Crystallization Behavior And Crystals Structure Of Poly(4,4'-aminocyclohexyl Methylene Dodecanedicarboxylamide)

In this thesis,crystallization behavior and crystals structure of poly(4,4'-aminocyclohexyl methylene dodecanedicarboxylamide),as a novel cycloaliphatic microcrystalline polyamide(named PA PACM12),were thoroughly studied with the aim of understanding of the crystallization process and microcrystalline structure of PA PACM12,from the aspects of thermodynamics, kinetics and morphologies.The main conclusions read as follows:Isothermal crystallization and melting behaviors of PA PACM12 were investigated by means of differential scanning calorimetry(DSC).The double melting behaviors were observed for both microcrystalline PA PACM12 and melt recrystallizated samples,implying the more complicated crystallization,melting behaviors and crystals structure of PA PACM12 than traditional polyamides.The results showed that after crystallization at the temperature range from 152℃to 168℃for 1 h,the temperature of low melting peaks(T_m¹) of microcrystalline PA PACM12 shifted to high temperature with increasing isothermal temperature,and exhibited a maximum value of 193.0℃.While the temperature of high melting peaks (T_m²) remained constant at about 250.0℃.The values of T_m¹,gradually increased with isothermal crystallization time at the crystallization peak temperature(168℃) for various time,and shifted to T_m² values,which were about 241.6℃.These results indicated that PA PACM12 could exhibit better thermal stability than traditional polyamides.Furthermore,as to melt crystallization of PA PACM12,the T_m¹ and T_m² increased from 217.1℃to 235.8℃and 248.5℃to 253.5℃at the crystallization temperature range from 195℃to 216℃for 1 h,respectively.The double melting peaks were attributed to the melting of two kinds of thickness lamellae, which gradually became thicker and more perfect under above-mentioned conditions. Theα-form structure crystals of microcrystalline PA PACM12 were established by wide-angle X-ray diffraction(WAXD).Analysis of isothermal crystallization kinetics of PA PACM12 was carried out by DSC,and the mechanism of nucleation and growth was discussed.In the temperature region of regime II,from 200℃to 216℃,with increasing the degree of supercooling, the nuclei formed more easily due to the stronger driving force during nucleation process,hence,crystallization rate increased.The Avrami exponent n was calculated to be about 2.2,indicating that the growth type of isothermal crystallization of PA PACM12 taken as needle-like or rod-like two dimensional space extension.T_M⁰, illustrating the melting temperature(T_m) of an infinitely extended crystals,was determined to be 271.8℃from the procedure suggested by Hoffman and Weeks.The apparent activation energyΔE was determined to be -101.5 kJ/mol from the Arrhenius equation,including the nucleation activation energy of about -20.2 kJ/mol, and the nucleation parameter K_g was determined to be 1.75×10⁵ K² by the spherulitic growth analysis.The lateral and folding surface free energies determined from the Lauritzen-Hoffman equation were 1.14×10^-6 J/cm² and 9.8×10^-6 J/cm²,respectively, and the work of chain folding q was about 6.70 kcal/mol.The crystallization temperature region of PA PACM12 was determined to be regime II by applying the Z-test of Lauritzen,that is,nucleation was the crystallization rate controlling step.Nonisothermal melt crystallization behavior of PA PACM12 was investigated by DSC.The results showed that with decreasing cooling rates,the temperature range of crystallization peaks gradually became narrower,and shifted to higher temperature region with the crystallization enthalpies(⊿H_c) increased.The Jeziorny modification of the Avrami equation was employed to describe the whole nonisothermal crystallization processes,with the Avrami exponent n of 2.38～2.58,which also suggested that the mode of nucleation and growth of nonisothermal crystallization for PA PACM12 was two dimensional space extension.Meanwhile,the Ozawa model with the exponent m of about 2.12 and combined method with the value of a of about 1.28 indicated the two methods were also valid for describing the nonisothermal crystallization behavior of PA PACM12,and they were in good agreement with results of Jeziorny analysis.The nonisothermal crystallization apparent activation energies of PA PACM12 determined by Kissinger and Arrhenius methods were about -174.6 kJ/mol and -172.1 kJ/mol,respectively.Morphologies of PA PACM12 crystals formed under various crystallization temperatures,crystallization time and various cooling rates were observed by polarizing optical microscopy(POM).The results showed that the small crystals became larger with increasing the crystallization temperature or crystallization time, implying that the size of crystallites was strongly affected by the crystallization temperature and time.With decreasing cooling rates of melt PA PACM12 from -10℃/min to -0.5℃/min,the size of crystals gradually increased to about 15μm,which indicated that crystallization process was also dependent on the cooling rates.These results will greatly improve the mechanical property,especially,the microcrystalline property of PA PACM12,by modulating the crystallization conditions,such as crystallization temperature,crystallization time or cooling rate from melt.Single- and pauci-chain crystals of PA PACM12 have been parpared from 1,4-butanediol solutions at 160℃by "self-seeding" technique,with the concentration of 3×10^-4 g/mL.The morphologies and aggregation features of the single- and pauci-chain crystals were examined by transmission electron microscopy (TEM).It was found that the PA PACM12 crystallized into small crystallites with the size of about 10 nm,and they aggregated randomly as a fractal growth pattern.