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This work reports a facile and versatile ring-opening metathesis polymerization of three- and four-armed star-shaped poly(epsilon-caprolactone) (PCL) macromonomers bearing a norbornenyl group at each chain end using Grubbs' third-generation catalyst under diluted condition to obtain graft polymers (GPs) comprising densely arrayed three- and four-armed cage-shaped grafted PCLs (GPCLs) with narrow dispersity (1.19-1.35) and a controllable number of cage repeating units up to 40 (molecular weight: similar to 320 000 g mol(-1)). The GPCLs were characterized using nuclear magnetic resonance spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. The cyclopolymerization proceeded via repetitive rapid intramolecular reactions to form cage-shaped units followed by slow intermolecular propagation. This synthesis was applicable to star-shaped poly(L-lactide), poly(trimethylene carbonate), and poly(ethylene glycol). Investigating the structure-property relationships regarding crystallization behavior, hydrodynamic diameter, and viscosity revealed that cage-shaped topological side chains reduced the chain dimensions and mobility compared to their linear and cyclic counterparts.

Block copolymers (BCPs) under nanoscale confinement can self-assemble to form novel nanostructures that are not available in the bulk state. Particularly, the ordering process of block copolymers a...

In fibers spun from polymer solutions, we investigated self-organization of ordered shish kebabs via the cascade evolution of various dissipative structures through multistep phase transitions at multiple length scales. We used transmission electron microtomography to discover for the first time crystalline fibrils with diameters of ∼10 nm that orthogonally bridge neighboring kebabs epitaxially overgrown from shishs. The fibrils evolved during the late-stage self-organization processes of the shish kebabs. The fibrils were classified as completely bridging fibrils and pairs of broken fibrils facing each other; the broken fibrils were formed by the following two steps, first by the flow-induced burst of the bridging domains driven by Laplace pressure and subsequent crystallization involved in the burst domains. The bridging and broken fibrils were observed at interkebab distances smaller and larger than the critical length of ∼80 nm, respectively. The bridging fibrils and the cores of the broken fibrils ha...

We investigate the formation of the ordered bicontinuous structures in a stereoregular diblock copolymer, isotactic polypropylene-block-polystyrene (iPP-b-PS), in which the minority PP block possessed isotactic configuration. This diblock displayed the conventional ordered bicontinuous double gyroid (OBDG) morphology upon heating above the crystal melting point of the iPP block from the as-cast state. The OBDG phase remained stable in the heating process up to the order–disorder transition. In the subsequent cooling process from the nearly disordered state, the OBDG phase first developed, but when the temperature was sufficiently low, an order–order transition from OBDG to the ordered bicontinuous double diamond (OBDD) phase occurred, and OBDD eventually became the dominant structure. The results attested that OBDD and OBDG represented the thermodynamically stable structure at the lower and the higher temperature, respectively, and the OBDG morphology formed in the as-cast state was metastable. The presen...

The phase behavior of polystyrene (PS) brushes in cyclohexane (CHX) was investigated, for the first time, by environmental atomic force microscopy as a function of the graft density and temperature. The polystyrene brushes of three different graft densities exhibited island-, bicontinuous-, and hole-shape microdomains in the direction parallel to the substrate. The size of such “in-plane” microdomains is close to the end-to-end distance of PS brush chain due to the anchoring of one of the chain ends of PS brushes to the substrate. The microdomain structure disappeared as the temperature increased, and new structure with same morphological features reappeared by lowering temperature. This reversible temperature response corresponds to the in-plane phase separation of the PS brush/CHX system. The UCST type binodal line shifted toward slightly lower temperature in the PS brush/CHX system compared to that of the corresponding nongrafted polymer solution, i.e., PS/CHX system, in excellent agreement with our pr...

A series of zwitterionic polyelectrolytes poly[3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate] (PMAPS) with a wide range of weight-average molecular weight (Mw) between 5.5 × 103 and 1.6 × 106 g mol–1 with narrow molecular weight distribution (Mw/Mn = 1.07–1.19) were thoroughly characterized in aqueous NaCl solutions for salt concentration (Cs) over a range from theta Cs (0.074 M) to 1.0 M by synchrotron radiation small-angle X-ray scattering (SAXS), light scattering, and viscometry at 25 °C. To determine the chain stiffness parameter (λ–1) and the excluded-volume strength (B) of PMAPS in an aqueous NaCl solution, SAXS profiles and the Mw dependences of the radius of gyration, the second virial coefficient, the interpenetration function, the hydrodynamic radius, and the intrinsic viscosity for PMAPS were analyzed on the basis of the (un)perturbed cylindrical wormlike chain model. The experimental λ–1 value for PMAPS chains in aqueous NaCl solutions barely decreased but was almost consta...

