Starch and starch derivatives are widely utilized pharmaceutical excipients. The concept of this study was to make use of starch as a biodegradable backbone and to modify it with low-toxic, but poor transfecting low molecular weight polyethylenimine (PEI) in order to achieve better transfection efficacy while maintaining enzymatic degradability. A sufficiently controllable conjugation could be achieved via a water-soluble intermediate of oxidized starch and an optimized reaction protocol. Systematic variation of MW fraction of the starch backbone and the amount of cationic side chains (0.8 kDa bPEI) yielded a series of starch-graft-PEI copolymers. Following purification and chemical characterization, nanoscale complexes with plasmid DNA were generated and studied regarding cytotoxicity and transfection efficacy. The optimal starch-graft-PEI polymers consisted of >100 kDa MW starch and contained 30% (wt) of PEI, showing similar transfection levels as 25 kDa bPEI, and being less cytotoxic and enzymatically biodegradable.

Atom transfer radical polymerization (ATRP) was applied to a novel synthesis of prototype copolymer brushes. The procedure included the following steps: (1) free-radical copolymerization of vinylbenzylterminated polystyrene (PS-VB) macromonomer and N-(4-hydroxyphenyl)maleimide gave well-defined alternating comb-shaped copolymers, (2) subsequent esterification reaction [N-(4-hydroxyphenyl)maleimide sites] of such comb-shaped copolymer with 2-bromoisobutyryl bromide yielded a comb-shaped polyinitiator, and (3) the graftingfrom ATRP method of methyl methacrylate (MMA) using comb-shaped polyinitiator provided PS/poly(methyl methacrylate) (PMMA) alternating copolymer brushes. Dilute solution properties and morphological results of both comb-shaped polyinitiator and prototype copolymer brushes were investigated by static and dynamic light scattering and transmission electron microscopy. As a result, prototype copolymer brush composed of short aspect ratio changed the shape from ellipsoid to starlike conformation because both polystyrene (PS) and PMMA side chains were stretched by introduction of PMMA grafted chains.

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Polystyrene (PS)/poly(ethylene oxide) (PEO) prototype brushes were prepared by alternating free-radical copolymerization of methacryloyl-terminated PS and ␣-vinylbenzyl--hydroxy or ␣-vinylbenzyl--perfluoroalkyl (R f ) PEO macromonomers with the addition of Lewis acid (SnCl 4 ). It was found from their dilute-solution properties that PS/PEO end-capped with R f (PBR f ), and PS/PEO having OH groups at terminal ends (PBOH) prototype brushes formed a single molecule in benzene and aggregates in chloroform, respectively. However, the brush PBOH formed a single molecule in N,Ndimethylformamide. Such aggregation behaviors seemed to be caused by the interaction between hydroxy groups of PEO chain ends. The brush PBOH was also converted into PBR ftype brush by chemical modification, using corresponding acid chloride. The substitution of R f groups was ϳ70% due to slipping of terminal hydroxy groups into PEO internal domains.