ON THE ROLE OF ENTANGLEMENTS IN THE EMBRITTLEMENT OF POLY(METHYL METHACRYLATE) BASED RANDOM COPOLYMERS

Composition dependences of the glass transition temperature (T-g), the molecular weight between entanglements (M(e)) and the thin film defor mation behaviour have been studied in two series of methyl methacrylat e-based random copolymers. When the comonomer is styrene, increases in both M(e) and brittle behaviour accompany the decrease of T-g. When t he comonomer is N-substituted maleimide, the same conclusions hold wit h increasing T-g. For both series of materials, a correlation is propo sed between the number of skeletal bonds in an entanglement strand, N- e, and the quantity (T-g - T-cs), where T-cs is the lower temperature at which shear deformation is observed in thin films in competition wi th crazing.