This paper investigates the cure kinetics for the ultraviolet (UV) cationic polymerization for both a cycloaliphatic and diglycidyl ether of bisphenol-A (DGEBA) epoxy system, using the photoinitiator triarylsulfonium hexafluoroantimonate salt. Using an autocatalytic kinetic cure model, the reaction rate values for both cycloaliphatic and DGEBA epoxy systems were determined for different photoinitiator amount (wt %) added, and at different UV exposure temperatures. The value for the cycloaliphatic epoxy increased significantly with addition of the sulfonium salt, reaching a limiting maximum after 2%. The value for the DGEBA epoxy system also increased, to a limiting maximum after 3%. Addition of the sulfonium salt significantly lowered the activation energy for the cycloaliphatic epoxy at all levels of addition, with the reduction proportional to the amount of salt added. In contrast, the sulfonium salt did not have a major effect on the DEGBA until the addition of at least 3% of the salt.
The ability to undergo predictable and controlled degradation allows biopolymers to release prescribed dosages of drugs locally over a sustained period. However, the bulk or homogeneous degradation of some of these polymers like poly(L-lactide) (PLLA) and poly(lactide-co-glycolide) (PLGA) work against a better controlled release of the drugs. Inducing the polymers to undergo surface erosion or layer-by-layer degradation could provide a better process of controlled drug release from the polymers. This study has demonstrated that surface erosion degradation of PLGA is possible with the use of a multilayer film system, with PPdlLGA [plasticized poly (D,L-lactide-co-glycolide) (PdlLGA)] as the surface layers and poly(L-lactide-co-glycolide) as the center layer. The use of the more hydrophilic PPdlLGA as the surface layer resulted in a faster degradation of the surface layers compared to the center layer, thus giving a surface erosion degradation effect. The rate of surface degradation could also be controlled with electron beam (e-beam) radiation, where e-beam irradiation was shown to alter the degradation time and onset of polymer mass loss. It was also shown that the more highly irradiated PPdlLGA surface layers had an earlier onset of mass loss, which resulted in a faster reduction in overall film thickness. The ability to control the rate of film thickness reduction with different radiation dose promises a better controlled release of drugs from this multilayer PLGA film system. 2007 Wiley Periodicals, Inc. J Biomed Mater Res 84A: [980][981][982][983][984][985][986][987] 2008
Demand for higher polymer performance with very short cure times has resulted in the development of low energy electron beam processes. This article presents the results of such a process for curing two epoxy systems, namely 3,4-epoxycyclohexylmethyl-3Ј,4Ј-epoxycyclohexane carboxylate and di-glycidyl ether of bisphenol A (DGEBA), using the cationic photoinitiator salts, triarylsulfonium hexafluoroantimonate, and diaryliodonium hexafluoroantimonate, respectively. Glass transition temperature measurements were done using a modulated DSC method while the degree of conversion was measured using FTIR spectroscopy. Results indicate that for both epoxy systems a relatively low dosage of not more than 5 Mrad was sufficient to achieve up to 60% conversion, with up to 80% conversion achievable using 30 Mrad. The diaryliodonium salt appeared to be more effective than the sulphonium salt in the above study. The effect of varying photoinitiator concentration and the resulting glass transition temperature has been studied.
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