Application of infra-red digital subtraction techniques to the microstructure of polychloroprenes: 2. Mechanism of oxidative degradation at 60°C

Experimental results obtained from the application of infra-red digital subtraction techniques to oxidized polychloroprenes are presented. These results demonstrate the involvement of 1,2- and 3,4- structural irregularities in the initial stages of oxidative degradation at 60°C. A free radical mechanism consistent with these observations is proposed.     

Application of infra-red digital subtraction techniques to the microstructure of polychloroprenes: 3. Effect of structural irregularities on the crystalline infra-red bands of chloroprene copolymers

Infra-red digital subtraction techniques have been applied to chloroprene copolymers containing relatively low concentrations of methyl methacrylate, acrylonitrile or styrene. The ‘crystalline’ bands of these chloroprene copolymers were obtained by subtraction of the amorphous spectrum obtained at 85°C from that of the semi crystalline spectrum recorded at room temperature. The presence of these comonomer units does not cause frequency shifts of the infra-red crystalline bands of polychloroprene. From these and previous results it is postulated that only the inverted trans-1,4- and 2,3-dichloro-2-butenylene units are capable of being included into the crystalline lattice and of causing the observed frequency shifts.     

Asymmetric addition of thiol to diene polymer in the presence of optically active amines as catalyst

The asymmetric addition reaction of thiolacetic acid or benzylmercaptan to diene polymer (natural rubber, cis- and trans-1,4-polyisoprene, _cis-1,4-polybutadiene, various styrenebutadiene copolymers and alternating acrylonitrile-butadiene copolymer) by optically active catalysts such as d-bornylamine ([α]d?45.2°), l-aspartic diethyl ester (?11.2°), l-aspartic dibutyl ester (?5.3°) were carried out in benzene at room temperature to 90°C. The optically active polymers were obtained from natural rubber and cis-1,4- and trans-1,4-polyisoprene, but were not obtained from cis-1,4-polybutadiene, styrene-butadiene copolymers, and butadiene-acrylonitrile copolymer. The [α]²⁵_D value of optically active derivatives was ?0.1° ～ ?1.0° (in benzene), and the optical rotatory dispersion curves were found to fit the simple Drude equation.     

N.m.r. studies of butadiene - styrene copolymers

An analysis of the ¹³C nuclear magnetic resonance spectra of copolymers of butadiene—styrene, both block or random type, shows the possibility of observing the microstructure of the copolymers themselves. The microstructure of the copolymers was analysed in terms of triads of monomeric sequences. The units present in the copolymers are of the type: trans-1,4-butadiene, cis-1,4-butadiene, 1,2-butadiene and styrene. An assignment for all the experimental bands observed is proposed on the basis of correlation with homopolymers as well as on the basis of the frequencies for the single triads, calculated by additivity rules.     

Polybutadiene modified by epoxidation. 1. Effect of polybutadiene microstructure on the reactivity of double bonds

The reactivity of low-molecular weight sodium polybutadiene (1,2-PB) and n-butyllithium polybutadiene (1,4-PB) has been studied during epoxidation with peracetic acid. The effect of the epoxy groups formed on the polymer solution viscosity has also been investigated. It was found that the rate constant of 1,4-PB epoxidation is ～1.9 times greater than that for 1,2-PB of a similar molecular weight. The reactivity of various structural polymer unit forms was studied by spectroscopic methods (i.r. and ¹H n.m.r.); it was found that reactivity depends on chain microstructure in the following way:for 1,2-PB: trans-1,4 >cis-1,4 ? 1,2for 1,4-PB: cis-1,4 >trans-1,4 ? 1,2An increase in the limiting viscosity number was observed with increasing epoxy content in the 1,2-PB chain, but the opposite effect was observed for 1,4-PB. The solubility parameter, δ, for both kinds of epoxy polybutadiene was found to be similar ($\text{19.8 × 10}{}^3\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{·}\text{m}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$).     

