On the toughening of unsaturated polyester resins using nadimide end-functionalized polyether telechelics

Copoly-propylene glycol (terephthalate-maleate) based unsaturated polyester resin (UPER) was modified with nadimide end-capped polyether telechelics namely, polypropylene glycol (PPG with molecular weight 2000, 1000, 400 g/mol), polytetramethylene oxide (PTMO with molecular weight 2000 g/mol) and polyethylene glycol (PEG with molecular weight 2000 g/mol) (NPPG/NPTMO/NPEG). The telechelic NPPG/NPTMO/NPEG were synthesized from the corresponding polyols (hydroxy telechelics) by reaction with 4-nadimido benzoyl chloride. These derivatives were characterized by chemical and spectral methods. Blends of UPER with varying amounts of NPPG/NPTMO/NPEG were prepared. Blending boosted the cohesive energy through enhanced crosslinking as reflected in the gel content of the cured matrices done in separate studies. It increased the fracture characteristics tremendously. The addition of 2.5 phr of the nadimide end functional polyether gave the maximum toughness. The crosslink density showed an initial increase on blending, but further addition of the telechelics did not make any change. The properties of the prepared blends were compared with maleimide end-capped polyether toughened UPE resins. It was concluded that the toughening effect of the polyether additive depends not only on its concentration but also on its distribution in the matrix as dictated by its reactivity ratio with styrene. The high reactivity of the nadimide groups did not create an ambiance good enough to get an acceptable distribution of the polyether segments conducive for a tough matrix. Whereas the maleimide end-capped polyether provides better toughening efficiency.