Crazing and shear deformation of polymer alloys

Crazing and/or shear yielding mechanisms in multiphase polymer alloys play a critical role in toughening. The present paper describes the use of finite element models (FEM) to simulate the crazing and shear deformation behaviour around the particles embedded in brittle or ductile matrices. The FEM simulation results on the stress distribution reveal that the dilatational stress within the rubber particles is high enough to cavitate. The stability of craze growth can be reached when the compliant particle is incorporated in a brittle matrix. On the other hand, shear yielding around the particle occurs in the equator of the particle/matrix interface when the stress locally exceeds the yield stress of the matrix. This yield-initiation stress increases with the increase in the elastic modulus and Poisson's ratio of the particles. The toughening mechanism, that cavitation occurs first followed by shear yielding to form a neck between the particles, is discussed based on the simulation results for the two-particle model.     

Photoinitiated Cationic Polymerization of 3-Ethyl-3-(phenoxymethyl)-oxetane in Nitrogen Atmosphere

Abstract

The photoinitiated cationic polymerizations of 3-ethyl-3-(phenoxymethyl)-oxetane (PhO) and phenyl glycidyl ether (PhE) with diphenyl-4-thiophenoxyphenyl sulfonium hexafluoroantimonate as the cationic photoinitiator were carried out in air and nitrogen atmospheres. A real time FT-IR method was used to estimate the polymerization rates. The number-average molecular weight (M _n) of the resulting polymers were measured by gel permeation chromatography. In nitrogen, the photopolymerization rate of PhO was more than four times greater than in air, while there was no essential difference for PhE. The M _n of the PhO polymer increased from 13,900 (in air) to 61,200 (in nitrogen) at the peak top. The fast polymerization mechanism in nitrogen was postulated to be the radical-assisted decomposition of the sulfonium salt.     

Palladium-catalyzed 1,2-addition of potassium aryl- and alkenyltrifluoroborates to aldehydes using thioether-imidazolinium carbene ligands

Palladium-catalyzed 1,2-addition of potassium aryl- and alkenyltrifluoroborates to aldehydes using thioether-imidazolinium carbene ligands proceeded readily under aqueous conditions. This process tolerated a diverse range of potassium trifluoroborate salts and aldehydes, giving a variety of carbinol derivatives with good to excellent yields.     

Asymmetric hydrogenation of aryl ketones mediated by a copper catalyst

[reaction: see text] A novel asymmetric hydrogenation protocol using a copper catalyst is reported. A Cu(I) complex in the presence of nonracemic BDPP hydrogenates aryl ketones with moderate to high enantioselectivity.     

Establishment of a microplate-formatted cell-based immunoassay for rapid analysis of nucleotide excision repair ability in human primary cells

DNA photolesions induced by UV, cyclobutane pyrimidine dimer (CPD) and (6-4) photoproduct (6-4PP), are repaired by nucleotide excision repair (NER) in human cells. Various immunoassays using monoclonal antibodies specific for the photolesions have been developed and widely used for the analysis of cellular NER activity. In this study, we have newly developed a microplate-formatted cell-based immunoassay, based on indirect immunofluorescence staining with lesion-specific antibodies combined with an infrared imaging system. Using this assay, we show the repair kinetics of CPD and 6-4PP in various fibroblasts from newborn and adult donors with no age-related difference. Furthermore, epidermal keratinocytes and melanocytes exhibit comparable NER activity, and calcium ion-induced differentiation of keratinocytes has no significant impacts on their NER activity. We also evaluated the effects of a proteasome inhibitor, MG132, and a histone deacetylase inhibitor, sodium butyrate, on NER efficiency using this assay. All these results suggest that the new assay is highly useful for the rapid and quantitative analysis of NER activity in various primary cells with limited growth activity and is applicable to a screening system for drugs affecting NER efficiency.     

Design and control of morphology for high performance polymer alloys

Ductile polymers are significantly toughened by the addition of an elastomeric phase. The rubber phase acts as a stress concentrator, cavitates during the loading process and initiates localized plastic deformation in matrix. This paper deals with the simulation of the deformation behavior of rubber toughened polycarbonate and the fracture process of the embedded rubber particle. A two-dimensional one particle- and two-particle model with varying surface-to-surface interparticle distances are established. The calculation showed that the polymer matrix has plastically deformed before cavitation for the one-particle model whereas cavitation occurs in the elastic state of the matrix for the two-particle model. Cavitation itself is proved to be a change from the particle-system towards a void-system for both cases. The toughness of the post-cavitated void-system is shown to be dependent on the surface-to-surface interparticle distance and the strain-hardening characteristic of the matrix polymer.