Copolymerization Of Isoprene Research Articles

Photooxidation mechanism of styrene–isoprene copolymer: evolution of the profile of oxidation according to the composition

The photooxidation of styrene–isoprene copolymers is investigated on the basis of infrared analysis of irradiated films. The results show that the polystyrene segments are stable under irradiation and degradation results only from the photooxidation of the polyisoprene segments. Oxidation of polyisoprene results in chain scissions and generates various carbonylated photoproducts. A three-dimensional structure is formed by cross-linking reactions resulting from additions on the double bonds and formation of ether linkage. In order to determine the influence of the polyisoprene content on the mechanism and the kinetics of oxidation, different compositions have been tested. The extent of degradation is found to be proportional to the polyisoprene content but the rate of photooxidation is constant whatever the composition. The distributions of the oxidation products within the polymer are similar whatever the composition. This behavior can be attributed to the incompatibility between the polyisoprene and the polystyrene segments, which leads to a phase demixion and the formation of nodules. Each nodule can be considered as an independent photochemical reactor.

Micelle Formation of Diblock Copolymers of Styrene and Sulfonated Isoprene in Aqueous Solution

Asymmetric diblock copolymers of styrene (St) and sulfonated isoprene (SI) with a short St block and a much longer SI block were synthesized by sulfonation of diblock copolymers of St and isoprene, and their micellization in aqueous solution was investigated. Three block copolymers having different degrees of polymerization of St block (DPSt) and SI block (DPSI) were employed, which include polymers with DPSt = 40 and DPSI = 240 (St−SI-20), DPSt = 60 and DPSI = 210 (St−SI-30), and DPSt = 130 and DPSI = 820 (St−SI-207). Dry samples of these St−SI block copolymers could be directly dissolved in water, undergoing intermolecular self-association to form core−corona type micelles. The micellar mass, hydrodynamic size and its distribution, critical micelle concentration (cmc), and aggregation number were estimated by light scattering and fluorescence techniques. It was suggested that the micelles and unimers coexist at equilibrium with a well-defined cmc on the order of 10-2 g/L, with St−SI-207 (with the longes...

Synthesis of Model PS(PI)5 and (PI)5PS(PI)5 Nonlinear Block Copolymers of Styrene (S) and Isoprene (I)

Synthesis of Model PS(PI)₅ and (PI)₅PS(PI)₅ Nonlinear Block Copolymers of Styrene (S) and Isoprene (I)

Synthesis of a novel diblock copolymer of isoprene and methacrylic acid

A new diblock copolymer of isoprene (I) and methacrylic acid (MAA) was prepared by combination of an anionic mechanism with a charge transfer complex mechanism. In the first step, the polyisoprene (PI) macroanion formed by initiation with butyllithium was capped by p-dimethylaminobenzaldehyde (capped polyisoprene = PId); a dimeric coupling product was not detected. Then the binary system constituting of PId and benzophenone was used to initiate the polymerization of MAA under UV irradiation. The resulting diblock copolymer (PI-b-PMAA) was characterized by IR, NMR and gel permeation chromatography (GPC) in detail.

Synthesis of a novel diblock copolymer of isoprene and methacrylic acid

A new diblock copolymer of isoprene (I) and methacrylic acid (MAA) was prepared by combination of an anionic mechanism with a charge transfer complex mechanism. In the first step, the polyisoprene (PI) macroanion formed by initiation with butyllithium was capped by p-dimethylaminobenzaldehyde (capped polyisoprene = PId); a dimeric coupling product was not detected. Then the binary system constituting of PId and benzophenone was used to initiate the polymerization of MAA under UV irradiation. The resulting diblock copolymer (PI-b-PMAA) was characterized by IR, NMR and gel permeation chromatography (GPC) in detail.

Self‐assembly in ω‐functionalized block copolymers of styrene and isoprene

AbstractThe spatial organization of end‐functionalized diblock copolymers of styrene and isoprene revealed two separate levels of microphase separation: one between the two blocks forming the microdomain and another between the polar and non‐polar material. The association produced by the latter process has a pronounced effect on the dynamics as revealed in rheology and dielectric spectroscopy. The introduction of a polar group into the different chain‐ends has a dramatic effect on the phase behavior of the diblock copolymers and provides new ways of controlling their miscibility.