Distribution of isomeric structures in polyisoprenes

The ¹³C-n.m.r. spectra of polyisoprenes were investigated. Polyisoprenes were prepared with $\text{n-Buli}\text{Et}{}_2\text{O}$, radical (emulsion polymerization), and Alfin catalysts. Poly(isoprene-4,4-d₂)s were also prepared with $\text{n-BuLi}\text{Et}{}_2\text{O}$ catalysts for the signal assignments. ¹³C-n.m.r. signals were assigned for dyad or triad sequences of cis-1,4-, trans-1,4-, and 3,4- units. Signals due to head-to-head (4,1-1,4) and tail-to-tail (1,4-4,1) linkages were also assigned. On the basis of signal assignments it was revealed that cis-1,4-, trans-1,4-, and 3,4-units were distributed almost randomly in $\text{n-BuLi}\text{Et}{}_2\text{O}$ catalysed polyisoprenes. It was confirmed that radical and Alfin polyisoprenes contained about 15% of each of head-to-head and tail-to-tail linkages. It was found that radical polyisoprene had cis-1,4- and trans-1,4-units distributed randomly along the polymer chain regardless of the head and tail arrangements.     

Icosahedron cage occupancy of structure-H hydrate helped by Xe -1,1-, cis -1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes

Four mixtures of 1,1-, cis-1,2-, trans-1,2-, and cis-1,4-dimethylcyclohexanes (hereafter abbreviated DMCH) including H₂O and Xe have been investigated in a temperature range over 274.5 K and a pressure range up to 2.7 MPa. The 1,1-DMCH and cis-1,2-DMCH generate the structure-H hydrate in the temperature range up to 295.2 and 280.2 K, respectively. Especially, very large depression of equilibrium pressure has been observed in the structure-H 1,1-DMCH hydrate system. On the other hand, neither trans-1,2-DMCH nor cis-1,4-DMCH generates the structure-H hydrate in the present temperature range. It is an important finding that the cis-1,4-DMCH does not generate the structure-H hydrate in the presence of Xe, while the mixture of cis-1,4-DMCH and methane generates the structure-H hydrate.     

Structural change in the Brill transition of Nylon m/n (1) Nylon 10/10 and its model compounds

Structural changes in the Brill transitions of Nylon 10/10 and its model compounds have been investigated by carrying out the temperature-dependent measurements of X-ray diffraction and infrared spectra along with the DSC measurement. The crystal structure at room temperature was found to be the so-called α form with the all-trans zigzag methylene segments. When the samples were heated, the infrared progression bands of the methylene segments, which are sensitive to the length of all-trans segmental parts, were found to change their spectral patterns in the transition temperature region: the progression bands decreased in intensity and disappeared above the transition region. At the same time several new bands were observed to appear, which were found to correspond to the progression bands of (CH₂)₇-(CH₂)₅trans-zigzag segments. These spectral changes indicate that the methylene segments were conformationally disordered by an invasion of some gauche bonds and as a result the effective length of trans-zigzag segments became shorter. This conformational disordering was found to occur more remarkably in the methylene segment of NH-(CH₂)₁₀-NH part than the CO-(CH₂)₈-CO part. At the same time the infrared bands of amide groups, in particular the bands sensitive to the twisting angles about the CH₂-amide bonds were found to show the remarkable change, indicating the local conformational change from planar-zigzag to twisted form in the CH₂-amide moiety. The frequency shift of amide A band (NH stretching mode) indicated a weakening of intermolecular hydrogen bonds, which however, did not disappear up to the melting region. From these data combined with the X-ray diffraction data, the structural disordering in the Brill transition phenomena was deduced concretely.     

