Photooxidation of styrene polymers and copolymers

Weak Links and Energy Sinks in the Photooxidation of Styrene Polymers and Copolymers in Solution... 

Photooxidation of styrene-based polymers and copolymers in solution involves a complex group of related and unrelated reactions. In part, the main chain scission process is subject to the competition for migrating absorbed energy by various labile moieties that can be termed weak links and by energytrapping species that may themselves be weak links or the source of subsequent degradation reactions. The intentional introduction of suitable trapping species can also serve as a means for the reduction of the rate of the scission process. 

After the examination of the PS photooxidation mechanism, a comparison of the photochemical behavior of PS with that of some of its copolymers and blends is reported in this chapter. The copolymers studied include styrene-stat-acrylo-nitrile (SAN) and acrylonitrile-butadiene-styrene (ABS). The blends studied are AES (acrylonitrile-EPDM-styrene) (EPDM = ethylene-propylene-diene-monomer) and a blend of poly(vinyl methyl ether) (PVME) and PS (PVME-PS). The components of the copolymers are chemically bonded. In the case of the blends, PS and one or more polymers are mixed. The copolymers or the blends can be homogeneous (miscible components) or phase separated. The potential interactions occurring during the photodegradation of the various components may be different if they are chemically bonded or not, homogeneously dispersed or spatially separated. Another important aspect is the nature, the proportions and the behavior towards the photooxidation of the components added to PS. How will a component which is less or more photodegradable than PS influence the degradation of the copolymer or the blend We show in this chapter how the... 

SAN is constituted of styrene and acrylonitrile units copolymerized statistically in the ratio 80 20 mol%. Previous studies on the photooxidation of PS [7,8] and PAN [3] have shown that the photooxidation rates of these polymers were very different PS degrades about 20 times faster than PAN. Consequently, the first steps of photooxidation of the copolymer SAN is presumed to involve mainly the styrene units. SAN samples have been irradiated and analyzed under the same conditions as PS samples. 

Oxidation of the styrene moiety and changes in the nitrogen environment in benzotriazole took place in 94. Available data confirm that the surface photooxidation of polymers containing aromatic moieties can differ from that of the bulk material [86]. This is due to the higher partial pressure of oxygen and incident photon flux in the surface area. Transmission IR data indicate that the quenching capabilities of benzotriazole moieties in the copolymer 94 are not active in inhibiting surface oxidation. 

Several studies of the spatial resolution of oxidation processes in HAS stabilized polymer appeared since the pioneering paper [25] and deal with events in PP [26 - 28] or commercial poly(acrylonitrile-co-butadiene-co-styrene) (ABS) copolymer plaques with thickness from 2 to 6 mm [27, 29], We preferred for our experiments plaques of 6 mm thickness providing more detailed information on the spatial distribution of nitroxides in both thermal and photooxidative stress situations [28],... 

Other applications in which the two techniques are not connected in line mainly include the determination of molecular weights of copolymers of MMA, butyl acrylate styrene, and maleic anhydride [283, 284], cyclic PS [285-288], thiophene-phenylene copolymers [289], methacryloxypropyltrimethoxy silane [290], various copolymers [291], PEG [287], polyetherimide photooxidation products [292], polyester-polyurethane [293], biodegradable polymers [294], and polyethylene-propylene oxide-ethylene oxide triblock polymers [295]. 

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