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Synthesis of micelle-forming cationic block copolymers

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Title: Synthesis of micelle-forming cationic block copolymers
Author(s): Duodu, John
Contributor: University of Helsinki, Faculty of Science, Department of Chemistry
Discipline: Polymer Chemistry
Language: English
Acceptance year: 2014
In this master's thesis research reversible addition-fragmentation chain-transfer polymerization (RAFT) was utilized to synthesize primary and tertiary amine-based cationic copolymers to be utilised as micelles for gene transfer. Materials that were synthesized included 2-aminoethyl methacrylamide hydrochloride (AEMA.HCl) monomer, homopolymers such as polymethyl methacrylate (PMMA) and poly (N,N-dimethylamino ethyl methacrylate) (PDAMEMA), and copolymers such as polymethyl methacrylate-block-poly (2-dimethylamino) ethyl methacrylate (PMMA-b-PDMAEMA), polymethylmethacrylate-block-poly(dimethylamino ethyl methylcrylate-statistical-2-aminoethyl methacrylamide hydrochloride) (PMMA-b-P[DMAEMA-co-AEMA.HCl]) and poly (dimethylamino ethyl methylcrylate-statistical-2-aminoethyl methacrylamide hydrochloride) (P[DMAEMA-co-AEMA.HCl]). Prepared polymers were characterized using nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC) methods. Also, via dialysis method aqueous micelles of PMMA-b-PDMAEMA block copolymer were prepared, and charaterized using dynamic light scattering (DLS). AEMA-hydrochloride monomer was synthesized via amidation process using methacrylic anhydride, and purified by recrystallization in isopropanol. Proton Neutron Magnetic Resonance (1HNMR) results revealed successful synthesis and production of a highly pure monomer. PMMA and PDMAEMA homopolymers of narrow molecular weight distribution were synthesized via RAFT using azobisisobutyronitrile (AIBN) initiator and 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPA) as chain transfer agent (CTA). With PMMA as a macro-CTA and AIBN initator DMAEMA was polymerized resulting in the formation of PMMA-b-PDMAEMA cationic block copolymer. 1HNMR analysis revealed a polymer consisting of PMMA and PDMAEMA blocks, and size exclusion chromatography (SEC) results also indicated production of a polymer with narrow molecular weight distribution. Results from dynamic light scattering (DLS) study showed PMMA-b-PDMAEMA (Mn=~23000 g/mol) diblock copolymer forms micelles with hydrodynamic radius in the range of 10-100 nm when THF-based copolymer solution was dialyzed in water. The size of micelle decreased at higher pH values. With respect to size PMMA-b-PDMAEMA copolymer micelles could be considered suitable for DNA transfer. Also, with AIBN initiator CPA and PMMA were used as CTA and a macro-CTA in two separate reactions to polymerize DMAEMA and AEMA-hydrochloride monomers simultaneously leading to formation of P(DMAEMA-co-AEMA.HCl) and PMMA-b-P(DMAEMA-co-AEMA.HCl) copolymers respectively. It was observed through SEC polymerization occured in both cases and resulting polymers exhibit very narrow molecular weight distribution. However, the molecular nature and composition of both copolymers cannot be reliably predicted based on 1HNMR results due to complications as a result of polymers poor solubility in various NMR solvents.

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