Search results for "PLASTICS"
showing 10 items of 2724 documents
Tuneable pH-regulated supramolecular copolymerisation by mixing mismatched dendritic peptide comonomers
2015
Charged phenylalanine-rich dendritic peptides form highly stable and pH-switchable rod-like supramolecular copolymers, when co-assembled with a matching oppositely charged dendritic comonomer. Here, we demonstrate that by mismatching a strong with a weak β-sheet encoded comonomer, both the stability and the pH-triggered disassembly of the copolymers shifts drastically from pH 4.2 to biologically relevant pH 5.8.
Enhanced polyurethanes based on different polycarbonatediols
2012
Segmented thermoplastic polyurethanes (PUs) were prepared from 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butanediol (BD) and different macrodiols with a molar mass of 1000. Properties of those PUs based on polycarbonatediol (PCD) were compared with their homologous based on polyesterdiol and polyetherdiol as macrodiols. The proportion used in this study was macrodiol:BD:MDI = 1:2:3, in mole ratio. The hard segment weight percentage is 48 wt% for different PUs. Thermogravimetric analysis, differential scanning calorimetry, differential mechanical analysis, Fourier transform infrared-attenuated total reflection spectroscopy, as well as mechanical properties and retention on flexural prope…
Complexes of star-shaped cationic polyelectrolytes with anionic liposomes: Towards multi-liposomal assemblies with controllable stability
2016
Abstract Complexes were formed via the electrostatic interaction between 30–50 nm anionic liposomes and a star-shaped polyelectrolyte, poly{[2-(methacryloyloxy)ethyl]trimethyl ammonium iodide}, having cationic arms that radiate from a silicon-based central core. The complexation was investigated with attention given to assessing the capacity of the cationic stars for the anionic liposomes (both liquid and solid); the integrity of the complexed liposomes; and the stability of the resulting star/liposome complexes in aqueous salt solutions. We have found that by changing the content of anionic groups in the liposomal membrane as well as the phase-state of membrane, the stability of star/lipos…
Synthesis and thermoresponsive properties of four arm, amphiphilic poly(tert-butyl-glycidylether)-block-polyglycidol stars
2011
Abstract A series of four arm stars with copolymer arms composed of poly(tert-butyl-glycidylether)-b-polyglycidol were prepared using a multi-step process based on anionic ring-opening polymerization. Control of the length of the arms and the number of functional (hydroxyl) reactive groups was achieved by anionic polymerization. Stars with molar masses up to 12200 g/mol were prepared. The amphiphilic character of the star structure was varied using different polyglycidol block lengths. The star structure and molar mass of the obtained stars were characterized by SEC–MALLS and NMR spectroscopy. The temperature behavior of an aqueous solution of the obtained polymers was also investigated. Th…
Control of end-of-life oxygen-containing groups accumulation in biopolyesters through introduction of crosslinked polysaccharide particles
2021
The formulation of bio-based materials with good performance in service and controlled end-of-life is imperative for an effective circular economy. In this work, an innovative approach to induce and control the end-of-life of biodegradable polyesters through introduction of crosslinked polysaccharide particles is proposed. Chitosan (Ch) has been subjected to ionotropically crosslinking and then added to polylactic acid (PLA) at different amounts (1.0–4.0%w) by melt mixing. All obtained results suggest that the addition of crosslinked Ch (cCh) particles does not modify significantly the investigated biopolyester properties. Specifically, the thermal analysis of the composites reveals that th…
Natural compounds as light stabilizer for a starch-based biodegradable polymer
2014
Abstract The photooxidation behavior of a commercial starch-based biodegradable polymer, i.e., new generation Mater-Bi, loaded with natural stabilizers was investigated in consideration for outdoor agricultural applications. The photooxidation behavior of the biodegradable films was monitored mainly by mechanical tests and spectroscopic analysis. In order to formulate biodegradable films without any synthetic compounds, suitable for outdoor applications and with good photooxidation stability, antioxidants such as α-tocopherol and quercetin (Q) were considered. The results obtained using natural compounds were compared with those obtained by using a synthetic antioxidant and a light stabiliz…
Photooxidation and Stabilization of Photooxidized Polyethylene and of its Monopolymer Blends
2003
The increasing use of products from recycled polymers, or from blends with recycled polymers exposed to the outdoors, implies the need for good weathering resistance. This is particularly important when the recycled material comes, in turn, from products exposed during their lifetime to the sun. In this case the presence of C=O groups in the macromolecular chains strongly increases the photooxidative degradation kinetics of these secondary materials. In this work the change of the photooxidative degradation of blends of virgin and photooxidized polyethylene was evaluated as a function of the C=O content present in the material. As expected, the presence of the C=O groups strongly increases …
Polyethylene composites filled with n‐alkyl‐functionalized siloxane‐silsesquioxane resins and sol‐gel silicas
2019
High‐density polyethylene (HDPE) composites filled with silicon‐based fillers were prepared by melt blending. The use of non‐functionalized and n‐octyl‐functionalized siloxane‐silsesquioxane resins and the sol‐gel silicas as fillers allowed us to evaluate the influence of functionalization of the fillers on the properties of the composites. The melting and crystallization temperatures of the composites were found to be only slightly affected by the addition of the silicon‐based fillers. In turn, the crystallization degree values were increased, in particular for the materials containing non‐functionalized fillers. The free‐volume properties of the composites did not change significantly in …
A Click Chemistry-Based “Grafting Through” Approach to the Synthesis of a Biorelevant Polymer Brush
2011
A new biorelevant polymer brush showing a polybenzofulvene backbone was synthesized by a ‘‘grafting through’’ approach based on click chemistry and spontaneous polymerization reactions. The easy polymerization of the relatively complex monomer (6-MOEG-9-TM-BF3k) suggests the existence of a particularly efficient recognition process capable of pre-organizing the monomer molecules for the spontaneous polymerization. 13C-NMR spectroscopy as well as UV-vis and fluorescence spectroscopy suggested for poly-6-MOEG-9-TM-BF3k the features of a vinyl (1,2) p-stacked polymer. The new polybenzofulvene derivative was found to interact with water at room temperature to give clear water solutions, but TEM…
(Co)polymerization behavior of supported metallocene catalysts. I. Ligand and substituent effect
2005
Ethylene polymerization and its copolymerization with 1-hexene with a set of supported metallocene catalysts were studied. As a carrier, the complex of mag- nesium chloride with tetrahydrofuran, which was previously pretreated with a triiso- butylaluminium (TIBA), was used. The investigated metallocene compound differs in the metal type (Zr or Ti), the nature of the alkyl substituent in the cyclopentadienyl ring, and the type of ligand (Cp or Ind). The effect of catalyst composition on the anchored metal content, catalyst activity, comonomer reactivity, and polymer proper- ties was investigated. The results obtained with supported catalysts were compared with those obtained with their homog…