Jan Pilař

Influence of testing conditions on the performance and durability of polymer stabilisers in thermal oxidation

Information on the efficiency of stabilisers in protecting polymers against thermal oxidation under service conditions is essential for selection and development of appropriate stabilizing systems. Accelerated tests are necessary to get data in an acceptable time and need carefully selected failure criteria. Appropriate testing severity, avoiding misuse of accelerated methods and understanding of the limitations of the methods are essential if reliable data are to be obtained. The potential and limitations of oven ageing tests, oxygen uptake measurements, differential scanning calorimetry (DSC) and chemiluminescence (CL) in stabiliser testing are reviewed.

Discoloration of polymers by phenolic antioxidants

Part of colour development in aged polyolefins stabilized with phenolic antioxidants can be attributed to the formation of conjugated diene compounds, arising as a consequence of sacrificial trapping of alkylperoxy radicals by phenolics. The discoloration depends on the structure and concentration of the phenol transformation products. Peroxycyclohexadienones are formed transiently in low concentrations and themselves do not discolour the polymer matrix. However, some products of their thermolysis are discolouring and accumulate slowly in the polymer matrix. The principal contribution to polymer discoloration is due to formation of quinone methides. Their discolouring effect is reduced in propionate-type phenolics, as a consequence of intramolecular rearrangement of a part of the primarily formed quinone methide, and is due to oxidative dimerization accounting for nonconjugated dimeric quinone methides. Attention was paid to transformations of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propanoate and related quinone methides and 4-hydroxycinnamates.

Poly(ethylene dimethacrylate) particles with poly(glycidyl methacrylate) functionalities

Abstract Macroporous particles, prepared by the suspension polymerization of ethylene dimethacrylate (EDMA), possessing high specific surface areas (558 m2g−1) and pore volumes (6.9 ml g−1), contain unreacted double bonds which are accessible for free radical polymerization. The amount of unreacted double bonds was determined by 13C CP/MAS n.m.r. These bonds were used for the functionalization of poly(EDMA) particles by the solution grafting copolymerization of glycidyl methacrylate (GMA) into the pore structure of the particles. The poly(GMA) formed in this way is permanently attached to the particles. By this method composite particles, containing up to 77 wt% of oxirane groups (determined by i.r. spectroscopy), were obtained. However, the presence of grafted polymer in the pores leads to a decrease in both the pore volume and the specific surface area. The oxirane groups can be chemically modified, as evidenced by their reactions with hydrogen chloride and 2,2,6,6-tetramethyl-4-aminopiperidine.