Kinetics and Cure Mechanism in Aromatic Polybenzoxazines
Modified Using Thermoplastic Oligomers and Telechelics
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Abstract
A series
of blends is prepared comprising 2,2-bis(3,4-dihydro-3-phenyl-2<i>H</i>-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<sup>–1</sup>). 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 PSU<sub>Cl</sub>-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