Design And Synthesis Of Aldehyde-functionalized Polymers

Synthesis of well-defined reactive functional polymers is an emerging research area in polymer science. Recent advances in"living"/controlled polymerization and"click"chemistry reaction techniques have facilitated access to synthesize well-defined complex architectures, controlled molecular weights, and precisely composition functional polymers; also expanding their application in biomedical and nanotechnology. Taking advantage of the tolerance to a wide range of monomers and mild reaction conditions, reversible addition-fragmentation chain transfer (RAFT) polymerization appeared to be the most versatile process in term of the architecture design among the"living"/controlled radical polymerization techniques. Herein, a series of novel complex architectures multi-functional materials involving organic/inorganic hybrid nanoparticles, star-graft and block copolymers were prepared by RAFT polymerization. The properties and potential application were also studied. The present dissertation consists of four chapters:Chapter 1 discribes the synthesis of magnetic, Reactive and thermoresponsive Fe3O4 nanoparticles via surface initiated RAFT copolymerization of N-isopropylacrylamide and acrolein. A RAFT agent was directly anchored onto Fe3O4 nanoparticles in a simple procedure employing a ligand exchange reaction of S-1-dodecyl-S?-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate (DDMAT) with oleic acid initially present on the surface of pristine Fe3O4 nanoparticles. The RAFT agent-functionalized Fe3O4 nanoparticles were then used for the surface initiated RAFT copolymerization of N-isopropylacrylamide (NIPAM) and acrolein to fabricate structurally well-defined hybrid nanoparticles with reactive and thermoresponsive poly(N-isopropylacrylamide-co-acrolein) shell and magnetic Fe3O4 core. Evidence of a well-controlled surface initiated RAFT copolymerization was gained from a linear increase of number-average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive and thermoresponsive core-shell nanoparticles exhibited temperature-trigged magnetic separation behavior and high ability to immobilize model protein BSA.Chapter 2 presents the synthesis of reactive and electrochemical active amphiphilic diblock copolymers and their redox-responsive micelles. Amphiphilic block copolymer with a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block containing the combination of reactive aldehyde and redox-active ferrocene groups was synthesized by RAFT polymerization of our previously designed monomer 2-formal-4-vinylphenyl ferrocenecarboxylate (FVFC) using a monomethoxy-terminated PEO-based macro-chain transfer agent. The structure and self-assembly behaviors of the copolymer were characterized. Aminooxy model drug, O-benzylhydroxylamine (BHA) was then conjugated to PEO-b-PFVFC via oxime linkages, generating PEO-b-PFVFC-BHA conjugate. The electrochemical behaviors of the conjugate were evaluated by cyclic voltammetry. The peak (oxidation or reduction) positions depended on the amount of the conjugated BHA, allowing one to detect quantificationally the conjugated molecules by simply measuring the change in potential response of cyclic voltammogram. Also the redox-responsive micellar properties of the conjugates were investigated by combination of UV-vis spectroscopy and scanning electron microscopy (SEM) and dynamic light scattering (DLS). The resulting PEO-b-PFVFC may combine potential applications such as bioconjugation, electrochemical detection and redox-controlled release of encapsulants.Chapter 3 focuses on the synthesis and characterization of amphiphilic star-graft copolymer. RAFT copolymerization of styrene (St) and acrolein (Ac) was achieved using AIBN as the initiator and S-1-dodecyl-S?-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate (DDMAT) as the RAFT agent at 60?C in THF. The polymerization exhibited first-order kinetics and the molecular weight increased linearly with increase of monomer conversion. Well defined aldehyde-functionalized copolymer poly(St-co-Ac) was prepared as characterized with SEC and NMR analysis. Star polymers with aldehyde-functionalized arms were then obtained by RAFT polymerization of divinyl benzene (DVB) using poly(St-co-Ac) as a macro-chain transfer agent (CTA) via arm-first approach. The aldhyde functionalized poly (St-co-Ac)m-polyDVB star polymers were subsequently used to couple the aminooxy-functionalized poly (ethylene oxide) (PEO-ONH2) via aldehyde-aminooxy click reaction, leading to the formation of amphiphilic poly (St-co-Ac)m-g-PEO-polyDVB star-graft copolymer. The crystalline and self-assembly behavior were investigated with polarized optical micrographs (POM) and transmission electron microscopy (TEM), and dynamic light scattering (DLS) respectively.Chapter 4 is directed to the synthesis of aldehyde-functionalized biodegradable amphiphilic copolymer for bioconjugation. RAFT copolymerization of 4-vinylbenzaldehyde (VBA) and 5,6-benzo-2-methylene-1,3- dioxepane (BMDO) was carried out in 2-butanone at 80oC using AIBN as the initiator and a monomethoxy-terminated PEO-based macro-chain transfer agent . Owing to the incorporation of BMDO units, the obtained PEO-b-(VBA-co-BMDO) block copolymers were degradable. The aldehyde bearing block copolymers could conjugate with aminooxy functionalized cholesterol via oxime linkages to form PEO-b-(VBA-co-BMDO)-cholesterol bioconjugate, which self-assemble into monodispersed nanometers scale micelles in aqueous solution.