Infra-red measurements on one-way drawn poly(ethylene terephthalalate) films subjected to constant strain

The infra-red spectrum of one-way drawn PET film was measured as a function of further applied strain, the specimens being maintained under fixed strain, while the spectra were obtained for the two polarization situations where the electric vector is, respectively, parallel and perpendicular to the draw direction. The changes in molecular orientation and conformation were determined from the reconstruction procedures outlined as a function of applied strain. The spectra, together with those of poly(ethylene terephthalate) (PET) in several different structural forms were reconstructed over the frequency range 700–1100 cm^?1 by a computational procedure using the method of damped least-squares. The minimum number of bands required to reconstruct all the spectra was chosen, and the existence of such bands in the second derivative spectrum was used as a criterion for their validity. With the exception of bands at 726 and 733 cm^?1, final fits were obtained on the basis that all the band shapes are Lorentzian. Comparison of the spectra of a number of model compounds showed that in nearly all cases the minor bands revealed by the curve fitting procedures could be identified with bands in the model compounds. It proved possible to relate the observed changes in the infra-red spectrum to the relaxed stress-strain curve of the film. The following picture emerges from the results for frequency shifts and changes in intensity. Up to the yield point there is considerable stress in the trans conformers (as reported by previous workers) and also in most of the gauche conformers. There is also a substantial increase in trans orientation, in contrast to the orientation of the terephthalate residue, which remains at the level observed at zero stress. The yield point marks the region where the stress on the trans and gauche conformers shows a sudden fall. At the same time there is a rapid increase in the trans-gauche ratio, a fall in the trans orientation, but an increase in the orientation of the terephthalate residues. It appears from these results that up to the yield point the elastic strains are concentrated in the glycol residues. After yield, both the stress and orientation decrease because conformational changes take place which allow the overall network structure to rearrange. When this occurs, there is some stress relaxation associated with the permanent flow, and the network as a whole achieves a higher degree of overall orientation, which is shown by changes in the orientation of the terephthalate residues. Subsequent deformation causes systematic changes in conformer content and molecular orientation which are consistent with continuum models for the plastic deformation of polymers.     

Synchrotron radiation ablation of polymers having double bonds in their main chains

Polyacetylene (PA), poly(cis- and trans-1,4-butadiene)s (cis- and trans-PBs), and poly(p-phenylene vinylene) (PPV) were ablated by synchrotron radiation (SR), aiming to deposit thin, uniform films of each on a substrate. When PA was irradiated by SR, gaseous phenyl compounds were produced, and a thin amorphous film was deposited on the substrate, exhibiting no characteristics of PA. In the cases of PPV and trans-PB, the source materials were reproduced in the form of thin film on the substrate by SR ablation. When alkali halides, e.g. NaCl and KBr, were used as deposition substrates, PPV was deposited, in an ordered way, on their cleavage surfaces. However, the deposited film of trans-PB by SR ablation was non-crystalline, because it was produced as a copolymer by 1,4- and 1,2-addition polymerizations of ablated butadiene-based fragments. In comparison, thin films of these polymers were also prepared by thermally evaporating them in a vacuum. When trans-PB and PPV were thermally evaporated, thin films with chemically and structurally identical features to the source polymers were produced, respectively. In contrast, a deposited film from cis-PB by SR ablation consisted of carbon compounds, showing no sign of hydrocarbon compounds in it, while trans-PB was produced from cis-PB by thermal vapor deposition.     

Sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer using H and C NMR

The triad-level sequence analysis of poly(ethylene/1,4-cyclohexanedimethylene terephthalate) copolymer was reported in a solvent system of o-chlorophenol/deuterated chloroform mixture (50/50 v/v) at 80 °C using 600 MHz ¹H NMR. The well-resolved alcoholic CH₂ proton peak of the glycol units was observed, which made the detailed sequence analysis possible. The peaks of the cis- and trans-forms of the 1,4-cyclohexanedimethylene glycol units were split into the triad sequence in the chain and could be assigned by a comparison of the spectra with those of homopolymers and by an additional two-dimensional heteronuclear multiple bond correlation observation. The triad sequence distributions centered on 1,4-cyclohexanedimethylene glycol units were determined, which was independent of the cis- and trans-forms of the units and controlled according to Bernoullian statistics.     

