Synthesis Of DOPO-based Epoxy Prepolymers For Chain Extension And Flame Retardation Of Nylon6

As one of the most widely used engineering thermoplastics due to its good overallperformances, PA6is susceptible to thermal oxidative degradation during melt processing,with decreases in molecular weight and mechanical properties. As for flame retarded PA6, it isfound that mechanical properties decrease significantly after flame retardants added, becausethermal oxidative degradation is promoted. Therefore chain extension is desirable for PA6andflame retarded PA6especially. However, ordinary chain extenders reduce flame retardation ofPA6. In order to obtain flame retarded PA6with better overall performances, novel chainextenders should be used in flame retarded PA6, which can improve flame retardation ratherthan reducing it.In this paper, novel DOPO-based epoxy prepolymers, P-PAP-EP and P-DDS-EP, weredesigned and synthesized. Their structures were characterized by FTIR and NMR, thermalstability tested by TG. Results showed that P-PAP-EP and P-DDS-EP matched the designedstructures well. The initial decomposition temperature of P-PAP-EP was270℃and itsresidue at800℃was25.5wt%, and the initial decomposition temperature of P-DDS-EPwas300℃and its residue at800℃was49.3wt%.Chain extension of PA6with DOPO-based epoxy prepolymers was investigated inHaake torque rheometer at240℃and60rpm. Chain extending effects were improved withincreasing DOPO-based epoxy prepolymers content. Compared with pure PA6, PA6with3wt%P-PAP-EP had increases in maximum torque of rheological curves from1.6Nm to17.7Nmand intrinsic viscosity from0.94dL/g to1.74dL/g, and PA6with4wt%P-DDS-EP had amaximum torque of17.8Nm and a intrinsic viscosity of1.78dL/g. Amino and carboxyl endgroup content was significantly reduced. When compared with ADR by rheological curves,P-PAP-EP or P-DDS-EP got higher maximum torque and higher reaction rate than ADR at thesame chain extender content.DOPO-based epoxy prepolymers in combination with diethyl phosphinate aluminum(AlPi) were used for preparation of halogen-free flame retarded PA6. PA6with15wt%AlPi alone achieved only UL94V-2@1.6mm rating, while PA6with13wt%AlPi and1.5wt%P-PAP-EP, or PA6with13wt%AlPi and1wt%P-DDS-EP achieved UL94V-0@1.6mmrating. As for flame retardancy mechanism, AlPi using alone mainly worked in gas phase,while flame retardative effects occurred in both condensed phase and gas phase afterP-PAP-EP or P-DDS-EP added, with lower PHHR, THR and RSR, and more residue in conecalorimeter test.The mechanical properties of PA6were greatly reduced after AlPi added. P-PAP-EP orP-DDS-EP effectively improved the mechanical properties of PA6/AlPi. Compared withmechanical properties of PA6with13wt%AlPi, PA6with2wt%P-PAP-EP and13wt%AlPiincreased its tensile strength, flexural strength and Izod impact strength by13%,9%and29%respectively, while2wt%P-DDS-EP and13wt%AlPi made it18%,16%and12%respectively. DOPO-based epoxy prepolymers extended chains of PA6, increased itsmolecular weight and thus improved its mechanical properties.