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Unsaturated polydienes are frequently hydrogenated to yield polyolefins that are more chemically stable. Here, the effects of partial hydrogenation on the phase behavior and nanostructure of polyisoprene-containing block copolymers are investigated. To ensure access to the order–disorder transition temperature (TODT) over a wide temperature range, we examine copolymers with at least one random block. Dynamic rheological and scattering measurements indicate that TODT increases linearly with increasing hydrogenation. Small-angle scattering reveals that the temperature-dependence of the Flory–Huggins parameter changes and the microdomain period increases, while the interfacial thickness decreases. The influence of hydrogenation becomes less pronounced in more constrained multiblock copolymers.

While numerous fundamental studies have sought to elucidate the effect of a parent homopolymer on the morphological characteristics and mechanical properties of microphase-ordered block copolymer blends, few comparable efforts have extended such studies to concentrated copolymer solutions in the presence of a low-molar-mass block-selective solvent. In this work, we investigate the microstructures that form in blends of a poly(styrene-block-isoprene-block-styrene) (SIS) triblock copolymer with a midblock-selective aliphatic mineral oil. To discern the influence of midblock/oil compatibility on blend morphology and properties, identical blends with a poly[styrene-block-(ethylene-alt-propylene)-block-styrene] (SEPS) copolymer, the hydrogenated variant of the SIS copolymer, have likewise been examined. The saturated midblock of the SEPS copolymer is responsible for the observed shifts in morphology stability limits and higher dynamic elastic shear moduli relative to the SIS analogue. These results reveal that...

In-situ rheo-optical methods are used to guide electron microscopy (TEM) and X-ray scattering (SAXS) studies of structure development during flow-induced alignment in a lamellar block copolymer melt (nearly symmetric polystyrene−polyisoprene diblock, ODT ≃ 172 °C). The progress of shear-induced alignment is recorded in real-time using flow birefringence; at selected points during alignment samples are taken for ex-situ characterization by TEM and SAXS along all three axes (v, ∇v, ∇ × v) of the flow geometry. Three different trajectories are examined: perpendicular alignment and two qualitatively different routes to parallel alignment in the high-frequency regime (ω > ω'_c). In general, the initial “fast” process not only enhances the projection of the orientation distribution that corresponds to the final state but also increases other projections of the distribution; the late-stage “slow” process eliminates these other projections and perfects a single alignment. For example, the highest frequency path to parallel alignment begins by transforming poorly organized regions into layers that are predominantly oriented along the parallel and transverse directions. The transition to the slow process is marked by the development of a characteristic texture in which tilt wall boundaries normal to the flow direction separate bands that form a repeating “chevron” pattern (layers tilted up and down about the ∇×v axis). The coarsening of this pattern dominates the slow process, during which the transverse projection is also eliminated.

The persistence length of isotactic poly(hydroxy butyrate) was measured using small-angle neutron scattering. The value obtained from these measurements reflects a high degree of local chain persistence. If this local persistence is accounted for, scattering from these chains can be globally fit with Gaussian scaling. A global scattering function, the unified equation, is used, which decomposes the chain structure into two levels, one corresponding to the Gaussian regime and one to the persistence regime. The persistence length obtained using this global scattering function is compared to that obtained using the graphical approach of Kratky and Porod with good agreement. Additionally, the global fitting approach of Sharp and Bloomfield is also considered. The Kratky and the Sharp and Bloomfield approaches appear to yield different values for the persistence length. Additionally, the Sharp and Bloomfield function does not allow inspection of the component parts of the fit. One advantage of both global functions is that the level of statistical confidence in the persistence length can be determined in a least-squares fit. Another advantage is the removal of ambiguity concerning an apparent regime of non-Gaussian scaling between the persistence scaling regime and the Gaussian regime.

