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By combination of high trapping free radical efficiency of the thioketone and resonance of the allylic radical, a new type of mediating agent, 1,3,3-triphenylprop-2-ene-1-thione (TPPT) has been successfully synthesized, and then is used to study controlled free radical polymerization of methacrylates. Very stable TPPT radicals at the end of poly(methyl methacrylate) (PMMA) are detected in the polymerization of MMA using TPPT and AIBN as the control agent and initiator. The MALDI-TOF MS spectra are used to identify terminal groups of the resultant poly(glycidyl methacrylate) (PGMA), and major component of the obtained polymer has the structure, (CH3)2(CN)C-PGMA-C7H9O3. Chain extension reaction tests ascertain formation of the dead polymers during the polymer storage and purification process of the polymers. Owing to very slow fragmentation reaction of the TPPT-terminated polymethacrylate radical and addition reaction of this radical with a primary radical, the growing chain radicals are difficult to be regenerated, leading to an unobvious change of the molecular weight with monomer conversion. The molecular weights of polymers can be controlled by the ratios of monomer/initiator and TPPT/initiator. However, the first order kinetics of the polymerization and the polymers with narrow polydispersity are obtained, and these phenomena are discussed. This study provides useful information on how to design a better controlling agent. [ABSTRACT FROM AUTHOR]

We investigated the effects of molecular weight and film thickness on the crystallization and microphase separation in semicrystalline block copolymer polystyrene- block-poly(L-lactic acid) (PS- b-PLLA) thin films, at the early stage of film evolution (when T < T < T) by in situ hot stage atomic force microscopy. For PS- b-PLLA 1 copolymer which had lower molecular weight and higher PLLA fraction, diffusion-controlled break-out crystallization started easily. For PS- b-PLLA 2 with higher molecular weight, crystallization in nanometer scales occurs in local area. After melting of the two copolymer films, islands were observed at the film surface: PS- b-PLLA 1 film was in a disordered phase mixed state while PS- b-PLLA 2 film formed phase-separated lamellar structure paralleling to the substrate. Crystallization-melting and van der Waals forces drove the island formation in PS- b-PLLA 1 film. Film thickness affected the crystallization rate. Crystals grew very slowly in much thinner film of PS- b-PLLA 1 and remained almost unchanged at long time annealing. The incompatibility between PS and PLLA blocks drove the film fluctuation which subsequently evolved into spinodal-like morphology. [ABSTRACT FROM AUTHOR]

A facile and versatile method to prepare mesoporous core-shell nanostructures with a reversibly switchable nanoshell is reported. Reversible addition-fragmentation chain transfer (RAFT) functionalities were anchored to the exterior surface of mesoporous silica nanoparticles (MSNs), forming RAFT agent coated MSNs. RAFT polymerization was then conducted to graft a poly(acrylic acid) (PAA) shell onto the exterior surface of MSNs, producing novel smart nanocontainers with a MSN as the container and a pH-responsive PAA nanoshell as a smart nanovalve. The PAA nanovalve can control the access of guest molecules to and from the MSN nanocontainer. This core-shell nanostructure should have potential applications in drug and gene delivery. [ABSTRACT FROM AUTHOR]

The preparation of exquisite hierarchical worm-like silica nanotubes by a simple sol–gel method is successfully achieved for the first time. Poly(2-(dimethylamino)ethyl methacrylate)-grafted multiwall carbon nanotubes (MWNT-g-PDMAEMA) were used as a sacrificial template, subsequent hydrolysis and polycondensation of tetraethoxysilane-produced MWNT–silica nanocomposites with lots of silica nanowires arranged on their surfaces. The length of the silica nanowires can be controlled by the deposition time of silica. After the templates were removed by calcination in air, hierarchical worm-like silica nanotubes with some of the characteristics of mesoporous materials, such as large surface area, multiple pore distribution and large pore volume, were obtained. [ABSTRACT FROM AUTHOR]

Three-armed star-shaped poly(ester amine) was synthesized by Michael addition polymerizations of equal molar ratio of ethylene glycol diacrylate (EGDA) and piperazine (PZ) in the presence of a small amount of multifunctional monomer, 1,3,5-triacryloylhexa-hydro-1,3,5-triazine (TT) in CHCl3. When the polymerization proceeded almost completely, the molecular weight of the polymers formed were determined by the feed molar ratio of difunctional monomer to multifunctional monomer, and the molecular weight distribution (Mw/Mn) approached the theoretical value (Mw/Mn =1+1/f). The mechanism of the polymerization was investigated by ¹H NMR and Gel permeation chromatography (GPC). The monomer concentration and the molar ratio of difunctional monomers/multifunctional monomer played an important role in the polymerization. [ABSTRACT FROM AUTHOR]

Heteroarm H‐shaped terpolymers, [(poly(L‐lactide))(polystyrene)]poly(ethylene oxide)[(polystyrene)(poly(L‐lactide))], [(PLLA)(PS)]PEO[(PS)(PLLA)], in which PEO acts as a main chain and PS and PLLA as side arms, have been successfully prepared via combination of reversible addition–fragmentation transfer (RAFT) polymerization and ring‐opening polymerization (ROP). The first step is the synthesis of the PEO capped with one terminal dithiobenzoate group and one hydroxyl group at every chain end, [(HOCH2)(PhC(S)S)]PEO[(S(S)CPh)(CH2OH)] from the reaction of carboxylic acid with ethylene oxide. Then, the RAFT polymerization of styrene (St) was carried out using [(HOCH2)(PhC(S)S)]PEO[(S(S)CPh)(CH2OH)] as RAFT agent and AIBN as initiator, and the triblock copolymer, [(HOCH2)(PS)]PEO[(PS)(CH2OH)], was formed. Finally, the heteroarm H‐shaped terpolymers, [(PLLA)(PS)]PEO[(PS)(PLLA)], were produced by ROP of LLA, using triblock copolymer, [(HOCH2)(PS)]PEO[(PS)(CH2OH)], as macroinitiator and Sn(Oct)2 as catalyst. The target products and intermediates were characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 789–799, 2007 [ABSTRACT FROM AUTHOR]

A facile strategy for control of the polymer topologies can be achieved simply by tuning the feed molar ratio of catalyst to transfer agent in the controlled radical polymerization. [ABSTRACT FROM AUTHOR]