Polymerization of phenylacetylene

The nature of this interaction is not yet clear, but there is no doubt that this is a manifestation of a polymer-monomer interaction, typical of PCSs. The process of polymerization of phenylacetylene on free ions is characterized by the 6th order in initiator and monomer and has an activation energy of=25 kJ/mol (6 kcal/mol). 

Some transition metal catalysts induce the living polymerization of various acetylenic compounds.68,69 Such polymerizations of phenylacetylene catalyzed by rhodium complexes are used in conjunction with a quantitative initiation and introduction of functional groups at the initiating chain end (Scheme 16).70 The catalyst is prepared from an [RhCl(nbd)]2/Ph2C=C(Ph)Li/PPh3 mixture and proceeds smoothly to give quantitatively the polymer 54 with a low polydispersity ratio. 

In certain cases, the halide impurities could be countered by using additives that serve to bind the halides, but this is not always a desired solution. In the rhodium-catalyzed polymerization of phenylacetylene (777), it was shown that the deleterious effect of halide impurities can be nullified by the addition of NEt3 co-catalyst to a Rh(diene)(acac)-containing catalyst. 

Scheme 5.11 Polymerization of phenylacetylene initiated by the vinyiidene intermediate.

Park KH, Jang K, Son SU, Sweigart DA. Self-supported organometallic rhodium quinonoid nanocatalysts for stereoselective polymerization of phenylacetylene. J Am Chem Soc 2006 128 8740-8741. 

In the metal carbonyl catalysts, the use of a catalytic amount of Ph2CCl2 enables the omission of CGI4. For example, the polymerization of phenylacetylene with W(CO)6 in the presence of Ph2GGl2 in toluene upon photoirradiation proceeds homogeneously to give a polymer with of ca. 2 x 127,128 MW polymers > 10 ) are attainable from sterically bulky aromatic and aliphatic acetylenes. It is also effective to use a catalytic amount of Lewis acids instead of GGI4 in the M(GO)6-based catalysts (M = W, Mo). ... 

A ternary Rh catalyst system, [(nbd)RhCl]2-LiCPh=CPh2-PPh3, " induces the living polymerization of phenylacetylenes. In the latter case, the initiating species is a vinylrhodium 10, which was isolated and well characterized by X-ray analysis.The details for the living polymerization are described in Section 11.16.4.1. 

Anionic polymerization of phenylacetylene to a trans-cisoid polymer in the presence of crown ether phase-transfer catalysts initiated by sodium amide has been reported.425 In contrast, the zwitterionic rhodium complex Rh+(COD)BPhJ yields a ds-transoid product in the presence of Et3SiH.426... 

Well-controlled polymerization of substituted acetylenes was also reported. A tetracoordinate organorhodium complex induces the stereospecific living polymerization of phenylacetylene.600 The polymerization proceeds via a 2-1 -insertion mechanism to provide stereoregular poly(phenylacetylene) with m-transoidal backbone structure. Rh complexes were also used in the same process in supercritical C02601 and in the polymerization of terminal alkyl- and arylacetylenes.602 Single-component transition-metal catalysts based on Ni acetylides603 and Pd acet-ylides604 were used in the polymerization of p-diethynylbenzene. 

Exclusive polymerization of phenylacetylene takes place, unexpectedly, under hydrosilylation conditions in the presence of a zwitterionic Rh(I) complex, [Rh(COD)]+BPh4, and HSiEt3 to give all-ds-poly(phenylacetylene)285. 

The loss of the addition ability of an ion by delocalization of the electron defect in a conjugated polyene chain is documented by the observation of Subramanian et al. They polymerized monomers with C=C and C=N bonds by electroinitiation. Anionic polymerization of phenylacetylene started very easily but it rapidly died out without any external cause [109]. The polymerization of n-alkyl-2-cyanoacrylatet in the presence of tetracyanoethy-lene yields only low-molecular-weight products. This is due to the formation... 

Table 21 shows solvent effects on the polymerization of phenylacetylene by the W(CO)6-based catalyst23. It is clear that halogen-containing solvents play an essential role in the formation of the active species. Among them, CO allows the highest polymer yield. Since catalytic amounts of CC14 have proved to be insufficient, it is most favorable to use CC14 as solvent for the polymerization by metal hexa-carbonyls. (Refer to Eq. (15) for the reaction mechanism.)... 

The difference in nature of the final products from these two isomers has been related to the trans influence. In the cis isomer, both acetylide groups are equally labilized by the two phosphine ligands and are easily replaced by chloride. In the trans isomer, however, PtCl(C=CPh)-(PPh3)2 is obtained since the acetylide trans to the chloride is not replaced as a consequence of the lower trans influence of the chloride as against that of triphenylphosphine. The catalysis of the linear polymerization of phenylacetylene by PtHCl(PPh3)2 may also involve the insertion of an acetylene into the hydroplatinum bond 153, 115). 

Neutral catalysts or catalyst precursors based on fluorinated ligand systems have been applied in compressed CO2 to a broad range of transformations such as Zn- and Cr-catalyzed copolymerization of epoxides and CO2 [53, 54], Mo-catalyzed olefin metathesis [9], Pd-catalyzed coupling reactions [43, 55, 56] and Pd-catalyzed hydrogen peroxide synthesis [57]. Rhodium complexes with perfluoroalkyl-substituted P ligands proved successful in hydroformylation of terminal alkenes [28, 42, 44, 58], enantioselective hydroformylation [18, 59, 60], hydrogenation [61], hydroboration [62], and polymerization of phenylacetylene... 

Subsequently, Tang et al. studied the polymerization of phenylacetylene and of para-substituted phenylacetylenes with lipophilic and water-soluble catalysts [148]. 

Besides this work with rather lipophilic catalyst precursors, two water-soluble analogues have been investigated [Rh(tos)(cod)(H2O)] (30 tos = tosylate) and the similar compound [Rh(tos)(nbd)(H20)] (31) [148]. The authors have verified that water is still the best reaction medium for polymerization of phenylacetylene compared to toluene, THF and neat monomer, thus indicating a possible involvement of water in the formation of the active catalyst (830 TO in water). With catalyst precursor 30, low polydispersities and a cis content of 90% are found, whereas catalyst precursor 31 affords a larger polydispersity but a higher cis content (100%). Interestingly, these catalysts proved to be tolerant to air since similar polymerization results are obtained with tap water without exclusion of air. 

The polymerization of phenylacetylene using the complex [(nbd) Rh(acac)] 9 (nbd = norbornadiene, acac = acetylacetonate) as a catalyst precursor was found to occur with considerably higher rates in compressed (liquid or supercritical) CO2 than in conventional solvent such as THF or hexane (Sche-... 

Table 2 Polymerization of phenylacetylene by Group VIA metal carbonyl ...

Scheme 4.7-20 Polymerization of phenylacetylene using a soluble rhodium phosphine catalyst in compressed CO2 [103].

Typical catalysts for the polymerization of phenylacetylene contain W, Rh and Fe. W catalysts produce an auburn polymer WCl6-P Sn is highly active, while W(CO)6-CCl4-hv is useful to achieve high molecular weight (Mn 1 x 10 ). The polymerization by Rh catalysts proceeds in alcohols and amines to form a yellow polymer When... 

TABLE 7. Effect of trimethylvinylsilane (TMVS) as transfer agent on the polymerization of phenylacetylenes by WCl6-Ph4Sn(l l) ... 

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