head addition incidence,the incidence of methacrylates and styrene(2?4×10^-4)about one order of magnitude smaller than that of acrylates(1?2×10^-3)due to steric repulsion effects.For acrylate monomers,higher head addition incidence would result in higher content of DDS(?10%)when high polymerization degree,and significantly affect subsequent block efficiency.In this paper,a series of poly(acrylate polyether)s was designed and synthesized by RAFT polymerization,and was used as dispersant to prepare POP.The effects of structures,dosage and feed ratio of these RAFT-type dispersants on the stability,viscosity and particle size of POP were discussed.The structure of the RAFT-type dispersant,including the molecular weight of the polyether side chain,the content of polyether ester,and polymerization degree of the dispersant,had a significant effect on the synthesis of POP.The feeding method of these dispersants had a remarkable effect on POP stability.When the degree of polymerization of the dispersant was 20,the molecular weight of the polyether side chain was higher than 400,and the molar content was more than 20%,the dispersant could provide good stability and to produce a stable POP.The stable POP could be prepared with the lowest dosage of 6%dispersant.When the solid content reached 42%,the viscosity was 2250 m Pa.s(without removing monomers).The dispersion polymerization process for producing POP was studied by GPEC technology,which indicated that the RAFT-type dispersant was rapidly consumed and block stabilizer was formed in the initial stage of reaction.Due to the heterogeneous isolation,the reaction rate of dispersant was lower than that in homogeneous reaction.At the end of the polymerization,some dispersants still existed in the continuous phase,which also provided good stability for the polymerization process.