Cationic polymerization of 1,3-pentadiene I. infrared, 1H-NMR and 13C-NMR investigations on the microstructure of poly(1,3-pentadiene) synthesized with cationic catalysts

This study deals with cationic polymerization of the cis- and trans-isomers of 1,3-pentadiene. The microstructure of the polymer chains is studied by ¹H-NMR, ¹³C-NMR and IR spectroscopies. It is shown that the trans-diene gives strictly trans-1,4 and trans-1,2 residual linear insaturations, whereas the cis-isomer yields also cis-1,4, cis-1,2 and 3,4-units whose overall content can reach 10 mol-%. According to the cyclization degree of the macromolecules, ranging from 30 to 70 mol-%, the number of trans-(1,2+1,4) units varies between 33 to 65 mol-% and that of trans-1,2 units between 4 and 20 mol-%. An analytical method is proposed to evaluate the average number of rings present in the polycyclic sequences. It is found that the cyclic fragments of the polymer chains consist of bi- or tri-cyclohexane fused rings containing α tetrasubstituted double bond.     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

Synthesis and characterization of polymers of 1,4-hexadienes

The homopolymerization of trans-1,4-hexadiene, cis-1,4-hexadiene, and 5-methyl-1,4-hexadiene was investigated with a variety of catalysts. During polymerization, 1,4-hexadienes undergo concurrent isomerization reactions. The nature and extent of isomerization products are influenced by the monomer structure and polymerization conditions. Nuclear magnetic resonance (NMR) and infrared (IR) data show that poly(trans-1,4-hexadiene) and poly(cis-1,4-hexadiene) prepared with a Et₃Al/α-TiCl₃/hexamethylphosphoric triamide catalyst system consist mainly of 1,2-polymerization units arranged in a regular head-to-tail sequence. A 300-MHz proton NMR spectrum shows that the trans-hexadiene polymer is isotactic; it also may be the case for the cis-hexadiene polymer. These polymers are the first examples of uncrosslinked ozone-resistant rubbers containing pendant unsaturation on alternating carbon atoms of the saturated carbon-carbon backbone. Polymerization of the 1,4-hexadienes was also studied with VOCl₃- and β-TiCl₃-based catalysts. Microstructures of the resulting polymers are quite complicated due to significant loss of unsaturation, in contrast to those obtained with the α-TiCl₃-based catalyst. In agreement with the literature, there was no discernible monomer isomerization with the VOCl₃ catalyst system.     

Donor-acceptor complexes in copolymerization. L. Preparation and microstructure of chlorine-containing alternating conjugated diene–acceptor monomer copolymers

Neighboring monomer units cause significant shifts in the infrared absorption peaks attributed to cis- and trans-1,4 units in conjugated diene-acceptor monomer copolymers. Conjugated diene-maleic anhydride alternating copolymers apparently have a predominantly cis-1,4-structure, while alternating diene-SO₂ copolymers have a predominantly trans-1,4 structure. Alternating copolymers of butadiene, isoprene, and pentadiene-1,3 with α-chloroacrylonitrile and methyl α-chloroacrylate, prepared in the presence of Et_1.5AlCl_1.5(EASC), have trans-1,4 unsaturation. Alternating copolymers of chloroprene with acrylonitrile, methyl acrylate, methyl methacrylate, α-chloroacrylonitrile, and methyl α-chloroacrylate prepared in the presence of EASC-VOCl₃ have trans-1,4 configuration. The reaction between chloroprene and acrylonitrile in the presence of AlCl₃ yields the cyclic Diel-Alder adduct in the dark and the alternating copolymer under ultraviolet irradiation. The equimolar, presumably alternating, copolymers of chloroprene with methyl acrylate and methyl methacrylate undergo cyclization at 205°C to a far lesser extent than theoretically calculated, to yield five and seven-membered lactones. The polymerization of chloroprene in the presence of EASC and acetonitrile yields a radical homopolymer with trans-1,4 unsaturation.     

