POLYMERS OF N-BUTYL METHACRYLATE WITH COVALENTLY BOUND 2-HYDROXYBENZOPHENONE U.V. STABILIZER - A CONSERVATION SCIENCE EVALUATION (CONSERVATION, VARNISHES, PROTECTION, ULTRAVIOLET

In art conservation, interest has been shown in increasing the durability of materials through the use of stabilizing additives. Additives may, however, be lost through volatilization or other migratory processes. Polymers of butyl methacrylate and butyl methacrylate with 2-hydroxybenzophenone substitution were synthesized by chemical modification of portions of a single batch of butyl methacrylate/methacrylic acid copolymer.;During oven aging at 55(DEGREES)C, it was found that added 2-hydroxy-4-methoxybenzophenone was lost in 150 hours whereas there was essentially no change in the near UV absorbance of polymers with chemically bound stabilizer.;Light aging when relatively high levels of UV radiation below 360 nm were present led to gelation of polymers with or without added or bound UV absorbers in relatively similar times. In exposures where proportionality lower levels of radiation below 360 nm were present and in exposures where radiation below 360 nm was removed by filtering with window glass, some increase in dosage was required to lead to partial insolubilization when either internal or external absorber was present. In view of the rapid loss of added absorber at the temperatures encountered in accelerated light aging, the relatively small difference in exposure required to start insolubilization was surprising.;A major difference was seen in the ease of removal of the exposed polymers from aluminum foil substrates. Films containing bound stabilizer were easily removed with solvent after lengths of exposure which had caused unstabilized polymers and polymers with added stabilizer to become very difficult to remove. Film integrity combined with ease of swelling of the insolubilized polymers containing bound stabilizer suggests a relatively rapid development of a low crosslink density, possibly through the hydroxybenzophenone substituent group. The continued presence of the bound UV absorber, however, stabilizes the polymer to a greater degree on long exposure.