Styrene-isoprene Copolymers Research Articles

Precipitation fractionation of block copolymers

Possibilities offered by classical precipitation fractionation in the preparative separation of polymer admixtures from block copolymers and in an estimate of the polydispersity in molar mass and of the heterogeneity in chemical composition of block copolymers have been examined. A mixture of a two-block copolymer, polystyrene-block-polyisoprene, with polystyrene was separated in the systems cyclohexane/1-propanol and 1,4-dioxan/1-propanol, and a mixture of three two-block styrene-isoprene copolymers having different chemical composition was fractionated in the system benzene/methanol. In the cyclohexane/1-propanol system, two commercial samples of three-block copolymers polystyrene-block-poly(ethene-co-butene)-block-polystyrene and their mixture were fractionated. The results showed that the polydispersity and chemical heterogeneity thus estimated are much lower than the real ones, especially due to the colloid properties of block copolymers.

Small-angle neutron scattering measurement of block copolymer interphase structure

The notion of an interfacial layer at the domain boundary in block copolymers is reviewed and the possibility of its measurement by small-angle X-ray and small angle neutron scattering discussed. Values of the interfacial layer thickness and its volume fraction have been obtained for a range of styrene-isoprene copolymers. Interfacial layer thickness is not strongly dependent on molecular weight whilst the volume fraction shows a dependence more in line with the theory of Helfand.

The Effect of the Temperature Dependence of the Dielectric Constant on Thermally Stimulated Currents in Polymers

A dipolar theory of thermally stimulated currents taking into account the thermal dependence of the equilibrium polarization has been tested in the glass transition range of a series of polymers selected for their well-resolved relaxation spectra and the absence of any significant bulk conductivity (triblock, diblock, and star-shaped styreneisoprene copolymers). Systematic studies of the effect exercized on thermally stimulated polarization currents (TSPC) and thermally stimulated depolarization currents (TSDC) by varying parameters such as field strength, electrode material, field polarity, and type of heating-cooling sequence, have been carried out and full qualitative agreement with the predictions of the theory has been found. In particular, these results imply that the variations of equilibrium polarization occurring during the nonisothermal steps of TSDC and TSPC experiments cannot be a priori neglected, as is still commonly done in classical treatments of experimental data.

The flow of polymer-thickened oils in convergent jet-thrust nozzles at a temperature of 84°C

It is shown that an existing form of jet-thrust device may be modified for satisfactory use at elevated temperatures. Jets are produced from a straight capillary tube and from three nozzles designed to provide different rates of uniaxial extension in the flowing oil, with shear present near the nozzle walls. The behaviour of three simulated multigrade motor oils with additives of different chemical type is compared with that of Newtonian oils at temperature of 84°C. In straight-tube flow, no measurable normal stress is detected in one of the oils (that with an alkylmethacrylate as polymer additive), but the other two oils give stresses which are measurable and, in one case, as high as those obtained at ambient temperature (that with the styrene-butadiene copolymer additive). For these oils the normal stresses measured in tubes are much closer to the axial stresses measured in nozzles than was the case at ambient temperature. In nozzle flow, axial stresses are detected in each oil which are rather lower than those measured at ambient temperature, the deviation increasing with increased jet velocity. The relative importance of axial stress, compared with shear stress, is shown to increase with increasing temperature and shear rate. The ration of axial stress to shear may reach a value of 3 or 4 at a shear rate of 10 5set −1, the oils with styrene-butadiene and styrene-isoprene copolymer additives being somewhat better performers than that with the alkylmethacrylate copolymer additive. It is suggested that the presence of normal, or axial, stresses might improve lubrication performance in those situations where normal load is applied with little relative movement of the bearing surfaces.

Anionic polymerization and copolymerization in heterogeneous systems on surfaces with aromatic structure

AbstractMethacrylaldehyde, methyl methacrylate, methacrylonitrile, styrene and isoprene readily polymerize on potassium–graphite inclusion compounds in ethereal and hydrocarbon solvents. The structure of polymethacrylaldehyde, poly(methyl methacrylate), and polyisoprene as well as the composition of styrene–acrylonitrile and styrene–isoprene copolymers have been investigated. The copolymers have a high content of styrene units which is interpreted in terms of selective adsorption of styrene on the initiator surface.

The Properties of Filled Copolymer Vulcanizates

In our previous paper1) of this series the properties of styrene-butadiene rubber vulcanizates in tensile fracture was discussed. In this paper the properties of three copolymer vulcanizates in tensile fracture are studied, namely isoprene-butadiene, styrene-isoprene and methyl methacrylate-isoprene, and the following conclusions have been obtained.(1) The fracture in the vulcanizates of these copolymers compounded with carbon black is mainly due to scission in the molecular chains of polymer, and there is almost no scission in the bonds between the rubber molecules and the surface of the carbon black.(2) The temperature which affords the maximum value of ultimate elongation depends entirely on the transition temperature Tg, though the rubbers used may vary in average molecular weights per piece, in the network chain densities and in the combined sulfur structure.(3) The ultimate elongation at reduced temperature is little affected by the composition of two copolymers that do not differ markedly in Tg of homopolymer, as in the isoprene-butadiene system, while the elongation is thought to be decreasing with the increasing variance between the two component copolymers in Tg of homopolymer. For instance the elongation of styrene-isoprene copolymer decreases with increased content of styrene.

Anionic Polymerization of Isoprene: Effect of Ionic Character of the Growing Ion Pair on Polymer Structure

The styrene content of styrene-isoprene copolymers initiated by alkali metals in different solvents is correlated with the total 1,4-adduct content of isoprene homopolymers initiated in the same manner. A very good linear relationship is obtained over the whole range which is dependent on the ionic character of the propagating species highly ionic systems (i.e., Na in ethers) give high styrene and low 1,4-adduct contents, while less ionic systems, i.e., butyllithium in aromatic ethers and in hydrocarbons, give progressively lower styrene and higher 1,4-adduct contents.