Negatively charged polystyrene latex was synthesized, and a copolymer shell of 2-(methyl-2′-chloropropionato)ethyl acrylate (HEA-Cl) and styrene was added, from which poly(N,N-dimethylacrylamide) (PDMA) was polymerized by atom transfer radical polymerization in aqueous suspension at room temperature. Increasing monomer concentration in the presence of CuCl or CuBr and one of three ligands (N,N,N′,N′,N′′-pentamethyldiethylenetriamine (PMDETA), 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), and tris[2-(dimethylamino)ethyl]amine (Me 6TREN)) produced grafts whose molecular weight increased to over 600 000 and polydispersities in the range of 1.3-1.8, determined from chains recovered following cleavage by base. Hydrodynamic brush thicknesses were 70-800 nm, and average chain separations, calculated from Mn and the mass of polymer recovered per particle, varied from 4.0 to 1.1 nm. Very high grafting densities were achieved with good molecular weight control, the highest densities yet reported for high molecular weight polymer chains grown from a surface. Control of the polymerization was improved by addition of Cu(II) to enhance deactivation of free radicals, by including a low concentration of exogenous hydrophobic initiator at high monomer concentration and by reducing latex concentration. Increasing the concentration of exogenous initiator reduced graft thickness but eliminated control over the polydispersity. The unusual conditions required for optimization of the reaction and the observation of decreasing chain separation as M n increased were explained by invoking a model of the particle surface that took into account the finite depth and high copolymer concentration of the region in which chains were initiated and particularly the fixed charges due to the sulfate initiator of shell copolymerization.
In this study, we investigate the complex formation behavior of random copolymers (RCPs) of methoxy
poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium
chloride (MAPTAC) with oppositely charged surfactant sodium dodecyl sulfate (SDS), which could be used
as a potential system in the field of drug/gene delivery research. A series of copolymers from MePEGMA
and cationic monomer MAPTAC were synthesized and characterized by 1H NMR and static light scattering
techniques. The complexation of SDS with synthesized cationic RCPs was investigated by turbidimetric
titration, steady-state fluorescence, light scattering, particle size analysis, and ζ-potential measurement.
Studies revealed that these complexes are qualitatively similar to the polyion complex micelles or block
ionomer complexes obtained from the block copolymers and oppositely charged surfactants. The complexes
obtained appear to be micelle-like aggregates with a core formed by the dodecyl sulfate neutralized cationic
unit of the polymer and a shell of threaded poly(ethylene glycol) units. The formation of hydrophobic
domains occurs at an SDS concentration which is about 2 orders of magnitude lower than its critical micelle
concentration. Copolymers with higher poly(ethylene glycol) content form hydrophobic domains at higher
SDS concentration. The solution behavior of these complexes mainly depends on the composition of cationic
and nonionic units present in the copolymers. Complexes with stoichiometric compositions of cationic units
of the copolymer and SDS are electroneutral. The sizes of the complexes vary from 30 to 70 nm depending
on the copolymer and the composition. The polarity index obtained from the pyrene fluorescence experiment
shows that they are highly hydrated. Overall, these complexes represent an additional class of lyophilic
colloids that could be used as a promising system in addressing various basic and practical problems in
drug delivery challenges.
DNA by virtue of its superlative ability to self-assemble has found use beyond biological research in the design and fabrication of nanomaterials. However, developing novel DNA-based materials for chemical applications might be restricted due to the insoluble nature of DNA in most common organic solvents. In this Communication, we are reporting the first demonstration of making DNA soluble in a variety of nonbiological solvents such as acetonitrile, benzene, dimethyl sulfoxide (DMSO), and tetrahydrofuran with the help of poly(ethylene glycol) (PEG)-based cationic random copolymers. Because of complex formation between cationic copolymer and anionic DNA, nanoparticles are formed. These nanoparticles are expected to exhibit micelle-like structures with a nanometric core of cationic units neutralized by phosphate anions of DNA, surrounded by a shell of PEG segments. As PEG is soluble in the organic solvents used in this study, nanoparticles are stable in these solvents, making entrapped DNA soluble in these organic solvents.
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