Radiation-induced crosslinking and cyclization in 1,2-polybutadiene

In order to get information on the radiolytic changes in 1,2-polybutadiene (1,2-PB) the sol and gel fractions, the conversion of double bonds, the structure and concentration of radicals, the formation of dienes and the formation of gaseous products were measured. In addition, the dose rate dependence and temperature dependence for the conversion of double bonds were determined. G values for double bond conversion depend on molecular weight and range from 20 to 200. G values for crosslinking are about 10. A mechanism for the double bond conversion is proposed which involves initiation by a transformation of the primary radical ion in the vinyl group into a carbonium ion and a radical. This is supported by ESR measurement. Reaction of the carbonium ion with a vinyl group in the same chain gives rise to cyclization, whereas reaction with a vinyl group in a neighboring chain results in crosslinking. A comparison of the G values for conversion of double bonds with the G values for crosslinking shows that the formation of cyclic rings exceeds the formation of crosslinks by a factor of about 10. The corresponding values in 1,4-cis- and 1,4-trans-polybutadiene are much smaller [G(cl) ? 2; G(db) ? 7]. The pendent vinyl groups in 1,2-polybutadiene therefore are more reactive than the vinylidene groups in 1,4-polybutadienes.     

Arylamino-derivatives of syndiotactic 1,2-polybutadiene

The chemical modification of syndiotactic 1,2-polybutadiene via interaction of the polymer with aromatic amines in the presence of sodium tetrachloroaluminate Na[AlCl₄] has been studied. With the use of IR and NMR spectroscopy data, the structure of the modified 1,2-polydiene has been examined.     

Chlorine derivatives of syndiotactic 1,2-polybutadiene

It is shown that chlorine-containing polymeric products may be produced on the basis of the syndiotactic 1,2-polybutadiene by incorporating chlorine atoms into macromolecules via double carbon-carbon bonds. The functionalization of the polydiene with halogen atoms markedly changes the viscosity of solutions, flowability of the melt, and thermal stability of polymeric products. Chlorine derivatives of the syndiotactic 1,2-polybutadiene may be used as high-molecular-mass modifiers improving rheological properties of polymeric compounds in poly(vinyl chloride)-based polymeric composites.     

Dichlorocyclopropane derivatives of syndiotactic 1,2-polybutadiene

Polymeric products containing hem-dichlorocyclopropane units with a degree of functionalization of up to 97% are synthesized via the reaction of syndiotactic 1,2-polybutadiene with dichlorocarbene obtained by the interaction of chloroform with an aqueous solution of sodium hydroxide in the presence of a phase-transfer catalyst. The incorporation of dichlorocyclopropane groups into units of polydiene substantially changes its molecular mass and polydispersity, the solution viscosity, the polymer melt flowability, and the glass-transition temperature and flow temperature of the polymer.     

Hydrochlorinated derivatives of syndiotactic 1,2-polybutadiene

Chlorine-containing polymeric products with a degree of functionalization of up to 70% are synthesized through the hydrochlorination of syndiotactic 1,2-polybutadiene via carbon-carbon double bonds. The introduction of chlorine atoms into polydiene units causes substantial changes in the viscosity of polymer solutions, the flowability of the polymer melt, the glass-transition and flow temperatures, and the thermal stability of polymers. The hydrochlorinated derivatives of syndiotactic 1,2-polybutadiene demonstrate good adhesion with respect to steel and can be used in adhesive compositions.     

Viscoelastic and rheological properties of syndiotactic 1,2-polybutadiene

The physicomechanical, viscoelastic, and rheological characteristics of syndiotactic 1,2-polybutadiene were studied and compared with those of the analogs produced in other countries.     

