Search results for "polymerization"
showing 10 items of 1689 documents
Effect of interfacial area on heterogeneous free radical grafting of vinyl monomers in supercritical carbon dioxide: Grafting of acrylic acid on poly…
2014
The role of the polymer interfacial area on free radical grafting of acrylic acid (AA) onto poly(vinylidenefluoride) (PVDF) was studied at 65°C using supercritical carbon dioxide (scCO2) as a solvent and swelling agent, benzoylperoxide (BPO) as chemical initiator and PVDF nanoparticles as polymer matrix. Under adopted conditions PVDF particles do not melt neither dissolve in the reaction medium and FTIR analyses performed on carefully washed nanoparticles confirmed the achievement of high grafting levels. The mass fraction of grafted AA increased with the grafting time and the BPO concentration while it decreased when the density of the fluid phase was enhanced. Collected results suggest th…
Synthesis and degradation of poly (2-hydroxyethyl methacrylate)-graft-poly (ε-caprolactone) copolymers
2004
Abstract Poly (e-caprolactone) macromonomers carrying a methacryloyl end groups were synthesized using different lanthanide derivatives as catalysts, and characterized by SEC and 1 H NMR. Hydrophilic–hydrophobic copolymers from macromonomers and 2-hydroxyethyl methacrylate (HEMA) were obtained by solution free radical polymerization. Depending on the feed ratio of the two components, different copolymer structures were obtained. The expected graft structure of the copolymers was confirmed by 1 H NMR. Thermal properties of the copolymers were determined by DSC and TGA. Hydrolytic and enzymatic degradations of the materials were performed. Poly (2-hydroxyethyl methacrylate)- graft -poly (e-ca…
The rate of polymerization in two loci reaction systems: VDF-HFP precipitation copolymerization in supercritical carbon dioxide
2011
When the copolymerization of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) is carried out in supercritical carbon dioxide (scCO 2) under heterogeneous conditions, the reaction occurs both in the continuous CO 2-rich phase and in the dispersed polymer-rich phase. The two phases being characterized by different values of reactant concentrations and kinetic parameters, one would expect that the reaction kinetics is affected by the polymer phase holdup in the reactor. However, the reaction rate is almost insensitive to the amount of produced polymer, at least at specific reaction conditions. This apparent contradiction is discussed and clarified in this paper by a series of comparativ…
Analysis of pectin biopolymer phase states using acoustic emissions.
2019
Acoustic emissions are stress or elastic waves produced by a material under external load. Since acoustic emissions are generated from within and transmitted through the substance, the acoustic signature provides insights into the physical and mechanical properties of the material. In this report, we used a constant velocity probe with force and acoustic emission monitoring to investigate the properties of glass phase and gel phase pectin films. In the gel phase films, a constant velocity uniaxial load produced periodic premonitory acoustic emissions with coincident force variations (saw-tooth pattern). SEM images of the gel phase microarchitecture indicated the presence of slip planes. In …
The Unique Versatility of the Double Metal Cyanide (DMC) Catalyst: Introducing Siloxane Segments to Polypropylene Oxide by Ring-Opening Copolymerizat…
2020
The combination of hydrophobic polydimethylsiloxane (PDMS) blocks with hydrophilic polyether segments plays a key role for silicone surfactants. Capitalizing on the double metal cyanide (DMC) catalyst, the direct (i.e., statistical) copolymerization of cyclic siloxanes and epoxides is shown to be feasible. The solvent-free one-pot copolymerization of hexamethylcyclotrisiloxane and propylene oxide results in the formation of gradient propylene oxide (PPO)-PDMS copolymers. Copolymers with up to 46% siloxane content with low dispersities (Ð < 1.2) are obtained in the molecular weight range of 2100-2900 g mol-1 . The polymerization kinetics are investigated by pressure monitoring and in situ 1 …
HPMA Based Amphiphilic Copolymers Mediate Central Nervous Effects of Domperidone
2011
In this study we give evidence that domperidone encapsulated into amphiphilic p(HPMA)-co-p(laurylmethacrylate) (LMA) copolymer aggregates is able to cross the blood-brain barrier, since it affected motor behaviour in animals, which is a sensitive measure for CNS actions. Carefully designed copolymers based on the clinically approved p(HPMA) were selected and synthesized by a combination of controlled radical polymerization and post-polymerization modification. The hydrodynamic radii (R(h) ) of amphiphilic p(HPMA)-co-p(LMA) alone and loaded with domperidone were determined by fluorescence correlation spectroscopy.
Copolymers of ethylene with monoalkenyl- and monoalkenyl(siloxy)silsesquioxane (POSS) comonomers – Synthesis and characterization
2017
Abstract The hybrid ethylene/POSS copolymers were obtained using the rac -Et(Ind) 2 ZrCl 2 catalyst activated by MAO. A series of monoalkenyl- and monoalkenyl(siloxy)silsesquioxanes derivatives with different structures of reactive alkenyl substituent and types of non-reactive groups attached to the T 8 POSS cage was used as comonomers. The kind and concentration of the POSS comonomer in the reaction feed as well as extended reaction time were found to strongly influence the catalyst efficiency and incorporation of POSS units into polymer chains. The comonomer reactivity was significantly dependent on the length of the alkenyl reactive substituent in the POSS molecule and it was highest for…
Kinetic studies of two-step polymerization of propylene over a titanium-aluminum catalyst
1997
The influence was studied of the modification of an unsupported titanium-aluminum catalytic system with an internal Lewis base incorporated, via prepolymerization, on the activity of this system in propylene polymerization. In order to clarify the reasons for the activating effect of prepolymerization, comparative studies were carried out on the kinetics of polymerization catalyzed by a titanium system and its prepolymerized counter part. Based on the kinetic model suggested for the polymerization mechanism, the concentration of active sites and rate constants were determined for chain propagation, chain transfer and termination reactions. The following conclusions were deduced: (i) the ini…
One-pot synthesis and characterization of aliphatic poly(oxytetramethylene) ionene
2002
Abstract One-pot synthesis of poly(oxytetramethylene) ionene (POI) composed of one dimethylammonium group in each repeating unit is described. POI was prepared by using the cationic polymerization of tetrahydrofuran, followed by the chain extension reaction of living poly(oxytetramethylene) (POTM) chain with N , N -dimethylaminotrimethylsilane. The weight average molecular weight of the ionene with bromide counter-anion (POI–Br) was 48,000 g/mol and the molecular weight of POTM between the ionic sites was ca. 2100. POI–Br showed polyelectrolyte behavior in polar solvent. The elastomeric film of POI–Br was prepared: its tensile strength at break and elongation at break were ca. 11 MPa and ca…
Cleavable Polyethylene Glycol: 3,4-Epoxy-1-butene as a Comonomer to Establish Degradability at Physiologically Relevant pH.
2016
Polyethylene glycol (PEG) has been used for decades to improve the pharmacokinetic properties of protein drugs, and several PEG-protein conjugates are approved by the FDA. However, the nondegradability of PEG restricts its use to a limiting molecular weight to permit renal excretion. In this work, we introduce a simple strategy to overcome the nondegradability of PEG by incorporating multiple pH-sensitive vinyl ether moieties into the polyether backbone. Copolymerization of 3,4-epoxy-1-butene (EPB) with ethylene oxide via anionic ring-opening polymerization (AROP) provides access to allyl moieties that can be isomerized to pH-cleavable propenyl units (isoEPB). Well-defined P(EPB-co-EG) copo…