1,4 polymerization of isoprene by titanate catalyst systems

Titanates are versatile in the 1,4 polymerization of isoprene. The (R′O)₄Ti/RAlCl₂ catalyst gives either cis- or trans-1,4-polyisoprene, depending on the nature of both the titanate and the solvent. Primary titanates give cis-1,4-polyisoprene in both aliphatic and aromatic solvents. Secondary titanates give cis-polyisoprene in aliphatic solvents, and trans-1,4-polyisoprene in aromatic solvents. Tertiary titanates give trans-polyisoprene in both aliphatic and aromatic solvents. A mechanism is postulated which takes into consideration the role of the solvent. ESR studies of the various titanate–RAlCl₂ catalysts were made; the paramagnetic structures are related to polymerization mechanisms.     

Polymerization by transition metal derivatives. XII. Factors controlling activity and stereospecificity in the 1,4 polymerization of butadiene by monometallic nickel catalysts

In the course of investigations of polymerization of diolefins by transition metal derivatives, we have synthesized various monometallic nickel coordination catalysts. The complexes were prepared by reacting 2,6,10-dodecatriene-1,12-diyl nickel with protonic acids; they were shown to initiate the stereospecific polymerization of 1,3-butadiene. The study of these catalysts showed the strong influence of the nature of the counteranion used on the stereospecificity and the polymerization rate. Moreover, by adding various ligands, we were able to modify the behavior of the catalytic systems and to prepare either pure cis-1,4 or pure trans-1,4 or cis–trans equibinary polybutadienes, starting from the same complex and keeping a high 1,4 specificity. Some of these modifications were shown to be reversible.     

STUDIES ON THE ~(13)C-NMR SPECTRA OF ALTERNATING COPOLYMERS OF CONJUGATED DIENES WITH METHYL ACRYLATE

The ~(13)C-NMR spectra of alternating copolymers of conjugated dienes, butadiene (BD), isoprene(IP) and chloroprene (CP), with methyl acrylate (MA) were studied. It is proved that they are allalternating copolymers. The BD units in Poly (BD-alt-MA) are joined to MA mainly in the formof trans 1,4-structure. The contents of trans 1,4-, cis 1,4-and 1,2-structure are 88, 7 and 5%, res-pectively. The IP and CP units in Poly(IP-alt-MA) and Poly(CP-alt-MA) exist essentially as trans1,4-configuration and connect with MA units in "head to head" arrangement predominantly, whileCP-CP units present in Poly(CP-alt-MA) in a small quantity.     

Radiation-induced polymerization at high dose rate. IV. Chloroprene in bulk

Bulk polymerization of chloroprene was studied at 25°C in a wide does rate range. Variations of the rate of polymerization (R_p) and molecular weight as a function of does rate were essentially the same as those in several monomers that are capab;e of radical and cationic polymerizations. The polymerization proceeds with radical mechanism at low dose rate ans with radical and cationic mechanism concurrently at high dose rate. The number-average molecular weight of the high-dose-rate was ca. 2400. Microstructure of the polymers was mainly of trans-1,4 unit with small fraction of cis-1,4 and 3,4-vinyl unit. Fractions of the vinyl unit and the inverted unit in trans-1,4 sequence which increased at high does rate inflected the change of dominant mechanism of polymerization.     

Radiation-induced polymerization at high dose rate. III. Isoprene in bulk

Radiation-induced polymerization of isoprene in bulk state was studied at 25°C in a wide dose rate range. Variations of the rate of polymerization and molecular weight of the products were essentially the same as those observed in the monomers which were capable of both radical and cationic polymerizations. At low dose rate, 7.0-230 rad/sec, radical polymerization took place. At high dose rate, 8.8 × 10³-2.2 × 10⁵ rad/sec, radical and cationic polymerizations took place concurrently. The average molecular weight of the high-dose-rate product was about 850, independent of dose rate. The microstructure of the products at high dose rate consisted mainly of trans- 1,4 units with only about 7% of cis- 1,4 and 10% of 3,4-vinyl units. The residual unsaturation in the high-dose-rate products was 90%. Decreases in cis units and residual unsaturation at high dose rate were accounted for by the change in predominant mechanism of polymerization with dose rate.     