Rheo-optical methods are used to examine the combined effect of shear frequency, strain amplitude, and temperature on the direction and kinetics of flow-induced alignment in lamellar block copolymers. The development of shear-induced alignment in a nearly symmetric polystyrene-polyisoprene diblock (ODT ≃ 164 °C) is recorded in real time using flow birefringence as a probe of the transient lamellar orientation distribution. As alignment progresses during large amplitude oscillatory shearing, the birefringence shows an initial fast and a later slow change. While increasing strain amplitude (γ o ) generally speeds both the fast and the slow processes, below a critical γ o the slow process is not observed and a well-aligned state is not achieved. The transient birefringence observed at a particular frequency and temperature, but different strain amplitudes, can be partially superposed by scaling time with γ o n(ω) . However, the fast and slow processes require different values of n(ω). Estimates of n(ω) show that effects of strain are highly nonlinear and stronger than the simple rescaling of time in terms of either cumulative strain (∼tγ o ) or cumulative flow energy (∼tγ o 2 ). The effect of temperature enters most strongly through the shift of time scale of molecular relaxations (a T ).

Recent experimental and theoretical efforts suggest that ordered diblock copolymer blends can be approximated as single-component systems of average composition or molecular weight (or both) if the...

Diblock copolymers order into a variety of periodic morphologies when the constituent blocks are sufficiently incompatible. Previous studies have demonstrated that classical dispersion (spherical and cylindrical) and lamellar morphologies, as well as complex morphologies (e.g., gyroid*, lamellar catenoid, and hexagonally perforated lamellae), can be selectively accessed through either tailored molecular synthesis or copolymer/homopolymer blends. In the present work, control over ultimate morphology is achieved through the use of binary copolymer blends composed of two strongly-segregated poly(styrene-b-isoprene) (SI) diblock copolymers of equal molecular weights but different compositions (one 50 wt % S and the other 85 wt % S). Blend morphologies are examined by electron microscopy (including three-dimensional imaging) and small-angle X-ray scattering, and a theoretical framework is proposed to describe strongly-segregated copolymer blends exhibiting the lamellar morphology. Results obtained here indicate that diblock copolymer blends of a given bulk composition may exhibit coexisting morphologies but in general behave as single-phase diblock copolymers of equal molecular composition, suggesting that such blends offer an alternative, and attractive, route by which to generate a desired morphology.

Blends of microbial isotactic poly[(R)-3-hydroxybutyrate] (P[(R)-3HB]) (M n =650 000) and synthetic atactic poly[(R,S)-3-hydroxybutyrate] (P[(R,S)-3HB]) (M n =56 000 and 3400) were investigated by optical microscopy and SAXS. The spherulites of isotactic P[(R)-3HB] were volume-filled, indicating the inclusion of P[(R,S)-3HB] within the spherulites. The radial growth rate of P[(R)-3HB] spherulites decreased with increased content of P[(R,S)-3HB]

The cocrystallization and phase segregation phenomena previously reported were reconfirmed by WAXS and SAXS measurements for blends of deuterated high density polyethylene with hydrogenous polyethylene species having various branching contents. On the basis of the WAXS, SAXS and SALS data in addition to previous FTIR data, a difference in the crystal structure, lamellar structure and spherulite structure was compared between the blend samples with various degrees of branching

Etude de l'influence des conditions de cristallisation (par refroidissement ou isothermiquement a 100 et 110°C) du melange 50/50 sur la morphologie des lamelles

The conformation of polymer chains in the melt near an impenetrable boundary has recently been studied by molecular dynamics and off-lattice Monte Carlo simulations. Both types of calculations show an enhancement of the chain end density within a distance of approximately two polymer segment lengths of the interface relative to the bulk. In the absence of preferential interactions between monomers and the interface, the segregation arises from minimizing the loss of conformational entropy near an impenetrable boundary; i.e., by positioning an end near the surface, only one unit rather than two is reflected. In order to obtain an experimental measure of this effect, monodisperse polystyrene (PS) chains of molecular weight 63 000 with short blocks of deuterated polystyrene (dPS) at each end were prepared. The block length was kept as short as possible, while yet producing sufficient neutron scattering contrast in order to minimize any preferential surface segregation due to isotopic effects. The synthesis was carried out via living anionic polymerization of a purified styrene monomer in cyclohexane at 60 C, utilizing sec-butyllithium as the initiator. The process was terminated using degassed methanol.