Design And Synthesis Of Miktoarm Star Copolymers And Branched Copolymers

A facile synthetic pathway to miktoarm star copolymers with multiple arms has been developed by combining reversible addition-fragmentation chain transfer (RAFT) arm-first technique and aldehyde-aminooxy"click"coupling reaction. Star polystyrene (PS) with aldehyde functionalized core was initially prepared by RAFT arm-first technique via crosslinking of the preformed linear macro-RAFT agents using a newly designed aldehyde-containing divinyl compound 6,6'-(ethane-1,2-diylbis(oxy))bis(3-vinylbenzaldehyde) (EVBA). It was then used as a multifunctional coupling agent for the subsequent formation of the second generation poly(ethylene glycol) (PEG) arms via the click coupling reaction between its aldehyde groups and aminooxy-terminated PEGs. The effect of the PS arms on the crystallization ability of PEG arms was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The possible formation of PS-PEG miktoarm star copolymer with Janus-like segregated structure in cyclohexanone was also investigated.A facile synthetic pathway to poly(N-isopropylacrylamide) (PNIPAM)- poly(ethylene glycol) (PEG) miktoarm star copolymers with multiple arms has been developed by combining reversible addition-fragmentation chain transfer polymerization and aldehyde-aminooxy"click"coupling reaction. Star PNIPAM with aldehyde functionalized core was initially prepared by RAFT arm-first technique via crosslinking of the preformed linear macro-RAFT agents using a newly designed aldehyde-containing divinyl compound EVBA. It was then used as a multifunctional coupling agent for the subsequent formation of the second generation PEG arms via the click coupling reaction between its aldehyde groups and aminooxy-terminated PEGs. The thermoresponsive micellization behavior of PNIPAM-PEG miktoarm star copolymer with different PEG arm numbers in water was also investigated. Opportunities are open both for thermo-induced intermolecular or intramolecular micellization of PNIPAM-PEG miktoarm star copolymers via controlling the content ratio of PNIPAM and PEG, forming multimolecular micelles and unimolecular micelles respectively.A newly designed chain transfer agent 2-formyl-4-vinylphenyl 2-(dodecylthiocarbonothioylthio)-2-methylpropanoate (FVDMPA) with aldehyde and vinyl was synthesized and copolymerized with N-isopropylacrylamide resulting branched poly(N-isopropylacrylamide). Relation between the number of branched point, branched length and the reaction stoichiometry were investigated. The preserved aldehyde groups in the branched points were used as initiators for ring opening polymerization ofε-caprolactone to form poly(N-isopropylacrylamide)- poly(ε-caprolactone) branched copolymers (bran-PNIPAM-b-PCL). The length of PCL branches was analyzed by 1H NMR.