PREPARATION AND CHARACTERIZATION OF cis-,4-POLYBUTADIENE CONTAINING A FRACTION OF trans-1,4-POLYBUTADIENE

Polymerization of butadiene catalysed first with V(acac)_3-Al(i-Bu)_2Cl, then with Co(acac)_3-H_2O-Al(i-Bu)_2Cl has been studied. The polymer obtained was identified to be a new variety of cis-1,4-polybutadiene which contained a fraction of trans-1,4-polybutadiene chemically bonded to the cis-1,4-polybutadiene chains. Its molecular weight and trans-1,4 content can be regulated by varying the catalyst composition and concentration as well as other polymerization conditions. The trans-1,4 fraction, although it presents only in 9—16%, forms a crystalline phase in the matrix at room temperature and facilitates the crystallization of the polymer.     

Equimolecular binary polydines. V. Equibinary poly(cis-1,4–trans-1,4)butadiene from bis(π-allyl nickel trifluoroacetate)

The preparation of equibinary poly(cis-1,4–trans-1,4)butadiene was investigated in the presence of bis(π-allyl nickel trifluoroacetate) modified with suitable additional ligands. The behavior of the catalytic species in the polymerization reaction as well as the specific basic properties of the equibinary polybutadiene produced support obviously a regular distribution of the cis and trans isomers in the polymer chains.     

Filler–polymer interactions in both silica and carbon black‐filled styrene–butadiene rubber compounds

Bound rubber in a filled rubber compound is formed by physical adsorption and chemisorption between the rubber and the filler. Styrene–butadiene rubber (SBR) is composed of four components of styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units. Filler–polymer interactions in both silica and carbon black‐filled SBR compounds were studied by analyzing microstructures of the bound rubbers with pyrolysis‐gas chromatography. Differences in the filler–polymer interactions of the styrene, cis‐1,4‐, trans‐1,4‐, and 1,2‐units were investigated. The filler–polymer interactions of the butadiene units were found to be stronger than that of the styrene unit. The interactions of the cis‐1,4‐ and trans‐1,4‐units were stronger with carbon black than with silica, whereas the 1,2‐unit interacted more strongly with silica than with carbon black. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 439–445, 2001     

The structure of chain segments and <Superscript>1</Superscript>H NMR spectra of polychloroprene

The ¹H NMR spectra (working frequencies of 500 and 600 MHz) of polychloroprenes are studied. The spin systems of protons for monomer units of different configurations (1,2, 3,4, 1,4-cis-and 1,4- trans- units), as well as for dyad and triad combinations of 1,4 units, are classified. A high working frequency, the method of double resonance, and the calculation of chemical shifts by empirical increments make it possible to refine the assignment of ¹H NMR signals.     

cis-1,4-Selective Copolymerization of Ethylene and Butadiene: A Compromise between Two Mechanisms

Introducing ethylene units into polybutadiene backbones is an approach to synthesize advanced rubber materials, which has been a research challenge because of distinct polymerization mechanisms of the two monomers. To date, only trans-1,4- and 1,2-regulated copolymers have been obtained. Herein, we reported the unprecedented cis-1,4 selective copolymerization of ethylene and butadiene by using the thiophene-fused cyclopentadienyl-ligated scandium complexes. The effects of the sterics and electronics of the catalytic precursors as well as the monomer loading mode on the activity and selectivity as well as the sequence lengths were investigated, and the mechanism was elucidated. Thus a novel ethylene-based rubber material possessing a high molecular weight, 80 % cis-1,4 regularity and a T_g=−94 °C without an obvious melting point owing to short polyethylene sequences even at its content up to 45 mol %, was isolated. This new rubber material exhibited excellent anti-flowing performance and strong tensile strength.     

Radical copolymerization of sulfur dioxide and chloroprene

The radical copolymerization of sulfur dioxide and chloroprene (CP) in benzene was carried out, especially as a function of the total monomer concentration ([SO₂] + [CP]). The composition of chloroprene polysulfones varies mainly with total monomer concentration and with polymerization temperature, but depends very slightly on feed composition. The microstructure of chloroprene units in chloroprene polysulfone was such that the trans-1,4 unit was predominantly over the cis-1,4 unit. Thus it would seem possible to rule out both radical copolymerization mechanisms, i.e., propagation of separate monomers as explained by the Lewis-Mayo equation, and propagation processes involving a monomer charge-transfer complex.     

