Synthesis Of Phasphozene-based Derivatives And Their Use As Additives In Epoxy Resin

Epoxy resin is a common kind of industrial material with a long historical source.It is widely used as coatings,adhesives,and electrical and electronic materials,because of its outstanding properties such as thermal stability,chemical resistance,and electrical insulation.Hexachlorocyclotriphosphazene(HCCP)is a unique symmetrical molecule with six active chlorine atoms that can be replaced through nucleophilic substitution reactions.As a consequence,it is often terminated with reactive groups and then employed as the core in the synthesis of functional star-shaped compounds/polymers.Moreover,compared to the flexible cores mentioned above,HCCP has a ring structure composed of alternating phosphorus and nitrogen atoms,usually endowing the star-shaped products with rigidity and thermostability.For this reason,it has been attracting great interest to synthesize/modify epoxy resins using HCCP.However,until now,there are few reports about the research on HCCP-based epoxy additives.1.Six-arm star-shaped polymer with cyclophosphazene core and poly(e-caprolactone)arms as modifier of epoxy thermosetsA six-arm star-shaped poly(e-caprolactone)(s-PCL)based on cyclophosphazene core was obtained by pre-synthesis of ahydroxy-teminated cyclophosphazene derivative and subsequent initiation of the ring-opening polymerization of e-caprolactone,and its use in different proportions as toughening modifier of diglycidylether of bisphenol A/anhydride thermosets was studied.The star-shaped polymer was characterized to have approximately 30 caprolactone units per arm.Differential scanning calorimetry revealed a nonsignificant influence on the curing process of the epoxy-anhydride formulation by the addition of s-PCL.The s-PCL modified epoxy thermosets exhibited a great improvement in both toughness and strength compared with the neat resin,as the result of a joint effort by the internal rigid core and the external ductile polyester chains of s-PCL.When the addition of the modifier was 3 wt %,an optimal mechanical and thermomechanical performance was achieved.The impact resistance and tensile strength of the cured epoxy resin were enhanced by 150% and 30%,respectively.The glass transition temperature was also increased slightly.Moreover,the addition of the star-shaped modifier had little harmful effect on the thermal stability of the material.Thus s-PCL was proved to be a superior toughening agent without sacrificing thermal and mechanical properties of the thermosets.2.Synthesis of mikto-arm star-shaped oligomer based on phosphazene core and its use as toughing agent in epoxy resinA star-shaped compound was synthesized by the nucleophilic reaction between hexachlorocyclotriphosphazene and p-hydroxybenzaldehyde with triethylamine as catalyst.Then subsequent Schiff Base reaction with oleylamine was performed to extend the arms of the star compound.After the reducing of imide produced in the Schiff Base reaction,the star-shaped compound was further mixed with bisphenol A diglycidyl ether to form a mikto-arm star-shaped oligomer to improve the compatibility with epoxy resin.The final product was found out to be transparent liquid with a relatively low viscosity and was used as a toughening agent in epoxy resin.FT-IR and NMR were used to characterize the molecular structure of the oligomer.Different amount of the oligomer was then added into the epoxy/anhydride system to see the effect caused by the addition of the star-shaped oligomer.Differential scanning calorimetry revealed a nonsignificant influence on the curing process of the epoxy-anhydride formulation by the addition of the oligomer.Further tests shows that an optimal mechanical and thermomechanical performance was achieved when the addition of the modifier was 5 wt %.The impact resistance of the cured epoxy resin were enhanced by 150% compared to the pure epoxy resin due the positive effect of ductile alkyl chain.The tensile strength of the cured resin was also increased slightly.The water absorption rate decreased due to the increase of crosslinking density and the introduction of hydrophobic alkyl chain into the network.Although the ductile alkyl chains have a negative effect,the addition of the star-shaped modifier had little harmful effect on the glass transition temperature and the thermal stability of the material due to the increased crosslinking density and the rigid inner phosphazene core.The mikto-arm star-shaped oligomer was proved to be a superior toughening agent without sacrificing the thermal and mechanical properties of the thermosets and may have potential application in electronic packaging material.3.Synthesis of imidazole carboxylate based on phosphazene core and its use as epoxy curing agent and curing acceleratorA star-shaped imidazole carboxylate was synthesized by a three step method.Firstly HCCP and p-hydroxybenzaldehyde were used to produce a compound with six aldehyde group,and then the aldehyde group was oxidized to carboxyl group by potassium permanganate.The carboxylic acid was finally reacted with 2-methylimidazole and form an imidazole carboxylate.FT-IR and NMR were used to characterize the molecular structure of the oligomer.DSC was used to obtain the optical ratio of epoxy resin and imidazole carboxylate.The results shows that when the addition of imidazole carboxylate was 20 wt%,the epoxy resin can be cured completely and obtain the optical glass transition temperature and thermostability.The viscosity of the mixture was tested and it was found that imidazole carboxylate can be used as latent curing agent compared with 2-methylimidazole.Moreover,the imidazole carboxylate was also studied as curing accelerator in epoxy/anhydride system.The curing temperature can be decreased to 140 °C with the addition of 4 wt% imidazole carboxylate.