Units In Polybutadiene Research Articles

Identification of the Structure of Polybutadiene Terminal Units by NMR Spectroscopy with T2-Filter

A new method for the identification of the structure of terminal units in polybutadiene synthesized by cationic polymerization has been developed. The method consists of conducting T2-filtered NMR experiments, which make it possible to reduce the intensities of the spectral signals of the main-chain carbon atoms and significantly increase the intensities of the signals of the carbon atoms in the head and end polybutadiene units characterized by higher mobility.

Gelation of soybean oil with polybutadiene

AbstractIn this study self‐supporting, resilient, load bearing polybutadiene ‐ soybean oil gels were obtained. The gels were made by dissolving polybutadiene (PBD) in soybean oil (SO) and selectively crosslinking PBD with a free radical source. PBD concentration, free radical source concentration, and the temperature and time of the crosslinking reaction were varied, and the effects of these changes on the mechanical properties of the gels were examined. Our experiments show that successful gelation is possible within PBD concentration limits of 7.5 to 12%, peroxide concentration between 25 to 100% (based on PBD), temperature between 110°C and 130°C and reaction times of 3 hours with tert.butyl‐peroxybenzoate as the free radical source. The crosslinking reaction was followed by IR and H‐NMR spectra, and the crosslinking density was followed by compression testing and swelling behavior. Higher radical source concentration and higher PBD concentration gave gels with better mechanical properties. The spectra and the viscosity increase of SO extracted from the gels indicate that there is dimer and trimer formation of SO during the reaction. The spectra of the PBD extracted from gels indicate that SO was added to PBD in a small but measurable amount. Integration of peak intensities in the NMR spectrum of methylene groups of PBD and methylene groups of triglyceride indicated one triglyceride molecule for approximately 45 repeating units in PBD. The modulus of the best gel sample (PBD 10%. peroxide 50%) was 1.96 × 10−2 MPa. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2240–2246, 2005

Synthesis of Segmented (PB(PS-block-PB)n) and (PB(SAN-block-PB)n) Block Copolymers via Polymeric Thermal Iniferters

A technique is described for the synthesis of segmented poly(butadiene-block-styrene) block copolymers and segmented poly(butadiene-block-(styrene-co-acrylonitrile)) block copolymers through polybutadiene-based thermal iniferters. Dihydroxy- and dicarboxy-terminated polybutadienes were transformed into secondary amine-terminated compounds, which were subsequently reacted with CS2 and iodine to obtain the corresponding polymeric iniferters containing approximately three polybutadiene units. By using these as an initiator for the thermal polymerization of styrene, multiblock copolymers of polybutadiene and polystyrene could be prepared. In the same way multiblock copolymers of polybutadiene and poly(styrene-co-acrylonitrile) could be prepared by thermal copolymerization of styrene and acrylonitrile, using the polymeric iniferter as an initiator. By varying polymerization time and iniferter concentration, the composition and vinyl sequence length of the segmented block copolymers could be regulated. The polymeric iniferters and block copolymers were characterized by GPC, elemental analysis, TGA, H-1 NMR, DMTA, and transmission electron microscopy.

Characterization of polybutadiene produced with CoBr2(PPh3)2‐based catalysts

AbstractPolymerization of 1,3‐butadiene was conducted with the CoBr2(PPh3)2(Ph: phenyl)‐methylaluminoxane (MAO) and MgCl2‐supported CoBr2(PPh3)2‐Al(CH3)3 catalyst systems. The microstructure of polybutadiene was analyzed in detail by 13C NMR spectroscopy after hydrogenation, which indicated that the distribution of the 1,2 and 1,4 units in polybutadiene is more random when the homogeneous CoBr2(PPh3)2‐MAO catalyst was used. The microstructure of these polymers was compared with that obtained using BuLi as catalyst.

Analysis of the sequence distribution of 1,2 units in polybutadiene by an ozonolysis-GPC method

Analysis of the sequence distribution of 1,2 units in polybutadiene by an ozonolysis-GPC method

Structure of initial, ultimate and inner chain units of polybutadiene obtained with a rare-earth catalyst as revealed by 13C nuclear magnetic resonance spectroscopy

The structure of initial, ultimate and inner chain units in polybutadiene produced with NdCl 3. 3(i-PrOH)HAl(i-Bu) 2 was studied by means of 13C nuclear magnetic resonance spectroscopy. Initial units are shown to be predominantly of trans-CH 3CHCHCH 2 structure. Conversely, 90% of inner units have cis configuration. Ultimate units obtained by quenching with H 2O (D 2O) are predominantly of 1,2 structure. On the basis of the data obtained, the polymerization mechanism was discussed.

