Study On The Preparation, Phase Morphology Control And Crystallization Behavior Of Polymer Nanoblends

Nano-materials have become a hot subject in recent years due to their unique properties. In polymer field, studies appeared in the literature mainly focused on the nano-composite materials, with inorganic nano-particles as additives, and only a few work were related to polymer nanoblends, in which both dispersed phase and matrix were polymer components. Hu et al. for the first time have proposed a novel approach of in situ polymerization and in situ compatibilization to prepare polymer nanoblends. Recently, Leibler et al. developed another new route to prepare polymer nanoblends, in which a major block copolymer component having self-assembly behavior was blended with a homopolymer component to form nanotructured blends. Nanoblends have attracted much attention not only due to their mechanical properties of the materials but also proposed a new subject of crystallization in polymer science due to their nanoconfined geometries.In this dissertation, we adopted the processes of in situ polymerization and in situ compatibilization to prepare the PPO/PA6 nanoblends, and used a self-assembly behavior of PS-b-PEO to prepare PPO/PS-b-PEO nanoblends. On the base of the works, the formation mechanism and crystallization behavior of the polymer nanoblends were discussed in detail.The main results obtained are as follows:1. A macroactivator of PPO(PPO-g-MPAA) modified with p-methoxyphenyl-propionate (MPAA) was synthesized and the structure was characterized using IR and NMR, with which, through the novel approach of in situ polymerization and in situ compatibilization, the nanoblend of polyamide 6 (PA6) dispersed in poly (2,6-dimethyl-1,4- phenylene oxide) (PPO) was obtained. The relationship between the composition and the morphology of the blends was discussed, and it was found that the amount of graft copolymer generated in situ had important effect on themorphologies formed. Furthermore, also it could be concluded that if the process of in situ polymerization and in situ compatibilization was performed via solution blending, the more homogeneous the blending system was, the more uniform the dispersed phases were, and the smaller the dispersed phase was. The DSC results showed that with increasing amount of the graft copolymer generated the melting point was toward decrease and the crystallization temperature also shifted to the lower temperature due to confined volume.2. The PS-MMA macroactivator was synthesized by bulk copolymerization, and the miscibility between PS-MMA and PPO was studied by DSC. The approach of in situ polymerization and in situ compatibilization was adopted to prepare the PPO/PS/PA6 ternary nanoblend. The DSC analyses indicated that the melting point shifted to lower temperature and melting process became longer.3. The effects of various parameters on the anionic polymerization kinetics of caprolactam(CL) in the presence of PPO were discussed. It was found that the polymerization temperature, the amount of microactivator, initioator and the initiating sites on macroactivator contributed positively in the rate of polymerization, while the increase of PPO concentration acted negatively on the polymerization rate due to diffusion and dilute effects. SEM observation indicated that the sizes of PA6 particles were gradually increased during reactive blending. Therefore, a microreactor mechanism was proposed based on the above analyses.4. The isothermal crystallization kinetics of PA6 in confined geometry were studied by DSC, and the equilibrium melting point was measured;meanwhile, the nonisothermal crystallization kinetics was analyzed by using Jeriorny, Ozawa and Mo methods. The results showed that for the PA6 droplets with the size of micrometer, the crystallization process was dominated by heterogeneous nucleation, and a phase and y phase coexisted;for the PA6 droplets with the size of nanometer, heterogeneous and homogeneous nucleation coexisted in the crystallization process, and more y phase formed;for more isolated PA6 droplets as in the case with very low content of PA6, the crystallization process was dominated by homogeneous nucleation with high supercooling degree, and mainly formed y phase.5. The well-defined diblock copolymer of PS-b-PEO was synthesized by atom transfer radical polymerization (ATRP) with bromo-ended MPEO as macroinitiator andCuBr/Bipy as catalysts. The nanoblends with PEO nanostructured dispersed phase were obtained by solution blending of PS-b-PEO and PPO. The observations of AFM and TEM revealed that under different preparation conditions, the different morphologies could be formed owing to the self-assembly of the amphiphilic PS-b-PEO block copolymers.6. The isothermal and nonisothermal crystallization kinetics of PS-b-PEO/PPO(70/30 wt%) blend and PS-b-PEO copolymer were studied by DSC. In the isothermal crystallization, the blend and the copolymer both exhibited nonconfined crystallization behaviors, with Avarami exponent of greater than 1;the perfect spherulites were observed with optical microscope due to the growth of crystallites which breaking through the grain boundaries with the connection of PEO microdomains;for nonisothermal crystallization, Jeriorny, Ozawa, and Mo methods were adopted to describe crystallization process, and nonconfined crystallization behavior was also found by the experiments results.