Synthesis And Properties Of UV/Thermal Curable Phosphorus-containing Flame Retardants

Over the last few decades the replacement of conventional materials by synthetic polymeric materials has increased dramatically owing to their versatility,low density, and some other novel properties.Although the polymers have become widely accepted in various areas,many of them are extremely flammable and,in presence of sufficient heat and oxygen,burn easily and rapidly.The problem is not only the destruction of the materials but the smoke and toxic gases generated which are the main causes of hazards in a fire.Although in the last few years there has been an increase of heteroelements used in flame retardants,the commercial market is still dominated by the compounds based on halogens.These compounds present exceptional efficiency,interfering with the reactions responsible of flame propagation.However,during the combustion they release toxic and corrosive gases.Therefore,the interest has increased in the research of halogen-free based flame retardants,such as phosphorus flame retardants,which are more environmentally friendly and less aggressive in a fire.The present thesis is aimed on the development of new environmentally flame retardant materials.The detailed outline is elaborated as follows:Five phosphate epoxy monomers were synthesized and the molecular structures were confirmed by FTIR,¹H-NMR and ³¹P-NMR spectroscopic analysis.The phosphorus-containing trifunctional cycloaliphatic epoxide resin, tri(3,4-epoxycyclohexylmethyl) phosphate(TECP) was used as a reactive-type flame retardant for cationically UV curing coatings.A series of flame retardant formulations by incorporating into a commercial difunctional cycloaliphatic epoxide resin, CYRACURETM UVR-6110,were prepared,and exposed to a medium pressure lamp to form the cured films under the presence of diaryliodonium hexafluorophosphate salt as a cationic photoinitiator.Their flame retardancy examined by the limiting oxygen index showed the improvement up to 27 for 50 wt%TECP addition compared with 21 for pure UVR-6110.The T_s and T_g decreased from 86℃and 131℃to 55℃ and 91℃,respectively,by using dynamic mechanical thermal analysis,whereas the tensile strength showed a slight increase(11%) with 50 wt%TECP addition.The thermogravimetric analysis(TGA) and real time FTIR measurement demonstrated the condensed-phase flame retardant mechanism.A novel epoxy-terminated hyperbranched polyphosphate(E-HBPP) was synthesized by employing an A₂+B₃ polycondensation and characterized by FTIR,¹H NMR and GPC.E-HBPP was used as a reactive-type flame retardant for Diglycidyl ether of bisphenol-A/ m-phenylene diamine(DGEBA/mPDA) system.A series of flame retardant resins were prepared and their flame retardancy was monitored by the limiting oxygen index.The results showed that the LOI value of the cured samples and the degree of expansion of the formed char after burning increased along with the E-HBPP content.Their thermal degradation behaviors were investigated by thermogravimetric analysis and in suit FTIR and showed that the phosphate group of E-HBPP first degraded to form poly(phosphoric acid)s at around 300℃,which had a major contribution to form the compact char to protect the sample from further degradation.The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis(DMTA) and the results showed a good miscibility between E-HBPP and DGEBA.The mechanical properties of the cured films were also investigated.Less than 20%E-HBPP addition improved both the tensile strength and elongation at break.Through Michael addition from piperazine as an A₂ monomer and tri(acryloyloxyethyl) phosphate(TAEP) as a B₃ monomer,a novel hyperbranched polyphosphate amine(HBPPA) was synthesized via the "A₂+B₃" approach.HBPPA was used as a multifunctional curing agent for bisphenol A epoxy resin.Dynamic mechanical thermal analysis showed the decrease of the glass transition temperature. The thermal degradation properties and flame retardancy were investigated by thermogravimetric analysis(TGA) and limiting oxygen index(LOI).The obtained results showed that the incorporation of HBPPA into bisphenol-A epoxy resin increased its thermostability and char yield during the decomposition by raising the second stage decomposition temperature.The LOI value significantly increased with the addition of HBPPA.A novel hyperbranched polyphosphonate acrylate(ttBPA),used as a reactive-type flame retardant in UV-curable systems,was successfully synthesized by the reaction of di(acryloyloxyethyl) benzenephosphonate(DABP) with N-(2-aminoethyl-) piperazine,and characterized by FTIR,¹H NMR and GPC measurements.HBPA was blended with DABP as a monomer in different ratios to obtain a series of flame retardant resins.Their maximum photopolymerization rates(R_p^max) and final unsaturation conversion(P^f) in the cured films at the presence of a photofragmenting initiator were investigated.The results showed that the P^f increased along with HBPA content and the pure HBPA has the maximum value of 81.0%in the photo-DSC analysis.Their flame retardancy was monitored by the limiting oxygen index(LOI), and showed that the UV cured films greatly expanded when burning,and the degree of expansion increased along with HBPA content.However,the LOI values varied from 36.0 to 39.0,which can be ascribed to the condensed phase mechanism.Their thermal degradation behaviors were investigated by thermogravimetric analysis and in situ FTIR spectroscopy,and showed that the phosphonate group of HBPA first degraded to form poly(phosphoric acid)s at around 300℃,which had a major contribution to form the compact char to protect the sample from further degradation. The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis and showed a good miscibility between HBPA and DABR The crosslinking density and T_g of the cured films decreased along with the content of HBPA in the blends.