Trans-polybutadiene

Polymers. The polymers used in this study comprised cis- and trans-1,4-polybutadienes (CB and TB), amorphous 1,2-polybutadiene (VB), a... 

Also the role of the different piperylene units present in the copolymer (1,2 and 1,4 trans) in depressing the melting point of trans-1,4-polybutadiene is still under investigation 1,2... 

In observing the time dependent changes in birefringence and stress-optical coefficient, for elongated samples at 25 C, it was found that the rate of crystallization of high trans SBR s was very much faster, some 10 times more rapid, than that for NR (8). This is consistent with the reported rates of isothermal crystallization for NR (2.5 hours at -26°C) and for 807. trans-1,4 polybutadiene (0.3 hours at -3°C) in the relaxed state (12). 

Figures 6 and 7 give the data of Fukuda et al. (3) and that of Saunders (52). The variation of stress optical coefficient of the high cis and high trans, 1,4-polybutadiene is plotted against Me in Figure 6, where it is compared with...

The polymer ra-l,4-polybutadiene (Tg = 170 K) is more flexible and has a lower Tg than trans- 1,4-polybutadiene (Tg = 190 K), and in general this is true of all geometric isomers. 

The energy difference AF between gauche and trans conformers, resulting from rotation about single bonds of the chain backbone in trans-1,4-polybutadiene, c/s-1,4-polybutadiene and 1,5-hexadiene, is evaluated from IR measurements on the bands characteristic of bending vibration of CH2 groups. Consideration of the experimental results, on the basis of the RIS model, leads to the conclusion that a value of 0.4 to 0.8 kJ mol-1 is the best estimate of AF. 

Natta, Porri, Carbonaro and Lugli (25) have prepared copolymers of 1,3-butadiene with 1,3-pentadiene in the whole range of compositions. The properties of the copolymers, in which all butadiene and pentadiene comonomer units are in the trans-1,4 configuration, clearly show the isomorphous replacement between the two types of units. The melting point/composition data show that the copolymer melting temperatures are a regular function of composition and are always comprised between those of trans-1,4-polybutadiene modification II and trans-1,4-polypentadiene. Also the X-ray diffraction spectra of the copolymers show that the trans-1,4-pentadiene units are isomorphous with the trans-1,4-butadiene units crystallized in the crystalline modification of the latter stable at high temperatures (form II). 

We will refer in the following to the interesting case of the form of trans-1,4-polybutadiene stable at high temperature, which was shown to... 

In this section information on possible condis states of the following macromolecules are reviewed polyethylene, polytetrafluoroethylene, poly(vinylidene fluoride), poly-chlorotrifluoroethylene, polypropylene, trans-1,4-polybutadiene, cis-l,4-poly(2-me-thylbutadiene), polyoxybenzoate, polyethylene terephthalate), nylon, poly(diethyl siloxane), and polyphosphazene. There is no reason to assume that this selection is complete. Station ni) has shown, for example, already in 1959 on a list of 29 macromolecules that longitudinal and lateral disorder may exist. Similarly, textbooks18> u2)... 

Fig. 22. Scanning differential calorimeter trace of heating (top) and cooling (bottom) of a melt crystallized trans-1,4-polybutadiene (Drawn after Ref.14S), Perkin-Elmer DSC, unspecified heating and cooling rates)...

Iwayanagi, S. and Miura, J. Nuclear magnetic resonance study of solid phase transition of trans- 1,4-polybutadiene, Rept. Progr. Polymer Phys. Japan 8, 303 (1965)... 

Corradini, P. On the chain conformation of the high temperature polymorph of trans-1,4-polybutadiene. Polymer Letters 7, 211 (1969) see also J. Polymer Sci., Symposia 50, 327 (1975)... 

Suehiro, K. and Takayanagi, N. Structural studies of the high temperature form of trans-1,4-polybutadiene crystal. J. Macromol. Sci. Phys. B4, 39 (1970)... 

Figure 1.12 Symbolic representation of cis-1,4- and trans-1,4-polybutadiene molecules.

Another type of geometric arrangement arises with polymers that have a double bond between carbon atoms. Double bonds restrict the rotation of the carbon atoms about the backbone axis. These polymers are sometimes referred to as geometric isomers. The X-groups may be on the same side (cis-) or on opposite sides (trans-) of the chain as schematically shown for polybutadiene in Fig. 1.12. The arrangement in a cis-1,4-polybutadiene results in a very elastic rubbery material, whereas the structure of the trans-1,4-polybutadiene results in a leathery and tough material. Branching of the polymer chains also influences the final structure, crystallinity and properties of the polymeric material. 

