Search results for "PLASTICS"
showing 10 items of 2724 documents
Interplay of Chiral Side Chains and Helical Main Chains in Polyisocyanates
1996
Here we describe the synthesis of seven new copolymer series prepared by copolymerization of hexyl isocyanate with seven new chiral azo chromophores with an isocyano functionality. The resulting copolyisocyanates (Nylon 1) possess a helical polymer conformation. In the cases in which the chiral group and polymer chain are linked to the same phenyl ring (copolymer series VI-IX) a transfer of chirality to the polymer chain is possible. I.e. one helical twist sense is preferred in this case. By variation of the chiral center, polymers with preferable right- or left-handed helical conformation are accessible. The photochemical isomerization of the azo chromophore (trans → cis) is possible in hi…
A facile way to build up branched high functional polyaminoacids with tunable physicochemical and biological properties
2016
Abstract Here, for the first time, branched polyaminoacids bearing α-amino acids as side functions, namely PAA-co-AA and PGA-co-AA, are prepared by heterophase ring opening of polysuccinimide (PSI) with l -arginine or glycine in aqueous environment and at controlled pH. The modulation of the pH of the reaction leads to high-molecular-weight copolymers with tunable functionalization and, as consequence, with tailor-made physicochemical properties. Furthermore, a branched polyaminoacid carrying a preformed bioactive peptide ( l -trileucine) and l -arginine as side pendants, named PATA-co-AA, was synthesized via a similar pathway thus leading to complex biomimetic materials potentially exploit…
Dynamic Light Scattering Investigation of the Kinetics and Fidelity of Supramolecular Copolymerizations in Water
2017
The self-assembly of supramolecular copolymers facilitates the preparation of multifunctional materials, with tunable mechanical, electronic, or bioactive properties. Compared to covalent copolymerization protocols, controlling the molecular weight, stability, and monomer sequence of a multicomponent supramolecular copolymer remains limited. Here, we report a light scattering investigation of the charge-regulated supramolecular copolymerization in neutral buffer of physiological ionic strength, supported with electron microscopy and circular dichroism spectroscopy experiments. Dendritic anionic and cationic peptide comonomers self-assemble into AB-type heterocopolymers with a nanorod-like m…
Studies on Adduct Formation of (+)-Anti-Benzo[a]pyrene 7,8-Dihydrodiol 9,10-Epoxide with the oligonucleotides 5′-d(CCTATCGTTATCC) and 5′-d(CCTATm5CGT…
1999
Abstract Adduct formation of (+)-anti-benzo[a]pyrene 7,8-dihydrodiol 9,10-epoxide [BPDE] and 5′-d(CCTATCGTTATCC) or 5′-d(CCTATm5CGTTATCC) (G = binding target) has been studied. The extent of trans-BPDE-N2-dG adduct formation was higher in the oligonucleotide with 5′-d(m5CG) sequence context in both single- and double stranded form compared to the non-methylated analogue. The stimulating effect of m5dC on adduct formation has previously been demonstrated in other experimental systems. The increase in yield could possibly be rationalized in terms of prestacking of the pyrenyl ring with the nucleobases prior to the nucleophilic addition. In the present study, both UV absorption and induced cir…
Calorimetric and structural investigation of the interaction between bovine serum albumin and high molecular weight dextran in water.
2005
This work studies specific interactions between a small globular protein and a highly flexible, branched polysaccharide using differential scanning calorimetry (DSC), circular dichroism (CD), fluorescence, and turbidimetry measurements. It uses the system water/bovine serum albumin (BSA)/dextran (D 2000) as a model. Dextran molecules are able to form interpolymeric complexes with BSA in water at both low and high temperatures if the polysaccharide is in excess and if the protein exists in its associated state. It leads to a partial destabilization of the secondary and tertiary structures of the protein and an additional exposure of the hydrophobic tryptophan residues to the surface of globu…
Genomic reaction norms inform predictions of plastic and adaptive responses to climate change
2022
Genomic reaction norms represent the range of gene expression phenotypes (usually mRNA transcript levels) expressed by a genotype along an environmental gradient. Reaction norms derived from common-garden experiments are powerful approaches for disentangling plastic and adaptive responses to environmental change in natural populations. By treating gene expression as a phenotype in itself, genomic reaction norms represent invaluable tools for exploring causal mechanisms underlying organismal responses to climate change across multiple levels of biodiversity. Our goal is to provide the context, framework and motivation for applying genomic reaction norms to study the responses of natural popu…
Phase behavior of aqueous solutions of bovine serum albumin in the presence of dextran, at rest, and under shear.
2006
The demixing conditions for aqueous solutions of bovine serum albumin (BSA, fraction V) and for joint solutions of BSA plus dextran (DEX, M(w) = 2000 kg/mol) were determined by turbidimetric measurements as a function of composition, temperature, and shear rate. Aqueous solutions of BSA phase separate upon heating. Within the region of BSA concentrations between 0.05 and 32 wt %, the demixing temperature, T1, falls from ca. 65 degrees C to an almost constant value of 45 degrees C. Adding DEX to the BSA solutions reduces the homogeneous region of the mixture drastically where the amount of DEX required to lower T1 to 25 degrees C decreases rapidly as the concentration of BSA is raised. Exper…
Modelling the influence of nanoparticles in the phase behaviour of an epoxy/polystyrene mixture
2007
Abstract The cloud point temperatures of four series of epoxy/polystyrene blends have been experimentally determined as a function of polymer mass and system composition. The phase diagrams show an UCST behaviour, increasing incompatibility as the molar mass increases. The Flory–Huggins theory with a concentration-dependent interaction parameter has been developed to study the compatibility of two polymers in presence of spherical nanoparticles. This theory has been first compared with the experimental cloud point curve in absence of nanoparticles, and secondly it has been used to predict the thermodynamic behaviour in presence of different volume fraction of nanoparticles. Nanoparticles co…
Shear-Induced Crystallization and Shear-Induced Dissolution of Poly(ethylene oxide) in Mixtures with Tetrahydronaphthalene and Oligo(dimethyl siloxan…
2003
Cloud point temperatures (T cp ) and crystallization temperatures (T 1/s ) were measured at different constant shear rates for the ternary system tetrahydronaphthalene/poly(ethylene oxide)/oligo(dimethyl siloxane-b-ethylene oxide) using a rheo-optical device and in the case of T 1/s additionnaly a viscometer. This system enables for the first time a joint investigation of both transitions with a given mixture. Shear favors the homogeneous liquid state and the formation of crystals. T cp (liquid/liquid demixing, UCST) shifts to lower and T 1/s (liquid/solid, segregation of PEO) to higher temperatures by several degrees as the shear rate, γ, is increased up to 500 s -1 . The normalized shift …
Complex miscibility behaviour for polymer blends in flow
1995
Abstract Experimental observations of the effect of shear flow on the miscibility of binary polymer blends are compared to calculations based on a generalized Gibbs energy of mixing Gγ˙. This mixing free energy characterizes the steady state established at shear rateγ˙, as the sum of G z , the equilibrium Gibbs energy and E s , the energy the system stores while flowing.