Repairability And Improved Processability Of Polybenzoxazine Resins

We have synthesized a healable polybenzoxazine resin,its monomer is1,6-bis(8-methyl-2H-benzo[e][1,3]oxazin-3(4H)-yl)hexane(OC-HE),which is synthesized from o-cresol,paraformaldehyde and 1,6-hexanediamine.Polybenzoxazine resin(POC-HE)is obtained by heating the OC-HE at 210℃ for 4 hours.It shows 50 MPa tensile strength,123℃ T_g and 1.8 GPa storage modulu.The POC-HE resin swells in DMF solvent at room temperature,but has fluidity and plasticity at temperatures above 180℃.The shear fracture surface of the cured resin can be healed by heating at 180℃ for 4 hours,and the mechanical healing rate is close to 100%.These properties suggest that POC-HE resin has a cross-linked network structure at room temperature,but is healable at high temperatures.By designing simulating tests of addition of 2,4,6-trimethylphenol in the polybenzoxazine resin and monitoring changes on solid NMR spectra before and after the heating treatments,it is concluded that the three-dimensional cross-linked network structure of the POC-HE resin contains a dynamic covalent bond,phenyl ether bond.Basing on the POC-HE composite materials that can heal fatigue damages is designed and prepared with cotton fabrics.This work opens up a feasible way to broaden the application of benzoxazine.Next,we tried to improve the processing properties of benzoxazine resin in the preparation of composites by using the water-slurry method.A benzoxazine monomer,3-mercapto-8-methoxy-3,4-dihydro-2H-1,3-benzoxazine(Bzf),was synthesized from the bio-based starting material in our laboratory,and a flowable slurry is prepared by mixing the Bzf powder(particle size is about 14μm)with water and a solid filler of calcium carbonate,montmorillonite,or hollow glass microspheres.When the ratio of Bzf vs the filler is fixed at100 phr and the water content is 180 phr,the slurry shows a suitable fluidity with an apparent viscosity of 0.443 Pa·s.The biobased composite prepared by the water-slurry method exhibits outstanding mechanical properties and antifatigue performance,which its tensile strength is24.6 MPa,and can be remained at 80%even after 10000 fatigue tests.