Study On The Behavior Of Conventional Radical Polymerization Of Methyl Methacrylate

The free radical polymerization reaction can provide theoretical basis for polymer industrial production and scientific research.In this paper,the molecular weight of polymethyl methacrylate（PMMA）obtained under different polymerization conditions was studied by using methyl methacrylate（MMA）induced by perphenylaloyl（BPO）,and the polymerization factors affecting the molecular weight size of PMMA were summarized.Low molecular weight PMMA was designed and synthesized,and the chemical displacement position of PMMA structure in NMR spectra was deeply analyzed,and the behavior of MMA polymerization reaction was analyzed at the same time.In order to further analyze the NMR spectra of PMMA structure,the model compound of benzoyl primary termination was first synthesized to illustrate that the reaction of PMMA-Br with benzoic acid can synthesize primary termination model polymers.Secondly,the synthesis process of PMMA-Br was studied.Gas chromatography（GC）,triple detection volume exclusion chromatography（TD-SEC）,nuclear magnetic resonance spectroscopy（NMR）and other measurement methods were used to characterize the polymer structure and reveal the polymerization reaction behavior,and the results showed:（1）The influence of polymerization factors on the molecular weight of PMMA:increasing the polymerization temperature,increasing the concentration of initiators,and reducing the concentration of monomers will reduce the molecular weight of PMMA.In different types of solvents,due to the different chain transfer constants,different degrees of chain transfer reactions occur,resulting in different molecular weight sizes of PMMA.The presence of trace amounts of solvents in the polymerization system has a certain effect on the molecular weight size of PMMA.（2）According to the polymerization factors conducive to the reduction of PMMA molecular weight,low molecular weight PMMA was synthesized,and a series of NMR spectra were used to analyze the PMMA structure.The localization and quantitative analysis of the chemical displacement position of the PMMA characteristic structure in the NMR spectra showed that the benzoyl primary radicals generated by the decomposition of the initiator BPO could not only induce MMA polymerization,but also decarboxylation reaction to generate benzene radicals.In addition to partial decarboxylation and initiation of monomer polymerization,primary termination reactions between benzoyl primary radicals and chain radicals also occur.In addition to initiating MMA polymerization,benzene radicals also undergo a primary termination reaction with chain radicals.The double-radical termination of the chain radicals in the bulk polymerization system is related to the polymerization factors:factors that reduce the molecular weight of PMMA,such as increasing the polymerization temperature and increasing the concentration of the initiator,are conducive to the double-radical termination reaction of the chain radicals.MMA radical polymerization disproportionation terminates to a single chain radical terminalβ-position methyl hydrogen radical transfer mechanism.（3）In order to further confirm that the BPO initiates the chemical displacement position of the primary radical in the NMR spectrum,the characteristic structure of the primary radical termination in the NMR spectrum is considered.First,the model compounds of benzoyl primary radical termination were synthesized by reactingα-bromoisobutyrate and ethylα-bromobutyrate with benzoic acid,respectively,indicating that the reaction of PMMA-Br with benzoic acid can synthesize primary termination model polymers.The ideal state of PMMA-Br should be low molecular weight,and the chain radicals are almost all terminated by halogen Br,that is,no chain radical double-base termination reaction occurs.Secondly,the synthesis of PMMA-Br by ATRP radical polymerization method,the prepared PMMA-Br is not all made of halogen Br stop chain radicals,which is inconsistent with the ideal PMMA-Br with a complete proportion of halogen Br.Finally,in the polymerization system present in Cu Br₂,Azo diisobutyronitrile（AIBN）is used to initiate MMA polymerization,and Cu Br₂is continuously supplemented during the polymerization reaction.The added Cu Br₂ will play the role of a polymerizer,terminate the chain free radicals,Cu Br₂ is involved in the polymerization reaction,so that the entire polymerization reaction process to maintain a very low free radical concentration,to obtain a lower molecular weight and halogen Br end groups accounted for a relatively complete PMMA-Br.