Synthesis And Characterization Of Cylindrical Polymer Brush

Cylindrical polymer brushes have been focused on in the past years due to their unique regular multibranched structure, which endows it many unusual properties and a wide range of potential applications in such fields as nanostructured materials, drug delivery systems, and sensor/actuator systems and so on. Three strategies, including the graft from, graft to and graft through could be adopted to synthesize the cylindrical polymer brushes. In this work, we reported a novel approach with regard to the preparation of cylindrical polymer brushes with high graft density and large size based on graft through technology. The polymerization occurred on the surface of aggregates formed by the macromonomer. The main contents are as follows:(1) Synthesis of macromonomers end-capped with the polymeric vinyl double bond. In this work, two kinds of macromonomers end-capped with the polymeric vinyl double bond were prepared by the two successive steps. Firstly, diblock copolymer of poly(N,N-dimethylacrylamide)-block-poly(N-isopropylacrylamide) (PDMA-b-PNIPAM) end-capped with alkynyl group (≡-PDMA-b-PNIPAM) and diblock copolymer of polystyrene-block-poly acrylic acid (PS-b-PAA) end-capped with hydroxyl group(HO-PS-b-PAA) were synthesized with reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP), respectively. And then the terminal alkynyl group of≡-PDMA-b-PNIPAM and the hydroxyl group of HO-PS-b-PAA were further transferred to double bonds through "click" chemistry or esterification reaction, respectively. This process resulted in the formation of macromonomers, v-PDMA-b-PNIPAM and v-PS-b-PAA. The obtained compounds were characterized by 1HNMR, FTIR, GPC, and MALDI-TOF MS, respectively.(2) Study on micellization behaviour of the macromonomers. Macromonomer of v-PDMA-b-PNIPAM could self-assemble into core-shell micelles using PNIPAM as core and PDMA as shell when the temperature is higher than that of lower critical solution temperature (LCST) due to the chain collapse of PNIPAM segment, and v-PS-b-PAA could self-assemble into micelles using PAA as core and PS as shell in selective solvent, such as toluene. In this work, the micellization behaviours of v-PDMA-b-PNIPAM and v-PS-b-PAA were investigated with dynamic light scattering (DLS), and the parameters of the obtained micelles were also characterized in detail. (3) Preparation of cylindrical polymer brushes via traditional radical polymerization. In this work, the polymeric double bonds of macromonomers located on the surface of micelles formed by the self-assembly of macromonomers. Therefore, cylindrical polymer brushes could be obtained after a radical polymerization process occurred on the surface of micelles. The polymerization took place in water using potassium peroxydisulfate (KPS) as initiator or in toluene using azodiisobutyronitrile (AIBN) as initiator, respectively. Overview our protocol, the flowing three virtues were considerable:(i) the polymerization could be took place in a dilute solution, and the entanglement of polymer chains and the embedding of terminal groups could be avoided to some extent; (ii) the polymerization rate could be expected to increased in dilute solution; (iii) cylindrical polymer brushes with high graft density and a large size could be expected. The worm-like conformations were observed by atomic force microscope (AFM) and transmission electron microscopy (TEM).