Photodegradation ethylene-carbon monoxide copolymers

Photodegradation of ethylene-carbon monoxide copolymers by Norrish reactions. 

It was reported from Union Carbide that the photooxidation products of ethylene-carbon monoxide copolymers do not reach low enough molar mass values to support bioassimilation. This conclusion may have been based, however, on a misinterpretation of the earUer work with unoxidized hydrocarbons and a very Umited number of microbial cultures. GuiUet, in contrast, demonstrated that photodegraded Ecolyte polyethylene and polypropylene are bioassimilated by common soil bacteria, albeit rather slowly. 

Photodegradation may involve use of inherently photo-unstable polymers or the use of photodegradant additives. An example of the former are ethylene-carbon monoxide polymers in which absorption of light by the ketone group leads to chain scission. The polymer becomes brittle and forms a powder. Such materials are marketed by Dow and by Du Pont. Other examples are the copolymers of divinyl ketone with ethylene, propylene or styrene marketed by Eco Atlantic. 

Palladium complexes figure prominently as well in the copolymerization of Q -olefins with carbon monoxide. Unlike the low molecular weight photodegradable random copolymers of ethylene and CO produced from a free-radical process, olefin/carbon monoxide copolymers produced from homogeneous palladium catalysts are perfectly alternating, the result of successive insertions of olefin and CO (Figure 19). Consecutive insertion of two similar monomers is either slow... 

The value of B (days" ) listed in Table 10.4 for films of LDPE, ethylene-carbon monoxide (1%) copolymer (ECO), and photodegradable LDPE (containing a metal catalyst pro-oxidant) quantify their rates of degradation. The ECO copolymer is the same as that used in photodegradable six-pack rings (and supplied by the manufacturer... 

Other recent patents include copolymers of tdnyl ketones with acrylates, methacrylates, and styrene (O Brien, 1993) an ethylene/carbon monoxide (1-7 wt%) blend as a photo initiator in polycaprolactone/polyethylene blends (Hirsoe, 1992) ethylene/ carbon monoxide for degradable golf tees (Akimoto) a vinyl ketone analog of Exxon s carbon monoxide/dioxapane/ethylene (Priddy, 1992) a photodegradable food wrapper based on blends of a polyolefin/starch and photo activators for the... 

The synthesis, properties and applications of ethylene-carbon monoxide (E/CO) copolymers are described. These photodegradable polymers are now used to control plastic litter caused by polyethylene loop carriers for beverage cans which have been reported to entangle and endanger wildlife. 

Although rings made of polyethylene work very well, as we have already found, polyethylene degrades extremely slowly in the environment. A small amount of carbon monoxide (CO) can be polymerized with ethylene to produce a copolymer that degrades in sunlight (undergoes photodegradation) ... 

Poly(vinyl ketones) such as poly(ethylene-a//-carbon monoxide) CAS 111190-67-1, poly(methyl vinyl ketone) CAS 25038-87-3, and poly(methyl isopropenyl ketone) CAS 25988-32-3, also have practical applications. For example, poly(ethylene-a/f-carbon monoxide) is used in photodegradable plastics and in various copolymers. Several studies were reported regarding the thermal stability of these polymers. It has been shown that poly(ethylene-a/f-carbon monoxide) decomposes upon heating with chain scission generating small molecular weight alkenes and ketones. Some literature reports discussing the thermal decomposition of poly(vinyl ketones) are summarized in Table 6.5.5 [13]. 

The synthesis of photodegradable copolymers of olefins with carbon monoxide and ketones are shown schematically below, when R = C0H5 the monomer is styrene, and R = H the monomer is ethylene (Scott, 1973 Cooney, 1981 Guillet, 1990). 

The photodegradation of copolymers of ethylene and carbon monoxide containing l-9mol% CO results in a decrease in molecular weight, accompanied by the evolution of carbon monoxide. The photodegradation reaction occurs by the Norrish Type I (radical) (3.71) and the Norrish Type II (non-radical) (3.73) mechanisms (cf section 3.2.1) [871, 917, 1334] ... 

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