Longitudinal volume viscosity of 1,4 cis polybutadiene

Volume flow of 1,4 cis polybutadiene (1,4 cis PB) of ¯M _n =311.900,T _g =156 K, andT _m =266 K, has been measured.Elastic modulus of the elastic wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at compression rates of ca. 1.0 to 200.0×10^–5 s^–1, and at temperatures of 293 K to 373 K, and pressures up to 150 MPa.Longitudinal volume viscosity decreases with increasing compression rate, and with decreasing volume deformation, the behavior being in all cases a typical non-equilibrium one. Longitudinal volume viscosity decreases with increasing temperature (except at 293 K), the volume flow activation energy being of about 18.2 KJ/mol.     

Phonon dispersion and heat capacity in polyoxacyclobutane modification I

Normal modes of vibration and their dispersion for polyoxacyclobutane modification I (POCB I) have been obtained by using Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. Characteristic features of the dispersion curves such as crossing, repulsion and regions of high density-of-states have been explained. Heat capacity measurements have been interpreted and the limitations of the present work discussed.     

Filler-polymer interactions in filled polybutadiene compounds

Bound rubber in a filled rubber compound is formed by physical adsorption and chemisorption between the rubber and filler. Polybutadiene (PB) is composed of three components of 1,2-, cis-1,4-, and trans-1,4-units. Filler-polymer interactions in PB compounds filled with carbon black or silica were studied by analyzing microstructures of the bound rubbers with pyrolysis-gas chromatography. Differences in the filler-polymer interactions of the 1,2-, cis-1,4-, and trans-1,4-units were investigated. The filler-polymer interaction of the 1,2-unit is stronger than those of the cis-1,4- and trans-1,4-units. The interaction of the 1,2-unit with silica is stronger than with carbon black. Bound rubber content is decreased by treatment with ammonia. Change of the bound rubber composition after the ammonia treatment was also studied.     

Thermal oxidation of polybutadiene. Part 2: Mechanistic and kinetic schemes for additive-free non-crosslinked polybutadiene

The thermal oxidation of an additive-free, uncrosslinked, hydroxy-terminated polybutadiene has been studied at temperatures ranging from 60 to 120 °C and oxygen pressures from 0.01 to 3.1 MPa by gravimetry, IR spectrophotometry and chemical titration of epoxides and hydroperoxides for samples of 20 and 265 μm thicknesses. A mechanistic scheme with 17 elementary steps among which radical additions to double bonds, decomposition of the resulting alkyl radicals and the corresponding terminations was proposed on the basis of qualitative observations and literature data. A kinetic scheme, composed of 8 differential equations for the 8 reactive species plus 4 equations for the measured quantities, has been derived from the mechanistic scheme. The kinetic parameters, essentially elementary rate constants, have been determined using an inverse approach. A set of physically reasonable parameter values has been obtained. With these parameters, the kinetic model is able to generate kinetic curves of the mass gain, carbonyl build-up, hydroxyl build-up, double bond consumption, epoxide build-up and hydroperoxide build-up, reasonably close to experimental ones, in the full domain of temperatures, oxygen pressures and sample thickness under consideration.     

FT-Raman spectroscopy of the reaction of polybutadiene with mercapto-thiadiazoles

Mercapto-thiadiazoles having potential anti-wear behaviour are reacted with polymers with existing viscosity index-improving properties in order to produce materials which may find a use as multifunctional lubricant additives. 2,5-Dimercapto-1,3,4-thiadiazole, 2-amino-5-mercapto-1,3,4-thiadiazole and 2-methyl-5-mercapto-1,3,4-thiadiadiazole were reacted with low MW polybutadiene containing vinyl-1,2, cis-1,4 and trans-1,4 (C=C) groups. The reactions were monitored using FT-Raman spectroscopy in order to determine quantitatively the consumption of the individual structural units when reacted with thiadiazoles. 2,5-Dimercapto-1,3,4-thiadiazole reacted readily with the polybutadiene, achieving 80% reaction within a few hours. The thiadiazole reacted selectively with the order of addition being cis>vinyl>trans. 2-Amino-5-mercapto-1,3,4-thiadiazole and 2-methyl-5-mercapto-1,3,4-thiadiazole were found to react more slowly and hence to a lesser extent (40 and 25%, respectively) over a similar time scale.     

