Oxygen Initiated High Temperature Free Radical Polymerization Of Methyl Methacrylate

Oxygen is an important component of air.Therefore,polymerization reaction is inevitably affected by oxygen.A large number of studies have shown that the influence of oxygen on free radical polymerization is more complex.In the early stages,oxygen is considered as the polymerization inhibitor of free radical polymerization.Later,it was found that oxygen can be involved in the reaction of free radical polymerization forming polyperoxides with vinyl monomer,indicating oxygen can be used as a comonomer for radical polymerization.In a recent work,it was found that oxygen can be used as initiator for free radical polymerization to initiate methyl methacrylate(MMA)polymerization at a high temperature condition.However,the specific mechanism,the structure and properties of the products are not clear,so it is necessary to conduct an indepth research.Oxygen is a cheap and easily accessible resource.It is of great significance for the development of free radical polymerization and the synthesis of some special polymers,such as polyperoxides,if the mechanism of oxygen induced polymerization is clearly studied.The kinetics of free radical polymerization of methyl methacrylate(MMA)initiated by oxygen was studied in deep.The structure of polymer were characterized by 1H NMR,the thermodynamic properties and degradation behavior of polymer were research by thermogravimetric analyzer(TGA)and differential scanning calorimeter(DSC).The following conclusions were drawn:(1)Only when the reaction temperature is over 110?C,oxygen can act as initiator to initiate the free radical polymerization of methyl methacrylate.(2)The free radical polymerization kinetics behavior of MMA initiated by oxygen is basically the same as that initiated by an initiator.The kinetic behavior of MMA radical polymerization initiated by oxygen is mainly affected by reaction temperature,oxygen content and oxygen addition mode.The molecular weight and its distribution of polymer decrease with the increase of reaction temperature and oxygen pressure,reaction rate.The modes of adding oxygen have not any effect on the molecular weight and its distribution of polymer,but it affects the polymerization of MMA.(3)The product of free radical polymerization of MMA initiated by oxygen is a random copolymer of MMA and a small amount of oxygen,this is,a small number of peroxy bonds exist in main chain.Its amount is determined by the reaction temperature,oxygen pressure and reaction time.(4)The thermal stability of the product is poor and its thermal degradation behavior is more complex than poly(methyl methacrylate).The initial thermal decomposition temperature and thermal degradation behavior are related to polymerization temperature and reaction time.(5)Use oxygen as the initiator of free radical polymerization of MMA,the reaction were initiated by the two kinds of radical generating by oxygen with the double bond of vinyl monomer and by the decomposition of poly(methyl methacrylate)peroxides jointly.