Amphiphilic, RAFT-capped, (acrylic acid) x (styrene) y diblock copolymers (x = 10, y ) 10, 5, 0) were synthesized and used as stabilizers in emulsion polymerization. Above the critical micelle concentration (cmc) of the diblocks and under appropriate reaction conditions micelles of the more hydrophobic diblocks were sufficiently nonlabile to be nucleated and act as seed particles for latex particle formation. The key parameters which allow control over the system are diblock hydrophobicity and initiator concentration. A homogeneous nucleation mechanism is most likely to operate below the cmc of the diblocks.

Summary: Controlled radical polymerization using RAFT has the potential to make polymers with virtually any desired molecular architecture. For this to be implemented on an industrial scale, it must be performed by polymerization in disperse media. However, simply adding a RAFT agent to a conventional emulsion polymerization recipe leads to a loss of molecular weight control and formation of coagulum, probably because of nucleation in droplets, which is normally an unlikely phenomenon in emulsion polymerizations. Recently, a method has been devised for implementing RAFT in ab initio emulsion polymerization that avoids droplets in the particle formation stage. The molecular weight distribution of the polymer thus formed shows that molecular weight control is maintained throughout the polymerization. A model is developed to predict the particle size formed in this new type of emulsion polymerization. The new methodology enables synthesis of novel dispersions where molecular architecture can be precisely controlled, such as structured core-shell particles.

A method is presented for synthesizing surfactant-free latexes comprising a starch-graft-vinyl polymer, (1) starting with a suspension of the highly branched starch amylopectin, either native or degraded, (2) then using ozonolysis to create free-radical initiation sites on this amylopectin scaffold, and (3) finally adding the monomer and inducing polymerization. The ozone simultaneously thins the starch and creates initiating/grafting sites on the starch, from which starch-graft-copolymer latexes can be grown. The encapsulation of starch inside the hydrophobic polymer particles created by a heterogeneous free-radical polymerization process is demonstrated with energy-dispersive spectroscopy; this is the first time that the particle morphology of such a latex has been so characterized. The data unambiguously prove that low-molar-mass degraded starch can be encapsulated within a latex particle. The underlying mechanisms have been explored, and data quantifying the rates of production of hydroperoxides by ozone, the thermal decomposition of the starch hydroperoxides so formed, and the degradation of amylopectin by ozone are reported. The activation energy for the thermal decomposition of the starch macroinitiator, determined in this work to be 125 6 8 kJ mol À1 , is consistent with the proposition that the initiating species are mainly hydroperoxides. Colloidally stable poly(styrene-co-n-butyl acrylate) latexes based on high-molar-mass amylopectin have been developed. These are stable against electrolytes (several months in 4 mol L À1 NaCl), with 20% of the starch effectively grafted to the particles. Films cast from such latexes are more pliable than starch films and are readily redispersed in water. V V C 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: [5832][5833][5834][5835][5836][5837][5838][5839][5840][5841][5842][5843][5844][5845] 2006

Summary: Oligo(acrylic acid)s, produced by RAFT polymerization, have been separated and analyzed for the first time by capillary zone electrophoresis. The resolution obtained by capillary electrophoresis in borate buffers is far higher than that currently achieved using size exclusion chromatography. This work demonstrates that capillary electrophoresis is the technique of choice for the characterization of oligomers of acrylic acid and of other water‐soluble monomers involved in emulsion polymerization processes.Electropherograms of different acrylic acid (AA) oligomers obtained by CZE.magnified imageElectropherograms of different acrylic acid (AA) oligomers obtained by CZE.

Model alkali-soluble rheology modifiers of different molar masses were synthesized by the reversible addition-fragmentation chain-transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well-controlled molar mass, molar mass linearly increasing with conversion, and the ability to chainextend by forming an AB block copolymer. The steady-shear and dynamic properties of a core-shell emulsion, thickened with the different model alkali-soluble rheology modifiers, were measured at constant pH and temperature. The steady-shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid-like (dominant GЈ) behavior as compared with the associative rheology modifiers that give the latex solution a liquid-like (dominant GЉ) character.

A method is presented for synthesizing surfactant‐free latexes comprising starch‐graft‐(vinyl polymer) starting with a suspension of amylopectin, either native or modified, then using cerium(IV) with either potassium persulfate or glucose to create grafting sites on the starch. Latex particles comprising polystyrene, poly(styrene‐co‐(n‐butyl acrylate)) and poly(vinyl acetate) grafted onto high molecular weight amylopectin were developed, with up to 80% of the starch effectively grafted to the particles. These latexes were colloidally stable against electrolyte (several months in 4 M NaCl). Reaction rates of Ce4+ with simple sugars and polysaccharides were investigated, as well as the gelation mechanism of the latex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4185–4192, 2007

Recent advances in the use of reversible addition–fragmentation chain transfer (RAFT) polymerization in dispersed phase systems have paved the way for the fine control of the morphology of latex particles that was not possible by conventional free radical polymerization techniques. With this approach, living amphiphilic block copolymers are synthesized that self-assemble to form micelles. The hydrophilic segment is formed from a water-soluble monomer which stabilizes the latex particles as polymerization proceeds and the latex particles grow. The hydrophobic ends of the RAFT diblocks ultimately grow into the polymer that forms the body of the particles. This paper presents examples of ways in which these advances can be used to engineer latex particles with unique morphologies that exhibit specific application properties.

Model alkali‐soluble rheology modifiers were synthesized through the reversible addition–fragmentation chain transfer polymerization of methyl methacrylate, methacrylic acid, and three different associative macromonomers containing 20, 50, and 100 ethylene oxide spacer units, respectively. The synthesized polymers showed well‐controlled molar masses and narrow molar mass distributions. The rheological properties of the model alkali‐soluble rheology modifiers were measured in alkali solutions and in the presence of a well‐characterized core–shell emulsion. The steady‐shear viscosity data for the emulsion solutions, thickened with the associative rheology modifiers, were described by the Carreau model. The rheology modifiers containing the macromonomers with the longest ethylene oxide spacer units produced the highest viscosity in the latex systems but the lowest viscosity in alkali solutions. The highest viscosities in alkali solutions were obtained for the rheology modifiers containing macromonomers with 50 ethylene oxide spacer units. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2502–2512, 2004