3 research outputs found
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 [polyÂ(<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 polyÂ(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), PMeO<sub>2</sub>MA. 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 PMeO<sub>2</sub>MA, i.e., PTMA<sup>+</sup><sub><i>x</i></sub>-<i>g</i>-(PMeO<sub>2</sub>MA<sub><i>n</i></sub>)<sub><i>y</i></sub>. They were investigated using variable-temperature turbidity, photon correlation spectroscopy (PCS), electrophoretic mobility, and <sup>1</sup>H 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
PEGylation of Nanosubstrates (Titania) with Multifunctional Reagents: At the Crossroads between Nanoparticles and Nanocomposites
Titania (anatase) nanoparticles were successfully PEGylated
through
the use of catechol (dopamine)-terminated PEG derivatives. The resulting
materials were characterized by excellent stability at neutral pH
and extremely low toxicity (phagocytic and nonphagocytic cell lines).
In
particular, we focused on the comparison between mono- and bis-catechol
PEGs. Due to the double terminal anchorage on the titania surface,
bis-catechol ligands can produce chains differing from classical monoanchored
PEG in conformation (horseshoe-shaped vs brush) and thus the possibility
of interactions with biomolecules. At the same time, less than quantitative
catechol binding may lead to the presence of dangling chains with
unbound catechols which can polymerize and eventually produce PEG/titania
nanocomposite colloids. Our results on double-functional PEG2000 show
the latter to be the case. Pluronic F127 was also used as a bifunctional
ligand, leading to nanocomposite aggregates with an even larger organic
content