油溶和水溶性羰基引发剂的光化学

本文回顾了在羰基引发剂的作用下烯烃单体光引发聚合的最新机理。报道了有关多种当前通用的新型羰基引发剂的光物理和光化学的近期工作,其中包括 UV 吸收,发光光谱和闪光光解的研究。还报道了油溶性引发剂对丙烯酸丁酯的光聚合效应。证明油溶性引发剂实质上是经过三重态来起作用,其中包含一个从溶剂中攫取氢的引发步骤。对于硫杂蒽酮衍生物来说,它们从叔胺接受电子的能力及其光聚合效应之间有一定的关系。从闪光光解获得的证据说明在这种情况下存在着自由基阴离子,但是基于二苯酮和苯基酮的引发剂则没有。预料后者直接从胺攫氢是通过三重态羰基或是引发剂的自由基。有证据表明联苯甲酰主要是通过光裂解来起作用。水溶性硫杂蒽酮引发剂的作用主要是经过单重态,其中包含引发时攫氢一步。在这种情况下,自由基的形成不受氧的影响。

Photochemistry of Oil and Water Soluble Carbonyl Photoinitiators

Current mechanisms for the photoinitiated polymerisation of vinyl monomers by carbonyl-based initiators are reviewed.Recent work on the photophysical and photochemical properties of various currently available and new types of carbonyl initiators is presented. This includes a UV absorption,luminescence and flash photolysis study.Photopolymerisation efficiencies in n-butyl methacrylate are also presented for the oil soluble types.Essentially,the latter are shown to operate mainly via the triplet state involving an initial step of hydrogen atom abstraction from the solvent.For thioxanthone derivatives a correlation exsits between their electron accepting ability with a tertiary amine and their photopolymerisationefficiency.Evidence from flash photolysis indicates the presence of the radical anion in thiscase but not with benzophenone or phenyl ketone based initiators.In the latter casesdirect hydrogen atom abstraction from the amine is predicted to occur by either the tripletcarbonyl or initiator free dicals.Evidence is presented to show that benzil appears to function primarily by photofragmentation.Water soluble based thioxanthone initiators operate primarily via the singlet-state involving an initial step of hydrogen atom abstraction.In this case,free radical formation is unaffected by the presence of oxygen.