Polymer, Vol.121, 217-227, 2017
Toughening and reinforcing of benzoxazine resins using a new hyperbranched polyether epoxy as a non-phase-separation modifier
A novel hyperbranched polyether epoxy (HBPEE) bearing a stiff fluorene unit and flexible aliphatic chains has been synthesized using a one-pot approach and used as a toughener for bis-benzoxazine resin (MDABOZ). Effects of loadings and molecular weight of HBPEE on curing behavior, rheology properties, static mechanical, dynamic mechanical and thermal properties of the hybrid systems have been studied. Results show hybrids containing medium-M-n (i.e. similar to 3900) HBPEE-2 modifier possesses optimal comprehensive properties. Synchronous improvement of impact strength, flexural strength and storage modulus was found in hybrids containing 5% HBPEE-2 and 5% HBPEE-3, where HBPEE served as a non-phaseseparation modifier confirmed by SEM and DMA. Notably, there was a 2.8-fold improvement in impact strength for hybrids containing 10% HBPEE-2, compared to the same properties of samples without HBPEE. This was achieved without any compromise of flexural modulus, flexural strength, E0, thermal stability and glass transition temperature (T-g). The results demonstrate that multiple factors, such as enhanced crosslinking density (v(e)), rigidity of the toughener, reduced hydrogen bond network and higher fractional free volume, contributed to such improvement. (C) 2017 Published by Elsevier Ltd.