Isoprene Diblock Copolymers Research Articles

Micellization of ω-Functionalized Poly(styrene-b-isoprene) Copolymers in n-Decane

Results are presented from static low-angle and dynamic light scattering as well as viscometry experiments for ω-functionalized diblock copolymers of styrene and isoprene in n-decane, a nonpolar se...

Rheology and Shear-Induced Alignment of Lamellar Diblock and Triblock Copolymers

The linear viscoelastic behavior of diblock and triblock copolymers of styrene and isoprene was studied in the lamellar phase both before and after alignment by large-amplitude oscillatory shear. The orientation of the lamellae, as determined by X-ray scattering, is controlled by the temperature and frequency of alignment. For triblocks, a high degree of alignment with the lamellar normal perpendicular to both the flow and shear gradient directions (perpendicular alignment) can be achieved, so that nearly terminal rheological behavior is observed at low frequencies. The diblock never aligns to this extent. Unlike the diblock, we were unable to align the triblock with the lamellae parallel to the shearing surfaces, presumably because triblocks can form bridges across lamellar domains and so hinder the sliding of lamellae past each other. The diblock lamellae have no bridges and can achieve parallel orientation at low temperatures and high alignment frequencies. This contrasts with the poly(ethylene-propylene)-poly(ethylethylene) (PEP-PEE) system, in which parallel alignment is only seen at low frequencies and low temperatures. 1

Temperature and Molecular Weight Effect of Styrene–Isoprene Diblock Copolymers on the Interfacial Tension between Polystyrene and Polyisoprene

The effect of styrene–isoprene diblock copolymers on the interfacial tension between polystyrene (PS) and polyisoprene (PI) has been investigated by direct measurement of the interfacial tension using a pendant drop interfacial tension apparatus. The interfacial tension is nearly independent of the temperature when the diblock copolymers are added, although the interfacial tension of PS/PI without copolymers decreases with increasing the temperature. A decrease in interfacial tension is observed with the addition of a small amount of copolymer, followed by a leveling off when the copolymer concentration exceeds a critical micelle concentration. The critical micelle concentration increases with temperature. The effect of the molecular weight of block copolymers on the interfacial tension is not significant.

Statics and Dynamics of .omega.-Functionalized Block Copolymers of Styrene and Isoprene

The statics and dynamics of ω-functionalized diblock copolymers of styrene and isoprene have been studied with small-angle X-ray scattering (SAXS) and with rheology and dielectric spectroscopy. The asymmetric diblock copolymers (ω PS 30%) had a dimethylamino or zwitterion group at either end of the chain, and the molecular weights were in the range (0.62-2.44) x 10 4 . Depending on the temperature, the SAXS results revealed two separate levels of microphase separation, one between the polystyrene (PS) and polyisoprene (PI) blocks forming the microdomain structure and another one between ionic and nonionic material. The latter process creates sufficient contrast notwithstanding the small fraction of the zwitterionic groups. When the zwitterion is linked to the PI chain end, aggregates are formed at low temperatures within the PI phase. These aggregates manifest themselves both in rheology and in dielectric spectroscopy, respectively, with an extended rubbery plateau and with a new dielectric process associated with restricted PI segmental relaxation. When the zwitterion is located on the PS chain end, association takes place, at high temperatures, within the PS phase and acts to stabilize the new microdomain up to very high temperatures. When compared with neutral diblocks, the ω-functionalized diblock copolymers constitute a new class of materials which provide the possibility of altering the phase behavior by introducing a small amount of a polar group at one chain end.

Association of End-Functionalized Block Copolymers. Light Scattering and Viscometric Studies

The dilute solution properties of diblock and triblock copolymers of styrene and isoprene with one dipolar sulfobetaine group at either or both ends of the chain were examined in CCl 4 by static and dynamic light scattering as well as by viscometry. The copolymers were prepared by anionic polymerization techniques using [3-(dimethylamino)propyl]lithium as initiator. The tertiary amine groups were converted to sulfobetaines by reaction with cyclopropanesultone. Aggregation numbers derived from static and dynamic methods are in good agreement and decrease with increasing molecular weight of the polymeric tail. Aggregates seem to be polydisperse and stable for long periods of time

Natural rubber and butadiene rubber blend using diblock copolymer of isoprene–butadiene as compatibilizer

AbstractBlends of natural rubber (NR) and butadiene rubber (BR) have been studied with or without diblock copolymers of isoprene–butadiene (BIR). It was found that NR/BR blends displayed the optimal properties at about 4 wt % of BIR from the tensile measurements of NR/BR blends. Increase of molecular weight of BIR resulted in the decrease of tensile properties, but had no significant effect on their hardness. Abrasion resistance of rubber blends containing BIR was about 30% higher than that without BIR. The molecular weight of BIR did not show a remarkable effect on the abrasion index. Differential scanning calorimetry and dynamic mechanical analyses of rubber blends suggested a two‐phase structure even in the presence of BIR. © 1993 John Wiley & Sons, Inc.

Stability of the chain structure of a styrene–isoprene diblock copolymer during the hydrogenation by diimide

AbstractOlefinic double bounds of a model styrene–isoprene diblock copolymer were hydrogenated using diimide (generated by a thermal decomposition of p‐toluenesulfonyl hydrazide). The presence of byproducts and/or main‐chain structural alterations (e.g., degradation or cross‐linking), as a possible side effect of this polymer analogous reaction, was checked by NMR spectroscopy, elemental analysis, static and dynamic light scattering, and GPC. A twofold concentration of Irganox 1010 antioxidant in the reaction mixture (as compared to the original reported procedure) seems to inhibit the formation of byproducts as well as to prevent any alterations on the macromolecular level. No reactions of isoprene monomer units (other than the addition of hydrogen atoms) and no changes in molar‐mass distribution of the substrate were detected by the methods used.