Search results for "kinetics"
showing 10 items of 2224 documents
Testing of a kinetics equation of mechanical degradation
1987
A modification of the kinetics equation of mechanical degradation of Harrington and Zimm is proposed to fit experimental data taken on a molten polystyrene. This equation is applied to each molecular weight of the discretized molecular weight distribution curve, and the limiting molecular weight is determined for each molecular weight. With this modification the theoretical curves fit both Mw and Mn curves well.
Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide-block-dimethylsi…
2004
The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane-b-ethylene oxide) (COP) and tetrahy- dronaphthalene (THN) was investigated. The crystallization kinetics was studied iso- thermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to h…
The poly(propylene oxide-co-ethylene oxide) gradient is controlled by the polymerization method: determination of reactivity ratios by direct compari…
2019
An investigation of the highly relevant copolymerization of ethylene oxide (EO) and propylene oxide (PO) by in situ1H NMR spectroscopy shows striking differences in the copolymerization kinetics, depending on the polymerization method. Examination of the EO/PO copolymerization kinetics using iBu3Al for the monomer-activated anionic ring opening polymerization (AROP) confirmed a strong monomer gradient of the microstructure (rEO = 6.4, rPO = 0.16) in contrast to the known weak gradient in the conventional AROP (rEO = 2.8, rPO = 0.25). The first study via in situ1H-NMR kinetics of the copolymerization of PO and EO under heterogeneous double metal cyanide (DMC) catalysis, a method that produce…
Processing, structure, property relationships and release kinetics of electrospun PLA/Carvacrol membranes
2018
Abstract In this work, polylactic acid (PLA) membranes at two different carvacrol (CRV) nominal concentration (i.e. 14 wt% and 28 wt%) were prepared via electrospinning technology. The membranes were characterized by scanning electron microscopy, ATR-FTIR and calorimetric measurements as well as tensile tests. Moreover, the release kinetics of CRV in phosphate buffered solution at 37 °C was monitored through UV–Vis measurements and the data were fitted with a power law model. Results indicated that the successful incorporation of CRV in the polymer matrix damaged the fibers morphology but increased all the mechanical parameters investigated (i.e. elastic modulus, tensile strength and elonga…
Modelling polycarbonate synthesis rates on the example of bulk heteropolyaddition of diphenyl carbonate and bisphenol A diglycidyl ether
2016
This paper investigates the effects of increased reaction mixture viscosity on the kinetics of linear polymer creation in a bulk polyaddition process of diphenyl carbonate and bisphenol A diglycidyl ether. The paper presents a method for solving a system of bulk polyaddition of diphenyl carbonate and bisphenol A diglycidyl ether process balance equations, allowing the determinatiof the process kinetic parameters. Determination of polymerisation reaction kinetic parameters was also made possible by the use of the so-called partial reaction rate constant. Such an approach enabled a significant simplification of the mathematical expressions describing the heteropolyaddition process and provide…
Tetrahydrofuran: More than a “Randomizer” in the Living Anionic Copolymerization of Styrene and Isoprene: Kinetics, Microstructures, Morphologies, an…
2020
The statistical anionic copolymerization of isoprene (I) and styrene (S) is commonly used to synthesize tapered block copolymers, enabling control of the phase behavior by adjusting the order–disor...
Adsorption of di-and triblock copolymers with functionalized butadiene-styrene blocks from dilute solution
1995
Abstract The adsorption behaviour of functionalized polystyrene-block-polybutadiene diblock copolymers, P(S-b-B), and polybutadiene-block-polystyrene-block-polybutadiene triblock copolymers, P(B-b-S-b-B), from dilute solutions in toluene onto silicon wafers was investigated by means of null-ellipsometry. Polar 4-(3,5-dioxo- 1,2,4-triazolidin-4-yl) benzoic acid groups (urazole groups) were attached randomly to the butadiene blocks. The PS blocks and the PB blocks adsorb not on the substrate surface, but only on the polar functional groups. It was verified that the adsorbed amount does not depend on the number of functional groups nor on the degree of polymerization of the polybutadiene block…
Photooxidation Behavior of a LDPE/Clay Nanocomposite Monitored through Creep Measurements
2017
Creep behavior of polymer nanocomposites has not been extensively investigated so far, especially when its effects are combined with those due to photooxidation, which are usually studied in completely independent ways. In this work, the photooxidation behavior of a low density polyethylene/organomodified clay nanocomposite system was monitored by measuring the creep curves obtained while subjecting the sample to the combined action of temperature, tensile stress, and UV radiation. The creep curves of the irradiated samples were found to be lower than those of the non-irradiated ones and progressively diverging, because of the formation of branching and cross-linking due to photooxidation. …
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…
Role of thermal history on quiescent cold crystallization of PET
2002
8 pags., 9 figs.