Ke Min

Diminishing catalyst concentration in atom transfer radical polymerization with reducing agents

The concept of initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) is introduced, whereby a constant source of organic free radicals works to regenerate the CuI activator, which is otherwise consumed in termination reactions when used at very low concentrations. With this technique, controlled synthesis of polystyrene and poly(methyl methacrylate) (Mw/Mn < 1.2) can be implemented with catalyst concentrations between 10 and 50 ppm, where its removal or recycling would be unwarranted for many applications. Additionally, various organic reducing agents (derivatives of hydrazine and phenol) are used to continuously regenerate the CuI activator in activators regenerated by electron transfer (ARGET) ATRP. Controlled polymer synthesis of acrylates (Mw/Mn < 1.2) is realized with catalyst concentrations as low as 50 ppm. The rational selection of suitable Cu complexing ligands {tris[2-(dimethylamino)ethyl]amine (Me6TREN) and tris[(2-pyridyl)methyl]amine (TPMA)} is discussed in regards to specific side reactions in each technique (i.e., complex dissociation, acid evolution, and reducing agent complexation). Additionally, mechanistic studies and kinetic modeling are used to optimize each system. The performance of the selected catalysts/reducing agents in homo and block (co)polymerizations is evaluated.

Atom transfer radical polymerization in aqueous dispersed media

During the last decade, atom transfer radical polymerization (ATRP) received significant attention due to its exceptional capability of synthesizing polymers with pre-determined molecular weight, well-defined molecular architectures and various functionalities. It is economically and environmentally attractive to adopt ATRP to aqueous dispersed media, although the process is challenging. This review summarizes recent developments of conducting ATRP in aqueous dispersed media. The issues related to retaining “controlled/living” character as well as colloidal stability during the polymerization have to be considered. Better understanding the ATRP mechanism and development of new initiation techniques, such as activators generated by electron transfer (AGET) significantly facilitated ATRP in aqueous systems. This review covers the most important progress of ATRP in dispersed media from 1998 to 2009, including miniemulsion, microemulsion, emulsion, suspension and dispersed polymerization.

Developing porous honeycomb films using miktoarm star copolymers and exploring their application in particle separation.

This paper reports for the first time the synthesis and application of miktoarm star copolymers to produce highly ordered honeycomb films using the breath figure technique. Miktoarm star copolymer containing a cross-linked core and two arm species, e.g., polystyrene and poly(t-butyl acrylate), is successfully synthesized using ATRP in a one-pot arm-first method. Various experimental parameters, including polymer architectures, solvents, polymer concentrations, and substrates, are explored to investigate their effects on the structure of the honeycomb films. It is found that miktoarm star copolymers with high molecular weight and spherical shape could readily produce ordered honeycomb films in a broader range of concentrations and humidity than linear block copolymers with similar chemical compositions but lower molecular weight. Partial hydrolysis of poly(t-butyl acrylate) arm species in the honeycomb film transforms the surface property from hydrophobic to hydrophilic while maintaining the films mechanical stability in water. This porous monolayer film with uniform pore size distribution and inter-connected pore channels is successfully applied for separation of microparticles with different sizes.