One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(<i>N</i>-vinyl formamide)

In this study we report the preparation of a new family of core–shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core–shell PNVF-<i>x</i>GMA [poly­(<i>N</i>-vinylformamide-<i>co</i>-glycidyl methacrylate)] particles (where <i>x</i> is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable “cane-ball”-like morphology with interconnected ridges, and this could be controlled by the value for <i>x</i>. The particle size was tunable over the range 0.8–1.8 μm. Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly­(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by <i>x</i>. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-<i>x</i>GMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels

Thermally Triggered Assembly of Cationic Graft Copolymers Containing 2-(2-Methoxyethoxy)ethyl Methacrylate Side Chains

Thermoresponsive copolymers continue to attract a great deal of interest in the literature. In particular, those based on ethylene oxide-containing methacrylates have excellent potential for biomaterial applications. Recently, some of us reported a study of thermoresponsive cationic graft copolymers containing poly(<i>N</i>-isopropylacrylamide), PNIPAm, (Liu et al., <i>Langmuir</i>, <b>24</b>, 7099). Here, we report an improved version of this new family of copolymers. In the present study, we replaced the PNIPAm side chains with poly(2-(2-methyoxyethoxy)ethylmethacrylate), PMeO₂MA. These new, nonacrylamide containing, cationic graft copolymers were prepared using atom transfer radical polymerization (ATRP) and a macroinitiator. They contained poly(trimethylamonium)-aminoethyl methacrylate and PMeO₂MA, i.e., PTMA⁺_<i>x</i>-<i>g</i>-(PMeO₂MA_<i>n</i>)_<i>y</i>. They were investigated using variable-temperature turbidity, photon correlation spectroscopy (PCS), electrophoretic mobility, and ¹H NMR measurements. For one system, four critical temperatures were measured and used to propose a mechanism for the thermally triggered changes that occur in solution. All of the copolymers existed as unimolecular micelles at 20 °C. They underwent reversible aggregation with heating. The extent of aggregation was controlled by the length of the side chains. TEM showed evidence of micellar aggregates. The thermally responsive behaviors of our new copolymers are compared to those for the cationic PNIPAm graft copolymers reported by Liu et al. Our new cationic copolymers retained their positive charge at all temperatures studied, have high zeta potentials at 37 °C, and are good candidates for conferring thermoresponsiveness to negatively charged biomaterial surfaces