Bis allyl benzoxazine: Synthesis, polymerisation and polymer properties

• Published in: European polymer journal 2007-06, Vol.43 (6), p.2504-2514
• Main Authors: Santhosh Kumar, K.S., Reghunadhan Nair, C.P., Radhakrishnan, T.S., Ninan, K.N.
• Format: Article
• Language: English
• Subjects: Allyl polymers; Applied sciences; Benzoxazines; Chemical properties; Exact sciences and technology; Polymer industry, paints, wood; Properties and testing; Pyrolysis-GC; Ring-opening polymerisation; Technology of polymers
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2007.03.028

A bis benzoxazine monomer with allyl groups viz: 2,2′-bis (8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was synthesized via a solventless method from 2,2′diallyl bisphenol-A, paraformaldehyde and aniline. The chemical structure of Bz-allyl was confirmed by FTIR, 1H NMR and 13C NMR analyses. The monomer manifested a two-stage thermal polymerisation pattern. The first stage was attributed to the polymerisation of the allyl groups and the second to the ring – opening polymerisation of benzoxazine moiety. The polymerisation profile was investigated with DSC, FT-IR, TGA and pyrolysis-GC techniques. A polymerisation mechanism involving the electrophilic addition of the propagating iminium cation on the aniline ring in lieu of the activated sites of bisphenol-A, (which are blocked by allyl and alkyl substituents) was proposed. Additional cross-linking was provided by thermal addition polymerization of allyl groups. As a result of altered cross-linking via the aniline moiety and the additional cross-linking via allyl groups, the cured polymer exhibited a T g of ca. 300 °C and high crosslink density. The thermal stability of this polymer was also substantially higher vis-à-vis that of the bisphenol-A based polybenzoxazine. The work focuses on the manipulation of benzoxazine monomer structure to alter the ring-opening polymerisation mechanism and cross-linking to derive polybenzoxazine with improved properties.