Oxidative degradation of water - soluble polyethers by HO• and HO2• generated photochemically: Ft-ir studies

Two water - soluble polyethers, poly(ethylene oxide) and poly(methyl vinyl ether) were UV irradiated in hydrogen peroxide (H₂O₂) solutions. It has been shown that HO• and HO₂• radicals accelerate oxidative degradation of these polymers. Hydroxy (HO•) and probably hydroperoxy (HO₂•) radicals can abstract hydrogen from methylene groups in both polymers. As a result of further oxidative reactions, different carbonyl, hydroxy and hydroperoxy groups are formed. A mechanism for the formation of these groups has been proposed.     

PHOTOCURING STUDY OF NEW DENTAL RESINS BASED ON MULTIFUNCTIONAL ACRYLIC ISOCYANURATE BY PHOTOCALORIMETRY

Photocuring of new dental resins composed of tri(2-hydroxyethyl) isocyanurate triacrylate (THITA)alone and its mixtures with trimethylolpropane triacrylate (TMPTA) or pentaerythritol triacrylate (PETA)initiated by camphorquinone/amine system was studied by photocalorimetry. Among several different aminesas coinitiators, 2-ethyl-4-dimethylaminobenzoate (AM-3), N,N-dimethylbenzylamine (AM-5) and 2,4,6-[tri-(dimethylaminomethyl)] phenol (AM-6) are most effective. Upon irradiation, photopolymerization can occurimmediately and no induction period appears in N_2 nor in air. Comparing the THITA/TMPTA andTHITA/PETA mixtures, the parameters of photopolymerization and hardness of photocured samples show asmall difference and only change slightly with varying molar ratios of mixture. In the presence of inorganicfiller, the hardness of photocuring resins is almost the same as that for commercial products.     

Photo-oxidation of copolymers of butadiene and acrylonitrile

The photo-oxidation of two copolymers of butadiene and acrylonitrile (NBR rubbers) with acrylonitrile contents of 21·7 wt% and 41·6 wt% was compared with the photo-oxidation of polybutadiene and polyacrylonitrile samples under the same experimental conditions. The general features of the photo-oxidation of NBR rubbers over the composition range studied reflect the behaviour of the pure homopolymers, polybutadiene and polyacrylonitrile. The main process observed is the photo-oxidation of butadiene units whereas the photo-oxidation of acrylonitrile units is negligible under the same experimental conditions.     

Studies on the photo-oxidation mechanism of polymers—IX. The photo-sensitized oxidation of cis-1,4-polybutadiene by n-methyl-2-benzoyl-β-naphthiazoline

This paper presents a study of mechanisms of photo-sensitized oxidation of cis-1,4-polybutadiene by N-methyl-2-benzoyl-β-naphthiazoline (BN) in solution. Detailed photochemical study of BN shows that the lowest triplet state of BN has an energy of 54.3 cal mol^?1 and a life-time of 0.20 s at 77 K. In addition, rate constants for the quenching of the triplet state of BN have been calculated. These results show the possibility of energy transfer from excited triplet state to molecular oxygen with formation of singlet oxygen, which can further react with another BN molecule (photo-decomposition of BN) or with cis-1,4-polybutadiene added. During light irradiation of BN, free radicals are formed; they can initiate polymer chain scission and crosslinking.