Polyisoprene photodegradation

It has been found that the photodegradation of several polders such as poly(vinyl chloride)(115).polyisoprene (109, 116).bisphenol A polycarbonate (117) is sensitized by peroxides. 

Rabek [500, 502] found that benzoyl peroxide, butyl peroxide and cumyl peroxide sensitize the photodegradation of c/s-l,4-polyisoprene in benzene. Similarly, anthracene peroxide added to a benzene solution of polystyrene shows a strong photosensitizing effect only when oxygen is present [504]. 

More detailed investigations by Rabek and Pajak [508] show that DPPH (concentration 10-3—10-4 mole l-1) added to a solution of cis-l,4-polyisoprene in benzene or n-heptane accelerates the photodegradation in the presence as well as in the absence of oxygen. It was discovered that the products of photochemical decomposition of DPPH have stronger sensitizing properties with respect to the photodegradation of diene polymers than has the undecomposed DPPH. 

This prompted us to review the work on the decomposition of hydroperoxides and in particular to determine what portion of the hydroperoxides that decomposes leads ultimately to bond scission. It is important to point out in this context that it is possible in principle for a polymer to oxidize extensively without losing its physical properties. The most important process in the breakdown of physical properties is bond scission in the backbone of the polymer chain. This can be best determined by measurements of the molecular weight of a photooxidizing or photodegrading polymer. In our laboratories we have studied this process by automatic viscometry which permits a very precise measurement of bond scission in polymers the apparatus has been described previously (12). For these studies we prepared a singlet-oxygen adduct of cis-polyisoprene by the following scheme ... 

Photoactive Additives.—Ferric compounds, in particular, the chloride, continue to attract much interest as photosensitizers for thermoplastics. " From e.s.r. work the mechanism appears to involve a redox reaction resulting in the formation of active hydroxy-radicals. Photodegradable polyethylene film has been developed by doping it with radiation-modified atactic polypropylene and hydroxyethyl-ferrocene. Several workers have studied the dye-sensitized photo-oxidation of polyisoprene and di-n-butyl sulphide embedded in Augustyniak and... 

A pioneer group of researchers in UKM has extensively studied utilization of liquid natural rubber (LNR) as a compatibilizer on various NR/polyolefin blends. LNR was produced by photodegradation of NR in toluene and exposure to the ultraviolet for 6 h. The LNR has the same microstructure as NR but with a short polyisoprene chain (of diflerent molecular weight, M )- The Mw of LNR is around 50,000 whereas for NR is 900,000. The formation of new functional groups such as H, C-O and C=0 via oxidation of photochemical sensitization of NR. The presence of the new functional groups is shown in Figure 17.1. The LNR with some active terminals like -OH is... 

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