Search results for "Precipitation 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…

Synthesis of hydrophilic polymers in supercritical carbon dioxide in the presence of a siloxane-based macromonomer surfactant: Heterogeneous polymeri…

2003

Batch free radical polymerization of 1-vinyl-2-pyrrolidone (VP) in super- critical carbon dioxide (scCO2) was studied in the presence of a reactive polysiloxane surfactant (PDMS-mMA). Phase behavior investigation showed that when the initial concentration of the surface active macromonomer was higher than 2.5% w/w with respect to the monomer, the reaction mixture, in the absence of efficient stirring, was initially opaque to the visible light, and it slowly turned to an orange tint. Polymeriza- tion experiments carried out with surfactant concentration higher than the aforemen- tioned value proceeded with a fast kinetics, and led to the formation of spherical nanoparticles with almost quant…

Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide stabilized with poly(ethylene glycol)-b-perfluoroalkyl compounds

2004

Abstract In this work selected components of an easily synthesible class of poly(ethylene glycol)-perfluoroalkyl block compounds were tested as stabilizers for the dispersion polymerization of methyl methacrylate in scCO 2 . As already observed in the case of different block surfactants the anchor soluble balance (ASB) of the stabilizer is the crucial parameter affecting the efficacy of the stabilization and the kinetics of the polymerization process. When stabilizers with appropriate ASB were used, high molecular weight poly(methyl methacrylate) was synthesized under the form of microspherical polymer particles with yields ranging up to 80%. In these experiments the occurrence of a gel-eff…

Liquid-Crystalline Colloidal Particles

2004

Here we report about the synthesis of colloidal particles of nematic and smectic liquid-crystalline polymers. For this purpose mesogen-containing acrylate monomers were synthesized and polymerized in a special modification of a precipitation polymerization called dispection polymerization. By variation of the polymerization conditions colloidal particles of different size and polydispersity could be obtained including very narrowly distributed samples in optimized batches. On azobenzene-containing colloidal particles switching experiments with polarized light were performed. It could be observed that the nematic director of the mesogens within the colloidal particles can be rotated due to t…

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 …

1980

Using a bifunctional initiator such as the tetrameric dianion of α-methylstyrene for the anionic polymerization of methyl methacrylate the rate constant is found to increase with conversion approaching that observed with a monofunctional initiator while the tacticity of the polymers obtained changes from that of an almost ideally atactic to a highly syndiotactic polymer. The results are explained by the assumption of an intramolecular association of the two terminal ion pairs yielding a new active species and gradually dissociating with increasing degree of polymerization of the chain. Using a polymeric dianion of α-methylstyrene as an initiator the association phenomenon is not observed.

Some kinetic effects in the polymerization of 1,3,5-trioxane

1960

Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin host-guest complexes of methyl methacrylate or styrene from homogenou…

2000

The polymerization of methylated β-cyclodextrin (m-β-CD) 1 : 1 host-guest compounds of methyl methacrylate (MMA) (1) or styrene (2) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K2S2O8)/sodium hydrogensulfite (NaHSO3) as radical redox initiator at 60°C. Unthreading of m-β-CD during the polymerization led to water-insoluble poly(methyl methacrylate) (PMMA) (3) and polystyrene (4). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′-azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields i…

Surfactant-Free Emulsion Polymerization of Various Methacrylates: Towards Monodisperse Colloids for Polymer Opals

2004

A systematic investigation of the surfactant-free emulsion polymerization (SFEP) on three different methacrylates (MMA, tert-butyl methacrylate and 2,2,2-trifluoro ethyl methacrylate) is described to obtain monodisperse colloids for the preparation of artificial polymer opals. The experimental results are in agreement with a model, in which seed particles are formed very early during the polymerization process. The particles are formed very early during the polymerization process. The particles grow afterwards into the colloids until all monomer is consumed. This gives rise to a linear relationship between the volume of the colloids and the ratio of monomer to water in the reaction batch. T…