Epoxidation of syndiotactic 1,2-polybutadiene with peracids

The epoxidation of syndiotactic 1,2-polybutadiene (84 and 16% 1,2 and 1,4 units, respectively) with carboxylic peracids prepared in situ and m-chloroperbenzoic acid was studied. In the course of epoxidation in the presence of carboxylic peracids, oxirane groups are formed only through epoxidation of double bonds in the macromolecular backbone, whereas m-chloroperbenzoic acid is responsible for the chemical modification of 1,2 and 1,4 units of polybutadiene. The basic kinetic parameters of 1,2-polybutadiene epoxidation with peracids of various chemical structures were determined.     

NMR relaxation study of crosslinked cis-1,4-polybutadiene

Proton relaxation measurements have been used to investigate the effects of crosslinking on the segmental motion in cis-1,4-polybutadiene samples. The temperature dependence of proton spin–lattice relaxation time T₁ and spin–spin relaxation time T₂ at 60 and 24.3 MHz are reported in cis-1,4-polybutadiene (PB) samples with different crosslink density including uncrosslinked PB and samples with 140, 40, and 14 repeat units between crosslinks. In addition, spin-lattice relaxation times in rotating coordinate frame, T_1p, have also been determined. The relaxation data are interpreted in terms of the effects of crosslinks on segmental chain motions. Because of their sensitivity to low-frequency motion, T₂ data are of major interest. At temperatures well above the T₁ minimum the small T₂ temperature dependence resembles solidlike behavior reflecting the nonzero averaging of dipolar interactions due to anisotropic motion of the chain segments between crosslinks. The magnitude of T₂ at 60°C is found to be proportional to the average mass between crosslinks.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. III. 1H- and 13C-NMR study of highly syndiotactic 1,2-polybutadiene

The ¹H and ¹³C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound–organoaluminum–CS₂ catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. S-PB (mp 210°C) has 99.7% 1,2 units, 0.3% isolated cis-1,4 units, and 99.6% syndiotacticity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)₃-AlEt₃-AlEt₂Cl-CS₂, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free Co(C₄H₆)(C₈H₁₃)CS₂ system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)_1.6(gg)(tt).     

Stress relaxation of polybutadiene at large deformation. Measurements of stress and birefringence in shear and elongation

The rheological behavior of an uncrosslinked polybutadiene on sudden application of finite strain was examined. The shear stress σ, two components of birefringence, and the extinction angle were measured in shear (magnitude of shear γ ≤ 3.5) and tensile stress and the birefringence were measured in uniaxial elongation (elongation ratio λ ≤ 3.8). Measurements were performed at 30°C with a tensile tester equipped with appropriate sample holders. The stress-optical coefficient was 3.01 × 10^?9Pa^?1. The first and second normal-stress differences v₁ and v₂ were separately evaluated with the use of stress-optical law. The Lodge—Meissner relation v₁ = γσ held good. The ratio v₂/v₁ was independent of time and varied from about ?0.3 to ?0.2 with increasing γ in the range of measurements. Each of the stress components was factored into a function of strain and one of time, and the latter was common to all the stress components. Simple formulas were proposed to represent stress components in step deformations.     

Synthesis and properties of epoxy derivatives of syndiotactic 1,2-polybutadiene

Samples of modified 1,2-polybutadiene were prepared by the reaction of the polymer with peracetic acid or tert-butyl hydroperoxide in the presence of a catalyst, hexacarbonylmolybdenum. The hydrodynamic characteristics of dilute solutions and the rheological properties of concentrated solutions of the starting and epoxidized polydiene in hydrocarbon solvents were studied. The Huggins constant K _x, second virial coefficient A ₂, root-mean-square size of macromolecular coils $(\overline {R^2 } )^{1/2} $ , and the enthalpy, entropy, and Gibbs energy of activation of the viscous flow of solutions of the starting and modified polydiene were estimated.     