The activity and stereospecificity of rc-allylic catalysts for conjugated diene polymerisation depend both on the kind of metal and on the nature of the ligand attached to this metal. For instance, Cr(All)3 [137] and Co(f/3-C8Hi3)(C4H6)-CS2 [103] catalysts yield 1,2-polybutadiene, while Cr (A11)2C1 [120], Cr(All)2I [134] and U(A11)3C1 [147] catalysts produce cis-1,4-polybutadiene, but an Nd(All)3.DOX catalyst gives trans-1,4-polybutadiene [146] and a Co(fj3-C4H7)3—I2 catalyst yields eb-c/.v-l, 4/1,2-poly butadiene [137,145] (Table 5.5). 

Catalysts based on 7r-allylic derivatives of transition metals supported on alumina, silica or silica-alumina gels exhibit generally enhanced activity by comparison with their unsupported counterparts, while the stereospecificity depends on the nature of the catalyst carrier. For instance, Cr(All)3, which predominantly produces 1,2-polybutadiene [137], becomes a stereospecific catalyst for the formation of trans- 1,4-polybutadiene when supported on silica or silica-alumina gel and for the formation of cis- 1,4-polybutadiene when supported on alumina [148]. However, an increase in the content of cis-1,4 monomeric units in polybutadiene with increasing silica concentration in n-allylnickel-alumina-silica catalysts has been observed [149]. 

Rhodium salts such as Rh(N03)3.2H20 and RhCl3.3H20 exhibit catalytic activity for polymerisation of butadiene in protic solvents or aqueous emulsions and yield trans- 1,4-polybutadiene (>99%) [27,28,150-154]. Propagation active species are proved to be formed in such systems by the insertion of... 

The reactions presented in scheme (10) also account for effects exerted by the addition of Lewis bases or acids (as well as other electron donors and acceptors) to the polymerisation system on the microstructure of the polymers formed. As shown in Tables 5.4 and 5.5, some catalysts that are highly stereospecific for the formation of cis- 1,4-polybutadiene yield trans- 1,4-poly butadiene (or eb-m-1,At trans-1,4-polybutadiene) after the addition of a Lewis base or other electron donor to the catalyst system. A plausible explanation of the observed phenomena is that the added component occupies a coordination site at the transition metal, thus forcing the incoming monomer molecule to coordinate as an s-trans-rf ligand. When the additional catalyst component has a basicity comparable with that of the monomer, a competitive monomer/ Lewis base (electron donor) coordination takes place, as shown below [7] ... 

Catalyst complexation with a Lewis base or other electron donor may affect the polymer microstructure in different ways. If the added component occupies one coordination site, a monomer coordinates to another site of the active species with one double bond, i.e. as an s-trans-rf ligand, which gives rise to the formation of trans-1,4 monomeric units via the pathway (a)-(b) [scheme (10)]. Depending on the lifetimes of metal species complexed with the monomer and with the Lewis base or the other donor [scheme (11)], mixed cis-1,4/trans- 1,4-polybutadienes or an eb-czs-1, 1 A trans-1,4-polymer can be formed. One should mention in this connection that equibinary cis-l,A/trans- 1,4-butadiene polymers can also be formed in systems without the addition of a Lewis base or other electron donor in such cases, the equilibrium of the anti-syn isomerisation is not shifted and there are equal probabilities for the reaction pathways involving coordination of a transoid monomer and a cisoid monomer [7]. 

Polymers containing over 60 mol-% THF diyl units and prepared from cm-1,4-polybutadiene showed a strong coordinating tendency toward metal ions whereas the polymer with 68 mol-% THF diyl units prepared from trans-1,4-polybutadiene does not form metal complexes. The difference in the coordination properties between these two types of polymers has been ascribed to the difference in the steric structure between the two polymers. 

Fig. 2. Molecular model of poly(THF diyl) (erythro form in trans-1,4-polybutadiene)551...

Since butadiene can also undergo coordinated anionic polymerizations, some of the differences in polymer microstructure are attributable to changes in mechanism. Based on the catalysts reported to date, the isotactic and syndiotactic 1,2-polybutadienes appear to arise from coordinated anionic mechanisms. Qs and trans 1,4-polybutadienes can probably be made by all mechanisms, with cis arising from soluble catalysts which are capable of multi-coordination at one metal site. Trans structure is favored by cationic mechanism and by anionic mechanism involving coordination at two metal centers. 

Bis(7r-crotylnickel chloride) is inactive in water medium with bromide a low yield of polymer with 50-60% trans, 40-50% cis-1,4, and 2-3% 1,2-units was obtained. (C4H7NiI)2 produces trans- 1,4-polybutadiene with 14-20% conversion. 

Our experimental finding supports the view that the active site of butadiene polymerization in the presence of bis(7r-crotylnickel iodide) is the complex with nickel bound to iodide. Thus, the butadiene addition across syn-7r-allyllic bond produces trans-1,4-polybutadiene. 

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