Phase equilibria in SBR/polybutadiene elastomer blends: Application of Flory–Huggins theory

Blends of anionically-polymerized polybutadiene (BR) and styrene–butadiene copolymer (SBR) must be treated as mixtures of terpolymers and tetrapolymers, due to the presence of three different BR isomers: cis-1,4, trans-1,4, and vinyl-1,2. Moreover, in the absence of specific interactions or chemical reactions that strongly influence miscibility, structural characteristics of the component polymers, such as BR isomer content, SBR styrene content, monomer sequence distribution, molecular weight, and molecular weight distribution, are expected to have an increased role in determining the blend miscibility characteristics. Small angle neutron scattering (SANS) studies of SBR/BR blends have resulted in the computation of the monomer–monomer segmental interaction energetics via a Flory–Huggins treatment. This allows quantitative prediction of miscibility behavior as a function of polymer structure. We have used the Flory–Huggins chi parameters, describing the styrene/cis-1,4, styrene/trans-1,4, and cis-1,4/trans-1,4 segmental interactions, to identify certain blend combinations expected to exhibit phase transitions in an experimentally accessible temperature range. The appropriate polymers were synthesized, solution blended, and the blends analyzed via optical microscopy and thermal analysis. Our results show that the blend behavior, observed experimentally, is consistent with the calculated cloud point curves. © 1994 John Wiley & Sons, Inc.     

On the structure of polybutadiene: 4. 13C n.m.r. spectrum of polybutadienes with cis-1,4-, trans-1,4- and 1,2-units

¹³C n.m.r. spectra of polybutadienes with different contents of cis-1,4- and 1,2-units are assigned in the resonance region of the cis and trans carbon double bond. The observed signals are assigned to configurational triads.     

Observation of phase separation of epoxidized trans-1,4-polyisoprene and mechanism exploration through 13C-NMR

Selectively epoxidized trans-1,4-polyisoprene (SETPI) and randomly epoxidized trans-1,4-polyisoprene (RETPI) were fabricated successfully through modified surface water-phase suspension epoxidation and solution random epoxidation, respectively. The effects of fabricated method and epoxy degree of ETPI on the glass transition temperature (T _g), dynamic mechanical properties and phase separation phenomenon of the as-fabricated polymer have been investigated by different scanning calorimetry, dynamic mechanical analyzer and phase contrast microscope. The double bonds and epoxy groups sequence structure distribution of different ETPI have been observed and analyzed by ¹³C-NMR. There is a great deal of difference in the microstructure and sequence distribution of epoxy group in ETPI with different synthesis methods and epoxy degree. The results show that distribution of epoxy group in SETPI is nonuniform which brings about the phase separation.     

Synthesis and characterization of stereotriblock polybutadiene containing crystallizable high trans-1,4-polybutadiene block by barium salt of di(ethylene glycol) ethylether/triisobutylaluminium/dilithium

A series of high trans-1,4-low-cis-1,4-high trans-1,4-stereotriblock polybutadienes (HTPB-b-LCPB-b-HTPBs) were synthesized through a sequential anionic polymerization of butadiene (Bd) initiated by barium salt of di(ethylene glycol) ethylether/triisobutylaluminium/dilithium (BaDEGEE/TIBA/DLi). The polymers consisted of elastic low-cis-1,4-polybutadiene (LCPB) chemically bonded with crystallizable high trans-1,4-polybutadiene (HTPB). The block ratios (HTPB:LCPB:HTPB) were designed at 25:50:25 (molar ratio) and finally determined by SEC. The microstructures and sequences of the specimens were investigated by FTIR and NMR. The resultant HTPB-b-LCPB-b-HTPBs consisted of LCPB block with 52.5% trans-1,4 content and HTPB block with 55.9–85.8% trans-1,4 content. According to differential scanning calorimetry (DSC), HTPB-b-LCPB-b-HTPB showed a significant cold crystallization which was discussed in terms of entanglement concept. The cold crystallization temperature (T_cc) decreased whereas the melting temperature (T_m) increased with the increasing trans-1,4 content of HTPB block.     

