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 14?m)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.