Design Of Cyclotriphosphazene-based Star-like Benzoxazine And Their Properties

Benzoxazine is a new type of thermosetting resin with excellent comprehensive properties.It shows high atom economy due to the wide range of reactants for monomers,ability of curing without the assistance of strong acid or base,and no small molecules release during curing.However,pure benzoxazines also suffer number of disadvantages too,in terms of high curing temperature,poor mechanical strength（brittleness）and difficulty in processing.Therefore,design and synthesis of new benzoxazine monomers or prepolymers to improve polymer performance,and the development of new application area have become the hotspots in this field.In order to systematically study the relationship between the structure and the performance,according to the Mark-Houwink-Sakurada（MHS）equation,a series of star-like benzoxazines with varied numbers of oxazine rings and high molecular weights were designed and synthesized in this work.Firstly,in order to study the effect of the numbers of oxazine rings on the polymerization behavior of benzoxazine and the performance of the corresponding polymer,four cyclotriphosphazene-based benzoxazine monomers（I,II,III,and IV）with relatively high molecular weight were synthesized by a nucleophilic substitution reaction.A new term,oxazine value（OV,similar to epoxy value）,was first proposed to explain the structure–property relationship of the cured polymers.An attempt was made to quantify the relationship between the numbers of oxazine rings and the polymer properties.The results showed that the melting point of four benzoxazines were low（32⁸5℃）.The melting viscosity were low（0.521²2 pa·s at 100℃）.All monomers possess a wide processing window（¹40℃）despite their high molecular weight.The peak exothermic temperature of polymerization was in the range of 244²48℃,and the temperature of ring-opening polymerization of the benzoxazines is not affected by OV.With the increased OV,the crosslinking density increased,also the thermal stability(Y₈₅₀℃=55%⁶0%)and T_g（115²18℃）of the polymer increased.Then,in order to discuss the effects of the adjacent groups of oxazine ring on the ring-opening polymerization,and to further improve the properties of polybenzoxazine,m-Trifluoromethylphenol（m-CF₃PhOH）,p-Trifluoromethylphenol（p-CF₃PhOH）and HO-BOZ were reacted with HCCP,to introduce the fluorine atoms into the molecular structure of benzoxazines.The containing fluorine high molecular weight star-like benzoxazines were got.The results showed that the melting point and melt viscosity of the six fluorinated benzoxazines were low,which significantly broadened the processing temperature window（¹89℃）.The numbers of oxazine rings had no obvious effect on the polymerization temperature of the two systems.With the same numbers of the oxazine rings,the-CF₃ in p-CF₃PhO-easily formed the intermolecular the organo fluorine hydrogen bond between-CF₃ with the oxazine rings,which made the polymerization temperature of the monomers（p-CF₃PhO-）higher（⁸℃）than that of the monomers（m-CF₃PhO-）,indicating that the ring opening polymerization of benzoxazine was affected by the adjacent groups indeed.The surface energies of six kinds of fluorinated polybenzoxazines were lower than that of fluorine free polybenzoxazine（PI^PIV）,and the T_g of the three polybenzoxazines containing p-CF₃PhO-were higher than 210℃,and the thermal oxygen stability also increased significantly(Y₈₅₀℃of PpF3 was 61.1%and 51%in nitrogen and air atmosphere,respectively).In the following work,the thermal curing kinetics of ten higher molecular weight star-like benzoxazines was studied by non-isothermal DSC method.The apparent activation energy（E_a）of the curing reaction was calculated by three kinetic models,Kissinger,Ozawa and Flynn-Wall-Ozawa.The curing mechanism was studied by Friedman method.The results showed that the E_a of four fluorine free monomers M I^M IV were 97¹03 kJ·mol^-1.The E_a of the monomer containing m-CF₃PhO-structure（mF1to mF3）were 90¹02 kJ·mol^-1,and the number of oxazine rings had no effect on the rate of ring-opening polymerization.However,the E_a of the monomer containing p-CF₃PhO-（pF1 to pF3）are 103¹20 kJ·mol^-1.That is,the groups near the oxazine ring have some influence on the ring-opening polymerization.The Friedman method was used to prove that the curing mechanism of the ten star-like benzoxazines were autocatalytic mechanism.Finally,in order to explore the new application field of benzoxazine,a branched urushiol analogue（CBCP）was first prepared by a ring-opening reaction of star-like benzoxazine containing a phosphazene core with renewable cardanol under solvent-free and catalyst-free conditions.In reference to the curing conditions of natural lacquer,CBCP undergoes cross-linking under ambient conditions,resulting in polymeric films（artificial urushi）that are optically transparent,high hardness and glossy surface.It means that,in comparison with natural lacquer,CBCP can be directly cured to become film without pre-polymerizaiton.The thermal stability,flame retardancy and mechanical properties of the Artificial Urushi films were studied.At the same time,the properties of the CBCP film compared with that of the film of a star-shaped cardanol oligomer（HCPP）,which derived from cardanol and hexachlorocyclotriphosphazene was prepared.The results showed that the thermal stability,flame retardant performance,mechanical properties and surface properties of the CBCP film were all better than that of the HCPP film with no oxazine ring-opening structure.