Synthesis Of Well-defined 8-shaped Polymers Via The Combination Of RAFT Polymerization And "Click" Reaction

Cyclic topological polymers including single and multiple cyclic polymers have attracted a growing interest for the past decades as a result of their unique properties comparing with their branched and linear counterparts. Double cyclic polymers, including 8-shaped, theta-shaped and manacle-shaped polymers are an important class of cyclic topological polymers. Among there three double cyclic polymer topologies, the 8-shaped polymer has been investigated the most. But most of the synthetic strategies reported are based on anionic, cationic, or ring-expansion polymerization. The monomers used are limited and rigorous experiment conditions are needed. In this thesis, a series of well defined 8-shaped polymers, including poly(N,N-dimethyl- acrylamide) (PDMA), poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-di- methylacrylamide)-b-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) with controll molecular weight and narrow polydispersity were synthesized by the combination of RAFT polymerization and"Click"chemistry.Firstly, four-arm star polymers with azido groups were prepared by RAFT polymerization using pentaerythritoltetrakis(3-(S-(2-azidoethylacetate)trithiocarbonyl) propanoate) (PeAATP) as the chain transfer agent. It can be concluded from the GPC results that the polymerization is preceded with good control. Then the intramolecular Click ring closure of the four-arm star polymers was conducted under highly dilute conditions, using N,N-bis(2-propargyloxycarbonyl ethyl)-2-hydroxylethyl amine (BPHA) as linker and CuBr/PMDETA as the catalyst, respectively, affording well-defined 8-shaped polymers. FTIR, 1H NMR, GPC, and MS analysis confirmed the complete consumption of azido group in four-arm star polymers and that the coupling reaction proceeded via the intramolecular manner. The self-assembly behavior of 8-shaped PDMA-b-PNIPAM was investigated by DLS. Comparing with their four-arm star precursor, the 8-shaped polymers possesse lower CMT and smaller hydrodynamic diameter (Dh). The difference in self-assembly behaviors between 8-shaped and four-arm star PDMA-b-PNIPAM should be due to the absence of chain ends and stringent restrictions on backbone conformation in the former.