Search results for "polymerization"
showing 10 items of 1689 documents
The effect of prepolymerization of a titanium catalyst on its deactivation in propylene polymerization
1997
Propylene polymerization rate was investigated in the presence of anunsupported titanium catalyst (TiCl3) that had been modified with a Lewis base (di-n-butyl ether) and activated (precat), or not activated (cat), by being used in a suspension prepolymerization (70°C, 0.6 MPa) of an identical monomer. The initial polymerization rate was higher with the precat than with the cat catalyst. Prepolymerization was also found to enhance the kinetic stability of catalyst's active sites, presumably by reason of the prepolymerization-induced modification of catalyst's morphology. Deactivation rate constants were evaluated for the active sites of either catalyst examined.
Studies of alumina as a support of titanium catalyst for low-pressure ethylene polymerization
1986
The effect of alumina treatment with aqueous solutions of hydrochloric acid and ammonium fluoride as well as temperature of its calcination on the activity of Al-Ti/Al2O3 supported organometallic catalyst for ethylene polymerization has been studied. The dependence between the specific surface area of the support and both the kind and concentration of the modifying agent, concentration of OH-groups on Its surface and concentration of active centres with various activities is discussed with reference to the activity of the supported Al-Ti/Al2O3 catalyst. It was demonstrated that there is no simple relationship between the concentration of OH-groups on the support and the activity of the Ti-…
Study of methyl methacrylate polymerization in the presence of rubbers
2001
Grafting of poly(methylmethacrylate) onto various unsaturated rubbers is described. The grafting is achieved through thermally initiated methylmethacrylate in-situ polymerization. The main features of the polymerization process, i.e. conversion vs. time, grafting to rubber and gel percentage, have been investigated. The chemical structure of the rubber influences the process: rubber with pendant unsaturations gives rise to higher level of grafting.
Hyperbranched poly(glycolide) copolymers with glycerol branching points via ring-opening copolymerization
2015
Abstract Sn(Oct) 2 -catalyzed synthesis of hyperbranched poly(glycolide) copolymers with glycerol branching points in the backbone is possible via ring-opening multi-branching copolymerization (ROMBP) of glycolide and 5HDON (5-hydroxymethyl-1,4-dioxan-2-one). Using this strategy, well-defined and soluble branched polyesters with apparent molecular weights (M n ) in the range of 1300–2000 g mol −1 and varying comonomer content (5HDON/glycolide = 30:70–70:30) were obtained. 2D NMR spectroscopy, thermal analysis and MALDI-TOF mass spectrometry confirmed the successful incorporation of both monomers and the resulting branched structure. Multiple end group functionality offers the possibility fo…
Surface characterization of functional poly(diacetylene) and poly(butadiene) mono- and multilayers
1982
The surface properties of Langmuir-Blodgett mono- and multilayers of a variety of amphiphilic poly(diacetylene)s and poly(butadiene)s were investigated by contact angle, streaming potentialζ, ellipsometry, and X-ray photoelectron spectroscopic (XPS) measurements. Captive air and octane angles varied between approximately 60° and 105° for hydrophobicx-layers and 31° to 46° for hydrophilic surfaces depending on the particular head group, whereas advancing angles determined via the vertical plate method are considerably higher. Negative streaming potentials were obtained for all surfaces. Positively charged monolayers yielded less negativeζ- potential values (−28 mV) than negatively charged (−…
Diene/polar monomer copolymers, compatibilisers for polar/non-polar polymer blends. A controlled block copolymerisation with a single-site component …
2002
A well-controlled two-step process, the polymerisation of isoprene or isoprene/hex-1-ene copolymerisation followed by e-caprolactone polymerisation, affords trans-polyisoprene or (trans-polyisoprene/hex-1-ene copolymer)–poly(e-caprolactone) diblocks of various lengths. The single component initiator is an allylsamarocene compound. An atomic force microscopy study shows that these copolymers are efficient compatibilisers for poly(e-caprolactone) and polyisoprene blends. Poly(e-caprolactone) chain growth from Sm–polyisoprene chain.
Synthesis and NMR characterization of new poly(ethoxyalkyl) maleates
1994
Polymerizable surfactants derived from maleic anhydride have been synthesized. The hydrophilic part is obtained by a controlled ethylene oxide polymerization according to a new heterogeneous catalytic process. Some maleates derivatives have been obtained and fully characterized by 1H and 13C NMR. Their cmc were also measured. Some of them have been engaged in styrene emulsion polymerization in which monodisperse latex particles have been produced.
Branched Acid-Degradable, Biocompatible Polyether Copolymers via Anionic Ring-Opening Polymerization Using an Epoxide Inimer
2022
The introduction of acid-degradable acetal moieties into a hyperbranched polyether backbone has been achieved by the design of a novel epoxide-based degradable inimer. This new monomer, namely, 1-(glycidyloxy)ethyl ethylene glycol ether (GEGE), has been copolymerized in the anionic ring-opening polymerization (AROP) with ethylene oxide (EO) or glycidol (G), respectively, yielding branched polyethers, that is, P(EO-co-GEGE) and P(G-co-GEGE), that possess an adjustable amount of acid-cleavable acetal units. In addition, a novel class of multiarm star copolymers P(G-co-GEGE-g-EO) with acid-labile polyether core and PEG side chains was synthesized by using the P(G-co-GEGE) copolymers as multifu…
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…
Submicron structured polymethyl methacrylate/acrylonitrile-butadiene rubber blends obtained via gamma radiation induced ?in situ? polymerization
2004
The morphology and properties of PMMA/rubber blends, obtained through gamma radiation induced “in situ” polymerization of methyl methacrylate (MMA) in the presence of small quantities of an acrylonitrile–butadiene based rubber (ABN), are presented. Different systems have been obtained by irradiating at a fixed irradiation dose rate and temperature, varying the integrated dose. All the blends obtained were characterized with respect to their melt state and solid state dynamic-mechanical response and mechanical tensile properties. In particular, the effect on the blend properties of prolonging the irradiation time was investigated. Furthermore, a morphological characterization through atomic …