Syntheses And Assembly Kinetics Of Polycations With Multiple Topologies

Polycations are one of the most promising non-viral gene delivery systems due totheir merits in condensation and delivery of DNA. Moreover, the polycationpolyethylenimine (PEI) is one of the most effective reagent. In this dissertation, aseries of block copolymers with particular topologies involving linear, graft, and cyclicdiblock copolymers were prepared in the combination of widely-noted controllingradical polymerizations (CRP), Ring-opening polymerization(ROP), and clickchemistry.On the other hand, previous reports of polycations mainly focused on theirsynthesis and application, much less has been explored concerning the mechanism ontheir ordered colloidal assemblies formation, which is expected to exhibit greatsignificance for various technological processes in practical applications. In currentstudy, the kinetics on their ordered assemblies formation and structural evolution havebeen systematically investigated by stopped-flow with light scattering.The dissertation includes the following six parts:1. The synthesis of poly(ethylene glycol)-g-polyethylenimine (PEI-g-PEG) graftcopolymers. Two series of block copolymers were prepared by grafting linear PEG ontoPEI. In the first series, the PEI (25000) was grafted with varied numbers of PEG blocks(Mn=5000). The second series was composed of copolymers with PEG of differentmolecular weights (Mn=550). In a two-step synthesis, both the activation ofmonomethyl-PEGs(mPEG) and the coupling reactions of the mPEG with PEI wereperformed with hexamethylene diisocyanate (HMDI), leading to water-solublecopolymers with hydrolytically stable urethane and urea bonds. The molecular structureof the resulting copolymers was evaluated by nuclear magnetic resonance (NMR)spectroscopy, gel permeation chromatography (GPC), and fourier transform infraredspectroscopy (FTIR).2. Novel AB diblock copolymers consisting of low molecular weight linear PEI asthe A block and PEG as the B block were prepared. The cationic polymerization of2-ethyl-2-oxazoline (EtOZ) using PEG-bis(tosylate) as a macroinitiator followed byacid hydrolysis afforded linear PEI-PEG diblock copolymers with controlledcompositions. The molecular structure of the resulting copolymers was evaluated spectroscopically (NMR, GPC, and FTIR).3. We report on the preparation of the well-defined cationic polymers cyclicPolyethylenimine (cyclic-PEI) via combine cationic ring-opening polymerization withclick chemistry.-Alkyne-ω-azido heterodifunctional poly(2-ethyl-2-oxazoline)precursor (linear-PEOZ-N3) was prepared by the cationic ring-opening polymerizationof2-ethyl-2-oxazoline in acetonitrile using propargyl p-toluenesulfonate as the initiator,followed by reacting with2-bromoisobutyryl bromide (BIBB) and NaN3to transformthe terminal bromide into azide group. The subsequent end-to-end intramolecularcoupling reaction under high dilution and “click” conditions leads to efficientpreparation of narrow-disperse cyclic-PEOz. Finally, cyclic-PEOz is acid-hydrolyzedto cleave off the N-propionyl groups to yield PEI. GPC,NMR, FT-IR all confirmed thecomplete transformation of2-Ethyl-2-oxazoline to cyclic-PEI.4. Utilizing stopped-flow technique the time-dependent polyplexes formation in response of diverse external stimuli can be monitored in terms of light scattering or fluorescence detectors. A variety of polycations are proposed including polyethyleniminewith different topological structures and molecular weights in order to elucidatethe internal relationship among structural parameters of gene carriers, polyplex formation and gene transfection efficiency.5. The formation of soluble polyion complexes (PICs) from anionic blockcopolymers and cationic block copolymers was investigated by fluorescencespectroscopy, laser light scattering (LLS), and stopped-flow light scattering. Thekinetics of the assembly process was studied via stopped-flow upon direct mixing of thetwo polymer solutions. Thermodynamic studies revealed that spontaneous complexationis entropy driven. The PIC dissociation process was further studied.6. The kinetics of thermo-induced sol-gel transitions in aqueous solution ofpoly(glycidyl methacrylate)-b-poly(β-hydroxypropyl methacrylate)(PGMA-b-PHPMA)were investigated by the stopped-flow temperature jump technique.