Search results for "Chain-growth polymerization"

Polymerization with heterogeneous metalorganic catalysts. VI. Differences in polymerization activity of α-olefins and some kinetic results on butene-…

1967

Relative changes in polymerization activity of ethylene, propylene, and butene-1 in Ziegler-Natta polymerization were compared by use of TiCl3 samples contaminated with O2 and H2O to various extents. Catalyst depletion varied for the three monomers which supported the existence of different active centers. In butene-1 polymerizations with the system Al(C2H5)2Cl–TiCl3, the formation of active centers involves an irreversible and a reversible (adsorption) reaction, the former pertaining to the formation of Al(C2H5)Cl2 and dependent upon the purity of the TiCl3. The kinetic treatment of the rate curves suggests a mixed order of catalyst deactivation and again points to the importance of Al(C2H…

Some New Copolymers by Ionic Polymerization

1980

In the first part the cationic polymerization of a homologous series of cyclic ether–acetals with ring sizes of 11, 14, and 17 atoms is described. During the polymerization of triethylene glycol formal (TGF) an equilibrium is reached and besides high polymers cyclic oligomers are formed. The oligomers and the polymers are built up of a regular sequence of one oxymethylene unit and three oxyethylene units –[–(OCH2) (OC2H4)3–]–x. They are therefore be labelled a “sequenced copolymer.” The equilibrium concentrations of the cyclic oligomers with a polymerization degree from 2 to 15 follow the Jacobson–Stockmayer equation. The 14- and 17-membered monomers POC and HOC forms cyclic oligomers and h…

Transition Metal Catalyzed Olefin, Cycloolefin, and Styrene Polymerization

2013

The sections in this article are History and Trends Polymerization Processes Supported Catalysts and Morphology Control Polymerization Mechanisms and Stereoselectivity History and Principles of Metallocene Catalysis Regio- and Stereoselective Polymerization of α-Olefins Polymerization of Cyclic Olefins, Cyclopolymerization, and Stereoselective Polymerization of Styrene Late Transition Metal Catalysts Transition Metal Catalyzed Copolymerization Acknowledgements

Synthesis of monodisperse oligomers of ɛ-aminocaproic acid up to a degree of polymerization of 25 by the Merrifield method (1)

1967

Dispersion Polymerization of Vinylidene Fluoride in Supercritical Carbon Dioxide

2006

The dispersion polymerization of vinylidene fluoride in supercritical carbon dioxide is investigated using two ammonium carboxylate perfluoropolyether stabilizers of different molecular weights. Under suitable operating conditions a polymer made of well-dispersed spherical particles has been obtained up to relatively high conversion. The experimental data of polymerization rate and molecular weight distribution are in good agreement with the predictions of a model previously developed. Such an agreement supports the conclusion that the polymerization kinetics is dominated by the interphase transport of the active radicals between the continuous phase and the polymer particles.

Polymerization of methyl methacrylate through ionizing radiation in CO2-based dense systems

2000

Herein, we report the use of ionizing radiation to induce a dispersion polymerization reaction in dense CO2. As a model system, the polymerization of methyl methacrylate in the presence of poly(dimethylsiloxane) stabilizers was investigated. It was demonstrated that the dose plays the key role in the progress of the reaction and in the morphology of the resulting polymer. Dispersion polymerization carried out in the presence of mono- and bifunctionalized surfactants gave differently structured polymers. The polymers obtained have been characterized by scanning electron microscopy, solubility tests, and gel permeation chromatography, and the molecular structure has been related to dynamic me…

Metal-free polymerization of phenylsilane: tris(pentafluorophenyl)borane-catalyzed synthesis of branched polysilanes at elevated temperatures.

2013

The strong organoborane Lewis acid B(C6F5)3 catalyzes the polymerization of phenylsilane at elevated temperatures forming benzene and SiH4 as side-products. The resulting polymer is a branched polysilane with an irregular substitution pattern, as revealed by 2D NMR spectroscopy. Having explored the mechanism of this novel metal-free polymerization by computational chemistry methods at the DFT level, we have suggested that unusual cationic active species, namely monomer-stabilized silyl cations, propagate the polymerization. Hydride abstraction of SiH3 moiety by the catalyst in the initiation step was found to be kinetically preferred by around 9 kcal mol(-1) over activation by coordination …

Carbanionic Polymerization: Kinetics and Thermodynamics

1989

For a kinetic analysis, the process of anionic polymerization has to be divided into at least three main reactions common to all types of polymerization (equations 1–3). I* denotes initiator, M monomer, Pi* and Pi′ an active or inactive polymer chain of degree of polymerization i, respectively, and X a terminating agent.

Solid-state polymerization of oxetanes. II. Investigation of the growth of the polymer phase as related to the mechanism of polymerization

1973

The radiation-induced solid-state polymerization of 3,3-bischloromethyloxetane (BCMO) was investigated by direct observation of the development of the morphology of the growing polymer phase in single crystals of the monomer. Electron microscopy shows that the polymerization gives rise to amorphous polymer in the first step. The polymer forms irregular platelets which aggregate into larger units without reflecting the crystalline order of the monomer. Subsequent to polymerization, the amorphous polymer crystallizes to the β-modification of poly-BCMO. If the partially polymerized crystals are extracted by solvents of the monomer, crystallization of the polymer is enhanced, and morphological …

What Limits the Molecular Weight and Controlled Synthesis of Poly(3-alkyltellurophene)s?

2016

Polytellurophenes are an emerging class of conjugated polymers; however, their controlled polymerization leading to high molecular weight materials has been a major challenge. Here we present a systematic investigation of the synthesis of poly(3-alkyltellurophene)s using the catalyst transfer polycondensation methodology. Learning that previous syntheses were limited by both polymerization reaction kinetics and polymer solubility, we design new tellurophene monomers to overcome these limitations. Controlled polymerization behavior up to Mn = 25 kDa, chain extension, block copolymerization, external initiation, and well-defined end groups are demonstrated for poly(3-alkyltellurophene)s with …