title: Examining the Initiation of the Polymerization Mechanism and Network Development in Aromatic Polybenzoxazines.
abstract: 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 andTgfor 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 ofn= 1.64 andm= 2.31 were obtained for the early and later stages of reaction (activation energy = 81 kJ/mol). Following recrystallization the same monomer yielded valuesn= 1.89,m= 0.89, andEa= 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.
authors.affiliation: Department of Chemistry and Department of Mechanical Engineering Sciences, Faculty of Engineering and Physical Sciences, University of Surrey , Guildford, Surrey GU2 7XH, U.K.
authors.forename: Ian
authors.initials: I
authors.lastname: Hamerton
authors.forename: Lisa T
authors.initials: LT
authors.lastname: McNamara
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Howlin
authors.forename: Paul A
authors.initials: PA
authors.lastname: Smith
authors.forename: Paul
authors.initials: P
authors.lastname: Cross
authors.forename: Steven
authors.initials: S
authors.lastname: Ward