Maleimide end- capped polyether telechelics as novel toughening agents for unsaturated polyester resin

This paper deals with a study on toughening of an unsaturated polyester resin (UPR) using maleimide end-capped oligomers of polypropylene glycol (M-PPG), polytetramethyene oxide (M-PTMO), and polyethylene glycol (M-PEG) of varying molecular weights. These macro bismaleimides with large spacing between the functional groups were synthesized from the corresponding polyols (hydroxy telechelics) by reaction with (4-Maleimido) benzoyl chloride (MBC). These derivatives were characterised by chemical and spectral methods. These were then blended and co-cured with a UP resin based on copoly-propylene glycol (terephthalate –maleate) and relying on maleic acid–styrene copolymerisation for curing. The impacts of the nature, concentration and molecular weight of the telechelic additive on the physical and mechanical properties of the resultant unsaturated polyester resin (UPR) blends have been examined. Addition of the telechelics improved the mechanical characteristics of the crosslinked systems significantly. The improvement in fracture properties for a telecheilc was directly correlatable to a decrease in overall crosslink density estimated exprimentally as well as theoretically. The additive’s backbone structure dictated the Tg and related properties of the blend. The properties were found to be the best for the blend toughened with M-PPG with a molecular weight 2000 g/mol, at 2.5 parts per hundred parts.The morphological features at this concentration as reflected in scanning electron microscopic analyses showed descrete poly ether particles microphase separation in the UPR matrix that acted as a crack path arrester.