Homogeneous copolymers polymerization

In practice, there are effective means for nearly eliminating the spread of chemical compositions (14). The essential condition for the formation of a chemically uniform copolymer is that the monomers must be maintained in the same ratio throughout polymerization. There are two procedures for maintaining this condition. First, it can be achieved by making a continuous addition of either the more reactive monomer alone or certain mixtures of the comonomers as the reaction proceeds. The second method of producing chemically homogeneous copolymers is to proportion a mixture of monomers whose composition is the same as that of the copolymer being formed. 

Effect of Solvents and Reaction Conditions Synthesis Capabilities Block Copolymers Functional End-Group Polymers Initiation Processes in Anionic Polymerization Initiation by Electron Transfer Initiation by Nucleophilic Attack Mechanism and Kinetics of Homogeneous Anionic Polymerization Polar Media Nonpolar Media... 

Block Copolymers. The manufacture of block copolymers became possible in 1956 by M. Szwarc s discovery (24) of "living" polymers prepared in homogeneous anionic polymerization. Diblock, triblock, and multiblock copolymers are produced ionically in the presence of sodium naphthalene, butyllithium, or Ziegler-type catalysts. 

More homogeneous copolymer cpmpositions are obtained with soluble Zieg-ler-Natta catalysts, especially where monomer compositions are maintained relatively constant during polymerization. Commercially important ethylene-propylene binary copolymers (EPM rubbers) and ethylene-propylene-diene ternary copolymers (EPDM rubbers) are made by this process. 

Homogeneous fluoroalkene polymerizations (and copolymerizations) also proceed in SC-CO2 after AIBN initiation. [24, 25] In this case it is advantageous that highly fluorinated polymers (>250000 g mol 0 and copolymers are very soluble (up to 25 %) in SC-CO2 at high pressures. This means that no chlorofluorocar-bons need to be employed as solvents. The homopolymer (270000 g mol ) shown in Scheme 5 can be obtained from FOA in sc-CO2 (59.4 °C, 207 bar, 48 h, no Trommsdorff effect [24]) in 65 % yield. The product can be precipitated from the homogeneous solu-... 

Membranes which may be used in the removal of alkali metal ions by electrodialysis are those which are impermeable to anions, but which allow the flow therethrough of cations. Such cation-selective membranes should, of course, possess chemical durability, high resistance to oxidation and low electrical resistance in addition to their ion-exchange properties. Homogeneous-type polymeric membranes are preferred, for example, network polymers such as phenol, phenosulfonic acid, formaldehyde condensation polymers and linear polymers such as sulfonated fluoropolymers and copolymers of styrene, vinyl pyridine and divinylbenzene. Such membranes are well known in the art and their selection for use in the method of the invention is well within the skill of the art. 

Ionic mechanisms for the preparation of block copolymers are a very important tool of the synthetic polymer chemist. A feature of many homogeneous anionic polymerizations in solution is that termination can be avoided by careful control of experimental conditions. In fact, an infinite life of the active chain end is theoretically possible, and this has led to the term living polymers. Polymer carbanions can resume growth after the further addition of monomer. By changing the monomer composition, block copolymerization is readily initiated, and this process can be repeated. A major advantage of this... 

The synthesis of copolymers of ethylene and a-olefins is one of the important commercial advances made possible by the development of homogeneous olefin polymerization catalysts. The difference in reactivity between ethylene and a-olefins with many homogeneous catalysts is often one or two orders of magnitude. Thus, the controlled synthesis of copolymers comprised of these simple molecules has been challenging. 

N-Vinyl-2-pyrrolidone-acrylamide copolymers were prepared by aqueous homogeneous solution polymerization in either distilled water or synthetic seawater. The initial monomer level in the polymerization solutions was either 9.1% or 20% (w/w). The solutions were initiated at either room temperature or 50 C by either 0.50phm or O.lOphm commercial free radical initiators. A temperature controlling water bath was used with the 50 C polymerizations. 

All these homogeneous graft polymerizations are covered by the term interpenetrating networks . The so-called block copolymer of polypropylene (PP) is an example. This is made by homopolymerizing PP followed by a mixture of ethylene and propylene. Some grafting takes place (from the living ends of the PP) but the bulk is an intimate blend of PP with EP. 

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