1,4-polyisoprene-polyacetylene copolymers

The Surface Excess Structure in 1,4-Polyisoprene-Polyacetylene Copolymer Solutions... 

Armes et al. [116] reported the synthesis of soluble polyisoprene-polyacetylene diblock copolymers with a cobalt catalyst system. The polyacetylene segment was suggested to have a molecular weight equal to 1200. A low-temperature polymerization resulted only in cw-polyacetylene blocks in the copolymer, although appreciable isomerization to a transisomer was observed over 23 h at room temperature. The electrical properties of this material have not yet been determined. 

Armes, S. P, Vincent, B., and White, J. W., A novel route for producing soluble polyacetylene-polyisoprene block copolymers, J. Chem. Soc. Chem. Commun., 28, 1525-1527 (1986). 

Abstract Copolymers of 1,4-polyisoprene-polyacetylene with up to 25% polyacetylene are soluble in organic solvents and, like native polyacetylene, have interesting electrical and non linear optical properties. Because the molecules are amphiphilic techniques analogous to Langmuir-Blodgett methods may prove useful for self assembly and so here we study the surface excess of toluene solutions by the specular reflection of neutrons. A surface layer structure with excess PA at the air/solvent interface is characterised using the isotopic replacement method in neutron scattering. 

Surface activity in 1,4-polyisoprene-polyacetylene, AB, block copolymer solutions was to be expected from the amphiphilic properties of such a diblock system with one moiety so insoluble because of the strong polyacetylene-polyacetylene attractive interactions. The present experiments allow access, for the first time, to some of the thermodynamic parameters of these interactions and give a structural model for the surface excess above and below the critical micelle concentration. This has been identified as about 10" moles/L for the lelated polymer 1,4-polyisoprene-polyacetylene (MW 8000 520) in toluene at 20 C using the drop weight method to determine surface tension. From ca. 10" molar to molar the surface tension drops by about 3.5% to a constant value of ca. 28.4 dyne cm at concentrations above 10 3 molar (ca. 1% w/w). Referring to Figure 3 we see that it is above ca 1% that a broad peak develops in the solution/solvent reflectivity ratio for 0.15 < k / < 0.25. The area per... 

Another approach to blending of polyacetylene with tough polymers is to form graft or block copolymers 280,281). Aldissi282) produced block copolymers by polymerizing acetylene at the ends of chains of anionic polyisoprene after conversion of... 

PA-polymethyl methacrylate graft copolymers were the products of the polymerization of methyl methacrylate on polyacetylene doped by Na [107]. Polystyrene, polyisoprene, and cis-1,4-polybutadiene were used as polymer carriers [108,109]. Acetylene was polymerized with Ti(OBu)4-AlEt3 in a toluene solution of the polymer carrier. The authors considered the formation of graft copolymers to be the result of the nucleophilic effect of a growing PA chain on the electrophilic sites in the polymer carrier. 

Small-angle neutron and x-ray scatterings were combined with electrochemical measurements for PA-enriched polyisoprene copolymers in order to understand the differences in oxidation-reduction properties and charge storage in the copolymer as compared with the behavior of separate homopolymers [121]. Microphase separation to micelle-like structures with the polyacetylene component surrounded by a nonoxidizable polyisoprene occurs in a solution, in electrodeposited films, and in solvent-cast films and affects the electrochemistry and the netics of charge storage. Electrodeposition of the copolymers is a possible route of copolymer separation from the mixed homopolymer. 

Figure 2.1. The formation of a polyacetylene graft copolymer using either polystyrene (with 3% butadiene) or polyisoprene as the carrier polymer. The electrophilic sites can be a combination of epoxides, aldehydes or ketones.

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