Functions of Substituted Polyacetylenes

This review describes the synthesis and properties of polyacetylenes with substituents (substituted polyacetylenes) mainly on the basis of our recent studies At first, Sections 2 and 3 survey the synthesis of substituted polyacetylenes with group 6 (Mo, W) and group 5 (Nb, Ta) transition metal catalysts respectively, putting emphasis on new, high-molecular-weight polyacetylenes. Then, Section 4 refers to the behavior and mechanism of the polymerization by these catalysts. Further, Section 5 explains the alternating double-bond structure, unique properties, and new functions of substituted polyacetylenes. Finally, Section 6 provides detailed synthetic procedures for substituted polyacetylenes. 

Sections 2-4 dealt with the syntheses of substituted polyacetylenes with group 5 and 6 transition metal catalysts. Section 5 deals with the structure, properties, and functions of substituted polyacetylenes, especially those in Table 19 which are featured by their bulky substituents as well as high MW (the polymer samples were prepared under the conditions shown in Table 19). For comparison, the structure and properties of polyacetylene will also be mentioned. 

The high solubility and high stability of substituted polyacetylenes are the two most important properties which are not seen with polyacetylene. Consequently, stable membranes can be easily obtained by casting solutions of substituted polyacetylenes. This will greatly facilitate their application. Here, we refer to several functions of substituted polyacetylenes, which might be applied to oxygen enrichment of air, separation of ethanol-water mixtures, and so on. 

When a new polymer has been synthesized and its structure and properties have been clarified, then it becomes an interesting problem to develop functions of the polymer. As has been stated above, the electrical conductivity of substituted polyacetylenes is much lower than that of polyacetylene, and therefore their application to electric and electronic fields might be restricted. The photoconductive behavior of poly(phenylacetylene) has been reported 103). 

Typical functions of substituted poly acetylenes are based on their (i) high gas permeability and (ii) electronic and photonic properties. The former originates from the rigid main chain and bulky substituents. Though electrical insulators, substituted polyacetylenes are more or less conjugated polymers, and this feature has been utilized to develop their electronic and photonic functions such as photoconductivity, electrochromism, optical nonlinearity and ferromagnetism. 

To increase the processability and provide various functionalities of polyacetylene, a study on the synthesis and characterization of substituted polyacetylenes has been extensively investigated.The introduction of functional substituents into polyacetylene causes a drastic change in various properties of the polymers, because of their solubility, fusibility, and interesting chemical, optical, and other properties. 

Many papers in the literature have followed the finding by Masuda and coworkers (9). This article covers the literature from the mid-1980s up to mid-2000. As a result of the rapid growth in the area, the chemistry of polymers from acetylene, 1,3-diacetylenes, and Q, < -diacetylenes are excluded (see Polyacetylene Diacetylene and Tbiacetylene Polymers). The first focus is on the polymerization reaction of substituted acetylenes with various transition metal catalysts. The synthesis of functionally designed polyacetylenes is also covered. Readers are encouraged to access other reviews and monographs on polyacetylene (10-14), on 1,3-diacetylenes (15-19), and on a,Previous review articles are also helpful to survey the chemistry of substituted polyacetylenes (10,13,22-29). 

Two approaches currently seem open. The first is directed toward conjugated polymers. Here substituted systems may hold potential. Cyclopol3nnerization is a viable method of synthesis of substituted polyacetylenes. Likewise, chemical modification of polyacetylene itself may have potential. The preparation of polyacetylenes by elimination reactions from precursor polymers needs more attention. The second approach is toward non-conju-gated polymers containing aromatic functionalities little work has been done in this area. Much creative chemistry remains to be explored and it will most likely involve new monomers and polymers. ... 

This chapter surveys the polymerization of substituted acetylenes focusing on the research during this decade. Monomers and polymers, polymerization catalysts, controlled polymerizations, and functional polyacetylenes are discussed. Readers are encouraged to access other reviews and monographs on the polymerization of substituted acetylenes, and a,cj-diynes. ... 

Although the literature of gas separation with microporous membranes is dominated by inorganic materials, polymer membranes have also been tried with some success. The polymers used are substituted polyacetylenes, which can have an extraordinarily high free volume, on the order of 25 vol %. The free volume is so high that the free volume elements in these polymers are probably interconnected. Membranes made from these polymers appear to function as finely microporous materials with pores in the 5 to 15 A diameter range [71,72], The two most... 

Substituted polyacetylenes, especially poly(4a), have unique functions (3). One application is the use of the polymer membrane to separate substances. 

In these two decades remarkable progress has been made in the development of excellent catalysts for living and stereospecific acetylene polymerizations (10,26-28). The r-conjugated polymers prepared by the sequential polsrmerization are strictly limited to polyacetylenes, except for only a few examples. Thus, synthesis of tailor-made conjugated macromolecules such as end-functionalized polymers, block copolymers, star-shaped polymers is possible only in the case of substituted acetylenes. 

Thanks to the tremendous progress in the transition metal-catalyzed polymerization of substituted acetylenes as described in the previous sections, it is now possible to access various acetylene-based polymers having desired flrst-order structures. This, in combination with highly advanced organic synthetic technology, provides novel fimctional materials based on polyacetylenes, and the following surveys examples of the design and synthesis of functional substituted polyacetylenes. 

Toshio Masuda is professor at Fukui University of Technology and Professor Emeritus of Kyoto University. His research interests indude substituted polyacetylenes, transition metal-catalyzed polymerization, gas separation membranes, and polymeric functional materials. So far he has published about 460 origiiral papers and about 50 review artides, and has been given several awards induding SPSJ Award for Outstandirrg Achievement in Polymer Sdence and T hrK)logy. He is currently the editor of Polymer. 

The ROMP of 136 may be used as the first stage in the preparation of polyacetylene molecules with mesogenic (liquid-crystalline) functional groups at the chain ends the ROMP of 136 is initiated by a molybdenum carbene complex and the living ends terminated by reaction with a substituted benzaldehyde bearing a mesogenic group, followed... 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

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