The present work focuses on the evolution in the mechanical properties of an unsaturated polyester resin (UPR) on blending with itaconimide‐end terminated polyethers, namely, polypropylene glycol (I‐PPG), polyethylene glycol (I‐PEG), and polytetra methylene oxide (I‐PTMO). Blends of an unsaturated polyester (UPR, based on propylene glycol, terephthalic, and maleic acids) resin with different loading of itaconimide end‐capped telechelics were investigated for their mechanical and thermal properties. Blending with these additives enhanced the mechanical and thermal properties of the crosslinked UPR. The impact strength and fracture toughness values were improved by more than 100% by small quantities of the additives. The improvement in fracture properties was correlatable primarily to a decrease in overall crosslink density. The distribution of the polyether chains in the cured matrix as dictated by the reactivity ratios of styrene and polyether macromer was found to have a role in deciding the properties. The properties were found to be the best for the blend toughened with I‐PPG with a molecular weight 2000 g/mole at a loading of 2.5 parts per hundred parts. On comparison with the resin blended with a maleimide‐encapped polyether of same molecular weight, the itaconimide end‐capped polyether was found to provide a better toughening of the UPR matrix. This could a priori be explained based on a difference in distribution of the end‐capped polyether as a consequence of the difference in the copolymerization behavior of itaconimide and maleimide functionalized telechelics toward UPR. The itaconimide enters into a random copolymerization with styrene and the probability for formation of the continuous sequences of the itaconic group is about 60%. This will permit polyether segments to come close enough to form micro or even sub‐micron clusters of the polyether which eventually forms the micro crystallites of poly ether that act as a crack stopper. This possibility cannot be envisaged in maleimides which forms invariably an alternating sequence with styrene. The morphological features as reflected in scanning electron microscopic analyses tallied with these observations. This work could help identify the ways for obviating the inherent brittleness of the UPR systems.
The free radical copolymerization of nadic anhydride (NA) and styrene (St) at 80°C has been investigated for the first time. The copolymerization was done in toluene using benzoyl peroxide as initiator. The monomer reactivity ratios were calculated from the copolymer composition (estimated from the acid value) by using Fineman–Ross, Kelen–Tüdös, and Extended Kelen–Tüdös methods. The reactivity ratios (rNA, = 0.34, rST = 0.84) implied a good copolymerizability for the monomer pair and existence of an azeotropic composition at fNA = 0.195. The unsaturation in nadic anhydride exhibited good copolymerizability despite the fact that the double bond is isolated and allylic in nature. The usual retardation by the allylic protons was not significantly felt in this case, as the allylic protons were located at a bridge head posing geometric restrictions for stabilization of the allylic free radicals. However, an increase in concentration of NA in the feed decreased the overall rate of copolymerization. Based on the reactivity ratio, the probability for formation of sequences of NA in its copolymer with styrene was computed for a few compositions.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.