No abstract

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer-clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (M w ) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d 001 ) in X-ray diffraction. However PEG with high molecular weight (Ն 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d 001 was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG-clay nanocomposites.

SYNOPSISGel permeation chromatography has been used to monitor the molecular weight changes that occur when polymers are degraded by photooxidation. Methods of sample preparation and procedures for conducting the chromatography measurements and for analyzing the results are discussed. Examples are given of applications to studies of polystyrene (PS) , polypropylene (PP) , and glass fiber-reinforced polypropylene (GFPP) exposed to ultraviolet (UV) irradiation in the laboratory. The results show that the degradation rate is fastest near the exposed surface, but in PS and PP, degradation is much faster at the unexposed surface than in the center of the molding, where the UV intensity is greater than at the unexposed surface. It is deduced that degradation at the center is slowed by a shortage of oxygen.