Copolymer photodegradation

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. 

Perhaps the most interesting feature is exhibited by the copolymers, rather than the homopolymers. We find that the reduction in the quantum yield of photodegradation always exceeds the abundance of o-methylbenzoyl chromophores (5.) Table I illustrates this effect. 

Rates of photodegradation of copolymer films were measured in air using a filtered medium pressure Hg arc as the source of radiation and o-nitrobenzaldehyde as the actinometer. Table 1 gives the dosage levels incident on these films. 

Figure 2. Rates of photodegradation of the copolymer when exposed to a broadband UV source (shortest wavelength 297 nm) (A) change in absorbance as a function of irradiation time in the wavelength range of 250-450 nm (spectrum measured on films) (B) change in absorbance at 3580 cm 1 measured by FTIR spectroscopy (rate of hydroxyl formation)...

Nanosecond flash kinetic spectroscopy was also carried out on 2-hydroxy benzophenone and the copolymer (11). No transients could be detected in the nanosecond time scale, suggesting that the ground state enol [S (lb) in scheme 1] has a lifetime less than 1 x 10 9 sec. These results strongly imply that processes (3) and (4) are responsible for the deactivation of singlet energy in these systems. A small, non zero triplet yield is postulated in the copolymer both to account for the photodegradation data and the transient spectral data. Triplet... 

Quantum yields and lifetimes of emission (fluorescence) as well as other principal rates of deactivation have been measured on 2-hydroxy benzophenone and 2-hydroxyphenyl benzotriazole derivatives. Polymerizable UV screening agents have been prepared and copolymerized with acrylics in order to obtain transparent films containing nonfugitive UV screening agents. Preliminary results of studies of photodegradation on these copolymers are also reported here. 

Grassie, N., "Photodegradation of Methacrylate/Acrylate Copolymers", Pure and Appl. Chem., 1973, 247-257. 

As noted above, there is experimental evidence to indicate that the carbonyl groups of (vinyl chloride)-(carbon monoxide) copolymers are effective sensitizers for the photodegradation of these materials (9,10,11). A reasonable sensitization mechanism can be formulated for this system on the basis of the information now on hand. 

Photophysical Processes and Photodegradation of Poly(ethylene terephthalate-co-2,6-naphtha1enedi carboxyl ate) Copolymers. We have recently reported the photophysical processes and the photo-degradative behavior of Doly(ethylene terephthalate-co-2,6-naphthalenedicarboxyl ate), PET-2,6-ND, copolymer yarns containing 0.5 - 4.0 mole percent 2,6-naphthalenedicarboxyl ate, 2,6-ND (1) and the parent naphthalenedicarboxyl ate monomer, Figure 3 and 4. 

Polymers which undergo accelerated photodegradation in the environment can be made by making a copolymer of the monomer with an unsaturated ketone. The principle of the method is shown in Scheme 9.6, using styrene as the monomer. 

Treatment of these samples with SF4 gas to convert the carboxylic acids produced in the weathering process into carbonyl fluorides showed [2, 11] that the acids are actually a mixture of aliphatic and aromatic acids (Figure 18.12). Aromatic acid species are by far the predominant ones, however. The origin of these acids will be discussed below in conjunction with the overall mechanisms of photodegradation. Aliphatic acid species were detected by GC/MS in the artificial device exposure of PECT [11], Note that the PECT copolymer produced more aromatic acids with the same exposure as PET but that the aliphatic acid production was several times higher for the PECT copolymer. The photo-oxidation of the co-glycol must be the reason for this difference. 

Figure 18.11 Effect of exposure in New River, AZ, on the GPC data for Spectar copolymer sheeting [10]. From Photodegradation in a copoly(ethylene/1,4-cy-clohexylenedimethylene terephthalate) with and without UV absorber, presentation given by D. R. Fagerburg at the 37th International Symposium on Macromolecules, IUPAC World Polymer Congress, Gold Coast, Australia, July 1998, and reproduced with permission of IUPAC...

Copolymers with carbon monoxide are also subject to photodegradation. 

One attractive possibility is the use of the a-keto-oxime chromophore. It has a strong absorption at 220 nm whose tail, which extends to 240-250 nm, would improve the absorption characteristics of PMMA. Also, the esters possess a N-O bond which is photochemically labile yet sufficiently thermally stable so as to be compatible with the various processing steps. The solution degradation of a-keto oximino methacrylate esters upon irradiation with light of X365 nm has been reported by Delz-enne (2), and we proceeded to investigate the solid state photodegradation of similar copolymers and their possible utility as deep UV photoresists. 

A few reports of pyrazine monomers have appeared in the literature (70Millloo). The most extensive study of pyrazine monomers involves their use to prepare photodegradable polymers <76MI11104). 2-Vinylpyrazine (145) copolymers and poly(2,5-distyrylpyrazine)... 

The copolymers of carbon monoxide with olefins are of considerable importance from several different standpoints. These include the low price and ready availability of carbon monoxide, the enhanced photodegradability of the copolymers, and their easy chemical conversion to other classes of functionalized polymers. This review summarizes the chemistry involved in the synthesis, characterization, degradation and the derivatization of the copolymers. In addition, work on the spectral characterization of the copolymers have been cited. 

The thermal and photochemical dehydrochlorination of the vinyl chloride—CO copolymer have been studied by two different groups56,57). The decomposition rate for the copolymer was significantly higher than that for poly(vinyl chloride), the rate increasing with increasing CO content of the copolymer. In addition, the thermal decomposition of the copolymer was accelerated in the presence of molecular 02 while the photodegradation was slowed down 57). As with poly(vinyl chloride), the dehydrochlorination of the copolymer resulted in the formation of polyene sequences. There was no appreciable decrease in molecular weight. 

The photodegradation of the CO-styrene copolymer has been studied in benzene... 

UV irradiation causes photodegradation of poly[methylcyclohexyl-co-methyl((3-tri-methylsilyl)ethyl]silane and PMPS solutions.104 It was found that branching of PMPS is induced by light exposure. The photochemistry of both pure solids and their toluene solutions has been studied. The UV absorption of the copolymer in solution has a maximum at 308 nm and at 303 nm for the... 

It should be noted that the development of such polymer systems is stimulated by existing experimental works. In particular, the experimental methods of preparation of nanometer-sized hollow-sphere structures have been suggested [58-63] because of their possible usage for encapsulation of molecules or colloidal particles. The preparation of hollow-sphere structures, generally, is based on self-assembling properties of block copolymers in a selective solvent, i.e., on the formation of polymer micelles with a nanometersized diameter. Further cross-finking of the shell of the micelle and photodegradation [64] of the core part produce nanometer-sized hollow cross-linked micelles. 

Heskins, M., Reid, W. J., Pinchin, D. J., Guillet, J. E., "Photodegradation of Vinyl Chloride - Vinyl Ketone Copolymer, " Chapter 19 UV-Light Induced Reactions in Polymers, S. S. Labana, Ed., No. 50, ACS Symposium Series, 1976. 

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