Phonon dispersion in polyguanylic acid

A study of the normal modes of vibration and their dispersion in polyguanylic acid along the chain axis (tetrad form) based on Urey-Bradley force field and Raman and Fourier transform infrared is reported. It has been greatly assisted by the vibrational analysis of guanine tetrad and spectral information for telomeric DNA d(G₁₂). Spectral relationship for polyG, telomeric DNA d(G₁₂) and characteristic features of dispersion curves such as regions of high density-of-states, repulsion and character mixing are discussed. Predictive value of heat capacity as a function of temperature is reported.     

Epoxides in the thermal oxidation of polybutadiene

Polybutadiene films were aged under air or high oxygen pressure (3.1 MPa). In both cases, the amount of epoxide formed was titrated. The results show that the epoxide formation rate is a decreasing function of oxygen concentration that validates the mechanism proposed by Mayo. According to this mechanism, epoxides are generated from the decomposition of β-peroxy alkyl radicals resulting from the addition of peroxy radicals on double bonds.     

A comparative study of vibrational dynamics of α- and β-forms of poly(β-hydroxybutyrate)

Normal modes and their dispersion are obtained for planar zig-zag form of poly(β-hydroxybutyrate) using Urey-Bradley force field. A comparison is made with the spectra of its helical form. Apart from detailed assignment of modes, various characteristic features of dispersion curves have been explained as arising due to internal symmetry in energy momentum space. The density-of-states have been used to calculate heat capacity in the temperature range 10-450 K using Debye's formalism.     

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.     

Phonon dispersion and heat capacity in poly(ε-caprolactone)

Normal mode of vibration and their dispersion for poly(ε-caprolactone) (PCL) chain have been obtained by using Urey-Bradley force field and the Wilson's GF matrix method as modified by Higgs. Characteristic features of the dispersion curves such as crossing, repulsion and regions of high density-of-states have been explained. Heat capacity measurements have been interpreted and the limitations of the present work discussed.     

Thermal oxidation of polybutadiene. Part 1: Effect of temperature, oxygen pressure and sample thickness on the thermal oxidation of hydroxyl-terminated polybutadiene

An additive-free, uncrosslinked, hydroxyl-terminated polybutadiene of predominant trans 1-4 structure was thermally oxidized at temperatures ranging from 60 to 120 °C, under various oxygen pressures (between 0.01 and 3.1 MPa). Samples of thickness ranging from 5 to 1000 μm were studied by gravimetry (mass changes due to oxygen absorption) and infrared spectrophotometry (hydroxyl and carbonyl build-up, double bond consumption). The effects of film thickness, oxygen pressure and temperature on oxidation kinetics are discussed in terms of branched radical chain mechanisms.     

A kinetic evaluation of the thermal oxidation of a phenol stabilised polybutadiene

The thermal oxidation of hydroxy telechelic polybutadiene stabilised with 2,2′-methylene-bis(4-methyl-6-tert-butylphenol) was studied at 100 °C using weight changes and stabiliser quantification by liquid chromatography. The extended induction time relative to the unstabilised sample and the initial rate of stabiliser depletion were found to be proportional to the initial stabiliser concentration.Previously published kinetic models, based on the hypothesis that the stabiliser is only consumed by reaction with peroxy radicals and that the stationary state assumption is appropriate, were examined and found insufficient to explain the observations. An improved model was suggested assuming the contribution of a phenol oxygen reaction that results in a competing oxidation of the stabiliser itself. Experimental and theoretical arguments in favour of this model refinement are proposed.     

Thermal rearrangement study of low molecular weight polybutadiene

Various polybutadienes (PBDs) of low molecular weight were heated below complete crosslinking at 250 °C under anaerobic nonpyrolytic conditions, and the structural changes were investigated. The predominant crosslinking reactions arise from the presence of 1,2-vinyl isomer and the most important one is intermolecular reaction accompanied with methyl group formation. The analysis showed that two crosslinking types as well as two types of methyl groups have been produced in which one was the result of 1,2-vinyl isomer of one chain crosslinked via methylene carbon of another chain of cis or trans isomer, and the second methyl group was the product of the reaction between 1,2-vinyl isomers of two PBD chains. Chain scission also occurred in two pathways due to the presence of 1,2-vinyl isomer, scission at two adjacent 1,2-vinyl isomer and scission at adjacent 1,2-vinyl with cis or trans isomer giving rise to methyl carbons.     

