Synthesis, ring-opening polymerization, and properties of benzoxazines based on o- and p-hydroxybenzyl alcohols

Abstract

Two series of bifunctional benzoxazines were synthesized from o- and p-hydroxybenzyl alcohols ( oHBA and pHBA), three aliphatic diamines containing ether linkage (Jeffamines D230 and D400 and 4,7,10-trioxa-1,13-tridecanediamine (TTDDA)), and paraformaldehyde. The chemical structures of the benzoxazines were confirmed by 1H and 13C nuclear magnetic resonance and Fourier transform infrared (FTIR) spectroscopy. The ring-opening polymerization of the benzoxazines was studied by differential scanning calorimetry and FTIR, respectively. oHBA-based benzoxazines respectively exhibit lower onset temperatures of ring-opening polymerization than pHBA-based counterparts due to the O–H∙∙∙O intramolecular hydrogen-bonding interaction between the hydrogen of ortho-methylol group and the oxygen in oxazine ring, and oHBA-based polybenzoxazines respectively show lower glass transition temperatures ( Tgs) than pHBA-based counterparts due to the difference in crosslinking density caused by the steric hindrance effect of the position of methylol group on the polymerization of benzoxazine monomers. In each of the two series of benzoxazines, the onset temperature of ring-opening polymerization of D230-based benzoxazine is close to that of TTDDA-based analogue and lower than that of D400-based counterpart owing to the steric effect of the chain length and chain volume of the bridging structure between the oxazine rings on the polymerization, and the Tg of D230-based polybenzoxazine is close to that of TTDDA-based analogue and much higher than that of D400-based counterpart owing to the difference in crosslinking density caused by the steric hindrance effect of the bridging structure on the polymerization of benzoxazine monomers. In addition, all the polybenzoxazines exhibit thermally induced shape memory effect. In each of the two series of polybenzoxazines, the shape recovery rate and ratio of D400-based polybenzoxazine are respectively close to those of D230-based counterpart and higher than those of TTDDA-based analogue due to the difference in network architecture.