Improved expression of the mean-square radius of gyration, 3. 1,4-polydienes

The mean-square radii of gyration of cis- and trans-1,4-polybutadiene and corresponding 1,4-polyisoprene were derived using Abe's and Flory's rotational isomeric scheme. Calculations performed using available experimental data showed that the dependence of the mean-square radius of gyration on the molecular weight for these stereoregular polydienes can be expressed as where a and b are constants characteristic of the polymer. This behaviour is analogous to that of vinyl polymers and poly-1,1-disubstituted ethylenes discussed in the preceding papers of the present series. The mean-square radius of gyration of 1,4-polyisoprene with predominantly trans units is more sensitive to stereoirregularity than with predominantly cis units. However, 1,4-polybutadiene chains are comparatively insensitive to the stereochemical composition.     

Characterization of diene polymers. I. Infrared and NMR studies: Nonadditive behavior of characteristic infrared bands

Extinction coefficients of the characteristic infrared bands due to isomeric structural units were measured for polybutadiene and polyisoprene in CS₂ or CCl₄ solutions and were compared with the isomer composition determined by NMR. The NMR signal assignments were made on the basis of the spectra of deutero derivatives of the polymers. In the case of polyisoprene, linear relations were obtained between the extinction coefficients and the isomer contents determined by NMR for the absorption bands at 1385 cm^?1 (characteristic of trans-1,4 units), 1376 cm^?1 (cis-1,4 units), and 889 cm^?1 (3,4 units). However, for the absorption bands at 840 cm^?1 (characteristic of cis-1,4 and trans-1,4 units), isomerized polyisoprenes did not give such a linear relationship. In polybutadiene, the extinction coefficient for the atactic 1,2 units was found to be lower than that of the syndiotactic 1,2 unit. These experimental facts lead to the conclusion that additivity of the extinction coefficients does not always hold for diene polymers. The deviation from the linear relation may be associated with regular sequences of one isomeric conformation in the chain.     

Stereoselective H2O eliminations in 3- and 4-arcylcyclohexanols under electron impact

The elimination of H20 from the molecular ions of trans-4- and trans-3-arylcyclohexanois takes place to a greater extent than in the corresponding cis isomers. The remarkable differences in abundance taken together with substituent effects and the results of deuterium labelling, show that configuration is retained in the molecular ions which undergo the elimination, and that this process is a cis-1,4 and cis-1,3 elimination in the trans-4- and trans-3- arylcyclohexanois, respectively. Possible mechanisms for the elimination in the cis isomers are discussed.     

Quantitative estimation of trans-1,4 and cis-1,4 isomers in polychloroprene by high-resolution NMR

In the ¹H-NMR spectrum of polychloroprene dissolved in C₆D₆, the ?CH proton signal was separated into two triplet peaks. These triplet signals were assigned to the ?CH proton in the trans-1,4 and cis-1,4 isomers by measurement of ¹H-NMR spectra of 3-chloro-1-butene and a mixture of trans- and cis-2-chloro-2-butene as model compounds for the 1,2, trans-1,4 and cis-1,4 isomers. In ¹H-NMR spectra (220 Mcps) of polychloroprene dissolved in C₆D₆, two triplet signals were separated completely from which the relative concentrations of trans-1,4 and cis-1,4 isomers could be obtained quantitatively.     

Hydroxybromierung und Methoxybromierung von (Z)-Cycloocten

In addition totrans-2-bromocyclooctanol andtrans-1,2-dibromocyclooctane,cis-4-bromocyclooctanol,cis-1,4-dibromocyclooctane,trans-1,4-dibromocyclooctane, and (Z)-5-bromocyclooctene are obtained, when (Z)-cyclooctene is treated with N-bromosuccinimide in the presence of water. Similarly the methoxybromination of (Z)-cyclooctene gives transanular products.