Preparation And Performance Studies Of PNIPAM-based Intelligent Polymeric Materials

Polymer materials have been applied extensively in many fields, including space technologies, military industry, domestic livings and so on. With the progress of polymer and material sciences, new requirements for polymer synthetic technology, such as controllability, high efficiency and high selectivity, are presented. According to those requirements, newly developed techniques, such as controlled free radical polymerization and"click chemistry", have been poured with great passion by the scientists. These techniques provide the scientists with powerful methods to synthesize various special-structured polymers as well as various organic/inorganic materials. Smart application of these techniques in polymer synthesis and material modification is one of the most important topics in the field of chemistry. Based on the research of the precursors, this dissertation describes several interesting researches in the synthesis of topologically structured polymers and the modification of nanomaterials. The main results obtained in this thesis are as followed.1. Twin-tail tadpole-shaped copolymer tail-PNIPAM-c-PEG [PNIPAM: poly(N-propylacrylamide), PEG [poly(ethylene gylocl)] was synthesized by the combination of SET-LRP (single-electron-transfer living radical polymerization) and"click chemistry". Firstly, we synthesized PNIPAM-b-PEG-b-PNIPAM with two azide side groups anchored at the junctions between PEG and PNIPAM blocks. Secondly, under high concentration, intrachain connection of the block junctions by dipropargyl oxalylate was done through click reaction. The thermal phase transition behaviors of twin-tail tadpole-shaped polymers and their linear precursors were investigated. We also studied the influence of polymer concentration on the thermal phase transition behaviors. It is shown that the lower critical solution temperature (LCST) values of cyclic polymers were higher than that of their linear precursors with the same block lengths. Polymers have lower LCST values under higher polymer concentration.2. We investigated the influence of varying block length of PEG chain and PNIPAM chains on the formation of twin-tail tadpole-shaped hydrophilic copolymers. The stability, structure and growth kinetics of the micelles formed from tail-(PNIPAM)2-c-PEG and its linear precursor with varying PEG and PNIPAM chains were studied in detail using stop-flow temperature jump technique and dynamic/static laser light. The study of temperature-jumped stop-flow was performed in the fast heating process to investigate the temperature-responsive behaviors. The results show that the thermal-induced re-organization of the micelles depends strongly on the topology and block length of those block copolymers.3. Combining with ATRP (Atom Transfer Radical Polymerization), ROP (ring-opening polymerization) and"click chemistry", we successfully synthesized well-defined Y-shaped copolymer PNIPAM-b-PLL2. [PLL: poly(L-lysine)]. Temperature and pH-responsive behavior of the core-shell micelles were studied. Structural stable micelles were obtained through the shell cross-linking of the micelles. These shell-cross-linked micelles were used as drug nanocarriers and the release profile was dually controlled by the solution temperature and the cross-linking degree. Decreasing the cross-linking degree or increasing temperature could accelerate the drug release rate.4. H-shaped copolymer (PNIPAM/PDMAEMA)-b-PEG-b-(PNIPAM/PDMAEMA) [PDMAEMA: poly(N,N-dimeythylaminoethyl methacrylate)] has been successfully prepared through a combination of SET-LRP, ATRP and"Click chemistry". These copolymers were employed to in suti prepare stable colloidal gold nanoparticles in aqueous solution without any external reducing agent. The formation of gold nanoparticles was affected by the length of PDMAEMA block, the feed ratio of the copolymer to HAuCl4 and the pH value. We also studied the temperature and pH responsive behaviors of the polymer-capped gold nanoparticles. The study results shows that with increasing PDMAEMA chains length, increasing [DMAEMA]:[AuCl4-] or increasing the solution pH values, the diameter of gold nanoparticles become bigger. Under acidic or neutral conditions, LCST of gold nanoparticles protected with polymers are higher, and their temperature-responsive behaviors is weaker, while under alkalic conditions, LCST of gold nanoparticles protected with polymers are lower, and temperature-responsive behavior of gold nanoparticles is stronger.5. Block copolymers PNIPAM-b-PLL were synthesized by the combination of ATRP and ROP. Gold nanoparticles were prepared through the common technique of citrate reduction and stabilized through the interaction of lysine residues of PLL with the gold surface. Gold nanoparticles protected with stimuli-sensitive copolymer PNIPAM-b-PLL were studied as a function of pH and temperature. Under acidic or neutral conditions, LCST of gold nanoparticles protected with polymers were higher. Gold nanoparticles didn't affect the secondary structure of PLL chains.