Three bis-benzoxazine monomers based on the aniline derivatives of bisphenol A (BA-a), bisphenol F (BF-a), and 3,3′-thiodiphenol (BT-a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The effect on the polymerization of the monomers is compared using two common compounds, 3,3′-thiodiphenol (TDP) and 3,3′-thiodipropionic acid (TDA), at a variety of loadings. It is found that the diacid has a greater effect on reducing the onset of polymerization and increasing cross-link density and Tg for a given benzoxazine. However, the addition of >5 wt % of the diacid had a detrimental effect on the cross-link density, Tg, and thermal stability of the polymer. The kinetics of the polymerization of BA-a were found to be well described using an autocatalytic model for which values of n = 1.64 and m = 2.31 were obtained for the early and later stages of reaction (activation energy = 81 kJ/mol). Following recrystallization the same monomer yielded values n = 1.89, m = 0.89, and Ea = 94 kJ/mol (confirming the influence of higher oligomers on reactivity). The choice of additive (in particular the magnitude of its pKa) appears to influence the nature of the network formation from a linear toward a more clusterlike growth mechanism.

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B i s ( 3 , 4 -d i h y d r o -3 -p h e n y l -2 H -1 , 3benzoxazine)propane (BA-a) is blended with oligomers of polyarylsulfone (PSU) and polyarylethersulfone (PES) of different low/intermediate molecular weights (3000−12 000 g mol −1 ) and terminal functionality (chloro-, hydroxyl-or benzoxazinyl-(Bz)). Fracture toughness (K IC ) is observed to increase from 0.8 MPa m 0.5 for cured BA-a to 1 MPa m 0.5 with the incorporation of 10 wt % PSU-Bz (12 000 g mol −1 ). Generally, greater improvements in K IC are observed for the PES oligomers compared with the PSU oligomers of equivalent molecular weight. The terminal functionality of the thermoplastic has a lesser effect on improving toughness than increasing the molecular weight or the nature of the polymer backbone. Surface analysis of the fractured surfaces show greater phase separation and crack pinning in the PES toughened system. Where crack pinning is less obvious, as in the case of hydroxyl-terminated PES (of 6000 g mol −1 ), this coincides with a drop in fracture toughness.

A series of blends is prepared comprising 2,2-bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine)propane (BA-a) with variously 5, 10, or 20 wt % of a selected oligomer represented by poly(arylsulfone) (PSU) or poly(arylethersulfone) (PES). The oligomers, comprising either chloro-, hydroxyl- or benzoxazinyl- (Bz) terminal functionality, are of low molecular weight (3000–12000 g mol–1). The introduction of the oligomers is shown to initiate the polymerization of a bisbenzoxazine monomer where the terminal functionality of the oligomer is coreactive (e.g., hydroxyl or benzoxazine) without having a detrimental effect on the polymerization kinetics (similar values for the activation energy and orders of reaction are obtained). The introduction of the nonreactive chloro-terminated oligomer appears to favor the formation of an interpenetrating network (IPN) with a higher energy of activation. The thermal stability of the blends is generally increased compared with the polybenzoxazine homopolymer, regardless of the molecular weight or thermoplastic loading. Aside from the aforementioned PSUCl-containing IPN, the nature of the resulting network is slightly modified by the addition of the thermoplastic with similar or slightly elevated cross-link densities recorded (compared with the polybenzoxazine homopolymer). The heterogeneity of the network increases with a broadening of the tan δ response, suggesting an improvement in the toughness of the resulting blend.

The construction of molecular models of crosslinked polymers is an area of some difficulty and considerable interest. We report here a new method of constructing these models and validate the method by modelling three epoxy systems based on the epoxy monomers bisphenol F diglycidyl ether (BFDGE) and triglycidyl-p-amino phenol (TGAP) with the curing agent diamino diphenyl sulphone (DDS). The main emphasis of the work concerns the improvement of the techniques for the molecular simulation of these epoxies and specific attention is paid towards model construction techniques, including automated model building and prediction of glass transition temperatures (Tg). Typical models comprise some 4200–4600 atoms (ca. 120–130 monomers). In a parallel empirical study, these systems have been cast, cured and analysed by dynamic mechanical thermal analysis (DMTA) to measure Tg. Results for the three epoxy systems yield good agreement with experimental Tg ranges of 200–220°C, 270–285°C and 285–290°C with corresponding simulated ranges of 210–230°C, 250–300°C, and 250–300°C respectively.