Atsushi Goto

Mechanisms and kinetics of living radical polymerizations

The polymerization rates and activation processes of several variants of living radical polymerization (LRP) are discussed on the basis of recent experimental and theoretical results. Because of bimolecular termination, which is inevitable in LRP as well as in conventional radical polymerization, the time-conversion curves of LRP have several characteristic features depending on the experimental conditions, such as the presence or absence of conventional initiation. Despite the presence of termination (and initiation, in some cases), polymers obtained by LRP can have a low polydispersity, provided that the number of terminated chains is small compared to the number of potentially active chains. A large rate constant of activation, kact, is another fundamental requisite for low polydispersities. Systematic experimental investigation into kact has clarified the exact mechanisms of activation in several LRP systems. The magnitudes of kact was found to largely differ from system to system.

Determination of the activation rate constants of alkyl halide initiators for atom transfer radical polymerization

The second-order activation rate constants kA for low-molar-mass alkyl halides catalyzed by cuprous halide complexes Cu(I)X/2L (X = Cl or Br; L = 4,4′-diheptyl-2,2′-bipyridine) were determined by the nitroxide capping method along with 1H NMR. The kA for 1-phenylethyl bromide, a typical initiator for atom transfer radical polymerization (ATRP), with the Cu(I)Br complex was found to be close to the known value of the kA for a polystyryl bromide, being large enough for the initiation to be completed at an early stage of polymerization. It was also found that kA strongly depends on the kind of halogen and the steric factor of the alkyl halide in question.

Comparative study on activation rate constants for some styrene/nitroxide systems

The activation rate constants k act of some polystyrene (PS) - nitroxide adduts were determined as a function of temperature by the GPC peak resolution method. The results showed that both the steric and polar factors associated with the structure of the nitroxides strongly affect the magnitude of k act . Steric factors contribute significantly to the entropy of the reaction, while polar factors take part in the C-O bond energy.

Penultimate unit effects in free radical copolymerization

The penultimate unit effects (PUEs) on the propagation, termination, and reversible addition-fragmentation chain transfer (RAFT) processes in free radical copolymerization are discussed on the basis of recent publications. The propriety of the implicit and explicit PUE models in propagation and chain transfer processes is commented. The penultimate termination model with the geometric-mean approximation and the related rate equation are highlighted.

Thermoresponsive micellization and micellar stability of poly(n -isopropylacrylamide)- b -DNA diblock and miktoarm star polymers

Linear and miktoarm star-shaped diblock copolymers consisting of single-stranded DNA and poly(N-isopropylacrylamide) (PNIPAAm) with various compositions were synthesized via atom transfer radical polymerization and click chemistry. The temperature-responsive phase transition behavior, micellization, was systematically examined using UV-vis spectrometry, high-sensitivity differential scanning calorimetry, dynamic light scattering, and small-angle X-ray scattering. The lower critical solution temperature (LCST) increased, and its enthalpy decreased with decreasing PNIPAAm content. The copolymers self-assembled into well-defined nanoparticles having a core composed of PNIPAAm and a coronal layer of DNA above LCST. The particle size and micellar aggregation number of copolymer chains depended on the macromolecular composition and chain architecture. On the other hand, regardless of their factors, the surface area occupied by one DNA strand was found to be almost unchanged. The hybridization of DNA on the nanoparticles with fully complementary one induced the aggregation of the particles in a non-cross-linking configuration. The nanoparticle composed of miktoarm star copolymer showed a quicker DNA-hybridization response in this non-cross-linking aggregation compared with the case of a linear analogue.

Hydration of basic granulite to garnet-epidote amphibolite in the Sanbagawa metamorphic belt, central Shikoku, Japan

Abstract Granulite in the Iratsu metagabbro of central Shikoku, with color-banding defined by the presence and absence of plagioclase, is surrounded by a narrow epidote amphibolite, which itself is encased in garnet-epidote amphibolite. The epidote amphibolite formed metastably under low PH2O conditions based on thermodynamic considerations. The granulite-epidote amphibolite boundary is formed by the hydration reaction of plagioclase to zoisite, kyanite and quartz, and that of clinopyroxene and orthopyroxene to amphibole. If it is assumed that the temperature range of the Sanbagawa epidote amphibolite facies is 600–650°C, we obtain a lithostatic pressure of 12–15 kbar and a H2O pressure of 1–3 kbar for the hydration conditions. The boundary between epidote amphibolite and garnet-epidote amphibolite is defined by the formation of garnet, which is more stable than the epidote amphibolite assemblages. Pargasitic amphibole occurs at the garnet rim. Up to 0.32 wt.% Cl is present in the amphibole from both of the hydrated facies, but is It is concluded that hydration did not take place in the presence of an excess fluid phase, based on the difference of the Cl contents of amphibole between observed and expected values from a qualitative infiltration metasomatic model and also on the estimated low fluid pressure. The formation of a sharp boundary between the granulite and epidote amphibolite suggests intracrystalline diffusion.

Reversible Chain Transfer Catalyzed Polymerization of Methyl Methacrylate with In-Situ Formed Alkyl Iodide Initiator

A method utilizing generation of an alkyl iodide (low-mass dormant species) in situ formed in polymerization was adopted to reversible chain transfer catalyzed polymerizations (RTCP) (living radical polymerizations) with several nitrogen and phosphorus catalysts. The polymerization of methyl methacrylate afforded low-polydispersity polymers (Mw/Mn ~1.2–1.4), with Mn values predicted to high conversions; where Mn and Mw are the number- and weight-average molecular weights respectively. This method is robust and would enhance the utility of RTCP.

Surface-Initiated Living Radical Polymerizations Using Iodine, Organotellurium, and Organic Catalysts

This chapter reviews surface-initiated living radical polymerizations via iodine transfer polymerization (ITP), organotellurium-mediated radical polymerization (TERP), and reversible chain-transfer catalyzed polymerization (RTCP) using organic catalysts. The successful application of these polymerizations made it possible to graft various polymers with well-defined structures onto flat substrates and nanoparticles. Living radical polymerizations, including ITP, TERP, and RTCP, also lead to a striking increase in the graft density. Because of their unique advantages as synthetic tools, ITP, TERP, and RTCP can be used to expand the scope of controlled surface modification.