Polyacetylene grafted

Solution and physical properties of a polyacetylene graft copolymer... 

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.

Figure 2.3. The formation of a polyacetylene graft comb-like copolymer by direct insertion of Ziegler-Natta catalysts onto the carrier polymer, (a) The catalyst is inserted directly onto the 1,2-vinyI units, and (b) the carrier polymer is first lithiated before the addition of a Ziegler-Natta catalyst.

The addition of diethylaluminum chloride onto the pendant unsaturations of 1,2-units in polybutadiene has been studied by Greber and others. " The aluminated polymer can be reacted with ethylene in the presence of a transition metal compound (TiClj), to yield polyethylene grafts (Scheme 11). A similar method has been used to grow polyacetylene grafts from a polybutadiene... 

Copolymerizations of benzvalene with norhornene have been used to prepare block copolymers that are more stable and more soluble than the polybenzvalene (32). Upon conversion to (CH), some phase separation of nonconverted polynorhornene occurs. Other copolymerizations of acetylene with a variety of monomers and carrier polymers have been employed in the preparation of soluble polyacetylenes. Direct copolymeriza tion of acetylene with other monomers (33—39), and various techniques for grafting polyacetylene side chains onto solubilized carrier polymers (40—43), have been studied. In most cases, the resulting copolymers exhibit poorer electrical properties as solubiUty increases. 

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... 

Polyacetylene appeared to be insoluble in all solvents tested [10,32]. Note, however, that units of polyacetylene in soluble form have been obtained by using graft or block copolymerisation methods, such as grafting polyacetylene to soluble polymers [33-37], grafting soluble polymeric chains on the main backbone of polyacetylene [38] and diblock copolymerisation [39-42]. In contrast to polyacetylene, polymers that can be obtained from substituted acetylenes are soluble in common solvents. 

Figure 5.6. Synthesis of graft copolymers containing poly acetylene. Active catalysts for acetylene polymerization are generated on the polymer backbone, and the polyacetylene grows from the backbone.

The results are consistent with a model of polyacetylene sidechains on the matrix polymer backbone. While the mechanistic origin of the proposed graft reaction is unknown, a CH activation of a bond geminal to the polar substituent could explain the range of polymers accessible by this novel synthetic route. 

IR spectra of the PA/EPDM blends indicated that the blends contain both EPDM and polyacetylene moieties. It was found that the polyacetylene was present in predominantly trans-configuration, as evidenced by a characteristic infrared absorption band at 1015 cm-1 (10). Furthermore, there was no evidence that any polyacetylene moieties were grafted onto the unsaturated sites of EPDM rubber. This was corroborated by an extensive extraction experiment. Virtually quantitative amounts of EPDM could be extracted from the blend with toluene. IR spectra of the fully recovered EPDM were identical to those of the virgin EPDM. 

Several approaches used to prepare hybrid polymers in which polyacetylene is an electroactive component are presented. Specifically, these involve the preparation of (1) composites by in-situ polymerization, (2) graft copolymers utilizing carbanions in n-type (CH)X as polymerization initiators, and (3) A-B diblock copolymers exploiting anionic-to-Ziegler-Natta transformation reactions. 

Grafts. Polyacetylene films were synthesized at -78°C using techniques similar to those developed by Shirakawa and coworkers (11). Reductive doping was carried out in a dry box by immersion of (CH)X films in 1 M sodium naphthalide/THF solutions for 2 minutes. The films were then washed several times with dry, 02-free THF and allowed to stand in fresh THF for approximately 1 hour. The conductivities and compositions of the films were in the range 5-50 S/cm and [CHNaQ O-0.25]x respectively. 

Virtually all polymeric organic semiconductors have a conjugated portion with the same sp configuration as polyacetylene. Fig. 2.fi shows three representative materials each of the three is a structure grafted onto a polyacetylene backbone. 

Figure 5.12. UV/vis spectra of polyacetylene/polystyrene block co-polymers, The ratio of acetylene to graft sites was increased from A to D. (Reprinted with permission from ref. 51)...

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. 

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