The epitaxial relationship in the thermal phase transition between double gyroid (DG) and hexagonally packed cylinder (HEX) phases in polystyrene-block-polyisoprene thin films on Si wafer was investigated using transmission electron microtomography and grazing incidence small-angle X-ray scattering. Two different types of epitaxial transitions were observed, and they appeared to be selectively favored depending on the transition direction. One type of epitaxial relationship prevails in the phase transition from DG to HEX upon heating in which {121}DG, {111}DG, and {220}DG are converted to {100}HEX, {110}HEX, and {001}HEX, respectively. The interphase planes are {220}DG and {001}HEX, and the cylinders meet the {220}DG plane perpendicularly (head-on, Type A) at the grain boundary between DG and HEX. Although there are small dimensional mismatch and distortion in the location of the cylinders in this epitaxial relationship, all cylinders are formed along the topologically equivalent DG skeletal path. On the ...

The control of microphase-separated structures in a poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) was investigated in three dimensions by transmission electron microtomography. Neat SBM self-assembled into a double-helical structure of polybutadiene (PB) domains around hexagonally packed core polystyrene (PS) cylinders in a poly(methyl methacrylate) matrix. When PS homopolymer with a lower molecular weight than that of the PS block in SBM was added to the SBM, the PB domains transformed from double-helical structures to spherical domains, while maintaining the helical trajectories. In contrast, adding a higher molecular weight PS to the SBM changed the helical structures from double- to triple-stranded structures and even to four-stranded structures. The helical structures of the PB domains were strongly affected by the distribution of the blended polystyrenes in the core cylindrical PS domains.

We investigated, via scanning and transmission electron microscopy, the arrangement of the microdomains of symmetric polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) confined in hemispherical cavities. The hemispherical cavities were prepared by using anodic aluminum oxide (AAO) template, where the inner surface of the cavities was modified by thin brush layers of PS, PMMA, and PS-ran-PMMA copolymer. When the inner surface of the cavity is strongly selective to PS chains, concentric rings consisting of PS and PMMA microdomains are formed, replicating the confined geometry of hemisphere. However, as the selectivity of a brush to PS chains becomes weaker, various interesting morphologies are formed that have not been reported in the literature. The experimentally observed microdomain arrangement confined inside the hemispherical cavities was compared with the simulation results based on the dynamic Metropolis Monte Carlo method.

Functionalized multiwalled carbon nanotubes (F-MWCNTs) were individually dispersed in a commercial polypropylene (PP) matrix using our well-established α-zirconium phosphate (ZrP) nanoplatelet-assisted dispersion approach. The F-MWCNTs remained uniformly dispersed in PP after melt mixing and injection-molding and were found to remarkably enhance modulus and strength at only 0.1 wt % loading. The individual F-MWCNTs were mostly oriented and extended in the flow direction and were shown to be integrated within the crystalline structure of the matrix. The change in mechanical properties is attributed to both the modification in crystal structure due to MWCNT-induced nucleation and the direct reinforcement of crystalline lamellae and amorphous regions by the MWCNTs. We propose that the compatibilized F-MWCNTs exhibit sufficient interfacial interaction with the PP matrix to anchor lamellae stacks and resist interlamellar slip. The F-MWCNTs also reinforce amorphous domains between crystallites and behave as “su...

We report on the formation of tetragonally perforated lamellae from a polybutadiene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) (BVT) triblock terpolymer, PB22P2VP29PtBMA49110, ...

Nanoparticles with concentric layered structures were generated from a lamellae-forming poly(styrene-b-isoprene) diblock copolymer using controlled precipitation from a tetrahydrofuran/water mixture. Chloroform, a good solvent for both blocks, was used to swell and anneal the nanoparticles suspended in aqueous media. The three-dimensional morphologies of particles were reconstructed by transmission electron microtomography throughout the process of solvent annealing. A transition from concentric lamellae to PI cylinders in a PS matrix occurred upon annealing, presumably due to a slight selectivity of chloroform for PS. These cylindrical microdomains were further divided into PS-core-PI-shell spherical structures in a PS matrix upon extended annealing, a structure that is unique among reported microphase separated morphologies of diblock copolymers.