Comparison of rubber reinforcement using various surface-modified precipitated silicas

The reinforcement of a natural rubber compound by various surface-modified precipitated silicas was compared. Compound physical properties were determined for two silicas differing in surface area and were used as controls to evaluate these silicas after surface modification by using either a bifunctional organosilane coupling agent (γ-mercaptopropyl–trimethoxysilane) or a new surface modification process. This new process is based on the in situ polymerization of organic monomers solubilized inside surfactant bilayers that are adsorbed onto the silica surface to afford silicas modified with styrene–butadiene and styrene–isoprene copolymers. Both surface modification processes afford materials that dramatically increase the compound cure rate, thereby significantly reducing T90 cure times, while also improving tensile properties, tear strength, abrasion resistance, and compression set of the cured compound. The silane-modified silica gives a higher flex-cracking resistance than do the silicas modified by the in situ polymerization of organic monomers, whereas these latter silicas significantly increase rebound resilience and offer greater overall improvements in rubber compound performance. The rubber compound physical properties obtained using the modified, higher surface area Hi-Sil® 255 silica are generally improved relative to those obtained using the modified Hi-Sil® 233 silica. © 1996 John Wiley & Sons, Inc.

Polar copolymer-surface-modified precipitated silica

To improve the performance of rubber compounds using precipitated silica as a reinforcing filler, the silica surface was directly modified by (1) adsorption of a surfactant onto the surface, (2) adsolubilization of an organic monomer, (3) in situ polymerization of the monomer in the surfactant bilayer, and (4) partial surfactant removal. Silica was thus modified using copolymers of isoprene or 1,3-butadiene with vinyl acetate, acrylonitrile, 4-methoxystyrene, 4-chlorostyrene, and methyl methacrylate on the silica surface. 4-Methoxystyrene/butadiene modification afforded the most promising candidate based on evaluation in a silica-filled, natural/styrene-butadiene rubber shoe sole compound that also has been used as a model tire compound. Physical testing showed that cure times were decreased, and break strength, tear energy, elongation to break, and cut growth resistance were increased. Thus, surface modification of silica by the in situ polymerization of organic monomers has been shown to be a flexible process capable of producing unique materials useful in improving rubber cure properties and the cured compound physical properties. © 1996 John Wiley & Sons, Inc.

Order–disorder transition and ordering kinetics in binary diblock copolymer mixtures of styrene and isoprene

The order–disorder transition (ODT) and the ordering kinetics have been studied in two symmetric diblock copolymers of styrene and isoprene and their binary mixtures with rheology. The binary mixtures formed a single microdomain (with lamellar morphology) composed of short and long chains as confirmed by small angle x-ray scattering (SAXS). The order–disorder transition temperature (TODT), obtained from the discontinuity in the storage modulus G′, varies linearly with the number average degree of polymerization. For shallow quenches, the ordering kinetics proceed via nucleation and growth. The characteristic time of this process scales with N̄−1/3, where N̄ is the Ginzburg parameter, in agreement with the theoretical predictions [G. H. Fredrickson and K. Binder, J. Chem. Phys. 91, 7265 (1989)]. Our results indicate that the ordering kinetics of symmetric diblock copolymers near the ODT are fluctuation controlled.

Microphase Separation in Star Block Copolymers of Styrene and Isoprene. Theory, Experiment, and Simulation

The order−disorder transition (ODT) and the ordering kinetics have been studied in four-arm star diblock copolymer melts of styrene (corona) and isoprene (core) by rheology and SAXS. The results are compared with the corresponding linear diblock and show that the transition shifts in the direction predicted by theory. The mean-field structure factor is used to describe the SAXS profiles at T ≫ TODT and to extract the temperature dependence of the interaction parameter χ(T). Because of the weak T dependence of χ, we can explore only a small region of the phase diagram, namely, 16.5 < χN0 < 14.6, for fPS = 0.25. The microphase-separated state consists of spherical microdomains of the minor component (PS) which resembles a bcc phase, however, not with the full symmetry. To explore the morphology over a broader T range, we use the results of computer simulation on equivalent chains, which for fPS = 0.25 provide the following succession of phases: hexagonal − a bicontinuous structure which resembles the gyroi...

Synthesis and Characterization of α,ω-Macrozwitterionic Block Copolymers of Styrene and Isoprene

The synthesis of a novel type of telechelic block copolymer is described: bifunctional poly(styrene-b-isoprene) diblock copolymers were prepared by anionic polymerization using [2-[(N,N-dimethylam...

