Synthesis and properties of an amide- and Meldrum's acid-functionalized mainchain-type polybenzoxazine and the corresponding crosslinked resin

Abstract

Mainchain-type polybenzoxazines (PBz) are self-crosslinkable polymers possessing high flexibility of molecular designs and property adjustments. The corresponding crosslinked PBz in different forms, such as films, porous membranes, electrospun fiber mats, have been prepared for various applications. This work aims on functionalization of PBz with amide groups and Meldrum's acid moieties, to bring hydrogen bonding interaction and additional covalent crosslinks to the crosslinked PBz. A bisphenol derivative possessing both MA and amide groups (MA/Am-BP) is synthesized from a biomass-based precursor of 3,4-dihydrocoumarine. MA/Am-BP is utilized as a monomer, together with 4,4′-oxydianiline and formaldehyde, for preparation of amide- and Meldrum's acid-functionalized polybenzoxazine (MA/Am-PBz) and the corresponding crosslinked polybenzoxazine (CR_MA/Am-PBz). The benzoxazine- and Meldrum's acid-involved crosslinking reactions have been investigated with temperature-dependent Fourier transform infrared spectroscopy. CR_MA/Am-PBz has demonstrated film formability and flexibility. In addition to the attractive thermal properties, including a thermal stability of 340 °C, a char yield of 52 wt% at 800 °C, a storage modulus of 1.44 GPa at 50 °C, and a Tg of 295 °C, CR_MA/Am-PBz also exhibits a high tensile strength of 97 MPa, which is superior over the data reported to crosslinked polybenzoxazine films.