Polymerization anionic type

Ring stability might be expected to lessen with increase in size and increasing proportion of SiOj because the silicate polyanions that correspond to compositions approaching 10 mol% of M O, would be very long. The critical 10% composition at which there is a radical change in many properties may be explained as that composition in the region of which a discrete polymerized anion type of structure becomes... 

Cyclopolymerizations, Onium polymerizations, Ziegler polymerizations, anionic-type initiation, 52, 53 cationic-type initiaton, 47-52 by ester interchange, 328-330 transannular, 33... 

One of the major advantages of radical polymerization over most other forms of polymerization, (anionic, cationic, coordination) is that statistical copolymers can be prepared from a very wide range of monomer types that can contain various unprotected functionalities. Radical copolymerization and the factors that influence copolymer structure have been discussed in Chapter 7. Copolymerization of macromonomers by NMP, ATRP and RAFT is discussed in Section 9.10.1. 

The process may be ascribed to the coordinated anionic type. Such a process which leads to the addition of a molecule of monomer in a polymeric chain, may be considered as divided into several consecutive steps. 

Extreme diversity is exhibited in the coupling of metal halide tetra-hedra to form polymeric halogenocuprate(I) and halogenoargentate(I) ions, there being an abundance of different types of infinite chains, layers, and three-dimensional arrays. Because the object of this article is to focus on variations in metal coordination number, and, in particular, on trends associated with the nature of the cation, structural description will be limited to those types of polymeric anion most frequently encountered hitherto in crystalline halogenocuprates(I) and halogenoargentates(I). 

Tsou, Magee and Malatesta (39) showed the effect of catalyst ratios on steric control m the polymerization of styrene with alkyllithium and titanium tetrachloride. These authors have shown that the isotactic polymer was produced when the butyllithium to titanium ratio was kept within the limits of 3.0 to 1.75. Outside of this critical range, amorphous polymers were produced. In the discussion of this paper, Friedlander (40) pointed out the cationic nature of the low-lithium-to-titanium-ratio-catalysts which also produced considerable rearrangement of the phenyl groups. Above 2.70 lithium to titanium ratio, an anionic type polymerization set in, which produced atactic polymer. At low ratios cationic catalysis also produced atactic polymer. Tsou and co-workers concluded that crystallinity of the catalyst is not important for steric order in the polymer. 

Bestian and Clauss proposed that the polymerization occured with isomerization on a cationic alkyltitanium species or one of its associated forms. Propagation by anionic and cationic species accounts for their results more easily. Most of the oligomer low molecular weight product was from anionic type propagation (Equation 8). However, the 7.8% of the dimer and the 30% of the trimer fractions were produced by cationic propagation of the n-butyl group (Equation 9). 

Monomeric alkyl lithium polymerizes isoprene through an anionic type propagating species. The transition between cis 1,4 and trans 1,4 polymerization is not clear since mono-ene polymerization also occurs in this region. Increased dielectric constant of the media, the addition of ethers, or the use of high lithium alkyl concentrations increased the character from that weakly anionic for the cis-diene polymerization to the slightly more anionic requirements for 3.4-monoolefinic polymerizations. 

This type of halogenation procedure involving active centers should be carefully examined since like a,a -dibromoxylene it is applicable to unsaturated polymeric anions such as poly(butadienyl)lithium and poly(isoprenyl)lithium whose double bonds would react directly with halogens. 

A Rohm and Haas group in 1958 (13, 21), reported that methyl methacrylate can be polymerized stereospecifically by an anionic type initiator under homogeneous conditions. Table 6 summarizes their results. 

A major objective of our research has been to introduce polar groups into polyolefin molecules. With the anionic type of catalysts, copolymerization is very difficult because most nonhydrocarbon vinylic monomers deactivate the catalyst system and stop olefinic polymerization. However, by the AFR route, the desired olefin is completely polymerized before polar monomers are introduced so that high yields of product are possible. 

Lactam polymerization with anionically activated monomer has its counterpart in the cationic processes of lactam polymerization. This type of mechanism has also been observed recently in some polymerizations of oxygen-containing heterocycles (see Chap. 4, Sect. 2.3)... 

The deciding factor which aroused increased interest in block copolymer production was the discovery of living anionic polymerization. New types of materials could be prepared by stepwise polymerization of several monomers. 

The formation of the polymeric carbanions 81 of the fluorenyl-type is successful starting from the poly(para-phenylene) ladder polymer 71 with butyl-lithium as metallating agent. The degree of lithiation lies in the range of 90-95% (NMR). The UV/VIS absorption spectrum of these polymeric anions (81) is comparable with that of the 9-phenylfluorenyl anion and indicates the presence of mostly localized (anionic) sub-structures [101]. 

The advent of the energy crisis has caused us to examine traditional views of the relative costs of different monomers and to consider the potential of less costly monomers for polymerization. One can expect that catalysis of the coordinated anionic type will play a major role in any new developments in olefin and diene polymerizations. Finally, one should recall that Ziegler catalysts have found many uses in other areas of chemistry such as metathesis of olefins, oligomerization, isomerization, hydrogenation, and alkylation. The vast scope of these catalysts will almost certainly achieve a wider range as these types of studies continue in the future. 

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