Syndiotactic polymethylmethacrylate

For instance, one of the various crystalline forms of polyoxacyclobutane is a hydrate [62], Syndiotactic polymethylmethacrylate also forms nonstoichiometric inclusion compounds with a variety of solvents [63,64]. 

Clustering (association or aggregation) as a result of dissimilar parts within one chain molecule is well-known in the field of biopolymers a recent example in the field of synthetic polymers is provided by poly (p-nitrophenylmethacrylate) which in dimethylformamide (105) forms threefold clusters, presumably because of the difference in polarity of backbone and ester groups. Liquori (118) has presented proof for a double-stranded helix of isotactic and syndiotactic polymethylmethacrylate. 

The formation of syndiotactic polymethylmethacrylate is the result of the prefered chain configuration in the free anionic polymerization, similar to the formation of syndiotactic structure by the free radical polymerization of methylmethacrylate. Bawn, James and North (77)... 

In THF or diglyme, 9-fluorenyllithium, which is dissociated extensively into ion pairs, catalysed through a strong anionic propagation to produce syndiotactic polymethylmethacrylate. The effectiveness of ethers to help dissociate the ion pairs was found to be related to the Lewis base strength of the ethers. 

The addition of the basic DME decreased the probability of isotactic placement by butyllithium. It also altered the nature of the already strongly anionic amylsodium and octylpotassium catalysts. This data shows that the more strongly anionic catalytic system looses the ability for isotactic steric control and produces instead the normal strongly anionic syndiotactic polymethylmethacrylate. 

Fluorescence depolarisation studies on mixtures of isotactic and syndiotactic polymethylmethacrylate have shown the formation of a 1 2 complex in toluene while fluorescence anisotropy studies on polybutadienes have shown viscous rotational diffusion with slipping boundary conditions OS. Fluorescence studies on quasi-rigid-rod like probes in anisotropic polyethylene have shown... 

Stereoregularity (tacticity) can also be determined by IR spectroscopy for some polymers. The IR spectra of isotactic and syndiotactic polymethylmethacrylate are indeed different and the same observations have... 

The influence of preformed stereoregular polymethylmethacrylate on the polymerization mechanism is particularly interesting. Grignard compounds at — 50 C in toluene give syndiotactic poly(methylmethacrylate) when preformed isotactic poly(methyl-methacrylate) is present, and vice versa [30,31]. In this replica polymerization, the primary structure formed is the 1 1 (isotactic/syndiotactic) complex. Further association between this complex and syndiotactic macromolecules results in the 1 2 (isotactic/syndiotatic) complex [32]. In the absence of preformed polymer, isotactic poly(methylmethacrylate) was obtained under the same conditions. 

The highly ordered planar stmctures, as obtained by stereospecific polymerization, were mentioned in Section 2.3. In contrast to the branched chains, we deal here with linear chains where side substitute groups appear regularly on the same side of the plane, or alternatively. These structures are named isotactic or syndiotactic, respectively, and the degree of order is termed "tacticity." In both cases, good conditions for crystallization exist, even when the polymer itself is known as difficult to crystallize (as in the case of polystyrene or polymethylmethacrylate). Any orderless structure is named atactic. 

Polymethylmethacrylate and polybutadiene are examples of polymers that can be prepared in the syndiotactic configuration. 

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