A novel bottom-up approach to obtain polymer nanocomposites using cubic silsesquioxanes (POSS) nanoparticles as building blocks is reported. The design is based on associative interaction between particles to form ordered nanostructure and limited crystal growth to render anisotropic shapes. Specifically, the affinity between POSS units causes these particles to aggregate and closely pack into a crystalline lattice. The organic polymer, covalently connected to each POSS unit, limits the crystallization into a two-dimensional lattice as demonstrated in random copolymers of polybutadiene and cubic silsesquioxanes. The copolymers were synthesized by ring-opening metathesis copolymerization of cyclooctadiene and POSS bearing a polymerizable norbornene group. The polymers were characterized using NMR, DSC, TEM, WAXD, and SAXS. The data from TEM and X-ray diffraction clearly show the formation of two-dimensional lamellar-like nanostructures of assembled cubic silsesquioxanes.
A heterobifunctional polyethylene glycol (PEG) derivative possessing both "click" and electrophilic functionalities was prepared for use in bioconjugation applications. We utilized a dibenzyl-protected amine functional initiator to prepare high purity amino-PEG-alcohol by the polymerization of ethylene oxide. Subsequent chain-end modification of the heterobifunctional PEG afforded the desired N-hydroxy succinimidyl-PEG-azide derivative in 33% overall yield. This PEG derivative allows for versatile bioconjugation chemistry where activated ester chemistry and "click" chemistry can be selectively performed, an area of orthogonal bioconjugation that has not previously been accessible.
Cationic polymers have received much attention as promising nonviral vectors for gene transfer. However, development of polymers with low cell toxicities and high transfection efficiencies continue to be a significant problem and a major hurdle to their success. Poly-D/L aspartate-diethylenetriamine poly(D/L Asp-DET) polymers were synthesized and evaluated as nonviral gene delivery agents. Poly(D/L Asp-DET) polymers display endosome buffering capacity. The polymers condense plasmid DNA above N:P ratios of 1 and form polyplex particles of $50-100 nm, with zeta potentials between neutral and þ40 mV. Transmission electron microscopy shows the polyplexes to be uniform in size and shape. Polyplexes maintain the structural integrity of DNA following incubation in nucleases and also show high transfection efficiencies with minimal toxicity in both HCT-116 and PC-3 cell culture. However, it is found that these poly(D/L Asp-DET)/DNA polyplexes immediately aggregate in salt and serum conditions, making them unsuitable for use in vivo. Therefore, the polyplexes were further modified by covalent addition of polyethylene glycol (PEG). Introduction of this second step produces PEG-polyplexes of uniform size (below 100 nm), with neutral zeta potentials that are also stable in both salt and serum conditions. These results suggest poly(D/L Asp-DET) cationic polymers as potentially safe and efficient nonviral gene delivery agents. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: [836][837][838][839][840][841][842][843][844][845][846][847][848][849][850] 2012
Long‐chain heteroatom‐containing telechelic diols with 29–32 atoms in the backbone were synthesized by a one‐step, free‐radical telomerization of 10‐undecene‐1‐ol with commercially available α,ω‐dithiols. The oxygen and sulfur atoms caused a decrease in the melting point and enthalpy of the diols, compared to the corresponding purely aliphatic diols. The heteroatom‐containing α,ω‐diols HO(CH2)11S(CH2)2X(CH2)2S(CH2)11OH, where X = CH2, O, or O(CH2)2O, were reacted in the melt with 1,6‐diisocyanatohexane OCN(CH2)6NCO, producing a series of polyurethanes containing an increasing amount of heteroatoms. Characterization by differential scanning calorimetry, infra‐red spectroscopy, thermogravimetric analysis, and wide angle x‐ray scattering of the m,n‐polyurethane series showed that, like the telechelic diols they were synthesized from, the heteroatoms caused a decrease in the melting point and enthalpy. However, they did not affect either the decomposition temperature or the crystal structure/packing.Typical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.magnified imageTypical decomposition behavior of all the heteroatom‐containing m,6‐polyurethane.
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