With Different Topology And Function Of Polymer Molecular Brush Synthesis

Polymer brushes are defined as densely grafted side chains attached to a surface or interface that the distance between neighboring grafts is less than twice of the gyration radius(R_g) of a free polymer chain in solution.Comblike or densely grafted brush(co)polymers have received significant attention over the past decades because of their unique structures and characters.And all the polymerization methods are suitable for the synthesis of molecular brushes.In this research,we used different polymerization methods,such as ATRP,AGET ATRP,RAFT,ROMP,combining with coupling methods like esterification reaction and "click chemistry",for the synthesis of polymer brushes with different structure and functional groups on different polymer backbones by grafting from approach.The synthesis of the polymer brushes,aqueous solution behaviors and applications of the brushes were studied in detail:1.Temperature sensitive polymer brushes with densely grafted poly(N-isopropyl acrylamide) side chains on a random copolymer backbone were successfully synthesized by the combination of atom transfer radical polymerization (ATRP),"click chemistry" and in situ RAFT polymerization.The successful synthesis of polymer brushes indicate that the combination of ATRP,"click chemistry" and in situ RAFT polymerization technique in the synthesis of molecular brushes is an ordenary high efficient method.FT-IR,GPC and ¹H NMR results indicate that the molecular brushes with well-defined structures,controlled molecular weights and narrow molecular weight distributions(M_w/M_n≦1.23) were prepared.The RAFT polymerization of NIPAM exhibited pseudo-first-order kinetics and a linear molecular weight dependence on monomer conversion.The polymer brushes that grafted PNIPAM side chains were temperature sensitive,and the LCST was 28.5℃.2.Janus molecular brushes with hydrophobic PS and hydrophilic PEO side chains on PGMA backbone were successfully synthesized by the combination of atom transfer radical polymerization(ATRP),"click chemistry" and in situ RAFT polymerization.FT-IR,GPC and ¹H NMR results indicate that the molecular brushes with well-defined structures,controlled molecular weights and narrow molecular weight distributions(M_w/M_n＜1.4) were prepared.The TEM image indicated that the PGMA-g-PEO/PS Janus polymer brushes in a seclective solvent,form spherical micelles.The hydrophobic PS side chains form the core of the micelles,the hydrophilic PEG block form the corona to stabilize the micelles,and the size of the micelles increase with the PS side chain lengh.3.The biotinylated PEG-b-(PCL/biotin)₂ triblock copolymers with biotin molecule on the junction points of PEG block and PCL block were synthesized via a combination of ring-opening polymerization and "click" chemistry using PEG-b-(OH/alkyne)₂ as macroinitiator.The ¹H NMR and FTIR results indicates the successful synthesis of PEG-b-(PCL/alkyne)₂ triblock copolymers. Avidin/2-(4-hydroxyphenylazo) benzoic acid(HABA) binding assay and optical fluorescence microscopy can further confirming that the existance of biotin molecule in the biotinylated triblock copolymers.Using the Avidin/HABA assay can also calculate the amount of biotin in the biotinylated PEG-b-(PCL/biotin)₂ triblock copolymers.The biotinylated triblock copolymers form spherical micelles,about 150 nm in diameter,and the biotin functional groups were reside at the periphery of these micelles.After the addition of pure avidin molecules,the average diameter of micelles decreased,from 150 nm to 100 nm.4.Brush macromolecules having poly(L-lactide)(PLLA) and poly(styrene)(PS) side chains were prepared on the backbone of partially esterified poly(2-hydroxyethyl methacrylate)(PHEMA) by using a combination of activator generated by electron transfer ATRP(AGET ATRP) and ring opening polymerization.The number-average degrees of polymerization of PLLA side chains and PS side chains were determined by ¹H NMR spectroscopy and the apparent molecular weights of the brush molecules were measured by gel permeation chromatograph(GPC).The relationship between the crystallization of PLLA with PLLA and PS side chain lengths was investigated. The glass transition temperature of PLLA was determined by side chain length.With the increase of side chain length,the glass transition temperature shifted to higher temperature.The crystallization of PLLA was greatly affected by PLLA and PS side chain lengths.The melting temperature of PLLA decreases with increasing PS chain length,and increases with increasing PLLA chain length.Inside a molecular brush due to the unfavorable interaction between PLLA brushes and PS brushes phase separation occurs and star like morphology with core-shell structure can be observed. Mixed polymer brush is a good compatibilizer in immisible polymer blends.5.Poly(L-lactide)-poly(ethylene glycol) methyl ether methacrylate (PLLA-PEOMA)(PLLA-PEOMA) comb-block-comb molecular brushes with controlled molecular weights and narrow molecular weight distributions were successfully synthesized based on a combination of AGET ATRP and ring-opening polymerization.The synthetic route is a combination of "grafting through" method for AGET ATRP of PEOMA comb block and "grafting from" method for the synthesis of PLLA comb block.The number-average degrees of polymerization of PLLA chains and PPEOMA comb blocks were determined by ¹H NMR spectroscopy, and the apparent molecular weights and molecular weight distributions of the brush molecules were measured by GPC.The crystallization of the components in the comb block comb copolymers was also investigated in this research.The crystallization of PLLA side chains is influenced by PLLA chain lengh and the content of PPEOMA in the molecular brushes.Because of the high content of PLLA combs in the molecular brushes,the crystallization of PPEOMA combs was limited.Molecular brushes adsorbed on mica tend to make worm like conformations.And with the increase of comb polymer brushes added to the blends,the dispersed phase gets smaller.The preparation of a series of polymer brushes with different structure was an exploration of new and efficient polymerization methods for the synthesis of polymer brushes.And find a new and effective approach for the synthesis of polymer brushes.These stimuli-responsive spherical brushes and micelles have attractive applications in the fields ofbiotechnology,medical analysis and drug delivery.