Polymerization of 1,3-cyclohexadiene

Bulk polymerization of //r/ .v-2-melhyI-1,3-pcntadiene lead only to 1,4-trans addition polymer, however it allows randomization of the trans structure, leading to an atactic polymer. The polymerization of the clathrate of rraw.v-2-mclhyl-1,3-pcntadiene yielded an isotactic 1,4-trans addition polymer. The polymer formed from the bulk had a molecular weight of 20,000 (240 monomer units), and that formed from the clathrate had a molecular weight of 1000 (12 monomer units). Similar results were obtained for other dienes, and the results are summarized in Table 4. It can be concluded that polymerization of dienes in the clathrate lead exclusively to a 1 A-lrans addition polymer, except in the case of 1,3-cyclohexadiene. For this monomer, although the polymer is formed entirely by 1,4-addition, the polymer formed is essentially atactic. In bulk polymerization, the polymerization proceeds in most cases through 1,4-addition (both trans and cis), but in the case of butadiene and 1,3-cyclohexadiene 1,2-additions were also observed. Actually, in the case of the bulk /-induced polymerization of 1,3-cyclohexadiene the 1,2-addition process was favoured over the 1,4-addition process by a ratio of 4 3. 

Li, X., Baldamus, J., Nishiura, M. et al. (2006) Cationic rare-earth polyhydrido complexes synthesis, structure, and catalytic activity for the cis-1,4-select polymerization of 1,3-cyclohexadiene. Angewandte Chemie International Edition, 45, 8184. 

The polymer composed of 2-cyclohexenyl-l,4 units can exhibit high Tg (176 °C) when the tacticity is controlled well [62]. Recently, [( -allyl)NiBr]2, in conjunction with MAO, was found to initiate stereo- and regiospecific polymerization of 1,3-cyclohexadiene [63]. Although the polymer has too poor solubility in organic solvents to be analyzed by NMR spectroscopy, the copolymers of 1,3-cyclohexadiene with 1,3-butadiene and norbornene prepared by the Ni catalyst show NMR spectra that indicate the presence of the 2-cyclohexene- 1,4-diyl unit formed via 1,4-polymerization of 1,3-cyclohexadiene (Eq. 11). X-ray diffraction analysis of the crystalline poly( 1,3-cyclohexadiene) as well as studies by molecular dynamics confirmed the cis-syndiotactic structure of the polymer [64]. 

As well as the polymerization of 1,3-cyclohexadiene derivatives, repetitive Diels-Alder polyadditions were widely used to prepare arylated PPPs. Stille and co-workers developed a set of suitable monomers (1,4-diethynylbenzene and 1,4-phenylenebis(triphenylcyclopentadienone) derivatives) to generate phenylated PPPs (e.g. 21) possessing molecular weights of 20000 — 100000 [46]. Uirfortu-nately, the repetitive polyaddition does not proceed in a regioselective way polymers containing para- as well as meta-phenylene units within the main-chain skeleton are formed. 

Chain Transfer Reactions Chain transfer reactions to polymeric organoalkali compounds can occur from solvents, monomers, and additives that have p/f values lower than or similar to those of the conjugate acid of the carbanionic chain end [3]. Relatively few monomers that undergo anionic polymerization exhibit chain transfer to monomer. Chain transfer has been well documented for the anionic polymerization of 1,3-cyclohexadiene. The chain transfer constant was calculated to be 2.9 x 10 at... 

Polymerization of 1,3-cyclohexadiene using a Ziegler catalyst gives a polymer consisting of cyclohexene units (c/. Scheme 4.3). 

Polymerization of 1,3-Cyclohexadiene (CHD) Using Various Transition Metal Catalysts... 

Longo, R Freda, C. de Ballesteros, O. R. Grisi, F. Highly stereoregular polymerization of 1,3-cyclohexadiene in the presence of Cp2Ni-MAO catalyst. Macromol. Chem. Phys. 2001,202,409-412. 

Natori, I. Synthesis of polymers with an ahcyclic structure in the main chain. Living anionic polymerization of 1,3-cyclohexadiene with the n-butyllithium/7V,7V,7V, 7V -tetramethylethylenediamine system. Macromolecules 1997, 30, 3696-3697. 

Natori, L Inoue, S. Anionic polymerization of 1,3-cyclohexadiene with alkyllithium/amine systems. Characteristics of w-butyllithium/7V,7V,7V, 77 -tetramethylethylenediamine system for living anionic polymerization. Macwmolecules 1998, 37, 4687-4694. 

The polymerization of 1,3-cyclohexadiene can be initiated by free radicals, Ziegler-Natta catalysts, and transition metal catalysts, both cationically and anionically [413-416]. The synthesis of high-molecular-weight poly (1,3-cyclohexadiene) containing 1,4-structures (62), especially has been of great interest, as unbranched poly(/ -phenylenes) are accessible from it after dehydrogenation [417-419]. 

Table 21 Polymerization of 1,3-cyclohexadiene with napthalene alkali metals. 

Several methods have been described for the synthesis of poly-p-phenylene. One of the more successful routes is by dehydrogenation of poly-1,3-cyclohexadiene obtained by polymerization of 1,3-cyclohexadiene with a Ziegler-Natta cata-lyst [3] ... 

NAU Naumova, S.F. and Vasil eva, V.V., Thermal effects of polymerization of 1,3-cyclohexadiene under the action of TiCLt in various solvents (Beloruss.), Vestsi Akad. Navuk BSSR, Ser. Khim. Navuk, (4), 26,1965. 

Poly(para-phenylene), with its rodlike structure composed of highly delocalized n-electron orbitals, satisfies most of the requirements for high thermal stability. Possessing Ti/2 > 400°C and an estimated melting point of 1400°C, PPP constitutes a reference for heat-resistant polymer. Poly(para-phenylene) can be synthesized by a number of routes, with the best heat-resistant material obtained by polymerization of 1,3-cyclohexadiene, followed by dehydrogenation of the polymer formed according to Eq. (35) [16]. 

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