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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.

Block copolymers have been extensively studied due to their ability to spontaneously self-organize into a wide variety of morphologies that are valuable in energy-, medical-, and conservation-related (nano)technologies. While the phase behavior of bicomponent diblock and triblock copolymers is conventionally governed by temperature and individual block masses, it is demonstrated here that their phase behavior can alternatively be controlled through the use of blocks with random monomer sequencing. Block random copolymers (BRCs), i.e., diblock copolymers wherein one or both blocks are a random copolymer comprised of A and B repeat units, have been synthesized, and their phase behavior, expressed in terms of the order–disorder transition (ODT), has been investigated. The results establish that, depending on the block composition contrast and molecular weight, BRCs can microphase-separate. We also report that large variation in incompatibility can be generated at relatively constant molecular weight and temperature with these new soft materials. This sequence-controlled synthetic strategy is extended to thermoplastic elastomeric triblock copolymers differing in chemistry and possessing a random-copolymer midblock.

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) was studied in detail using time-resolved small-angle X-ray scattering. This polyester was found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the polyester was always larger than that of the amorphous layers. Secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

While theoretical and experimental efforts have thoroughly addressed microphase-ordered AB diblock copolymer blends with a parent homopolymer (hA or hB) or a second block copolymer, surprisingly few studies have considered comparable ABA triblock copolymers in the presence of hB or an AB diblock copolymer. In this study, we elucidate the roles of additive molecular weight and constraint by examining three matched series of miscible ABA/hB and ABA/AB blends. Self-consistent field theory is employed to analyze molecular characteristics, e. g., segmental distributions, microdomain periods and midblock bridging fractions, as functions of blend composition. Predictions are compared to morphological characteristics discerned by transmission electron microscopy and small-angle X-ray scattering. The corresponding mechanical properties of these blends are measured by dynamic mechanical analysis. The results of this comprehensive work reveal that addition of hB swells the B-lamellae of the ABA copolymer and has a generally deleterious effect on both the dynamic elastic modulus and midblock bridging fraction. In contrast, addition of a lamellar or cylindrical AB copolymer to the same ABA copolymer can promote an increase or decrease in lamellar period and bridging fraction, depending on relative block sizes.

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...

Recent experimental evidence and theoretical predictions indicate that binary blends of relatively monodisperse diblock copolymers remain miscible if the molecular weight disparity of the constituent copolymers is not too great. In this work, we examine the effect of moderate copolymer polydispersity on both the microstructural characteristics and phase behavior of blends prepared from four compositionally symmetric poly(styrene-b-isoprene) (SI) diblock copolymers ranging in polydispersity (Mw/Mn) from 1.02 to 1.30. Blend periodicities, measured by small-angle X-ray scattering, compare favorably with predictions from a strong segregation theory proposed for lamellar diblock copolymer blends composed of monomolecular copolymers. Transmission electron microscopy, employed to ascertain the real-space morphological characteristics of these blends, reveals that a lamellar → cylindrical transition occurs in macrophase-separated blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2653–2658, 1997

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.

Polymeric materials undergo dramatic changes in orientational order in response to dynamic processes, such as flow. Their rich cascade of dynamics presents opportunities to create and combine distinct alignments of polymeric nanostructures through processing. In situ rheo-optical measurements complemented by ex situ x-ray scattering reveal the physics of three different trajectories to macroscopic alignment of lamellar diblock copolymers during oscillatory shearing. At the highest frequencies, symmetry arguments explain the transient development of a bimodal texture en route to the alignment of layers parallel to the planes of shear. At lower frequencies, larger-scale relaxations introduce rearrangements out of the deformation plane that permit the formation of lamellae perpendicular to the shear plane. These explain the change in the character of the pathway to parallel alignment and the emergence of perpendicular alignment as the frequency decreases.

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.

Linear multiblock copolymers, like their diblock analogues, are capable of ordering into periodic microstructures when the blocks are sufficiently incompatible. In this work, a series of four linear poly(styrene-b-isoprene)n (SI)n (1 ≤ n ≤ 4) multiblock copolymers with nearly equal block lengths has been synthesized via living sequential anionic polymerization. All of the copolymers are microphase-separated, as discerned by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), and exhibit lamellar morphologies in which the microdomain periodicity decreases with n. This behaviour suggests that the middle blocks contract the microdomains along the lamellar normal. Microstructural characteristics are compared with predictions from formalisms proposed for linear multiblock copolymers and, along with conformational considerations, are used to interpret the thermal and tensile properties of the copolymers.

Linear multiblock copolymers, like their diblock analogs, undergo microphase separation and order into periodic morphologies when the blocks are sufficiently incompatible. To explore the conformations of such materials, four symmetric poly(styrene-[ital b]-isoprene)[sub [ital n]] copolymers with 2[ital n] (1[le][ital n][lt]=4) perfectly alternating blocks of nearly equal mass have been synthesized. Small-angle x-ray scattering reveals that the microdomain periodicity decreases with [ital n] along the lamellar normal, thereby confirming theoretical predictions and providing direct evidence for bridging among the 2([ital n][minus]1) middle blocks.

