Polymers polyacetylene-type

The relatively high electronic conductivity of conducting polymers is connected with the presence in polymers of internal system of poly-7t-conjugated bonds. This is easy to understand on the example of a simplest type of conducting polymer (polyacetylene) in the main and activated states (Figure 6). 

A polyacetylene-type helical polymer having chiral amino alcohol pendant groups has also been prepared by the polymerization of chiral (S )-threonine-based... 

In this chapter the second moment studies are mainly reviewed for the two typical conjugated polymers Shirakawa-type (S-PA) [20-22,27,30-32] and Naar-mann and Theophilou-type (NT-PA) polyacetylenes [24] and polyparaphenylene [23,28,29]. The characteristic of NT-PA is a high degree of chain orientation attained by mechanical stretching, [33] which provides additional information on tlie polymer chain arrangement how much misorientatioii of the chains is left behind and how much of the amorphous portion exists [34]. From an analysis of the second moment M2... 

The polymers prepared are coloured solids, fairly stable on air (in most cases). The structure was estimated by spectroscopic methods (IR, NMR and UV-VIS). In all cases, the polyacetylene type polymer (i.e. conjugated polyene main chain with corresponding pendant groups) was confirmed. The polymer microstructure reflecting the catalyst type used was determined in most cases. 

Polydiacetylene LB films showed a conductivity of 10 S/cm after iodine doping [323,324] or ion irradiation [325], and polyacene-type ladder polymer can be formed by the irradiation of an electron beam or excimer laser [182,326]. The polyacetylene-type LB films were prepared using a diblock copolymer (Figure 14.44). The precursor block of the LB films could be converted to tra 5-polyacetylene by heat treatment, and the film showed a conductivity value of 2 x 10 S/cm after iodine doping [305]. LB films of carotene derivatives have also been reported [129,327,328]. 

Much effort has been expended toward the improvement of the properties of polyacetylenes made by the direct polymerization of acetylene. Variation of the type of initiator systems (17—19), annealing or aging of the catalyst (20,21), and stretch orientation of the films (22,23) has resulted in increases in conductivity and improvement in the oxidative stabiHty of the material. The improvement in properties is likely the result of a polymer with fewer defects. 

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

Figure 13 shows the irreversible conversion of a nonconjugated poly (p-phenylene pentadienylene) to a lithiun-doped conjugated derivative which has a semiconducting level of conductivity (0.1 to 1.0 S/cm) (29). Obviously, the neutral conjugated derivative of poly (p-phenylene pentadienylene) can then be reversibly generated from the n-type doped material by electrochemical undoping or by p-type compensation. A very similar synthetic method for the conversion of poly(acetylene-co-1,3-butadiene) to polyacetylene has been reported (30), Figure 14. This synthesis of polyacetylene from a nonconjugated precursor polymer containing isolated CH2 units in an otherwise conjugated chain is to be contrasted with the early approach of Marvel et al (6) in which an all-sp3 carbon chain was employed.

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