Structure of initial and ultimate chain units of polydienes obtained with rare-earth catalysts as revealed by 2H nuclear magnetic resonance spectroscopy

The structure of initial and ultimate chain units in polybutadiene and polyisoprene was studied by means of 2H nuclear magnetic resonance spectroscopy. Polydienes were prepared with a neodymium catalyst; quenching was performed with deuteromethanol. The enrichment of quenched ultimate units by trans-1,4 structures at the expense of cis-1,4 structures at high polymer yields was observed. When using diisobutylaluminium deuteride DAl(i-Bu) 2, as chain transfer agent, it was shown that the principal site of chain transfer reaction was the Al-D bond. The initial unit of polybutadiene was predominantly of trans-1,4 structure.

Formation and reactions of paramagnetic particles in irradiated polystyrene and butadiene-styrene block copolymers and model systems

To identify the features of energy transfer and migration of active particles in microheterogenous polymeric systems the authors have investigated the formation and photochemical reactions of paramagnetic particles in irradiated butadiene-styrene block copolymers and model systems. It is shown that the effectiveness of far-energy migration in such colloidal systems is low. It is concluded that the processes of energy transfer occur between the polystyrene and polybutadiene units present in direct contact. It is shown that on photobleaching the electrons stablized in polystyrene and the polystyrene phase of the block copolymers react with neutral radicals and in the case of block copolymers the electrons may pass into the polybutadiene phase and interact there with allyl radicals.

The effect of fillers on the interfacial polymer properties from cryogenic dynamic mechanical measurements

Dynamic mechanical measurements were used to study the effect of high surface area carbon black and fused silica fillers and a number of simple organic diluents on the SBR (31.6 mol% styrene) β peak, which is associated with small main chain motions of trans polybutadiene units. The amount of molecular motion eliminated from the glassy state by carbon black was greater than fused silica, indicating stronger polymer-filler interaction. The degree of interaction between polymer and filler at the interface affects polymer motion further removed from the filler surface. The reasons for this phenomenon are discussed. It is proposed that dilatational stresses resulting from the mismatch in the coefficients of expansion of filler and matrix are the cause of shifts in relaxation spectra to lower temperatures, which are more pronounced when polymer-filler interaction is weak. The toughness of the matrix near the interface is discussed in terms of polymer-filler interaction, the dilatational stresses and resulting shifts in the relaxation spectra. The effect of diluents on polymer motion in relation to diluent structure show no significant trends and is difficult to interpret without information on the percentage of diluent molecules existing in diluent clusters.

Influence of temperature on microstructure of anionic‐initiated polybutadiene

AbstractApplication of the Arrhenius relationship for temperature and ratio of isomeric units in polybutadiene made in the presence of butyllithium initiator is consistent with the existence of three simultaneous competing reactions. Evidence in the literature is cited to support the possibility that the growing chain end exists in a composite equilibrium producing localized structures which on reacting with monomer result in fixed isomeric units. The compliance of the data with the thermodynamic relationship permits the extrapolation of a narrow set of data to a broad temperature range.

Amorphous state transitions in butadiene–acrylonitrile copolymers

AbstractDifferential thermal analysis, creep measurements, and gas permeation rates are used to confirm the existence of a transition zone in three butadiene acrylonitrile copolymers in a temperature region that starts at roughly 15° to 25°C above the main glass transition temperatures of the copolymers and extends over a broad temperature range. The change appears to be slightly endothermic and softens the copolymers upon heating. It is speculated that the copolymers are in a mesomorphic state above their main glass temperature in which there is either a degree of ordering or a low‐grade crystallinity of polybutadiene units along the copolymer chains. It is not until the copolymers are 50° to 75°C above their main glass temperature that they become truly amorphous.

