Preparation And Characterization Of Norbornene-based Copolymer With Well-defined Composition Distribution And Novel Terpolymers

Cyclic olefin copolymer (COC) has excellent transparency, high heat resistance and low moisture absorption etc. It is an important class of industrial materials with a broad range of applications in optical, electric and medical fields etc. Preparation of Ethylene-norbornene copolymers (ENC) by addition copolymerization has been studied by many research groups. These studies are mainly focused on the choice and development of copolymerization catalysts. The object is to improve the catalyst activity, norbomene content in copolymer and molecular weight. The kinetics model of ethylene-norbornene copolymerization is also investigated for predicating the polymerization rate and copolymer composition. However, the simulation results are not satisfactory. In addition, the control of copolymer composition distribution based on the model has not been reported and new type of COC is also needed to be exploited.ENC with～50%,～25%and～15%norbomene (NB) mole fraction in a wide range of molecular weight are produced by rac-[Et(Ind)2]ZrCl2/MAO catalysts. By coupling the gel permeation chromatography (GPC) with the intrinsic viscosity data in 1,2,4-trichlorobenzene at 150℃, the Mark-Houwink parameters of ENC are determined and compared. The results indicate that parameter K is considerably increased with decreasing NB fraction in ENC but parameter a was only increased slightly. Based on parameter a as constant, the relationship between NB fraction in ENC and parameter K can be optimized. Furthermore, the structure characteristics and correlative rheological parameters of resultant ENCs are also calculated and discussed by the Stockmayer-Fixman analysis. It can imply that the craze resistance of ENC enhances when the incorporating ethylene is increased. The molecular weights of obtained ENCs are calculated by the resulting Mark-Houwink parameters and effects of molecular weight on thermal property and optical property are studied. Tg increases and crystallinity decreases with an increase in molecular weight if it is not very high. The molecular weight seems to give little effect on the optical properties of ENC.Terminal and penultimate models in ethylene and norbomene copolymerization are developed by taking into account the variation of active site concentration with the initial comonomer ratio. The models are validated by batch polymerization experimental data. The terminal model gives better correlation with the composition data while the penultimate model has a better fit to the rate data. The terminal model is then used to design norbomene feeding strategy in semi-continuous processes for controlling copolymer composition distribution (CCD). Based on the model results, a series of ethylene-norbornene copolymers with various NB contents are prepared. With the same NB content, the semi-continuous process produces a uniform composition, while the batch process yields broad CCD. The batch samples have lower Tg values and broader transition ranges, even yield crystalline materials. In contrast, the semi-continuous samples overcome the disadvantages. The uniform samples also give better transparency. With NB content increasing, both the refractive index and the hydrophilicity of ENC increase.Terpolymerization of ethylene, norbornene and polar a-olefins with different carbon numbers, including 3-buten-1-ol,5-hexen-1-ol and 10-undecen-l-ol, catalyzed by rac-[Et(Ind)2]ZrCl2/MAO is investigated. The polar a-olefins are protected by triisobutylaluminium (TIBA) before polymerization. The addition of TIBA-protected polar monomer causes slight reduction in the catalyst activity. Similar to ethylene-norbornene copolymerization, with increasing the cyclic olefin/a-olefin ratio, the activity decreases and the cyclic olefin incorporation increases for terpolymerization. With an increase in the carbon number of polar a-olefin, both the activity and polar monomer incorporation increase. The polar monomer content in the terpolymer is up to 7.7 mol% and can be readily adjusted through varying reaction conditions. Similar to the ENC, the thermal properties of the obtained terpolymers are mainly determined by their norbornene contents. Higher polar a-olefin incorporation favors improving refractive index. With polar a-olefin incorporation, contact angles of the film decrease.For some obtained terpolymers, the bimodal molecular weight distributions including one negative peak and one positive peak are obtained by the GPC instrument equipped with a differential refractive index detector. A plausible mechanism is proposed:Two types of active sites, i.e. non-polar-monomer-coordinated active site and polar-monomer-coordinated active site, are formed during the polymerization process. Polymers with low NB content and high NB content, corresponding to the negative peak and the positive peak in the GPC curves respectively, are generated on these two different kinds of active sites separately. The ratio of these two active sites can be adjusted by varying the monomer ratio. Both terminal model and penultimate model for terpolymerization of ethylene, norbornene and polar a-olefins with metallocene catalyst are developed. The results indicate that the penultimate model gives better fitting in comparison with the terminal model. With the estimated propagation rate constants for two active sites, the kinetic characteristics for each active site are analyzed and the two active sites are identified.