Synthesis of spherical trans-1,4-polyisoprene/trans-1,4-poly(butadiene-co-isoprene) rubber alloys within reactor

Trans-polydiene rubber family as high-performance tire stock possessed excellent dynamic properties, including excellent anti fatigue, low rolling resistance, low heat buildup, good green strength, and low abrasion loss. Here, Reactor Granule Technology (RGT) was introduced into the field of synthetic rubber for the first time to produce trans-1.4-polyisoprene/trans-1,4-poly(butadiene-co-isoprene) rubber alloy, which showed significant improvement in rubber synthetic technologies and great development in abundance of trans-rubber family. A series of trans-polyisoprene alloys with excellent spherical morphology were successfully synthesized by using sequential multistage polymerization. The alloy was fractionated into four fractions by temperature-gradient fractionation, and the fractionation was analyzed by ¹H NMR, ¹³C NMR, DSC and WAXD.     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Selective Hydrogenation of 2-Butyne-1,4-diol to 1,4-Butanediol Over Particulate Raney® Nickel Catalysts

The current study describes the results on the selective hydrogenation of the 2-butyne-1,4-diol to 1,4-butanediol over Raney^® nickel catalysts both in batch and in CSTR mode. The detailed kinetic analysis of the reaction in batch mode revealed the existence of three characteristic regions. In the first region, A, the starting 2-butyne-1,4-diol produces primarily cis-2-butene-1,4-diol. In the second region, B, the dominant species is cis-2-butene-1,4-diol, which is either hydrogenated to 1,4-butanediol or isomerizes to trans-2-butene-1,4-diol. In the third region, C, the accumulated 4-hydroxybutanal is slowly hydrogenated to 1,4-butanediol. When the same reaction was carried out in a CSTR mode, the only products detected initially are the 1,4-butanediol and n-butanol. The first by-product detected immediately after the end of the first stage is the linear hemiacetal between the 4-hydroxybutanal with 1,4-butanediol. This species has been used as convenient tracer for determining the length of the selective region of the catalyst performance.     

Deformation of trans-1,4-polyisoprene spherulite: small angle X-ray diffraction,thermal differential analysis and density studies

The deformation behaviour of melt crystallized spherulitic samples of trans-1,4-polyisoprene was investigated by small-angle and wide-angle X-ray measurements and by density and differential thermal analysis. The X-ray diffraction experiments were carried out both on the fibres under strain with the two ends clamped and on the fibres after relaxation at room temperature. A substantially different trend is obtained in the plots of the long-spacing versus the degree of elongation for the clamped and free fibres. A limiting axial long-spacing L_T is found only in the case of the fibres with both ends fixed. The way in which isotropic trans-1,4-polyisoprene deforms seems to be dependent on the stretching conditions, on the thermal history, the pre-stretching conditioning and on the relative amount of polymorphic modification in the samples. A comparison with the deformation behaviour of polyethylene and polypropylene is made. The overall density and the mass crystallinity increase with the degree of elongation though a lowering in the melting point is observed. Linear relationships are obtained between the reciprocal of the long-spacing and the fusion temperature of the plastically deformed fibres.     

Cathodic reduction of phenacyl thiocyanate

The cathodic reduction of phenacyl thiocyanate in aprotic medium leads to an enolate, which acts as nucleophile in addition or substitution reactions as well as electrogenerated base. The products of these reactions were isolated and identified as 2,4-diphenylthiophene, 1,4-diphenyl-1,4-butanedione, 1,5-diphenyl-3-benzoyl-1,5-pentanedione, trans-1,2,3-tribenzoyl cyclopropane and acetophenone.