Preparative fractionation of a random copolymer (SAN) with respect to either chain length or chemical composition

The possibilities to fractionate copolymers with respect to their chemical composition on a preparative scale by means of the establishment of liquid/liquid phase equilibria were studied for random copolymers of styrene and acrylonitrile (san). Experiments with solutions of san in toluene have shown that fractionation does in this quasi-binary system, where demixing results from marginal solvent quality, take place with respect to the chain length of the polymer only. On the other hand, if phase separation is induced by a second, chemically different polymer one can find conditions under which fractionation with respect to composition becomes dominant. This opportunity is documented for the quasi-ternary system dmac/san/polystyrene, where the solvent dimethyl acetamide is completely miscible with both polymers. The theoretical reasons for the different fractionation mechanisms are discussed

Potential range of impact of an ecological trap network: the case of timber stacks and the Rosalia longicorn

Although the negative impact of timber stacks on populations of saproxylic beetles is a well-known phenomenon, there is relatively little data concerning the scale of this impact and its spatial aspect. Beech timber stored in the vicinity of the forest can act as an ecological trap for the Rosalia longicorn (Rosalia alpina), so in this study we have attempted to determine the spatial range of the impact of a network of timber stacks. Timber stacks in the species’ range in the study area were listed and monitored during the adult emergence period in 2014–2016. Based on published data relating to the species’ dispersal capabilities, buffers of four radii (500, 1000, 1600, 3000 m) were delineated around the stacks and the calculated ranges of potential impact. The results show that the percentage of currently known localities of the Rosalia longicorn impacted by stacks varies from 19.7 to 81.6%, depending on the assumed impact radius. The percentage of forest influenced by timber stacks was 77% for the largest-radius buffer. The overall impact of the ecological trap network is accelerated by fragmentation of the impact-free area. It was also found that forests situated close to the timber stacks where the Rosalia longicorn was recorded were older and more homogeneous in age and species composition than those around stacks where the species was absent. Such results suggest that timber stacks act as an ecological trap in the source area of the local population

Thermodynamics of pseudo-ternary systems as a tool to predict the morphologies of cellulose acetate/polystyrene blends cast from tetrahydrofuran solutions

The demixing behavior of the ternary system THF/CA/PS (tetrahydrofuran/cellulose acetate/polystyrene) was investigated at 25degreesC. Cloud point measurements show that the system exhibits a large miscibility gap caused by the incompatibility of CA and PS. Both ends of the experimentally determined tie lines are located inside the two-phase area of the phase diagram. By means of the measured critical composition of the ternary system and the Flory-Huggins interaction parameters published for two of the binary subsystems (X-CA/(THF) = 0.442 and X-PS/(THF) = 0.475) the polymer/polymer interaction parameter was adjusted (directly minimizing the Gibbs energy) to X-CA/(PS) = 0.057. These thermodynamic data were used to calculate the extension of the metastable and the unstable regions of the phase diagram. This procedure permits a realistic prediction of the morphologies of the (solvent-free) blends from the location of the starting composition of the casting solutions in the Gibbs phase triangle, as demonstrated by means of optical micrographs and field emission scanning electron micrographs. (C) 2002 Published by Elsevier Science Ltd.4441075108

Polydispersity effects on the phase diagram of the system chloroform/poly-L-(lactic acid)/poly(methyl methacrylate) and morphology of PLA/PMMA films

Cloud point curve, critical composition and several critical coexistence curves were measured at 25 degrees C for the ternary system poly-L-(lactic acid) (PLA), poly(methyl methacrylate) (PMMA) - where both polymers exhibit broad molecular weight distributions - and the common solvent chloroform; In contrast to the situation encountered in the absence of the second polymer both branches of the critical coexistence curves are located without any doubt inside the miscibility gap as defined by the cloud point curve. This unexpected experimental finding is corroborated by model calculations on the basis of continuous thermodynamics. The removal of solvent from the ternary mixtures yields films of different morphology, depending on the particular path through the metastable or unstable regions of the phase diagram. The structures observed by means of optical microscopy confirm the theoretically postulated phase separation mechanisms. (C) 2000 Elsevier Science B.V. All rights reserved.1714167121923

Osseointegration of biochemically modified implants in an osteoporosis rodent model

The present study examined the impact of implant surface modifications on osseointegration in an osteoporotic rodent model. Sandblasted, acid-etched titanium implants were either used directly (control) or were further modified by surface conditioning with NaOH or by coating with one of the following active agents: collagen/chondroitin sulphate, simvastatin, or zoledronic acid. Control and modified implants were inserted into the proximal tibia of aged ovariectomised (OVX) osteoporotic rats (n = 32/group). In addition, aged oestrogen competent animals received either control or NaOH conditioned implants. Animals were sacrificed 2 and 4 weeks post-implantation. The excised tibiae were utilised for biomechanical and morphometric readouts (n = 8/group/readout). Biomechanical testing revealed at both time points dramatically reduced osseointegration in the tibia of oestrogen deprived osteoporotic animals compared to intact controls irrespective of NaOH exposure. Consistently, histomorphometric and microCT analyses demonstrated diminished bone-implant contact (BIC), peri-implant bone area (BA), bone volume/tissue volume (BV/TV) and bone-mineral density (BMD) in OVX animals. Surface coating with collagen/chondroitin sulphate had no detectable impact on osseointegration. Interestingly, statin coating resulted in a transient increase in BIC 2 weeks post-implantation; which, however, did not correspond to improvement of biomechanical readouts. Local exposure to zoledronic acid increased BIC, BA, BV/TV and BMD at 4 weeks. Yet this translated only into a non-significant improvement of biomechanical properties. In conclusion, this study presents a rodent model mimicking severely osteoporotic bone. Contrary to the other bioactive agents, locally released zoledronic acid had a positive impact on osseointegration albeit to a lesser extent than reported in less challenging models

Thermodynamics of Block Copolymer Solutions As Compared with the Corresponding Homopolymer Solutions: Experiment and Theory

The interaction of butadiene-styrene block copolyincis of different molecular architecture with tetrahydrofuran (THF) was studied by vapor pressure and light scattering experiments in the temperature range from 25 to 55 degrees C The thus obtained Flory-Huggins interaction parameters, chi, as a function of phi, the volume fraction of the polymers, were compared with that of the corresponding homopolymersim in the same solvent The results are very similar for all block copolymers (diblock, triblock and star-shaped, butadlene In the chi(phi) Curves of the homopolymers, which are always located center) and for all temperatures In contrast to they chi(phi) curves of the homopolymers, which are always located above their tangents, the dependencies for the block copolymers exhibit it maximum in the range of moderate polymer concentrations, where the heats of dilution are close to athermal ill the range of low phi values but become pronouncedly endoiliernial rot high phi values These Findings call be well modeled by all approach considering the phenomena of chain connectivity and conformational relaxation of polymers , If one accounts for the unfavorable interactions between the monomeric units of the different block