Crosslinking investigation of polybutadiene thermal degradation by carbon-13 nuclear magnetic resonance

Thermal degradation of polybutadiene (PBD) in anaerobic atmosphere at 250 °C had been studied by carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR) before complete crosslinking. In this investigation four types of low molecular weight PBD with different 1,2-vinyl isomer content had been chosen, then pure and mixed samples of PBD were heated in different time periods. ¹³C NMR spectra showed that two kinds of crosslinking mechanisms occur that both of them produce methyl groups. The first mechanism is a reaction between 1,2-vinyl isomers of two PBD chains, and the second one occurs between 1,2-vinyl isomer of one chain via methylene carbon of cis or trans isomer in another chain. Also ¹³C NMR results showed that the presence of 1,2-vinyl isomer in the PBD structure is necessary and without it none of the mentioned reactions will occur. Furthermore isomers sequence is another important parameter which affects crosslinking. Results show that cis or trans isomer which is not adjacent to 1,2-vinyl isomer does not take part in crosslinking reaction. Moreover such cis or trans isomer can take part in second mechanism of crosslinking that 1,2-vinyl isomer was attached from head to cis or trans isomer, thus in this arrangement of isomers second mechanism of crosslinking will become dominant rather than first mechanism of crosslinking.     

分散聚合技术及其研究进展

介绍了分散聚合体系中各组分及反应条件对反应过程和最终产物性能的影响,简要归纳了分散聚合成核机理、稳定机理及其反应动力学,并着重阐述了近年来分散聚合发展的新技术以及制备的功能微球在各领域的应用等方面的研究进展.分散聚合与其它非均相聚合方法相比,是制备粒径范围在1-10μm且单分散性较好的聚合物微球的有效方法.最近,许多新思路不断引入分散聚合体系,如采用水和超临界CO2作为分散介质,尝试微波和辐射引发聚合以及按照活性聚合机理进行反应等.     

Preparation and characterization of spherical polymer packings from polybutadiene for size-exclusion chromatography

Porous polymer spherical particles for column packings in nonaqueous size-exclusion chromatography (SEC) were prepared from 1,2-syndiotactic polybutadiene by suspension and evaporation method. The polymer microbeads obtained were crosslinked by radical reaction between 2-vinyl groups in polybutadiene with ultraviolet radiation, to render them insoluble. These microbeads have wider chromatographic separation width than polystyrene column packings. In addition, the polybutadiene microbeads did not show the excessive retention observed with commercial polystyrene columns for polycyclic aromatic compounds. Therefore, a close correlation between the elution volume and M, for polycyclic aromatic compounds was observed with polybutadiene microbeads columns.     

双组分体系分散阈值的测定及应用

双组分体系分散阈值的测定及应用陈宜,郭士岭,程爱珠（郑州工学院化工系郑州,４５０００２）关键词分散阈值,分散量,ＣｕＯ,ＮｉＯ,ＨＺＳＭ－５分散阈值与活性组分及载体相互作用有关,是催化研究中的重要参数。对分散阈值的研究大都仅涉及了单组分活性物质在载体...     

分散聚合研究

介绍了分散聚合制备聚合物微球的研究进展，对分散聚合的成核与稳定机理、聚合过程、动力学、反应参数对聚合物微球粒径及分散性的影响以及运用分散聚合制备功能性聚合物微球及聚合物－－磁性材料复合微球的研究现状进行了回顾。     

Low molar mass polybutadiene made crosslinkable by the introduction of styrenic moieties via urethane linkage: synthesis, kinetic and crosslinking studies

The introduction of styrenic moieties was chosen for the radical crosslinking of polybutadiene bearing hydroxy functions. The modifications were carried out with 3-isopropenyl-α,α-dimethylbenzyl isocyanate (TMI) with or without catalyst (DBTL). A 2nd order kinetic fits our experimental results up to high conversion. Arrhenius parameters were calculated. Thermally catalyzed crosslinking was studied. The reaction was followed by measuring swelling (Q) in toluene as well as mechanical parameters (storage modulus E^′ at the rubbery plateau and tanδ). The influence of temperature, the nature and concentration of initiators, the number of styrenic groups per chain (n=1.2, 2, 2.4) were investigated. In the range of our experimental conditions, a “reaction master curve” was established to predict the evolution of E^′ and Q as a function of time, for any temperature, initiator concentration and value of n.