Theoretical Study On The Synthesis And Properties Of The Gradient Copolymer

The gradient copolymer is a special kind of copolymer that the composition chain gradually along the chain backbone. Owing to its gradient compositon profile, this kind of copolymer has distinct response to the thermal and mechnical stimulation as well as special interfacial properties. As the result, gradient copolymer has great potential to be damping material and compatibilizer in immicible polymer blends. This thesis focus on questions in two aspects: one is how could the gradient copolymer with various composition profiles be prepared, the other is how these different composition gredients affect properties of the polymer.The first part of the thesis discussed some fundamental aspects in living radical polymerization, based on which the gradient copolymer is synthesized. At first, a mathematical model is developed to describe the kinetics of reversible addition-fragmentaion chain transfer (RAFT) in miniemulsion polymerization. Through comparing the theoretical results with experimental data, we discussed the reason for the retardation in RAFT miniemulsion polymerization. By making the advantage of the spatial compartmentalized system, we discriminated the mechanism of RAFT polymerization and provided a method to accurately measure the RAFT equilibrium constant. In addition, the apparent RAFT equilibrium constant in copolymerization process is expressed, and related to the copolymerization rate. Then, the copolymerization model is applied to describe the RAFT crosslinking process. Both the criteria of the gel point and analytical expression for gel conversion were provided. The effect of intramolecular crosslinking on gelation process was investigated and the branching distribution in hyperbranched polymers was also calculated.Based on the comprehension of living radical polymerization kinetics, we combined the methodology of chemical engineering, that is the reactor policy, with living radical polymerization techniques to synthesize the gradient copolymer in the second part of this thesis. Through modeling both RAFT and ATRP process, the feasibility of using semi-batch operation with programmed monomer feeding to control the composition profile in gradient copolymer was theoretically proved. The targeted products involved uniform, linear gradient, hyperbolic gradient Copolymers and block Copolymers with gradient segments. We also discussed some kinetic problems appearing in semi-batch process and try explaining them in analytical way.In the last part of the thesis, some theories in polymer physics were employed to investigate the phase behaviors in ternary gradient copolymer/homopolymer blends. First, the random phase approximation suggested by de Gennes was used to study the critical phenomenon. The effect of chain gradient on the position and physical nature of Lifshitz Point was dicussed. Sequentially, self-consistent field theory was employed to calculate the phase diagrams of the blends. The poisiton of different phase region were located. In addition, the relation between chain gradients and swelling ability of copolymer layer as well as the dissolvability of copolymer chains in homopolymer phase were also investigated. Finally, we analyze the mesophase structure of the blends. The density profiles of both copolymer and homopolymer were calculated, and the interfical properties of different gradient copolymer were also studied. We suggested that, by designing the composition profile of gradient Copolymers, the interfacial structure as well as the morphology and property of the whole blend will be fine-tuned.