Cis-Trans Isomerization in Natural Polyisoprenes

Abstract The cis and trans isomers of many simple olefins and conjugated polyolefins can be interconverted by the action of heat, light, and various catalysts, and in many such systems the changes in geometric configuration can be readily followed and the isomers separated and identified. Previous attempts to isomerize natural rubber and gutta-percha by treatment with ultraviolet light and various chemicals gave no detectable cis-trans isomerization, and in general configurational changes in unconjugated polyolefins have been unknown until recently when Golub converted the cis-1,4 units in polybutadiene into the corresponding trans units. This isomerization was achieved by irradiation of the cis-polymer with ultraviolet light in the presence of various organic bromides and sulfur compounds, but apparently this method did not isomerize natural rubber. In attempts to retard the rate of crystallization of natural rubber at moderately low temperatures—i.e., −10° to −40° C—by the attachment of side groups which would interfere with the molecular packing, it was observed that very small amounts of thiol acids were remarkably effective. This suggested that structural changes other than simply the attachment of side groups were occurring in the polyisoprene molecule. Recently it was found that thiol acids could interconvert the cis and trans forms of a simple trialkyl ethylene—e.g., 3-methylpent-2-ene—and subsequently, the isomerization of natural rubber and gutta-percha by these reagents was also observed. Following this, natural rubber, gutta-percha, squalene and cis and trans forms of 3-methylpent-2-ene have also been isomerized by treatment with sulfur dioxide and allied compounds; this work, including an investigation of the physical properties of the vulcanizates obtained from some of the isomerized polyisoprenes, is described in the present paper.

Cis-Trans Isomerization of Natural Rubber under the Influence of Organo-Aluminum Compounds and Titanium Tetrachloride

Abstract Ziegler catalysts have become of prime importance for synthesis of polymers with regular structure, particularly cis-polyisoprene. The disruption of the structure of the chain by the formation of trans units was, until now, connected only with the influence of the physical and chemical properties of the catalyst on the nature of the addition of the diene monomers during the polymerization process. In the present work it is shown that destruction of regularity of structure can be caused by isomerization of cis units in complete polymer chains into trans units under the influence of the compounds used for initiating the polymerization process. Attempts to isomerize natural rubber by means of ultraviolet light and iodine did not give the expected effect. Ferri established for the first time that under the influence of zinc chloride and titanium tetrachloride natural rubber undergoes changes accompanied by disappearence of crystallization on stretching as shown by x-ray structure analysis. On the basis of these results the authors presumed that under the influence of these agents isomerization of cis units to trans units occurs in the natural rubber chain. The isomerization of cis-1,4 units to trans units in polybutadiene by means of ultraviolet light in the presence of organic bromine or sulfur compounds was first accomplished and proved by Golub. The formation of trans units in natural rubber under similar conditions was not observed. The study of the isomerizing effect of TiCl4 and organo-aluminum compounds was conducted by us on solutions of milled natural rubber (NK) in benzene in sealed glass ampoules. The benzene used was dried and distilled over sodium. All work was conducted in an atmosphere of dry argon. Unsaturation and microstructure of the chain was determined on each sample. The study of microstructure of polyisoprenes was carried out by means of infrared spectra, the relative content of the different configurations of the polymer chain being determined by the absorption in the 800–1000 cm−1 region. The method previously developed by one of us was used for this purpose.

Cis-Trans Isomerization in Polybutadiene

Abstract About twenty years ago, in an effort to transform natural rubber into gutta-percha, Meyer and Ferri irradiated a solution of Hevea in cyclohexane with ultraviolet light, but were unable to detect any cis-trans isomerization in polyisoprene. Later, Ferri showed that treatment of both Hevea and Gutta with certain chemicals, such as chlorostannic acid and titanium tetrachloride, gave rise to closely resembling products which were considered at the time to have structures intermediate between the two geometric forms of naturally-occurring polyisoprene. These resulting polymers were, however, crosslinked in the course of chemical treatment and probably also cyclized, so that in the light of present knowledge about the cyclizing tendencies of the materials employed, this change cannot be regarded as a genuine interconversion of cis and trans double bonds. No true instance of cis-trans isomerization unaccompanied by other structural changes has been reported heretofore for a high polymer, except for the polyenes which are conjugated structures of relatively very low molecular weight. This communication reports the successful transformation of the cis-1,4 units in polybutadiene into corresponding trans units by means of ultraviolet irradiation in the presence of a suitable sensitizer, which may be any one of a wide variety of organic bromine or sulfur compounds. Surprisingly, this isomerization could not be induced in natural rubber.