低密度聚乙烯丙烯酸气相光接枝体系反应机理的研究

研究了以二苯甲酮 (BP)为光敏剂 ,丙烯酸在低密度聚乙烯 (LDPE)膜上两步法气相光接枝聚合 ;从反应的基本要素出发 ,利用紫外光分光光度计跟踪测定了二苯甲酮在LDPE膜中的扩散情况 ,发现其扩散系数随BP浓度的升高而降低 ,约在 0 8～ 2 0× 10 -12 m2 ·s-1之间 .同样方法跟踪测定了BP在不同条件下的光还原反应 ,结果表明 :当远紫外光被滤掉后 ,其半衰期大大加长 ,氧气的存在更是加剧了这一效应 ;并且通过测定不同条件下气相光接枝聚合的一些基本规律 ,提出单体扩散为该气相光接枝聚合的控制步骤

STUDY ON THE MECHANISM OF LDPE-AA VAPOR-PHASE PHOTOGRAFTING SYSTEM

With benzophenone as photoinitiator,a two|step vapor|phase photografting of AA in LDPE film has been studied mechanically.The diffusion of BP into LDPE film has been carried out by dipping LDPE film into BP acetone solution for various periods of time and monitoring the concentrations in the film by measuring its absorption at 254nm on a 756|MC spectrophotometer.The diffusion coefficient,which decreased with the increasing of the concentration of BP,was between 0.8～2.0×10 -12 m+2·sec -1 .This monitoring method was also used in the study of the photoreduction of BP.The results showed that,when far UV( λ <300nm) was filtered,the photoreduction became slow down apparently ( τ 0.5 ～5 min),while τ 0.5 was about 1 min when it was irradiated by UV directly,and this tendency became more obvious when the oxygen was present.Like other photo reaction,the photoreduction has little dependence on the temperature,and it resulted in the crosslinking of LDPE film also,the percent of gel depended on radiating condition and amount of BP in LDPE film.The results of photografting under different conditions showed that the percent of graft ( G ) increased quickly at first,and then leveled up.While the far UV was filtered, G became lower at the beginning of the reaction than that while it was radiated by UV directly,but about 5 min later,there was little difference.Raising temperature could increase the percent of graft remarkably.Furthermore,the grafting system showed some living polymerization character:The graft yield increased continually even BP has been used up,which can be interpreted by the re|cleavage of the weak bond formed by LDPE chain and semipinacol radicals.Based on these facts,a monomer diffusion controlling principle,which was thought the main factor affecting the graft yield was discussed.