Thermal degradation of halogen derivatives of syndiotactic 1,2-polybutadiene

Thermal degradation of halogen derivatives of syndiotactic 1,2-polybutadiene, differing in the kind of the halogen, its content in the polymeric product, and its position in the monomeric unit, was studied by thermal gravimetric analysis. Comparative evaluation of the heat resistance of the halogenated polymers under consideration was made.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. I. Preparation,properties, and application of highly crystalline syndiotactic 1,2-polybutadiene

Highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point (mp) up to 216°C was obtained by using a Co(acac)₃-AIEt₃-CS₂ catalyst. The polymer with mp 208°C was found to have 99.7% 1,2 content and 99.6% syndiotacticity by ¹H and ¹³C-NMR measurements. The s-PB can be molded by addition of a stabilizer such as 2,6-di-t-butyl-4-hydroxymethylphenol into fiber, film, and various shaped articles. The physical properties presented in the present article include stress-strain and dynamic mechanical behavior. The highly crystalline syndiotactic 1,2-polybutadiene was applied to a carbon fiber and UBEPOL VCR (cis-1,4-polybutadiene reinforced by fibrous syndiotactic 1,2-polybutadiene).     

Radiation-induced addition reaction of carbon tetrachloride onto 1,2-polybutadiene

The γ-ray-induced addition reaction of carbon tetrachloride onto syndiotactic 1,2-polybutadiene film and liquid 1,2-polybutadiene was carried out at room temperature. In the film gelation was pronounced and the rate of addition increased as the crystallinity of the polymer decreased. In the liquid gelation, which makes the polymer insoluble in carbon tetrachloride, did not take place, although a definite crosslinking reaction was noticed. In this case the appearance of the product changed from a viscous liquid to a white powder as the reaction proceeded. Its structure was compared with that of chlorinated 1,2-polybutadiene. The addition of carbon tetrachloride to the vinyl group in liquid 1,2-polybutadiene caused an anti-Markownikoff-type reaction and was accompanied by an unexpectedly large vinyl depletion in the polymer. The total decrease in the vinyl group was found to be much larger than that brought about by the addition of carbon tetrachloride. This discrepancy was attributed to a cyclization and crosslinking reaction ascribed to the vinyl group bound by the main chain. Cyclization and crosslinking were less noticeable in the chlorination than in the carbon tetrachloride.     

Properties of modified polymers based on syndiotactic 1,2-polybutadiene

The influence of the chemical modification on the properties of syndiotactic 1,2-polybutadiene derivatives that contain various functional groups in macromolecules and show promise for practical use was studied. The dependence of the glass transition point and the fluidity and rheological properties of modified polydiene melts on the nature of the functional group in the macrochain and on the degree of the polymer functionalization was revealed. The possibility of directional synthesis of modified polymer products with the required operation characteristics on the basis of syndiotactic 1,2-polybutadiene was demonstrated.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. II. Catalysts for stereospecific polymerization of butadiene to syndiotactic 1,2-polybutadiene

Butadiene is polymerized by cobalt compound–organoaluminum–CS₂ catalysts to give highly crystalline syndiotactic 1,2-polybutadiene (s-PB) having melting point up to 216°C. An aluminum-free catalyst, Co(C₄H₆)(C₈H₁₃)-CS₂, is also effective. Syndiotactic polymerization with Co(C₄H₆)(C₈H₁₃)-CS₂ is not interrupted by the addition of protic substances such as water and alcohol, but is influenced by donor or acceptor substances. The donor molecule, e.g., dimethylsulfoxide or dimethylformamide, decreases the stereoregularity, i.e., syndiotacticity and 1,2 content. An acceptor molecule of organoaluminum with appropriate acidity such as AlEt₃-AlEt₂Cl or tetraethylaluminoxane increases the molecular weight, stereoregularity, and yield of the polymer. In the presence of CS₂ a mixture of cis-PB and s-PB was obtained by using Co(octoate)₂-AlEt₂Cl-H₂O, with molar ratio H₂O/Co less than unity. In the case of H₂O/Co > 1, only cis-PB was obtained. By the addition of donor substances such as ester, ether, nitrile, and AlEt₃, s-PB was obtained even when H₂O/Co > 1. The amount and ratio of cis-PB and s-PB are dependent upon the nature and amount of the additives.