This Perspective summarizes the recent advances and perspective in three-dimensional (3D) imaging techniques and their applications to polymer nanostructures, e.g., microphase-separated structures of block copolymers. We place particular emphasis on the method of transmission electron microtomography (TEMT). As a result of some recent developments in TEMT, it is now possible to obtain truly quantitative 3D images of polymer nanostructures with subnanometer resolution. The introduction of scanning optics in TEMT has made it possible to obtain large volumes of 3D data from a micrometer thick polymer specimens using conventional electron microscopes at relatively low acceleration voltage, 200 kV. Thus, TEMT covers structures over a wide range of thicknesses from a few nanometers to several hundred nanometers, which corresponds to quite an important spatial range for hierarchical polymer nanostructures. TEMT provides clear 3D images and a wide range of new structural information, which cannot be obtained usin...

Lamella-, cylinder-, and sphere-forming block copolymers (BCPs) of polystyrene-b-polybutadiene (PS-b-PBD) were drawn into the pores of anodized aluminum oxide (AAO) membranes in the melt by capillary forces. After thermal annealing, the nanorods of the BCP were removed by dissolution of the AAO with a weak acid, and transmission electron microscopy (TEM) was used to investigate the resultant morphologies of the confined BCPs. The diameters of the pores in the AAO and the molecular weight of the block copolymers were varied to investigate the effect of confinement on the microphase separation of the BCP. Concentric cylinders were observed for the lamella-forming BCPs under 2D confinement, and deviations of the lamella repeat period were measured as a function of AAO pore diameter. In addition, torus-like morphologies were observed as the degree of confinement increased. For the bulk cylinder-forming BCPs, a rich variety of morphologies, not seen in the bulk, were observed that included stacked torus-like m...

Microphase-separated structures in poly(styrene-block-isoprene) (SI) block copolymer thin films were investigated by transmission electron microtomography (TEMT). The SI block copolymer showed cylindrical microdomains in the bulk state. Several block copolymer thin films with different thicknesses were prepared by spin-coating and were extensively annealed before the TEMT experiments. Intriguingly, although the cylindrical morphology orienting parallel to the substrate was observed in most of the cases, spherical microdomains were found at certain film thicknesses. The thickness dependence was investigated using a computer simulation based on the self-consistent-field theory, producing a morphological phase diagram based on minimizing free energy. We find that the distortion of the hexagonal lattice of the cylindrical microdomains caused the morphological transition to the spherical microdomains.

Internal structures of the opaque poly(N-isopropylacrylamide) gel obtained at the preparation temperature (TP) higher than 24.5 °C was found to have hierarchical structures by means of a combined small-angle-scattering (CSAS) method of small-angle light scattering (SALS), ultra-small-angle neutron scattering (USANS), and small-angle neutron scattering (SANS) with an aid of laser scanning confocal microscopy (LSCM). The combined CSAS and LSCM studies revealed that a global structure of the gels had a sponge-like two-phase structure. The polymer-rich phase of the sponge was filled with microgels having highly cross-linked network (“tight network”) chains that are interconnected by loosely cross-linked network (“loose network”) chains swollen with water, while the other phase of the sponge was mostly composed of water. These two phases were cocontinuous in three-dimensional space, hence, forming macroscopic gels. The SALS and USANS studies clarified that the sponge had a characteristic spacing of ≈12 μm and ...

The single-chain distribution in a poly(styrene-block-isoprene) block copolymer in the bulk state was studied by the combined method of transmission electron microtomography and three-dimensional mesoscale computer simulations. The local frustration of the block chains on a nanoscale can be analyzed using the size of the gyration radius, Rg. Two representative morphologies in the lamellar morphology have been examined, i. e., flat and bent lamellae. The Rg obtained from the proposed new method gave reasonable agreement with the previously measured values. It was shown that the single polymer chains in the bent lamella is more stretched out than those in the flat lamella. This method provides a new insight into understanding the self-assembled structure in the bulk microdomains.

The effect of various end-functional groups on the phase behavior of polystyrene-block-poly(n-butyl methacrylate) copolymer (PS-b-PnBMA) was investigated by using small-angle X-ray scattering, conventional and 3-D transmission electron microscopy, rheology, and Fourier-transformed infrared spectroscopy. A PS-b-PnBMA with maleic anhydride (SBM66-MAH) exhibited an unexpected thermoreversible transition occurring at higher temperature than its disorder-to-order transition temperature. The transition was very fast and induced a large increase in shear modulus. However, the transition at higher temperature was not observed in other PS-b-PnBMAs with carboxylic acid, diester, and hydrogen end groups.

