Photochemical synthesis and cationic photopolyermization of α,ω‐diepoxyalkanes

Abstract

Keywords: hydrodimerization epoxy resins synthesis curing cationic photopolymerization INTRODUCTIONThe photoinitiated cationic polymerization of di-and multifunctional epoxides has been a long-term topic of investigation in this laboratory.' These polymerizations are of considerable current commercial interest since they are rapid, low-energy processes which are essentially pollution-free. Although a number of epoxy monomers are available from commercial sources, these materials are not specifically intended for use in cationic polymerizations. Consequently, these materials often contain undesirable impurities which inhibit cationic polymerizations or reduce their rates. In addition, the range of materials available is not sufficient to meet many of the mechanical and chemical requirements of many potential applications. For these reasons, current work in this laboratory has focused on the design and synthesis of novel multifunctional epoxide monomers by both conventional and unconventional routes.Recently Crabtree and his c o -~o r k e r s '~~ have developed a novel mercury photosensitized reaction by which olefins can be hydrodimerized in high yields in the presence of hydrogen gas to give branched alkanes. It was demonstrated by these workers that the reaction is very general and can be applied to olefins bearing a variety of different functional groups including unsaturated epoxides. The mechanism proposed by Crabtree and his co-workers for this hydrodimerization reaction is shown in Scheme 1. The reaction is carried out in a quartz vessel to which the alkene and a drop of mercury is added. The vessel is filled with hydrogen gas which is dissociated by photoexcited mercury atoms [ eqs.( 1 ) and ( 2 ) 1. Hydrogen atoms produced by the latter reaction add to the alkene generating carbon-centered free radicals [ eq. ( 3 ) ] which subsequently dimerize [ eq. (4)]. The reaction occurs only in the vapor state. As the dimer is formed, it becomes less volatile and remains in the liquid state at the bottom of the reaction vessel and is thus, largely protected from further reaction. However, during hydrodimerization dehydrodimerization also takes place as a side reaction by the abstraction of hydrogen atoms from the substrate and the product by photoexcited mercury atoms. This gives rise to a small amount of by-products with complex structures which are apparent by the pale yellow color of the product.This brief study was undertaken to determine whether the above photosensitized hydrodimerization reaction can be applied to the synthesis of novel difunctional epoxides. It was also of some interest to determine reactivity of these epoxides in photoinitiated cationic polymerization. EXPERIMENTAL Materials1,2-Epoxy-5-hexene, 1,2-epoxy-7-octene, and 1,2,7,8-&-epoxyoctane were used as purchased from the Aldrich Chemical Company. The photoinitiator, (4-octyloxyphenyl) phenyliodonium hexafluoroantimonate ( IV ) was prepared as previously de~cribed.~ 'H-NMR data were obtained in CDC13 with a VarianModel XL 200 spectrometer equ...

Review on UV-Induced Cationic Frontal Polymerization of Epoxy Monomers

“…However, before the inception of the concept of frontal photopolymerization, the group of Crivello published several important studies that were focused on cationic photopolymerization of various in-house synthesized epoxy monomers requiring prolonged UV irradiation of the entire formulation. These studies were mostly focused on the reactivity of epoxy monomers based on their chemical structures, effect of various functional groups and experimental parameters such as UV intensity, temperature and so on with the help of FT-IR spectroscopy and photocalorimetry [ 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ].…”