Octadecyl acrylate – Methyl methacrylate block and gradient copolymers from ATRP: Comb-like stabilizers for the preparation of micro- and nano-particles of poly(methyl methacrylate) and poly(acrylonitrile) by non-aqueous dispersion polymerization

Inhibiting the Thermal Gelation of Copolymer Stabilized Nonaqueous Dispersions and the Synthesis of Full Color PMMA Particles

Polymeric particle dispersions have numerous potential applications; currently one of the most relevant is their use as inks in electrophoretic displays. These colloidal particles are synthesized from the appropriate monomer using nonaqueous dispersion (NAD) polymerization in a nonpolar solvent, which requires a stabilizer to control particle size and morphology. We have previously reported the facile synthesis of poly(methyl methacrylate)-block-poly(octadecyl acrylate) (PMMA-b-PODA) by atom transfer radical polymerization (ATRP), and its use in the NAD polymerization of MMA in hexane/dodecane solvent mixtures. Here we report the synthesis of monodisperse PMMA particles in dodecane following a standard "industrial" procedure using these PMMA-b-PODA stabilizers. However, it was observed that the particle suspensions solidified when they were left at temperatures below ∼18 °C yet redispersed upon being heated. Differential scanning calorimetry, dynamic light scattering, and rheological studies demonstrated that this thermoresponsive behavior was due to a liquid-gel transition occurring at 17.5 °C as a consequence of the upper critical solution temperature of PODA in dodecane being traversed. Consequently, new copolymers were synthesized by ATRP with an ethylhexyl acrylate (EHA) co-monomer incorporated into the lyophilic (dodecane compatible) block. Dispersions stabilized by these PMMA-b-P(ODA-co-EHA) polymers with high EHA contents exhibited lower gelation temperatures because of the greater solvent compatibility with dodecane. The use of a PMMA65-b-(ODA10-co-EHA45) copolymer stabilizer (with the highest EHA content) gave PMMA dispersions that showed no gelation down to 4 °C and monodisperse cross-linked PMMA particles containing organic dyes (cyan, magenta, red, and black) giving colored particles across the size range of approximately 100-1300 nm.

Thermodynamic Interactions between Polystyrene and Long-Chain Poly(n-Alkyl Acrylates) Derived from Plant Oils

Vegetable oils and their fatty acids are promising sources for the derivation of polymers. Long-chain poly(n-alkyl acrylates) and poly(n-alkyl methacrylates) are readily derived from fatty acids through conversion of the carboxylic acid end-group to an acrylate or methacrylate group. The resulting polymers contain long alkyl side-chains with around 10-22 carbon atoms. Regardless of the monomer source, the presence of alkyl side-chains in poly(n-alkyl acrylates) and poly(n-alkyl methacrylates) provides a convenient mechanism for tuning their physical properties. The development of structured multicomponent materials, including block copolymers and blends, containing poly(n-alkyl acrylates) and poly(n-alkyl methacrylates) requires knowledge of the thermodynamic interactions governing their self-assembly, typically described by the Flory-Huggins interaction parameter χ. We have investigated the χ parameter between polystyrene and long-chain poly(n-alkyl acrylate) homopolymers and copolymers: specifically we have included poly(stearyl acrylate), poly(lauryl acrylate), and their random copolymers. Lauryl and stearyl acrylate were chosen as model alkyl acrylates derived from vegetable oils and have alkyl side-chain lengths of 12 and 18 carbon atoms, respectively. Polystyrene is included in this study as a model petroleum-sourced polymer, which has wide applicability in commercially relevant multicomponent polymeric materials. Two independent methods were employed to measure the χ parameter: cloud point measurements on binary blends and characterization of the order-disorder transition of triblock copolymers, which were in relatively good agreement with one another. The χ parameter was found to be independent of the alkyl side-chain length (n) for large values of n (i.e., n > 10). This behavior is in stark contrast to the n-dependence of the χ parameter predicted from solubility parameter theory. Our study complements prior work investigating the interactions between polystyrene and short-chain polyacrylates (n ≤ 10). To our knowledge, this is the first study to explore the thermodynamic interactions between polystyrene and long-chain poly(n-alkyl acrylates) with n > 10. This work lays the groundwork for the development of multicomponent structured systems (i.e., blends and copolymers) in this class of sustainable materials.

One-step preparation of uniform cane-ball shaped water-swellable microgels containing poly(N-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-xGMA [poly(N-vinylformamide-co-glycidyl methacrylate)] particles (where x 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 x. 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 x. 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-xGMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels.