A strategy for synthesis of ion-bonded supramolecular star polymers by reversible addition-fragmentation chain transfer (RAFT) polymerization

We have developed a novel strategy for the preparation of ion-bonded supramolecular star polymers by RAFT polymerization. An ion-bonded star supramolecule with six functional groups was prepared from a triphenylene derivative containing tertiary amino groups and trithiocarbonate carboxylic acid, and used as the RAFT agent in polymerizations of tert-butyl acrylate (tBA) and styrene (St). Molecular weights and structures of the polymers were characterized by H-1 NMR and GPC. The results show that the polymerization possesses the character of living free-radical polymerization and the ion-bonded supramolecular star polymers PSt, PtBA, and PSt-b-PtBA, with six well-defined arms, were successfully synthesized.

The fragmentation of gold nanoparticles induced by small biomolecules

Spherical gold nanoparticles (3-5 nm) undergo a surprising fragmentation without extra energy imput and are converted into ultrasmall particles (less than 1.5 nm), which is a direct result of electron transfer between gold nanoparticles and cysteine.

Reversible addition-fragmentation chain transfer mediated radical polymerization of asymmetrical divinyl monomers targeting hyperbranched vinyl polymers

Reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerizations of allyl methacrylate and undecenyl methacrylate, compounds containing two types of vinyl groups with different reactivities, were investigated to provide hyperbranched polymers. The RAFT agent benzyl dithiobenzoate was demonstrated to be an appropriate chain-transfer agent to inhibit crosslinking and obtain polymers with moderate-to-high conversions. The polymerization of allyl methacrylate led to a polymer without branches but with five- or six-membered rings. However, poly(undecenyl methacrylate) showed an indication of branching rather than intramolecular cycles. The hyperbranched structure of poly(undecenyl methacrylate) was confirmed by a combination of H-1, C-13, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer 135 NMR spectra. The branching topology of the polymers was controlled by the variation of the reaction temperature, chain-transfer-agent concentration, and monomer conversion. The significantly lower inherent viscosities of the resulting polymers, compared with those of linear analogues, demonstrated their compact structure,

2-cyanoprop-2-yl dithiobenzoate mediated reversible addition-fragmentation chain transfer polymerization of acrylonitrile targeting a polymer with a higher molecular weight

The reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2-cyanoprop-2-yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANS were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. H-1 NMR analysis confirmed the high chain-end functionality of the resultant polymers.

A novel route to polyethylene-polystyrene blends through the fragmentation of porous polystyrene beads supported metallocene in ethylene polymerization

Polyethylene-polystyrene blends were synthesized by in situ ethylene polymerization with polystyrene porous beads supported metallocene; the influence of fragmenting support beads on the morphology and the mechanical performance of the blends was investigated.

Dibenzyl trithiocarbonate mediated reversible addition-fragmentation chain transfer polymerization of acrylonitrile

Reversible addition-fragmentation chain transfer polymerization has been successfully applied to polymerize acrylonitrile with dibenzyl trithiocarbonate as the chain-transfer agent. The key to success is ascribed to the improvement of the interchange frequency between dormant and active species through the reduction of the activation energy for the fragmentation of the intermediate. The influence of several experimental parameters, such as the molar ratio of the chain-transfer agent to the initiator [azobis(isobutyronitrile)], the molar ratio of the monomer to the chain-transfer agent, and the monomer concentration, on the polymerization kinetics and the molecular weight as well as the polydispersity has been investigated in detail. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and H-1 NMR analyses have confirmed the chain-end functionality of the resultant polymer.

Fragmentation reactions of adduct ions [M+CH3CO](+) of isomeric phenylenediamines

The dissociation routes of the adduct ions [M+CH3CO](+) formed by ion-molecule reaction of isomeric phenylenediamines with acetyl ion from acetone under chemical ionization condition were investigated by using collision-induced dissociation (CID) technique performed at ion kinetic energies of 40eV. The adduct ions are intermediate ion-neutral complexes.

Mass spectrometry study combined with theoretical calculation on the unimolecular fragmentation of tetrahydroimidazole-substituted methylene beta-diketones

Studies of low-energy collision-induced dissociation and isotopic labeling on ionized tetrahydroimidazole-substituted methylene P-diketones by tandem mass spectrometry showed that their unimolecular fragmentations may involve the reactions of intermediate ion/neutral complexes and multistep rearrangements. The corresponding mechanisms were proved by semiemipirical calculations of PM3 and AM1 methods.

Sites of protonation and unimolecular fragmentation of protonated N-hydroxyphthalimide in the gas phase

The low energy collision-induced dissociation, linked scan techniques and isotopic labeling experiment were used to investigate the unimolecular fragmentation of protonated N-hydroxyphthalimide under electron impact and chemical ionization conditions. It was found that this compound shows an unusual reactivity towards protonation. Two possible sites of protonation have been proposed to explain the corresponding fragmentation processes, one is that the protonation takes place on the oxygen atom of hydroxyl group, resulting in the loss of water and the other is the formation of an intermediary proton-bound complex in the fragmentation process, giving rise to the fragment ions of m/z 133 and m/z 135. The results show both cases are coexistence in the fragmentations of protonated N-hydroxyphthalimide, and the unimolecular fragmentation pathways are available.

Theoretical study on the unimolecular fragmentation of ionized tetrahydroimidazole-substituted methylene beta-diketones

Semiempirical molecular orbital calculations on the unimolecular mass spectrometric fragmentation of tetrahydroimidazole-substituted methylene beta-diketones are carried out by Austin Model 1 method, and the calculated results give a strong support to our experimental results reported previously. The optimum of the investigated molecular configuration indicates that the two hydrogen atoms attached to nitrogen atom have different activities due to their chemical environment; the relative energies of the ions in fragmentation pathway of ionized tetrahydroimidazole-substituted methylene beta-diketones provide indirectly an evidence for both the existence of ion/neutral complex and the stabilities of these ions.

Hybrids between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus: karyotype, allozyme and RAPD analyses

The hybrid between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus was produced by artificial insemination of olive flounder eggs with stone flounder sperm. Sinistral and dextral are two types of hybrid progeny after metamorphosis. Karyotypes of both hybrid flounders are the same as those of the two parental species. Of the 22 loci examined from 12 allozymes, 12 confirmed hybridization of the paternal and maternal loci in hybrids and no difference was found in allozyme patterns of sinistral and dextral hybrid fishes. RAPD patterns of these specimens were also studied with 38 primers selected from 104 tested. Among them, the PCR products of 30 primers showed hybridization of the paternal and maternal bands. Genetic variation between hybrids and their parental stocks was analyzed by RAPD using 10 of the above 38 primers. The average heterozygosity and genetic distance were calculated. The results suggested that the filial generation could inherit a little more genetic materials from paternal fish than that from maternal fish.

Building with Scottish Stone.

Building with Scottish Stone aims to encourage more use of stone sourced from Scotland’s working quarries and to provide a better understanding of those mineralogical properties which give each stone its distinctive quality. The nation’s architectural history is synonymous with the use of natural stone, and the principles of construction developed over generations in response to Scotland’s particular climatic conditions still find relevance today in the design and detailing of new buildings. Equally, an understanding of the ways in which stone is extracted and processed is as fundamental to its contemporary use as having up-to-date knowledge of the continuously changing legislation that affects its specification and procurement. Building with Scottish Stone is a stimulating introduction to these and many other factors to be considered when using this richly-varied and timeless resource in the design of new buildings.