Synthesis And Application Of Norbornene Copolymers

Addition polynorbornene is a kind of colorless and transparent material with excellent heat resistance and low dielectric constant,but it is difficult to be used directly because of low elongation and poor solubility.The copolymerization of norbornene andα-olefin can improve the activity and processability without sacrificing other properties of polynorbornene,then the application would be broadened.Based on the above ideas,the copolymers of norbornene/maleic anhydride（NB/MAH）and N-phenylmaleimide/norbornene/maleic anhydride（NPMI/NB/MAH）were synthesized via free radical polymerization.By the reaction of anhydride groups,copolymers were introduced into the polyimide（PI）films and epoxy curing systems to improve the thermal,mechanical,optical and dielectric properties of the substrate.（1）Compared with the binary copolymer NB/MAH,the synthesis process and polymerization kinetics of the terpolymer NPMI/NB/MAH were investigated.The copolymer composition can be controlled by changing the molar ratio of monomers.NPMI/NB/MAH has good thermal properties.When the molar ratio of monomers is 1:2:1,the 5%weight loss temperature(T_d5%)is 388.0℃ and the glass transition temperature（T_g）is 277.8℃,which is61.6℃ and 19.6℃ higher than that of NB/MAH,respectively.（2）As the dianhydride co-monomer,norbornene copolymers were introduced to3,3’,4,4’-biphenyl tetracarboxylic diandhydride-p-xylylenediamine（BPDA-XDA）type PI,the films were still colorless and transparent,at the same time,its heat resistance and mechanical properties were also improved.Compared to the pure PI film,T_g of the modified film was increased from 272.1℃ to 283.9℃,and tensile modulus,tensile strength and elongation at break were increased by 25.8%,23.2%and 96.1%,respectively,when the addition of copolymer NB/MAH is 5 wt%.Moreover,the transmittance of the film at 400 nm is 83.4%.（3）Both norbornene copolymers and methylhexahydrophthalic anhydride（MeHHPA）were used as the curing agents for DGEBA E-51,and a series of cured epoxy resins were obtained.The effect of copolymers on the curing reaction was studied by non-isothermal DSC.The results showed that the apparent activation energy（E_a）of the curing systems containing norbornene copolymers was higher than that of E-51 cured with MeHHPA only.Meanwhile,norbornene copolymers can obviously improve the thermal properties of cured epoxy resins.When the content of copolymers is 20 wt%,T_d5%of the cured epoxy resin can reach above390℃.T_g can be increased from 144.2℃ to 170.6℃.With the increase of norbornene copolymers content,the rigidity and modulus of cured epoxy resins were enhanced,but the toughness was decreased.