Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed for the preparation of homopolymer and copolymer (co)networks based on four monomer units, belonging to three monomer types: methacrylates, acrylates, and styrenics. In particular, n-butyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) (hydrophobic and hydrophilic-ionizable methacrylate monomers, respectively), n-butyl acrylate (hydrophobic) and styrene (hydrophobic) were used. Amphiphilic block copolymer conetworks were prepared by RAFT via the cross-linking of linear triblock copolymer precursors possessing two active polymer ends, which were subsequently interconnected by chemical cross-linking to a three-dimensional network, by using the appropriate cross-linker: ethylene glycol dimethacrylate for methacrylates, ethylene glycol diacrylate for acrylates, and 1,4-divinylbenzene for styrenics. The homopolymer and copolymer precursors to the (co)networks were characterized by gel permeation chromatography and 1 H NMR spectroscopy for their molecular weights and compositions, respectively. The degrees of swelling (DSs) of all (co)networks were determined in tetrahydrofuran and, where the ionizable (DMAEMA) was present, the DSs were also measured in neutral and acidic water. The conetworks swelled more in acidic than in neutral water due to the ionization of their DMAEMA units.
The quality of surface coating of magnetic nanoparticles destined as nanoprobes in clinical applications is of utmost significance for their colloidal stability and biocompatibility. A novel approach for the fabrication of such a coating involves the synthesis of well-defined diblock copolymers based on 2-(acetoacetoxy)ethyl methacrylate (chelating) and poly(ethylene glycol)methyl ether methacrylate (water-soluble, thermoresponsive), prepared by reversible addition-fragmentation chain transfer polymerization. Fabrication of magneto-responsive micelles was accomplished via chemical coprecipitation of Fe(III)/Fe(II) in the presence of diblock copolymers. Further to the characterization of micellar morphologies, optical and thermal properties, assessment of magnetic characteristics disclosed superparamagnetic behavior. The hybrid micelles did not compromise cell viability in cultures, while in vitro uptake by macrophage cells was significantly lower in comparison to that of the clinically applicable contrast agent Resovist, suggesting that these systems can evade rapid uptake by the reticuloendothelial system and be useful agents for in vivo applications.
Four linear amphiphilic multiblock copolymers based on 2-(dimethylamino)ethyl methacrylate (DMAEMA, hydrophilic) and methyl methacrylate (MMA, hydrophobic), bearing from two to five blocks, were synthesized using reversible addition-fragmentation chain transfer polymerization and stepwise monomer additions. The degree of polymerization of each hydrophilic polyDMAEMA block was ∼50, while that of the hydrophobic polyMMA blocks was ca. 20. The stepwise monomer addition procedure secured that each higher multiblock was composed of its immediately lower homologue plus exactly one extra block. The molecular weights (MW) of the synthesized (co)polymers, as measured by gel permeation chromatography (GPC), were close to the theoretically expected. GPC also indicated rather narrow molecular weight distributions which, however, broadened with the number of blocks. The compositions of the copolymers, as determined by proton nuclear magnetic resonance spectroscopy, were also close to the expected values. The cloud points of the copolymers, measured by turbidimetry, were found to increase with the number of blocks. The sizes of the micelles formed by the copolymers in aqueous solution were characterized using dynamic light scattering and small-angle neutron scattering. The determined values of the hydrodynamic radii, the radii of gyration, and the aggregation numbers of the micelles increased slightly with the block number from the triblock to the pentablock copolymer, implying extensive folding of the chains of the tetrablock and the pentablock copolymers in their micelles. The aggregation number of the tetrablock copolymer was approximately one-half that of the diblock copolymer whose unimer MW was onehalf that of the tetrablock, suggesting that the micellar cores of these two types of micelles were composed of the same number of hydrophobic units.
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