Preparation And Characterization Of Polymeric Micelles From Thermo-Sensitive Poly(N-Isopropylacrylamide-Co-N, N-Dimethyla Mide)-B-Polycaprolactone Block Copolymers

Chapter 1PNIPAAm and its aqueous solution are very important thermo- -sensitive polymer, and the LCST is about 32℃.The thermo-sensitive mechanism, copolymerization modification and the controlled release system of drugs of PNIPAAm are researched detailedly in this Chapter. In addition, the formation, shape and characterization methods of micelles are also related. At last, the purpose and methods of our research are put forward.Chapter 2Arcylic acid was first protected by benzalcohol to produce benzyl acrylate which polymerize with PNIPAAm to get copolymer P(NIPAAm-co-Benzyl A). P(NIPAAm-co-Benzyl A) was deprotected by hydrogen in the presence of Pd/C (10%) as catalyst so that the effect of introducing arcylic acid on LCST of polymer was studied. Arcylic acid was polymerized with PNIPAAm to obtain P(NIPAAm-co-AAc). LCST of P(NIPAAm-co-Benzyl A) and P(NIPAAm-co-AAc) and their differences of transmittance under the same condition were compared. Caprolactone was initiated to carry out ring-open polymerization by P(NIPAAm-co-AAc) and hexanedioic acid. The structure of polymer was determined by NMR and IR. And their molecular weights were determined by end-group titration method. LCST of polymer was measured by UV spectrophotometer and the effect of condition acid or alkali on LCST was also measured.The experimental results exhibited that carboxyl was successfully protected. The molecular weight of polymer can be measured by end-group titration method and results shows that Polymers with different molecular weight can be synthesized by regulating the quality of chain transfer agent 2-mercaptoethanol. And the mass of initiator and reaction time have some effects on conversion to some extent. Different quality of Crylic acid can obviously advance LCST of PNIPAAm.The reason of the inapparent changes of the rate of transmittance of P(NIPAAm-co-Benzyl A) solution was the insufficiency of deprotection. Also, P(NIPAAm-co-AAc) had the properties of thermo-sensitive and pH-sensitive, and the LCST was raised with the increasing of pH.In the process of caprolactone ring-opening by using the end hydroxyl groups of P(NIPAAm-co-DMAAm) as initiators, caprolactone was produced. So the work about carboxyl whether to participate reaction must be further studied. Chapter 3Firstly, DMAAm was used to increase the LCST of PNIPAAm to about 40℃. Then, Amphipathic block copolymers (P(NIPAAm-co-DMAAm)-b-PCL) were prepared via bulk ring-opening polymerization of caprolactone (CL) by using the end hydroxyl groups of P(NIPAAm-co-DMAAm) as initiators and stannous octoate as catalyst. Subsequently, a reactive group containing unsaturated double bond was introduced to the end of PCL chain of P(NIPAAm-co-DMAAm)-b-PCL. The UV was used to make micelles core-crosslinked. The obtained polymers were analyzed and characterized by ~1H NMR, GPC and low critical solution temperature (LCST) measurement. The CMC, sizes and distribution of micelles were also studied and compared.The results indicated that the value of CMC was reduced with the increasing of molecular weight of PCL chain segment; the sizes of core-crosslinked micelles were smaller, and size distribution was narrower.