Guangqun Zhai

Radical emulsion polymerization with chain transfer monomer: an approach to branched vinyl polymers with high molecular weight and relatively narrow polydispersity

Radical polymerization with 3-mercapto hexyl methacrylate as the chain transfer monomer (CTM) to prepare branched vinyl polymers with high molecular weights and relatively narrow polydispersities has been carried out in aqueous emulsion. Potassium persulfate was used as the initiator, and sodium dodecyl benzene sulfate or hexadecyl trimethyl ammonium bromide was used as the emulsifier. The obtained polymers were characterized using NMR and size exclusion chromatography. Compared with polymers obtained from solution polymerization and results reported in the literature, branched polymers can be prepared at higher monomer/branching monomer feed ratios (100/25) with high monomer conversion (usually >95%) without gelation. The obtained branched polymers also showed considerably higher molecular weights and relatively narrower polydispersities at the same feed ratio of monomer/branching monomer. The unique radical termination mechanism in emulsion reaction determines that soluble branched polymers with high molecular weight and relatively narrow polydispersity can be prepared at a wide range of monomer/CTM feed ratios without gelation.

Quadrangular Prism: A Unique Self‐Assembly from Amphiphilic Hyperbranched PMA‐b‐PAA

The novel hyperbranched poly(methyl acrylate)-block-poly(acrylic acid)s (HBPMA-b-PAAs) are successfully synthesized via single-electron transfer-living radical polymerization (SET-LRP), followed with hydrolysis reaction. The copolymer solution could spontaneously form unimolecular micelles composed of the hydrophobic core (PMA) and the hydrophilic shell (PAA) in water. Results show that the size of spherical particles increases from 8.18 to 19.18 nm with increased pH from 3.0 to 12.0. Most interestingly, the unique regular quadrangular prisms with the large microstructure (5.70 μm in length, and 0.47 μm in width) are observed by the self-assembly of unimolecular micelles when pH value is below 2. Such self-assembly behavior of HBPMA-b-PAA in solution is significantly influenced by the pH cycle times and concentration, which show that increased polymer concentration favors aggregate growth.

Polymerization behaviors and polymer branching structures in ATRP of monovinyl and divinyl monomers

Polymerization behaviors and polymer branching structures in atom transfer radical polymerizations of styrene with 1,6-bismaleimidohexane (BMIH), tri-ethylene glycol dimethacrylate (tri-EGDMA) and divinylbenzene (DVB) as the branching agents have been studied, the mole ratio of monomer to branching agent is 30/1.0. Their polymerization behaviors are quite different because of the different levels of interaction between styrene and the branching agents. The charge transfer complex effect between BMIH and styrene causes core-formation. The DVB system exhibits the slowest evolution of branching because there is no interaction between styrene and DVB. The branching structure indicator b(g′ = gb) from the Zimm branching factor at the same molecular weight proves that polymers formed in the tri-EGDMA and DVB systems are randomly branched molecules because tri-EGDMA and DVB were randomly distributed in their primary chains, while the BMIH system contained randomly branched molecules besides the star-like molecules due to the subsequent coupling reactions between the branched molecules after core-formation.