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...

Relaxation and viscoelastic properties of complex polymer systems

Dynamic behavior of various polymer melts is studied on the basis of a comparison of viscoelastic properties with the information obtained from dielectric spectroscopy. The experimental observations are compared with results of computer simulation of corresponding systems. The studies include simple melts of linear chains, block copolymer systems of miscible components, as well as the behavior of melts with molecular objects of complex topology-like stars or microgels. In the case of polyisoprene linear chain melts an equivalence of terminal relaxation times determined from mechanical and dielectric measurements is demonstrated. Using linear block copolymers of isoprene and butadiene, relaxation times of chain fragments (isoprene blocks) in relation to relaxation times of whole copolymer chains are determined and compared with theory and simulation. Both the experimentally determined block relaxation times and relaxation times of chain fragments in simulated linear chain melts show a disagreement with predictions of the reptation theory. In the case of multiarm star polymers and microgel melts, the slow relaxation modes observed in viscoelastic spectra are assigned to cooperative translational motions detected in corresponding simulated systems in which an ordering of such molecules is demonstrated. This suggests that the terminal relaxation in multiarm star or microgel melts is governed by another relaxation mechanism than in linear chain melts. High efficiency of the Cooperative Motion Algorithm in simulation of dense systems of complex molecules is demonstrated.

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

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

Block copolymers of isoprene and tertiary butyl acrylate: Synthesis, characterization and micelle formation

Block copolymers were synthesized by sequential anionic polymerization of isoprene and 1-butyl acrylate using sec-butyl lithium as initiator and tetrahydrofuran as solvent. The copolymers were fractionated by liquid/liquid separation to remove traces of homopolymer impurities, using toluene/methanol as a solvent/non-solvent system. Molecular characterization of the block copolymers was carried out using gel permeation chromatography, elemental analysis, Fourier transform infrared spectroscopy and static light scattering. The copolymers were shown by light scattering to form micelles in n-octane, a selectively bad solvent for the poly(t-butyl acrylate) block. Increasing the temperature led to a shift in the micelle/free-chain equilibrium in favour of free-chains. Contributions to the standard Gibbs energy of micellization were evaluated. A large, negative standard enthalpy of micellization is shown to provide the driving force for micellization.

Polymers Capable of Undergoing Crosslinking without Volume Shrinkage. Synthesis of Polymers Containing a Spiroorthoester Moiety by Copolymerization of Isoprene with Spiroorthoesters Having Radically Polymerizable Groups

The copolymerization of 2-methylene-1,4,6-trioxaspiro[4.6]undecane and 2-[(methacryloyloxy)methyl]-1,4,6-trioxaspiro[4.6]undecane with isoprene and the cationic cross-linking of the obtained polymers are investigated

End-Functionalized Block Copolymers of Styrene and Isoprene: Synthesis and Association Behavior in Dilute Solution

Di- and triblock copolymers of isoprene and styrene having a highly polar sulfozwitterion group on one or both ends of the chain were prepared by anionic polymerization using high-vacuum techniques with [3-(dimethylamino)propyl]lithium as initiator. The dimethylamino end group of the chain was transformed to a zwitterion by reaction with cyclopropanesultone. The monofunctional zwitterion-capped copolymers were found to associate in CCl 4 (a good solvent for polystyrene and polyisoprene) whereas the difunctional versions formed gels even below the coil overlap concentration c * . The aggregation number was found to decrease with increasing base molecular weight due to the excluded vulume repulsions of the copolymeric tails

DieneN-(2,4,6-Tribromophenyl)maleimide Copolymer Membranes for Pervaporation of Ethanol-Water Mixtures

Alternating copolymers of butadiene or isoprene with N-(2,4,6-tribromophenyl)maleimide and the copolymer of chloroprene containing 42.7 mole % N-(2,4,6-tribromophenyl)maleimide structure units were synthesized by radical copolymerization. Along with copolymerization, the Diels-Alder addition of comonomers proceeded. DSC revealed some crosslinking of the copolymers occurring even at room temperature. Homogeneous membranes were prepared from the copolymers by solution casting and tested in pervaporation of variously concentrated aqueous ethanol. Separation factors of the membranes related to the preferentially transported water increased with increasing content of ethanol in solutions to be separated. In contrast to hydrophilic maleimide groups, the incorporated diene units lowered separation efficiency due to their affinity to ethanol.