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

The density of an amorphous polymer near its interface with a flat solid surface was investigated using neutron reflectometry. Bulk poly(methyl methacrylate) with a monodisperse molecular weight in contact with a silicon single crystal wafer was the first system studied, and the emphasis was placed on the temperature dependence of the interface density profile. The temperature range studied encompassed the glass transition temperature of the polymer and a reversible change in the density profile was discovered.

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) (PHB) and its copolymers [P(HB-co-HHx)] containing 2.5, 3.4, and 12 mol % 3-hydroxyhexanoate (HHx) comonomer and the melting of the resultant crystals were studied in detail using time-resolved small-angle X-ray scattering and differential scanning calorimetry. The polyesters were found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the PHB homopolymer was always larger than that of the amorphous layers. In the copolymers, by contrast, the randomly distributed HHx comonomer units were found to be excluded from the lamellar crystals into the amorphous regions during the isothermal crystallization process. This interrupted the crystallization of the copolymer chains, resulting in the formation of lamellar crystals with thicknesses smaller than those of the amorphous layers. The lamellar crystals in the copolymers had lower electron densities compared to those formed in the PHB homopolymer. On the other hand, secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

Properties of polymer alloys comprising poly (lactic acid) and Nodax copolymers are investigated. Nodax is a family of bacterially produced polyhydroxyalkanoate (PHA) copolymers comprising 3-hydroxybutyrate (3HB) and other 3-hydroxyalkanoate (3HA) units with side groups greater than or equal to three carbon units. The incorporation of 3HA units with medium-chain-length (mcl) side groups effectively lowers the crystallinity and the melt temperature, T m , of this class of PHA copolymers, in a manner similar to that of alpha olefins controlling the properties of linear low density polyethylene. The lower T m makes the material easier to process, as the thermal decomposition temperature of PHAs is then relatively low. The reduced crystallinity provides the ductility and toughness required for many plastics applications. When a small amount of ductile PHA is blended with poly(lactic acid) (PLA), a new type of polymer alloy with much improved properties is created. The toughness of PLA is substantially increased without a reduction in the optical clarity of the blend. The synergy between the two materials, both produced from renewable resources, is attributed to the retardation of crystallization of PHA copolymers finely dispersed in a PLA matrix as discrete domains.

Introduction Experimental Chemical Synthesis Biological Production Molecular Weight Determination NMR Thermal Analysis X-ray Analysis Crystallization Kinetics Mechanical Analysis Rheological Measurements Properties Breaking Down Isodimorphism Increasing Flexibility, Ductility Crystallization Rate Melt Properties Melt Stability Deformation Properties and Morphology Conclusions Acknowledgements Keywords: poly(3-hydroxyalkanoates); poly([R]-3-hydroxybutyrate); poly(3-hydroxybutyrate-co-3-hydroxyvalerate); poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); poly(3-hydroxybutyrate-co-3-hydroxyoctanoate); poly(3-hydroxybutyrate-co-3-hydroxydecanoate); poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate); physical properties; melt properties; polymer processing; bacterial copolyester; mechanical properties; crystallinity

While numerous efforts have been put forth to correlate the morphology of microphase-separated diblock and triblock copolymers with molecular characteristics such as composition and chain length, far fewer studies have been devoted to elucidating the role of molecular architecture on microstructure in more complex linear copolymers. This is particularly surprising since many segmented copolymers, for example, have found their way into commercial applications. In this work, we present some of our recent work to bridge the gap between well-defined di/triblock copolymers and segmented copolymers. Here, a novel set of well-defined linear (AB) n multiblock copolymers possessing equal compositions and chain lengths, but different numbers of AB block pairs (n= 1,2,3,4), have been synthesized. Their microphase-separated morphologies have been characterized using both transmission electron microscopy (TEM) and small-angle x-ray scattering (SAXS). A recently-developed thermodynamic model based on confined-chain statistics is presented, and predictions are found to compare well with experimental data.

The crystalline/amorphous interface is a region where there is a transition from the ordered to disordered state. It must accommodate chain folds and defects which cannot lie within the crystal. This transition must occur over a finite distance, estimated to be of the order of 20A and represents a zone of intermediate mobility and order. Consequences are (1) an intermediate Tg, (2) loss peaks associated with limited mobility, (3) lower miscibility in this region arising from the lower entropy of mixing, and (4) concentration of excluded species in this region. Evidence for this comes from (1) Kratky analysis of small-angle x-ray scattering data, (2) observation of an enhanced concentration of excluded species by small-angle neutron scattering, and (3) rheo-optical studies of mobility. Previous NMR studies can also be interpreted in terms of this model. The model suggests how this “interphase” may be controlled via the nature and amount of the excluded species.