Macromolecules syndiotactic

Note In a syndiotactic macromolecule, the configurational repeating unit consists of two configurational base units that are enantiomeric. 

Note 2 A syndiotactic macromolecule consists of racemo diads. 

Ideal syndiotactic macromolecules possess a symmetry plane only when the total number of main chain tertiary carbon atoms is odd the polymer, however, should be optically active when each macromolecule contains, in the main chain, an even number of asymmetric carbon atoms and no pseudo asymmetric (42) carbon atoms. In the second case the molar optical activity, referred to one single monomeric unit, is large when the number of asymmetric carbon atoms n is small, as for instance in low-molecular-weight model compounds, but will become extremely small when n becomes very large. 

The first thoroughly documented case of cationic intramolecular hydride shift polymerization was reported recently (158—163). In the course of fundamental studies on cationic polymerization, Huggins (164) prediction (i.e., the possibility to obtain ordered macromolecules at increasingly low temperatures) was applied to cationic systems in an effort to obtain crystalline syndiotactic macromolecules by low tern-... 

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. 

Syndiotactic macromolecule - A tactic macromolecule, essentially comprising alternating enantiomeric configurational base units which have chiral or prochiral atoms in the main chain in a unique arrangement with respect to their adjacent constitutional units. In this case the repeating unit consists of two configurational base units that are enantiomeric. [8]... 

Thus, in vinyl polymers, only atactic macromolecules can be chiral in the first model with infinite length chain. The atactic and the syndiotactic macromolecules with an even number of monomer residues are chiral in the finite chain model with identical end groups, whereas all isotactic, syndiotactic and atactic chains have a chiral structure for the last model with different end groups [1,2]. 

Guerra, G. Vitagliano, V. M. De Rosa, C. Corradini, P., Polymorphism in melt crystallized syndiotactic polystyrene samples, Macromolecules 1990, 23, 1539 1544... 

De Rosa, C. Guerra, G. Petraccone, V. Pirozzi, B., Crystal structure of emptied clathrate form (8e form) of syndiotactic polystyrene, Macromolecules 1997, 30, 4147 4152... 

Guerra, G. Manfredi, C. Musto, P. Tavone, S., Guest conformation and diffusion into amorphous and emptied clathrate phases of syndiotactic polystyrene, Macromolecules 1998, 31, 1329 1334... 

Figure 38 Force field-calculated potential energy as a function of backbone dihedral angle for (a) H-(Ar2Si)3o-H and (b) syndiotactic H-(ArAr Si)30-H (where Ar = 4-n-butylphenyl, and Ar = 4-(S,)-2-methylbutylphenyl).248Reprinted with permission from Koe, J. R. Fujiki, M. Motonaga, M. Nakashima, H. Macromolecules 2001,34, 1082-1089, 2001 American Chemical Society.

The extension of the term isotactic to condensation polymers was made by Natta in his first article discussing poly-L-a-amino acids (22). In itself the term isotactic is redundant here as the configuration of the repeating unit is sufficient to identify the macromolecular stmcture. It is, however, useful to distinguish a system, racemic or not, in which each macromolecule is composed of only l or only D residues from a mixture of macromolecules made up of random or alternate sequences of L or d units. Similarly the term syndiotactic serves in the identification of oligopeptides or polypeptides composed of alternate sequences of D and L units, like those synthesized by Lorenzi and Tomasic (77). 

Analogous but even more complex is the analysis of syndiotactic vinyl polymers. In the first model, 7, individual macromolecules are achiral through the presence of the c and m planes the sequence of tertiary atoms (stereogenic but not chirotopic) will be. . . r, j, r, j, r, s. . . . 

Ajellal N, Bouyahyi M, Amgoune A, Thomas CM, Bondon A, Pillin I, Grohens Y, Carpentier J-F (2009) Syndiotactic-eirriched Poly(3-hydroxybutyrate)s via stereoselective ring-opening polymerization of racemic (3-butyrolactone with discrete yttrium catalysts. Macromolecules 42 987-993... 

These materials, however, as a rule exhibit rather broad chemical composition distribution. Block copolymers may contain important amounts of parent homopolymer(s) [232,244,269], In any case, it is to be kept in mind that practically all calibration materials contain the end groups that differ in the chemical composition, size, and in the enthalpic interactivity from the mers forming the main chain. In some cases, also the entire physical architecture of the apparently identical calibration materials and analyzed polymers may differ substantially. The typical example is the difference in stereoregularity of poly(methyl and ethyl methacrylate)s while the size of the isotactic macromolecules in solution is similar to their syndiotactic pendants of the same molar mass, their enthalpic interactivity and retention in LC CC may differ remarkably [258,259]. 

The distributions of isotactic (1) and syndiotactic (s) diad together with isotactic (I), heterotactic (H) and syndiotactic (S) triad sequences were determined from the resonances due to methylene and methine carbons Oguni N, Lee K, Tani H (1972) Macromolecules 5 819... 

It is worth noting that the absolute configuration of the tertiary carbon atoms in isotactic or syndiotactic polypropylene molecules has, in principle, no practical significance for the polymer properties, which might result from the presence of these carbon atoms in the main chain of the macromolecule. 

Iodine readily reacts with polymers bound to coordination centres, yielding macromolecules containing iodide end groups. The C—I bond can react with silver salts of superacids yielding carbocations essentially in the sense of the last steps of eqn. (32). Doi et al. [251, 252] have used this reaction for the synthesis of the copolymer poly(propene)-Mocfc-poly(tetramethylene oxide) with blocks of syndiotactic polypropylene. 

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