A new polymerization method and kinetics for acrylamide: Aqueous two-phase polymerization

Synthesis of block cationic polyacrylamide precursors using an aqueous RAFT dispersion polymerization

Synthesis of cationic polyacrylamides (CPAMs) by introducing cationic polymer precursors followed by chain extension of acrylamide (AM) homopolymer blocks via RAFT polymerization is a promising approach for engineering high-performance CPAMs. However, the aqueous solution polymerization of AM usually leads to high viscosity, thus limiting the solid content in the polymerization system. Herein a novel approach is introduced that uses a random copolymer of AM and methacryloxyethyltrimethyl ammonium chloride (DMC) as a macro RAFT chain transfer agent (mCTA) and stabilizer for aqueous RAFT dispersion polymerization of AM. The AM/DMC random copolymers synthesized by RAFT solution polymerization, having narrow dispersities (Đ _s) at different molecular weights and cationic degrees (C _s), could serve as the mCTA, which was confirmed by mCTA chain extension in aqueous solution polymerization of AM under different C _s, solid contents, AM addition contents, extended PAM block lengths, and mCTA chain lengths. The block CPAMs had a Đ value of less than 1.2. A model was developed using the method of moments with consideration of the diffusion control effect, for further understanding the chain extension kinetics. Predicted polymerization kinetics provided an accurate fit of the experimental data. The AM/DMC random copolymers were further used for aqueous RAFT dispersion polymerization of AM under different polymerization temperatures, C _s, and mCTA chain lengths. The resulting products had a milky appearance, and the block copolymers had Đ _s of less than 1.3. Higher C _s and longer chain lengths on mCTAs were beneficial for stabilizing the polymerization systems and produced smaller particle sizes and less particle aggregation. The products remained stable at room temperature storage for more than a month. The results indicate that aqueous RAFT dispersion polymerization using random copolymers of AM and DMC at moderate cationic degrees as a stabilizer and mCTA is a suitable approach for synthesizing CPAM block precursors at an elevated solid content.

Role of salt in the aqueous two-phase copolymerization of acrylamide and cationic monomers: from screening to anion-bridging

Mechanism for the anions effect on the aqueous two-phase copolymerization (ATPP) of acrylamide and cationic monomers in poly(ethylene glycol) (PEG) aqueous solution was proposed.

Location and Influence of Added Block Copolymers on the Droplet Size in Oil-in-Oil Emulsions

We have investigated the effect of added polystyrene-b-poly(ethylene oxide) (SO) copolymer on the stability of oil-in-oil (O/O) emulsions containing polystyrene (PS) and poly(ethylene glycol) (PEG) in chloroform (CHCl3) and directly visualized the location of SO in the emulsions by using dye-labeled SO (SO*) with confocal laser scanning microscopy (CLSM). The emulsion formed by PS/PEG/CHCl3 = 14/6/80 (wt %) consisted of a droplet phase of PS in CHCl3 and a continuous phase containing PEG in CHCl3. SO*s with various molecular weights (Mn,SO) and volume fractions of the PS block in SO (fPS) were prepared via living anionic polymerization and subsequent end-esterification. The effect of SO on the droplet size in the emulsions was investigated as a function of both Mn,SO and fPS. Increasing Mn,SO and decreasing fPS were effective at reducing the droplet size down to less than 1 μm, which is 100 times smaller than in the absence of SO. The location of SO*s in the O/O emulsions was further investigated by CLSM. We found that the location of SO*s changed from the droplet interior to the liquid-liquid interface and then to the continuous phase with decreasing fPS. We discuss the possible mechanism in terms of the relation of SO* location to the droplet size.

A novel and controllable route for preparing high solid-content and low-viscosity poly(acrylamide-co-acrylic acid) aqueous latex dispersions

High solid-content and low-viscosity poly(acrylamide-co-acrylic acid) aqueous latex dispersions were obtained through a novel strategy, which involves swelling followed by diffusion and redox initialized polymerization inside the seed particle.

Unique multiple soluble-insoluble phase transitions in aqueous two-phase copolymerization of acrylamide and a weakly charged comonomer

A unique phenomenon of multiple soluble-insoluble phase transitions was found in the two-phase copolymerization of acrylamide (AM) and a weakly charged comonomer, N,N-dimethylaminoethyl methacrylate (DMAEMA), in the aqueous solution of poly(ethylene glycol) (PEG). As the DMAEMA molar fraction increased from 0 to 0.30, the insoluble-soluble (I-S) phase transition first appeared and then disappeared. Varying the PEG concentration, the salt concentration, or the pH of reaction mixture, the phase transitions were tuned dependently. The volume fractions and refractive indices of continuous and disperse phases, as well as the viscosity change in the phase transitions were investigated, and the results showed that phase reentrance had occurred in the I-S phase transition. The transitional conversion for the first S-I phase transition increased with the DMAEMA molar fraction, indicating the solubility enhancement of charged polyelectrolytes. The content of DMAEMA in the resulting copolymer first increased and then decreased as the polymerization progressed. Accordingly, the droplet size increased in the two S-I phase transitions and decreased in the I-S phase transition. And it was proved that the copolymers were molecularly solubilized after the I-S phase transition. The multiple soluble-insoluble phase transitions were ascribed to the synergistic effect of polymer concentration, solubility enhancement of charged copolymers, and the salting-out effect of ionic comonomers. A generalized mechanism for the multiple soluble-insoluble phase transitions was proposed, which showed that the effects of polymer concentration were dominant in the two S-I phase transitions, while the effects of solubility enhancement played a key role in the I-S phase transition.

Water-in-water emulsions based on incompatible polymers and stabilized by triblock copolymers-templated polymersomes

Aqueous solutions containing a mixture of polyethylene glycol (PEG) and dextran homopolymers form an aqueous two-phase system which can be emulsified to give a water-in-water emulsion. We show how these emulsions can be stabilized using triblock polymers containing poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA), poly (n-butyl methacrylate) (BuMA), and poly[2-(dimethylamino) ethyl methacrylate] (DMAEMA) blocks of general structure Pp-Bb-Dd, in which the middle BuMA block is hydrophobic. Low-energy input stirring of mixtures containing equal volumes of PEG- and dex-rich aqueous phases plus 1 wt % of Pp-Bb-Dd stabilizer all form dex-in-PEG emulsions (for the range of Pp-Bb-Dd triblock polymers used here) which have a polymersome-like structure. In favorable cases, the emulsion drop (or templated polymersome) sizes are a few micrometers and are stable for periods in excess of 6 months. The emulsions can be inverted from dex-in-PEG to PEG-in-dex by increasing the volume fraction of dex-rich aqueous phase. We demonstrate that both high and low molecular weight fluorescent solutes "self-load" into either the dex- or PEG-rich regions and that solute mass transfer across the water-water interface occurs on a timescale of less than 1 min.