A series of completely soluble hyperbranched polymers were synthesized by polycyclotrimerization of diynes for the first time. TaCl
5-Ph
4Sn was found to be the effective catalyst and toluene to be the efficient solvent. The hyperbranched polyphenylene structures of the polymers were confirmed by IR, NMR, UV, TGA and light scattering analyses. A possible polycyclotrimerization mechanism via tantalacyclopentadiene intermediates is proposed. The polymerization processes including initiation, propagation and termination are analyzed.
The unique backbiting reaction was found to be a plausible way to terminate the propagation chain. Conformations of the diynes greatly affect the occurrence of backbiting reaction and affect the solubility of resultant polymers to certain extent. Diynes HC[is equivalent to]C(CH
2)
mC[is equivalent to]CH with short spacers (m) such as 1,5-hexadiyne (21; m = 2), 1,6-heptadiyne (22; m = 3), 1,7-octadiyne (23; m = 4) and 1,8-nonadiyne (17; m = 5) possess a conformation in which the two triple bonds locate closely. Such a conformation makes the backbiting termination to occur easily. Thus, soluble polymers are readily formed from these diynes.
Owing to the difference in the Zigzag conformation, the diynes with odd number spacers have a conformation in which the two triple bonds locate on the same side, which facilitates the backbiting termination reaction. The diynes with even number spacers, however, possess a conformation in which the two triple bonds locate on the opposite sides, which hampers the backbiting termination. As a result, the diynes with odd number spacers offer polymers with better solubility than their cousins with even number spacers
For the diynes of long spacers, a conformation with two far-separating triple bonds dramatically reduces the chance of backbiting reaction. Consequently, only partially soluble or insoluble polymers could be prepared. The two triple bonds of 1,4- diethynylbenzene (29) locate at the two ends of a straight line of a rigid 1,4-phenyl spacer, which makes the backbiting termination impossible to occur. Highly crosslinked polymer was thus the only product.
In the polycyclotrimerization of internal diynes, hexasubstituted benzene rings were formed. The steric effect of the terminal substituents plays an important role in the polymerization reaction. Internal diynes with bulky substitutents such as 1,9- bis(trimethylsilyl)- 1,8-nonadiyne (74), 1,6-bis(dimethylphenylsilyl)- 1,5-hexadiyne (75), 1,8-bis(dimethylphenylsilyl)- 1,7-octadiyne (76) gave little amount of polymers. Internal diynes with less bulky substituents and short spacers [e.g. 3,9-dodecadiyne (78) and 2,9-undecadiyne (79)] offered soluble polymers.
It was elucidated that the poly(3,9-dodecadiynes) obtained from different catalysts have different structures. Poly(3,9-dedecadiyne)s prepared by Mo(CO)
4(nbd) and NbC1
5 are mainly linear polyenes, formed via a metathesis polymerization mechanism. The poly(3,9-dedecadiyne)s obtained from Pd/C-ClSiMe
3 and PdCl
2-ClSiMe
3 possess a mixed structure of poly(alkenephenylene) and polyene. Poly(3,9- dodecadiyne) (84) synthesized by TaCl
5-Ph
4Sn is a pure poly(alkenephenylene) formed via polycyclotrimerization mechanism.
The copolycyclotrimerization of diynes and monoynes was studied to incorporate functional groups into the polymers. A general process including initiation, propagation and termination was proposed. Incorporating monoyne moieties into the polymers significantly improves their solubility. Completely soluble hyperbranched polyphenylene (95) was synthesized by copolycyclotrimerization of 1,4-diethynylbenzene (29) with phenylacetylene (91). Optical limiting properties of the polyphenylene (95) were discovered. A carbazole-containing monoyne, i.e. 5-[2-(9- benzylcarbazol)oxy]-1-pentyne (94) was copolycyclotrimerized with 1,7-octadiyne (23). Completely soluble copolymer 102 with highly fluorescent emission properties was prepared. All the above hyperbranched polymers are complete amorphous.
In the study on hyperbranched organometallic polymers, a new methodology for the preparation of hyperbranched polysilynes was developed. A series of hyperbranched poly[1,l'-ferrocenyl(alkyl)silynes] 117-122 were synthesized.
Ceramization of the hyperbranched polymers produced mesoporous magnetoceramic materials. The hyperbranched polymers are superior to their linear counterparts in terms of the pyrolytic conversion to inorganic networks and the retention of elemental iron in the ceramic products.
The compositions of the ceramic products 125-133 change with the pyrolytic conditions. Ceramics 129 prepared under argon at 1200 ℃ contains mainly Fe
3Si. The iron silicide (Fe
3Si) nanocrystals make the ceramics an excellent soft ferromagnetic material, exhibiting a high magnetizability and a negligibly small hysteresis loss. The ceramics 125-128 and 130-133 prepared under nitrogen or argon at 700-1000 ℃ consist of mainly α-Fe
2O
3 and Fe
3O
4, which give the materials lower magnetizability and some hysteresis loss.
Transition metal carbonyl complexes M(CO)
3(mes) (M = Mo, W) and Mo(CO)
3(nbd) (mes = mesitylene, nbd = norbornadiene) were found to be the effective, are-stable, and single-component catalysts for the polymerizations of acetylenes with both nonpolar and polar functional groups. No additives (cocatalysts) nor UV pre-activation was needed for a successful polymerization. Curable substituted polyacetylenes were also prepared by introducing pendent C=C or C[is equivalent to]C groups to the polymer structures.
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