Search results for "PLASTICS"
showing 10 items of 2724 documents
School Tracking and Mental Health
2019
To understand how the type of education affects long-term mental health, we examine the effects of a comprehensive school reform on mental health–related hospitalizations and deaths. The reform postponed the tracking of students into vocational and academic schools from age 11 to age 16, thus affecting the set of peers and the curriculum to which these students were exposed. The reform was implemented gradually across Finnish municipalities between 1972 and 1977. We use difference-in-differences variation and administrative data. Our overall results show no discernible effects on mental health–related hospitalizations or deaths, but heterogeneity analysis shows an adverse effect on hospital…
Directing the self-assembly of semiconducting copolymers: the consequences of grafting linear or hyperbranched polyether side chains.
2013
The synthesis and self-assembly of novel semiconducting rod-coil type graft block copolymers based on poly(para-phenylene vinylene) (PPV) copolymers is presented, focusing on the ordering effect of linear versus hyperbranched side chains. Using an additional reactive ester block, highly polar, linear poly(ethylene glycol), and hyperbranched polyglycerol side chains are attached in a grafting-to approach. Remarkably, the resulting novel semiconducting graft copolymers with polyether side chains show different solubility and side-chain directed self-assembly behavior in various solvents, e.g., cylindrical or spherical superstructures in the size range of 10 to 120 nm, as shown by TEM. By adju…
Stable, hydroxyl functional polycarbonates with glycerol side chains synthesized from CO(2) and isopropylidene(glyceryl glycidyl ether).
2012
A series of functional polycarbonates, poly((isopropylidene glyceryl glycidyl ether)-co-(glycidyl methyl ether) carbonate) (P((IGG-co-GME) C)) random copolymers with different fractions of 1,2-isopropylidene glyceryl glycidyl ether (IGG) units, is synthesized. After acidic hydrolysis of the acetal protecting groups, a new type of functional polycarbonate prepared directly from CO(2) and glycerol is obtained, namely poly((glyceryl glycerol)-co-(glycidyl methyl ether) carbonate) (P((GG-co-GME) C)). All hydroxyl functional samples exhibit monomodal molecular weight distributions with PDIs between 2.5 and 3.3 and M(n) between 12 000 and 25 000 g mol(-1) . Thermal properties reflect the amorphou…
Squaric Acid Mediated Synthesis and Biological Activity of a Library of Linear and Hyperbranched Poly(Glycerol)-Protein Conjugates
2012
Polymer-protein conjugates generated from side chain functional synthetic polymers are attractive because they can be easily further modified with, for example, labeling groups or targeting ligands. The residue specific modification of proteins with side chain functional synthetic polymers using the traditional coupling strategies may be compromised due to the nonorthogonality of the side-chain and chain-end functional groups of the synthetic polymer, which may lead to side reactions. This study explores the feasibility of the squaric acid diethyl ester mediated coupling as an amine selective, hydroxyl tolerant, and hydrolysis insensitive route for the preparation of side-chain functional, …
Cytotoxicity and chemosensitizing activity of amphiphilic poly(glycerol)-poly(alkylene oxide) block copolymers.
2014
All polymeric chemosensitizers proposed thus far have a linear poly(ethylene glycol) (PEG) hydrophilic block. To testify whether precisely this chemical structure and architecture of the hydrophilic block is a prerequisite for chemosensitization, we tested a series of novel block copolymers containing a hyperbranched polyglycerol segment as a hydrophilic block (PPO-NG copolymers) on multi-drug-resistant (MDR) tumor cells in culture. PPO-NG copolymers inhibited MDR of three cell lines, indicating that the linear PEG can be substituted for a hyperbranched polyglycerol block without loss of the polymers' chemosensitizing activity. The extent of MDR reversal increased with the polymers affinity…
Phosphonylation Controls the Protein Corona of Multifunctional Polyglycerol-Modified Nanocarriers.
2018
Nanocarriers are a platform for modern drug delivery. In contact with blood, proteins adsorb to nanocarriers, altering their behavior in vivo. To reduce unspecific protein adsorption and unspecific cellular uptake, nanocarriers are modified with hydrophilic polymers like poly(ethylene glycol) (PEG). However, with PEG the attachment of further functional structures such as targeting units is limited. A method to introduce multifunctionality via polyglycerol (PG) while maintaining the hydrophilicity of PEG is introduced. Different amounts of negatively charged phosphonate groups (up to 29 mol%) are attached to the multifunctional PGs (Mn 2-4 kg mol-1 , Ð < 1.36) by post-modification. PGs are …
Effect of plasticizers (water and glycerol) on the diffusion of a small molecule in iota-carrageenan biopolymer films for edible coating application.
2006
Translational diffusion of a fluorescein probe has been measured in iota-carrageenan edible films containing different amounts of glycerol (0, 15, 30, and 45%), using fluorescence recovery after photobleaching (FRAP) experiments. The effects of this plasticizer as well as the plasticizing effect of water on the diffusion of fluorescein have been studied in this edible coating mainly composed of natural biopolymer. Diffusion coefficients of about 10(-13) m2 s(-1) have been measured in these films for water activity (aw) lower than 0.7. Above this water content threshold, fluorescein translational diffusion coefficient increases up to 10(-12) m2 s(-1). Another interesting information obtained…
Beyond Poly(ethylene glycol): Linear Polyglycerol as a Multifunctional Polyether for Biomedical and Pharmaceutical Applications
2014
Polyglycerols (sometimes also called "polyglycidols") represent a class of highly biocompatible and multihydroxy-functional polymers that may be considered as a multifunctional analogue of poly(ethylene glycol) (PEG). Various architectures based on a polyglycerol scaffold are feasible depending on the monomer employed. While polymerization of glycidol leads to hyperbranched polyglycerols, the precisely defined linear analogue is obtained by using suitably protected glycidol as a monomer, followed by removal of the protective group in a postpolymerization step. This review summarizes the properties and synthetic approaches toward linear polyglycerols (linPG), which are at present mainly base…
Functionalization of a polyaspartamide with glycidyl methacrylate: A useful method to prepare hydrogels through gamma irradiation
1999
α-β-Poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) was derivatized with glycidyl methacrylate (GMA). Aqueous solutions of the obtained copolymer PHEA-GMA (PHG) were irradiated by gamma rays with a dose rate of 0.5 KGy/h and at zero °C in the presence or in the absence of N,N'-methylenebisacrylamide (BIS). New hydrogel systems were obtained and characterized by FT-IR analyses and swelling measurements in aqueous medium at different pH values.
Hydrogels containing 5-Fluorouracil obtained by γ-irradiation. Synthesis, characterization and in vitro release studies
2001
The functionalization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) with glycidyl methacrylate (GMA) gives rise to a water-soluble copolymer PHEA-GMA (PHG) containing double bonds and ester groups in the side chain. Aqueous solutions of PHG alone or in combination with N,N′ methylenbisacrylamide (BIS) have been exposed to a γ-ray source at different irradiation doses in order to obtain polymeric networks. All samples have been prepared both as water-swellable microparticles and as gel systems. Microparticles have been characterized by FT-IR spectrophotometry and swelling measurements in aqueous media mimicking biological fluids. The effect of irradiation dose and BIS presence on rheol…