Based On (N-vinylcaprolactam) Tadpole-shaped Block Copolymers And Cyclic Homopolymers

Cyclic and tadpole-shaped polymers exhibit distinctively unique characteristics and physical properties compared to their linear analogues. Thus, they have important applications in the field of biomedicine,modified materials and nanotechnology. But the synthsis of cyclic and tadpole-shaped polymers is so difficult that their invesitigation and application are limitted. For example, cyclization of linear polymers by coupling end-groups together to form cyclic polymers need to be conducted in very low concentrations over long periods of time. This dramatically reduces efficiency and output for cyclic polymers. Poly(N-vinyl caprolactam)(PNVCL) has good biocompatibility and thermoresponsiveness, and its lower critical solution temperature(LCST) is within the scope of the physiological temperature, so that it has potential applications in drug controlled release. However, to the best of our knowledge, NVCL-based tadpole-shaped polymers have not been reported.In this thesis, recent advances regarding the living/controlled radical polymerization of N-vinyl caprolactam was summarized firstly. Then tadpole-shaped block copolymers of poly(N-vinylcaprolactam)(PNVCL) and poly(DL-lactide)(PDLLA) were successfully synthesized by a combination of atom transfer radical polymerization(ATRP), supramolecular self-assembly and “selective” Cu(Ⅰ) catalyzed alkyne group/azide(Cu AAC) click cyclization at a relatively high concentration(10 mg/m L). The polymers were characterized by 1HNMR, IR and gel permeation chromatography-multi-angle laser light scattering(GPC-MALLS). Their thermoresponsive and aqueous self-assembly properties were investigated by UV-vis spectrometer, fluorescent probe technology and transmission electron microscopy. The result showed that tadpole-shaped block copolymers and their linear precursors have concentration-dependent LCST values. The LCST values of tadpole-shaped block copolymers are higher than those of their linear precursors. They can self-assemble into spherical micelles in aqueous solution. The tadpole-shaped block copolymers have higher CMC values than their linear precursors. The introduction of hydrophilic PNVCL destroyed the crystallinity of PDLLA.Well-defined hydroxyl-containing cyclic PNVCL homopolymer with narrow molecular weight distribution(PDI <1.5) was synthesized using the above method. The result of investigation on properties showed that the hydroxyl group-containing cyclic-PNVCL and its linear precursor were concentration-dependent, and cyclic-PNVCL has a higher LCST and CMC value than its linear precursor. The LCST and CMC value of hydroxyl-containing cyclic PNVCL in the acidic and alkaline buffer solution is lower than in neutral conditions.