Effects of Core Microstructure on Structure and Dynamics of Star Polymer Melts: From Polymeric to Colloidal Response

The structure and linear viscoelastic behavior of four different model star polymer melts were investigated experimentally. The star polymers were prepared via different synthetic routes based on atom transfer radical polymerization (ATRP). Stars with small elongated (linear backbone) cores exhibited slight differences in the asymmetry of the core, which however did not affect the rheological properties significantly. The relaxation behavior of these stars with an asymmetric core was well-described by available tube models. On the other hand, stars with large cross-linked cores exhibited a core–shell morphology and their stress relaxation was dominated by a power-law decay over about 8 decades, akin to gel-like soft systems. This behavior reflected their liquid-like ordering and small intercore distances, and bares analogueies to that of interpenetrating soft colloids and microgels

Synthesis of Poly(OEOMA) Using Macromonomers via “Grafting-Through” ATRP

Atom transfer radical polymerization (ATRP) of oligo­(ethylene oxide) methyl ether methacrylate (OEOMA, <i>M</i>_n = 950 or 2080; OEOMA is also termed poly­(ethylene glycol) methyl ether methacrylate, PEGMA) macromonomers was investigated as a function of initial monomer concentration, [OEOMA]₀, ranging from 50 to 300 mM, and up to 4.5 kbar. Polymerizations were successfully carried out in organic solvents with [OEOMA]₀ > 75 mM, whereas with [OEOMA]₀ = 50 mM no monomer conversion was observed at ambient pressure, indicating that the macromonomer concentration was below its equilibrium monomer concentration ([M]_e). High pressure reduced [M]_e to a level lower than under ambient pressure, allowing polymerization at [OEOMA]₀ = 50 mM up to high monomer conversion and yielding polymers with narrow molecular weight distribution. By varying the targeted degree of polymerization of OEOMA, brushlike or starlike poly­(OEOMA) were prepared under both ambient and high pressure

Star Polymers with a Cationic Core Prepared by ATRP for Cellular Nucleic Acids Delivery

Poly­(ethylene glycol) (PEG)-based star polymers with a cationic core were prepared by atom transfer radical polymerization (ATRP) for in vitro nucleic acid (NA) delivery. The star polymers were synthesized by ATRP of 2-(dimethylamino)­ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA). Star polymers were characterized by gel permeation chromatography, zeta potential, and dynamic light scattering. These star polymers were combined with either plasmid DNA (pDNA) or short interfering RNA (siRNA) duplexes to form polyplexes for intracellular delivery. These polyplexes with either siRNA or pDNA were highly effective in NA delivery, particularly at relatively low star polymer weight or molar ratios, highlighting the importance of NA release in efficient delivery systems

Preparation of Cationic Nanogels for Nucleic Acid Delivery

Cationic nanogels with site-selected functionality were designed for the delivery of nucleic acid payloads targeting numerous therapeutic applications. Functional cationic nanogels containing quaternized 2-(dimethylamino)­ethyl methacrylate and a cross-linker with reducible disulfide moieties (qNG) were prepared by activators generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) in an inverse miniemulsion. Polyplex formation between the qNG and nucleic acid exemplified by plasmid DNA (pDNA) and short interfering RNA (siRNA duplexes) were evaluated. The delivery of polyplexes was optimized for the delivery of pDNA and siRNA to the Drosophila Schneider 2 (S2) cell-line. The qNG/nucleic acid (i.e., siRNA and pDNA) polyplexes were found to be highly effective in their capabilities to deliver their respective payloads