The Solid State Polycondensation Of SA Type Transparent Polyamide And Study On Its Structure And Properties

Since the first transparent polyamide was synthesized by Nobel Dynamite company in 1960s, it has attracted more and more attention in recent years. On one hand, more and more transparent polyamide is needed in China presently; on the other hand, costly transparent polyamide is imported because of the lack of side-chain diamines and diacids. In order to resolve the problem, a new type semi-aromatic transparent polyamide (SATPA) has been successfully developed using cheaper monomers at Zhengzhou University by means of poly-copolycondensation since 1999. It has been produced by Ping dingshan Plastics Co. Ltd., China. Yet, compared with foreign transparent polyamide, SATPA still has some shortcoming, for example, its glass transition temperature, the impact strength and molecular weight are low.Solid state polycondensation (SSP) is an effective method of producing high-molecular-weight polymer. Compared with melt polymerization, the reaction temperature of solid state polymerization is low, the technics is simple, it needs less energy, the side reaction is little and it will not pollute environment. Because of its advantage, it was used in the development and production of more and more high-molecular-weight polymer. But the solid state polycondensation of transparent polyamide hasn't been reported, so the study on the subject has actual significance.In order to increase the molecular weight of SATPA, enhance its mechanical properties and heat resistance, and widen its applied range, solid state post polycondensation is adopted firstly to prepare a series of SATPA having different Melt Flow Rate. And the work has developed around them, which includes structure analysis, characterizations on thermal behavior, rheological behavior, water affinity, mechanical properties and so on. Factors to influence solid state post polycondensation of SATPA and the impact of molecular weight on properties are studied. The results show that: (1) The polycondensation of SATPA takes place in vacuum. At constant temperature, the longer the reaction time is, the higher the molecular weight is; during the same time, the higher the reaction temperature is, the higher the molecular weight is. The reaction rate decreases with the prolonging of the reaction time and the reducing of reaction temperature.(2) SATPA after solid state polycondensation is still amorphous, and has outstanding transparency.(3) SATPA's glass transition temperature enhances from 102℃to 120℃, indicating its better resistance to effect of heat. And the relation between glass transition temperature and melt flow rate accords with the equation Tg=131- 20.87MFR.(4) The starting heat decomposition temperature of SATPA synthesized by SSP is about 440℃and doesn't change with the variety of the molecular weight. It has good thermal stability. The heat decomposition reaction in Nitrogen is one-step reaction and the mechanism of the heat decomposition is deduced preliminary as one-dimensional phase boundary control.(5) Three mechanical relaxations, which includeα,β, andγrelaxations, are examined in the DMA curves of SATPA synthesized by SSP. With the rising of frequency, the temperature of the relaxations and storage module rise. SATPA is tough at low temperature because of the existence ofγrelaxations at-130℃. With the increasing of the molecular weight, the temperature ofα,βandγtransition moves to high temperature. TMA shows that the glass transition temperature of SATPA falls with increase of pressure.(6) The value of n (non-Newtonian index) of SATPA is less than 1, implying the pseudoplastic nature of SATPA in the molten state. The apparent viscosity decreases with increasing of temperature, shear rate and shear stress. It is propitious to extrusion molding and injection molding. And with the increase of the melt flow rate of SATPA, the pseudoplasticity strengthen, the apparent viscosity augment and become less sensitive to temperature. It is an advantage for extrusion molding and a disadvantage for injection molding.(7) Although the molecular weight of SATPA greatly increases, it can still be injection molded in a wide range, but technological conditions influence the products' presentation qualities. The optimum injection molding technological conditions is determined by the molecular weight of SATPA.(8) After solid state polycondensation, the tensile strength of SATPA keeps changeless and flexural elastic modular increases from 2448MPa to 3194MPa; izod notch impact strength improves from 4.08kJ/m~2 to 6.62kJ/m~2; and Rockwell hardness enhances from 108 to 118. It possesses more excellent mechanical properties. After treated in water at high temperature and normal temperature, the mechanical properties increase little, on the contrary, rupture elongation and Rockwell hardness reduced obviously; after anneal treatment, mechanical properties all improve.(9) SATPA's water absorption is low and is independent on the molecular weight. The temperature of water and humidity of environment have effect on its water absorption. The higher the temperature of water and the higher the air humidity is, the higher the water absorption of SATPA is. After dipping in the water for 24h, the dimension of the sample doesn't change basically, and it shows that SATPA has nice dimension stability.