Mechanistic Pathways for the Polymerization of Methylol-Functional Benzoxazine Monomers

Abstract

The polymerization mechanism of methylol-functional benzoxazine monomers is reported using a series of monofunctional benzoxazine monomers synthesized via a condensation reaction of ortho-, meta-, or para-methylol–phenol, aniline, and paraformaldehyde following the traditional route of benzoxazine synthesis. A phenol/aniline-type monofunctional benzoxazine monomer has been synthesized as a control. The structures of the synthesized monomers have been confirmed by 1H NMR and FT-IR. The polymerization behavior of methylol monomers is studied by DSC and shows an exothermic peak associated with condensation reaction of methylol groups and ring-opening polymerization of benzoxazine at a lower temperature range than the control monomer. The presence of methylol group accelerates the ring-opening polymerization to give the ascending order of para-, meta-, and ortho-positions in comparison to the unfunctionalized monomer. Furthermore, rheological measurements show that the position of methylol group relative to benzoxazine structure plays a significant role in accelerating the polymerization.

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

“…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.…”

The curing reaction of benzoxazine with bismaleimide/cyanate ester resin and the properties of the terpolymer

“…Benzoxazine resins are a new class of high performance polymers that are characterized by several unique properties such as near-zero volumetric shrinkage upon curing [1], flexibility in molecular design [2], minimal moisture absorption, excellent resistance to chemicals [3], and high glass transition temperature [4]. Additionally, polybenzoxazines are obtained by the ring-opening polymerization of monomers by thermal cure without any added initiator or catalyst [5].…”

Study on an amine-containing benzoxazine: Homo- and copolymerization with epoxy resin

“…Although the peak at 190°C is close to the second peak position in Figure 4b, it is impossible due to large consumption of amine during amine-Ep reaction. In fact, it is probably caused by Bz ring-opening, which is promoted by the hydroxyl group due to the same reaction [26]. The rest small amount of excess Ep can react with phenol (generated after Bz ring-opening) or hydroxyl group, which results in the third peak in Figure 4c.…”

“…Besides, the conversion rate of P-deta/Ep mixture is higher than P-deta and BA-a. This is attributed to the hydroxyl group generated from the reaction between epoxide and amine, which can promote the ring-opening polymerization of Bz [26].…”