Polyacetylene stereoregularity

A striking feature of the stereoregular polyacetylenes is their simple NMR spectral patterns, which facilitates elucidation of the polymerization mechanism as well as the polymer structure. A co-polymer of phenylacetylene with partly G-labeled phenylacetylene (Ph G= GH) shows two doublet carbon signals with /i3c-i3C of 72 Hz, indicating the presence of G= G bond in the polymer backbone.This is a clear indication of the insertion mechanism instead of the metathesis pathway. 

The product contains (besides some residual F and H) also inserted NBU4 , i.e. it is naturally n-doped. Even in the absence of BuOH, reactive nucleophiles like [(CH3)2NCHO] or (CH3)2N can be generated by preelectrolysis of dimethylformamide solutions [59]. Such a process allows electrochemical deposition of diamond-like carbon on an aluminum electrode [78] and it also produces polyyne from PVDF (cf. Eq. 4.22a). At similar conditions, PTFE shows no reactivity [59] and polyvinylchloride is dehydrohalogenated only to polyacetylene [79-82]. However, Zra 5-poly-acetylene, which was stereoregularly chlorinated by FeCh, is carbonizable by electrochemically generated BuO (cf. reactions 4.22 and 4.22a) [83] ... 

A recent study related to the current topic concerns the chlorination of polyacetylene, and addresses a new aspect of chemical doping. Akagi et al. [157] show that iodine doping of stretched polyacetylene films followed by chlorination produces stereoregularly chlorinated... 

In 1958 Natta with employees are polymerized acetylene on catalyst system Al(C2Hj))3—Ti(OC3H ) [7, 8]. The subsequent researches [9-11] led to reception of films stereoregular polyacetylene. The catalyst system Al(Et)3—Ti(OBu)4 provides reception of films of polyacetylene predominantly (up to 98%). 

Stereoregular ds-transoidal polyacetylenes can take a regular helical conformation. The main-chain stereoregularity is important in inducing a single-handed helical conformation. Rhodium catalysts such as [Rh(norbor-nadiene)Cl]2 are often used to obtain a stereoregular polymer. The helical structure of polyacetylenes is... 

Classification of Polymers Free-Radical Chain-Growth Polymerization Cationic Chain-Growth Polymerization Anionic Chain-Growth Polymerization Stereoregular Polymers Ziegler-Natta Polymerization A WORD ABOUT... Polyacetylene and Conducting Polymers Diene Polymers Natural and Synthetic Rubber Copolymers... 

In this chapter, the stereoregularity of polyacetylene and its derivatives are discussed in correlation with monomer, catalyst type, polymerization mechanism, polymer properties, and so forth. 

STEREOREGULARITY OF POLYACETYLENE 21.2.1 Polymerization Catalysts and Other Conditions... 

Polyacetylenes are the most typical and basic r-conjugated polymers, and can ideally take four geometrical structures (trans-transoid, trans-cisoid, cis-transoid, cis-cisoid). At present, not only early transition metals, but also many late transition metals are used as catalysts for the polymerization of substituted acetylenes. However, the effective catalysts are restricted to some extent, and Ta, Nd, Mo, and W of transition metal groups 5 and 6, and Fe and Rh of transition metal groups 8 and 9 are mainly used. The polymerization mechanism of Ta, Nd, W, and Mo based catalysts is a metathesis mechanism, and that of Ti, Fe, and Rh based catalysts is an insertion mechanism. Most of the substituted polyacetylenes prepared with W and Mo catalysts provide trans-rich and cis-rich geometries respectively. Polymers formed with Fe and Rh catalysts selectively possess stereoregular cis main chains. 

Tabata, M. Tanaka, Y Sadahiro, Y Sone, T. Yokota, K. Miura, 1. Pressure-induced cis to trans isomerization of aromatic polyacetylenes. 2. Poly((e-ethoxyphenyl)acetylene) stereoregularly polymerized using a Rh complex catalyst. Macromolecules 1997, 30, 5200-5204. 

Sato, M. A. Maeda, K. Onouchi, H. Yashima, E. Synthesis and macromolecular helicity induction of a stereoregular polyacetylene bearing a carboxy group with natural amino acids in water. Macromolecules 2000, 33, 4616 618. 

Stereoregular polyacetylenes have been attracting great attention due to the characteristic features based on their hehcal structure and the conjugated main chain [22, 23], The dynamic structure change in the helical polymers is particularly attractive. Stereoregular polyacetylenes with the c/s-transoidal structure have been synthesized by rhodium catalysts from various acetylene derivatives. 

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