Anionic homogeneous

Three kinds of polymer segments are formed in the polymerization of dienes 1-4 cis-, 1-4 trans-, and 1-2 segments (or 3-4 in polymerization of isoprene or other monosubstituted dienes). The latter may form isotactic or syndiotactic diads when the proportion of the 1-2 form is sufficiently high, e.g. a syndiotactic, highly 1-2 polybutadiene was described recently by Ashitaka et al. 123), although the so far examined 1-2 polybutadienes produced by homogeneous anionic polymerization were found to be atactic (unpubl. results of Bywater, Worsfold). 

Selenocyanate complexes, 17 354, 356 homogeneous anionic, 17 354, 355 infrared spectra, 17 255 mixed-ligand, 17 354, 356 electronic effects, 17 355 steric effects, 17 354, 355 Selenocyanate ions, see also Chalcogeno cya-nates... 

L. J. Fetters, Procedures for Homogeneous Anionic Polymerisation, J. Res. Natl. Bureau of Standards, A. Phys and Chem, 70A, 421 (1966). 

Because of the strong interest in homogeneous anionic polymerization, especially during the past 20 years, there have been substantial advances, both in the understanding of the mechanisms involved as well as in the utilization of these systems for the synthesis of new materials. This overview will attempt to highlight the more important advances in both of the above areas, although admittedly with somewhat of a bias toward those particular endeavors pursued in our own laboratories. 

The current status of homogeneous anionic polymerization by alkali metal derivatives is reviewed along two lines ... 

A brief review is presented of the unique synthetic capabilities inherent in these homogeneous anionic systems, including the following macromolecular structures l) block copolymers,... 

Hg(CNO)2 is decomposed by heat (equation 8).4 It crystallizes in the orthorhombic form and contains linearly coordinated mercury.21 It reacts with alkali metal fulminate solutions to form the highly explosive compounds M2Hg(CNO)4 (M = K, Rb, Cs) with larger cations such as Ph4As+ more stable complexes are formed.219,220 Besides the homogeneous anionic mercury(II) fulminato complexes there are a few mixed species with unknown structures, e.g. Na Hg(CNO)2X (X = Cl, Br) or Na2S203-2Hg(CNO).221... 

Eq. (17) predicts that, when Pn is 100, the polydispersity is equal to 1.01, so that the polymer is virtually monodisperse. However, such ideal monodisperse polymers have scarcely been synthesized. The lowest values of polydispersity (Mw/Mn = 1.05-1.10) have been attained in homogeneous anionic polymerization 43). Gold 41) calculated the polydispersity of a polymer in the living polymerization with a slow initiation reaction and showed that the value of Pw/Pn increases slightly to a maximum (1.33) with an increase in polymerization time, followed by a decrease toward 1.00. Other factors affecting the molecular weight distribution of living polymer have been discussed in several papers 5S 60). 

A homogeneous anion-exchange membrane can be obtained by introducing a quaternary amine group into polystyrene by a chloromethylation procedure followed by an amination with a tertiary amine according to the following reaction scheme ... 

The mode of thiocyanate coordination in known homogeneous anionic complexes is listed in Table XXXVIII. Although further... 

Table XLI summarizes the structures of known, homogeneous, anionic selenocyanate complexes. Although fewer examples exist than for the corresponding thiocyanate complexes, it is apparent that a similar pattern exists for the two sets of complexes. Class a metals are coordinated by the nitrogen atom, whereas selenium is the donor for the class b metals. In mixed metal complexes containing bridging seleno-oyanate groups the nitrogen atom coordinates to the harder or class a metal, and the selenium atom bonds to the softer or class b metal, as was observed with the corresponding thiocyanate complexes.

The detailed kinetics of homogeneous anionic propagation reactions differ in hydrocarbon solvents and in media like ethers and amines which can solvate the metal counterion. These systems are discussed separately below. 

Cationic polymerizations differ from free-radical and homogeneous anionic syntheses of high polymers in that the cationic systems have not so far been fitted into a generally useful kinetic framework involving fundamental reactions like initiation, propagation, and so on. To explain the reasons for the peculiar problems with cationic polymerizations we will, however, postulate a conventional polymerization reaction scheme and show where its inherent assumptions are questionable in cationic systems. 

Volume 15 deals with those polymerization processes which do not involve free radicals as intermediates. Chapters 1 and 2 cover homogeneous anionic and cationic polymerization, respectively, and Chapter 3 polymerizations initiated by Zeigler-Natta and related organometallic catalysts. Chapters 4, 5 and 6 deal with the polymerization of cyclic ethers and sulphides, of aldehydes and of lactams, respectively. Finally, in Chapter 7 polycondensation reactions, and in Chapter 8 the polymerization of AT-carboxy-a-amino acid anhydrides, are discussed. 

The mechanism of the initiation of the radical polymerisation of polar monomers in systems comprising organometallic compounds Homogeneous anionic polymerisation of unsaturated monomers Metallopolymers... 

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. 

The tetramers are also useful initiators of homogeneous, anionic polymerization. 

The same homogenous anionic rhodium catalyst is also active for the carbonylation of methyl acetate to acetic anhydride. The "immobilized" form on Reillex , a polyvinyl pyridine resin, has been reported for the carbonylation of methyl acetate to acetic anhydride. Literature procedures readily allow for the preparation of 2 to 5% by weight of rhodium on Reillex " (7). These catalysts... 

There are some cases in homogeneous anionic polymerization in which the initiator dissociates completely with quantitative transformation into the active ionic form and the process is also virually instantaneous (stoichiometric polymerization). This is the case, for example, when one uses, as initiators, alkali organic... 

Unlike free-radical and homogeneous anionic polymerizations, cationic polymerizations cannot be described by conventional kinetic schemes involving reactions like initiation, propagation, and so on. This is due to the complexity of the cationic initiation and the variable extents of ion-pair formation at the propagating chain end [cf. Eq. (8.1)]. The possibihty of the reaction being heterogeneous due to the limited solubility of the initiator m the reaction medium further adds to the complexity of the kinetics. 

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