Abstract
Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.
Highlights
Benzoxazine (Bz) monomer is typically synthesized via Mannich-like condensation of a phenolic and a primary amine derivative in the presence of formalin or paraformaldehyde to form 1,3-benzoxazines (e.g., 3,4-dihydro-3-methyl-2H-1,3-benzoxazine)
And Cope [1] first reported the synthesis of benzoxazine monomers, which was extended by Burke et al [2,3] followed by Schreiber [4,5] and Higginbottom [6] to PBz resins
Cationic ringopening polymerization (ROP) occurred at a lower temperature with a faster polymerization rate than ordinary benzoxazine resins in liquid crystalline (LC) benzoxazine resins [379]
Summary
Benzoxazine (Bz) monomer is typically synthesized via Mannich-like condensation of a phenolic and a primary amine derivative in the presence of formalin or paraformaldehyde to form 1,3-benzoxazines (e.g., 3,4-dihydro-3-methyl-2H-1,3-benzoxazine). It was proposed that benzoxazine with free o-position in phenol or two free hydroxyl groups in an open benzoxazine ring reveals co-occurrence of both inter- and intra-molecular H-bond between –OH—N–, depending on the pKa value of the involved species This led to the formation of asymmetric product due to preoccupancy of such van der Waals forces. The p-substituted phenol-based monomers undergo self-terminated ROP as soon as dimer forms instead of giving linear oligomer or polymer, with varied reaction conditions as supported by TLC, HPLC, FTIR, 1H-NMR and elemental analysis [80,132].
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