Shirakawas Method for the Polymerization of Acetylene

The Shirakawa PA films are shiny, flexible, polycrystalline, and completely insoluble in any solvent. Tb determine the molecular weight of the polymer, a sample of doped Shirakawa PA was hydrogenated to polyethylene at 175-260° C for 20 h under a high hydrogen pressme of 30 atm [10-12]. The resulting hydrogenated sample was totally soluble in tetralin. Since linear polyethylene is completely soluble in hot tetralin, it was assumed that Shirakawa s Ti(OBu)4/AIEt3 synthesis produced PA with no 

Four types of cis and tram structures are possible for PA (Fig. 1). Generally the trans-tramoid structure is simply termed tram, and the cis-tramoid structure is called cis. With the Shirakawa method either cis- or tram-YA can be synthesized. At a polymerization temperature of —78°C, ds-PA is formed exclusively. With increased temperature, a higher percentage of tram-PA forms (Ikble I). tram-PA forms exclusively at 150° C. At low temperatures a dr-structure arises predominantly from a cis insertion of the acetylene into the active site of the catalyst. Fukui and Inagaki suggest that a 

Ikble I. Percentage cir-Structure in PA Prepared by Ti(OBu)4/AlEt3 (1 4) As a Function of Reaction Temperature [9] 

PA has a highly complex, semicrystalline fibrillar morphology. The diameters of the fibrils vary from 30 A to 1 /zm, as seen by electron microscopy [19-21]. The specific size of the fiber depends on the method of polymerization and, more specifically, the type and 

A slightly more dilute catalyst solution ([Ti] = 10 M) yields a foam product. With a very dilute catalyst solution ([Ti] = 10 M) a black powder is formed. 

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