Acrylic polymers photodegradation

SCHEME 14.1 The general stmcture of an acrylic polymer and the estahhshed photodegradation mechanism via Norrish I a-cleavage of the carhonyl side chain, leading to main-chain polymeric radical a and oxo-acyl radical b. The secondary P-scission rearrangement reaction leading to the propagating radical c is also shown. 

The TREPR experiments and simulations described here have provided an enormous amount of structural and dynamic information about a class of free radicals that were not reported in the hterature prior to our first paper on this topic in 2000. Magnetic parameters for many main-chain acrylic radicals have been established, and interesting solvent effects have been observed such as spin relaxation rates and the novel pH dependence of the polyacid radical spectra. It is fair to conclude from these studies that the photodegradation mechanism of acrylic polymers is general, proceeding through Norrish 1 a-cleavage of the ester (or acid) side chain. Recently, model systems have... 

The majority of the work on the fundamental processes of photodegradation of acrylic polymers has been carried out by Grassie and co-workers (5-7). For radiation with wavelength A > 300.0 nm photodegradation is initiated by absorption of a photon by the carbonyl group of the ester side chains. Subsequent fragmentation depends on local stereochemistry and temperature. The principal modes of fragmentation are described by the Norrish I and Norrish II processes (8). 

Ultraviolet radiation is the other main stress encountered by polymers in the coatings arena. One hundred percent acrylic polymers are highly resistant to photodegradation because they are transparent to the vast majority of the solar spectrum (59). When uv-absorbing monomers, such as styrene, are incorporated into the polymer backbone, the uv-resistance of the resulting polymer decreases dramatically and a more rapid deterioration in polymer/coating properties is observed. On the other hand, a noncovalently bound uv absorber, such as hydroxybenzophenone [117-99-7], further improves the uv stability of 100% acrylic polymers (59). 

Photodegradation of stabilized UV-cured polyurethane-acrylate polymer... 

C. Decker, K. Zahouily, Photodegradation and photooxidation of thermoset and UV-cured acrylate polymers , Polym. Degr. Stab., 1999, 64, 293-304. 

Another important consideration was the fact that the absorption maxima of oxime acrylate monomers could be tuned to the desired wavelength by the selection of desired ketone or aldehyde chromophore from whence the oxime was originally synthesized. In our design, UV photocrosslinking followed dye-sensitized visible polymerization which formed a soft gel. It is very important to be able to choose the absorption window for the crosslinking reaction to prevent interfering absorption, if any, from the residual dye initiator. Acyl oximes as part of the backbone of a photodegrading polymer chain have been studied by Smets [217],... 

As reported in Table 15, the kinetic data clearly indicate that the photoinitiation activity of poly(BMOA-co-MtA) is not substantially affected by the content of BMOA co-units along the polymer chain and is of the same order of magnitude as that found for the model compound BMOAc. The absence of a polymer effect in the above photoinitiators has been interpreted [84] in terms of a photodegradation mechanism of the macromolecules involving the ftee radical species anchored to the main chain, even in the presence of acrylic monomers, analogous to what is reported in Scheme 18. Moreover, the induction period of the HDDA/BA photoinduced polymerization increases, on decreasing the content of... 

Natural Polymers and Cellulose Esters The photodegradation of painted wood panels has been found to fail at the wood paint interface 4 while acid treatment of methylcellulose accentuates its rate of photodegradation . Silk fibres have been found to form a roll-like structure after laser ablation with 193 nm light whereas the weatherability of lacquer coated leather has been investigated in a number of weatherometers . Poly(acrylic acid) up to 25% w/w has been found... 

To achieve an optimum efficiency of a copolymeric HAS in a particular polymer, the stabilizer has to have an optimum mol. wt. The principle of photodegradable polymers was exploited for a new class of degradable polymeric HAS. A rubbery terpolymer 194 containing 50-60% of 2,2,6,6-tetramethylpiperidyl acrylate moiety as a stabilizing component, n-octadecyl... 

The photodegradation and photo-oxidation of poly(organosiloxanes), poly(iV-vinylcarbazole), polyCalkoxyphosphazones)," thymine-containing polymers/ cellulose triacetate, cellulose acetophthalate complexes with poly(vinyl alcohol)/ acrylonitrile-butyl acrylate-vinylene chloride terpoly-... 

Dickinson, H.R, Rogers, C. E Simha, R., Photodegradation of poly(normal-butyl acrylate), in Polymers in Solar Energy Utilization, A.C.S. Symposium Series, 220, Chapter 18, pp. 275-292 (1983). 

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