Kinetics and Cure Mechanism in Aromatic Polybenzoxazines Modified Using Thermoplastic Oligomers and Telechelics

Abstract

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.

Significant Improvement on Polybenzoxazine Toughness Achieved by Amine/Benzoxazine Copolymerization‐Induced Phase Separation

“…Blending with other materials such as liquid rubber and thermoplastic has been reported to effectively improve the toughness of various polybenzoxazine‐based materials. These modifiers usually induce phase separated structures, which are able to change crack direction and absorb impact energy, leading to improved toughening properties when compared to the pure polybenzoxazine resin synthesized via a bulk polymerization.…”

A curing system of benzoxazine with amine: reactivity, reaction mechanism and material properties

“…7 Benzoxazines are typically synthesized from phenol, amine, and formaldehyde via a Mannich reaction. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] To cure 1,3-benzoxazines, thermally accelerated polymerization has been the main focus for most researchers for a long time. There have been a lot of successful reports on the development of benzoxazine monomers to improve material performance or expand the range of their applications, 8 for example, lowering the polymerization temperature by introducing hydroxyl, 9,10 acetylene, 11,12 N-allyl, 13 and carboxylic acid groups 14 to benzoxazine compounds, increasing the cross-linking density by the incorporation of polymerizable groups, [15][16][17] improving ame retardancy by phosphorylation of the cured products, 18 and others.…”

“…Desired benzoxazines can be synthesized using specially selected phenol derivatives and primary amines. 19,20,[33][34][35] The basic concept of the reaction mechanism is the protonation of the oxygen atom in the oxazine ring, followed by the formation of a zwitter iminium ionic structure, and its subsequent Scheme 1 The polymerization mechanisms of benzoxazine proposed by previous reports. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] To cure 1,3-benzoxazines, thermally accelerated polymerization has been the main focus for most researchers for a long time.…”

“…[19][20][21][22][23][24][25][26][27][28][29][30][31][32] To cure 1,3-benzoxazines, thermally accelerated polymerization has been the main focus for most researchers for a long time. To date, very few compounds, including phenolic compounds, [39][40][41][42][43][44] thiols, [45][46][47][48][49] benzimidazoles, 50 benzoxazoles, 26,51,52 chitosan ammonium, 53 and some polymers containing aromatic structures 19,21,23 have been reported to construct chemical linkages with benzoxazines. 19,20,[33][34][35] The basic concept of the reaction mechanism is the protonation of the oxygen atom in the oxazine ring, followed by the formation of a zwitter iminium ionic structure, and its subsequent Scheme 1 The polymerization mechanisms of benzoxazine proposed by previous reports.…”

Developing toughened aromatic polybenzoxazines using thermoplastic oligomers and telechelics, part 1: Preparation and characterization of the functionalized oligomers

“…It has been proposed that increased interaction between the thermoplastic and the benzoxazine matrix will prevent “pulling out” of the thermoplastic at the crack front, so increasing the force required to progress a crack or diverting the crack front and dissipating its energy that way . The hydroxy‐terminated thermoplastics have been observed to be more reactive than the corresponding chloro‐oligomers towards benzoxazine monomers. The acidic phenolic protons not only initiate the ring opening reaction, but also improve toughness through hydrogen bonding interaction with the benzoxazine polymer network …”