Synthesis And Properties Of Highly Cross-linked Wholly Aromatic Polymers

Highly cross-linked polymer materials such as epoxy resin, unsaturated polyester resin and phenolic resin, have been widely used in various fields such as composite materials, adhesives, encapsulating materials, anticorrosion materials, insulation materials, friction materials and coatings, due to their creep resistance, dimensional stability, high mechanical strength, wear resistance, excellent chemical and heat resistance characteristics. In recent decades, the development of novel highly cross-linked polymer materials with special functions is becoming one of the most attractive research topics in material chemistry field. Owing to the special chemical properties, as well as light, electricity, heat and other physical properties, these materials, as potential adsorbent materials, optical materials and low dielectric materials, could have application in the frontier field of functional polymer materials. However, the current knowledge with respect to the relationship between properties and structures for highly cross-linked polymer is still far less sufficient. In-depth study on the correlations between properties and physicochemical nature of polymers has practical significance to the novel material development. This dissertation is aimed to, on the basis of rational molecular design, prepare a series of novel highly cross-linked polymers with porous or optical properties. The properties were investigated by various measurements, and the relationship between properties and structures was systematically discussed by the aid of theoretical calculations as well as molecular simulation. The main contents and results are as follows:Synthesis and properties of cross-linked polycyanurates networks with tetrahedral and triangular pyramidal structures. Three cyanate monomers, tetrakis(4-cyanatophenyl)silane, tetrakis(4-cyanatobiphenyl)silane and tris(4-cyanatobiphenyl)amine were designed and synthesized, and the corresponding highly cross-linked networks with systematically varied nodes and linking struts were obtained via thermal cyclotrimerization reaction in diphenyl sulfone solution. The chemical structures of monomers and polymers were confirmed by1H NMR, FTIR, solid-state13C CP/MAS NMR spectra, and elemental analysis. The products are amorphous with5%weight-loss temperatures over428℃. The results based on N2and CO2adsorption isotherms show that the pores in these polymers mainly locate in the microporous region, and the BET surface areas are up to960m" g, which is the highest value for the porous cyanate resin reported to date. The nitrogen-and oxygen-rich characteristics of cyanate resins lead to the networks strong affinity for CO2and thereby high CO2adsorption capacity of11.1wt%at273K and1.0bar. The adsorption behaviors of H2, CO2, benzene, n-hexane, and water vapors were investigated by correlating with the chemical composition and porosity parameters of the networks as well as the physicochemical nature of adsorbates.Synthesis and properties of cross-linked polycyanurates networks with planar triangular structures. Two cyanate monomers with different arm lengths,1,3,5-tricyanatobenzene and1,3,5-tris(4-cyanatophenyl)benzene were designed and synthesized, and the corresponding highly cross-linked networks Ph-1and Ph-2were obtained via thermal cyclotrimerization reaction in diphenyl sulfone solution. The physical properties, porous properties and gas adsorption properties were characterized through various measurements, and the relationships among the spatial structure and chemical composition of the monomer, physicochemical nature and adsorption properties of polymers were researched and discussed. The results showed that long arms of Ph-2network exhibited a high BET surface area of630m2g-1and major pore size distribution of0.567nm with loose pore morphology consisted of tiny aggregate particles. While, Ph-I had defective triazine-based networks containing residual intermediate segments, which was caused by steric hindrance of cyanate groups in excessively short strut, resulting in a low surface area, small pore volume and relatively smooth surface morphology due to the dense packing of the flexible intermediate segments. However, due to the high contents of oxygen atoms and triazine ring units, it showed a high limiting enthalpy of CO2adsorption (37.1kJ mol-1). In addition, Ph-2displayed good gas storage capacity and selectivity, CO2uptake at273K. was up to9.21wt%, H2uptake at77K was up to1.05wt%, and CO2/N2adsorption selectivity was37.8:1at ambient temperature.Synthesis and properties of cross-linked poly(benzimidazole) networks with triangular pyramidal and tetrahedral structures. Triangular pyramidal tris(4-carboxyphenyl)amine and tetrahedral tetrakis(4-carboxypheyl)silane were designed and synthesized, and the corresponding highly cross-linked poly(benzimidazole) networks were obtained via polycondensation with3,3’-diaminobenzidine in solution. The chemical structures of monomers and polymers were characterized by FTIR and1H NMR measurements. N2adsorption results showed that the cross-linked networks had porous structures, but the chains in networks were relatively densely packed owing to the biphenyl units with high degree of freedom, which led to a decrease in pore size and volume. CO2adsorption results showed that the cross-linked networks contained amounts of ultramicropores. PB1-1with a high content of nitrogen atoms showed a high CO2storage capacity (13.2wt%), limiting enthalpy of adsorption (34.2kJ mol-1) and CO2/N2selectivity of12.3. Vapor adsorption research suggested that polymer networks had relatively strong polarity. Synthesis and properties of highly cross-linked polyaryletherketones. The linear carboxyl-containing polyaryletherketone was prepared, and then reacted with thionyl chloride to obtain poly(aryletherketone) bearing pendant acyl chloride group (PEK-COCl), which exhibited good solubility in some polar organic solvents. The film obtained from the mixture solution of PEK-COCl with hydroquinone (HQ) or phenolphthalein (PPH) could be thermally cross-linked readily at the temperature below200℃without using any catalyst. The crosslinked polymers became insoluble in any organic solvents, displaying excellent chemical resistance. Moreover, the films were very smooth with roughness values of0.29-0.52nm. Compared to the linear PEK, the cured PEK-HQ and PEK-PPH did not display obvious change in refractive indices, but the birefringences were significantly decreased. Especially for PEK-PPH, the twisted crosslinker structure resulted into its birefringence at1550nm decreased from0.011to0.002, and the optical loss value decreased by about78%due to the disappearance of OH group.