Microphase-separated structures of a poly(deuterated styrene-block-2-vinylpyridine) (dPS-b-P2VP) block copolymer in thin films were studied by neutron reflectivity (NR) and transmission electron microtomography (TEMT). The dPS-b-P2VP block copolymer shows a cylindrical morphology in the bulk state. The block copolymer was spun-coated on a Si substrate, which was extensively annealed (170 °C for 14 days) before the NR experiments. The annealed thin film showed a featureless NR profile, the reflectivity monotonically decreased with the increasing scattering vector along the depth direction of the thin film, qz. The portion of the dPS-b-P2VP block copolymer thin film used in the NR experiment was examined by TEMT, from which a three-dimensional (3D) morphology of the block copolymer thin film was successfully obtained. The 3D image clearly showed that the microphase-separated structure inside the thin film had a cylindrical morphology with some order along the depth, but almost no in-plane order. In order to...

Ming Xiong, andHongxia Guo*State Key Laboratory of Polymer Physics and Chemistry,Joint Laboratory of Polymer Science and Materials,Institute of Chemistry, The Chinese Academy of Sciences,Beijing 100080, P. R. ChinaHiroshi Jinnai* and Takeshi KanekoDepartment of Macromolecular Science and Engineering,Graduate School of Science and Engineering,Kyoto Institute of Technology, Goshokaido-cho,Matsugasaki, Kyoto 606-8585, JapanReceiVed February 6, 2007ReVised Manuscript ReceiVed May 14, 2007Closure of block copolymer bilayer in the solution generatesthe so-called polymeric vesicles or polymersomes with thesolvent fills in their internal spaces. Recently, polymeric vesicleshave attracted a great attention not only from academia but alsofrom application field for drug delivery.

The grain boundary morphology of a lamella-forming poly(styrene-b-isoprene) (SI) diblock copolymer was investigated by transmission electron microtomography. The twist grain boundary, at which two lamellar nanodomains orthogonally intersect, was successfully observed in three dimensions (3D). A two-dimensional periodic minimal surface, the Scherk's first surface, was once hypothesized as a model of such a grain boundary morphology but never experimentally ascertained. The area-averaged curvatures of the interface between the PI and PS nanodomains as well as the interfacial area per unit volume suggested that the grain boundary morphology had characteristics of the saddlelike hyperbolic surface and was found to be quite similar to Scherk's first surface.

The electric field alignment of cylindrical microdomains in diblock copolymer thin films was studied using small-angle neutron scattering and transmission electron microscopy. The alignment process was followed with the block copolymer films in different initial states. Starting from a poorly ordered state, the cylindrical microdomain orientation was biased by the surface field that initially drove the cylindrical microdomains to be oriented parallel to the film surface. With further annealing, the cylinders were disrupted locally and formed ellipsoid-shaped microdomains that, with time, connected into cylindrical microdomains oriented in the field direction. Starting from an ordered state with cylinders parallel to the surface, the applied electric field enhanced fluctuations at the interfaces of the microdomains. The growth of the fluctuations continued until the cylindrical microdomains broke up into spherical microdomains, similar to that seen in the thermoreversible cylinder-to-sphere order−order tra...

Transmission electron microtomography (TEMT) has proven to be useful for investigating three-dimensional (3D) nanostructures in polymeric systems. However, the conventional TEMT that uses a tilt series around an axis occasionally fails to reconstruct nanostructures, especially when the nanostructure is highly anisotropic. Namely, if a certain geometrical relationship between orientation of the nanostructure and the tilt axis is fulfilled, the nanostructure does not appear in the 3D reconstruction. This problem can be solved by tilting the specimen around two (orthogonal) tilt axes and combining the resulting two 3D reconstructions after precise alignment between them. The strategy, called “dual-axis tomography”, is used to observe one of the commonly observed anisotropic polymer nanostructures, cylindrical morphology, of poly(styrene-block-isoprene) block copolymer. It was experimentally observed that the cylindrical nanodomains that were “missing” in one of the two tomograms were complementary reconstruc...

Laser scanning confocal micrographs for blends of poly(styrene-ran-butadiene) (SBR) and polybutadiene (PB) demonstrated the existence of fine structures inside one of the well-characterized macroscopically phase-separated bicontinuous domains, in the depth range of the blends belonging to the bulk. The average size of the fine structures was on the submicrometer length scale, while the characteristic spacing of the macroscopically phase-separated domains was on the order of 10 μm. Fluorescence laser scanning confocal micrographs revealed that the fine structures exist only in the SBR-rich phase. Although the driving force for the formation of the fine structures needs to be investigated further, a small amount of PB molecules in the SBR-rich domains seems to play an important role. Illumination and highlights were shed on the advantage of using laser scanning confocal microscopy for investigation of fine structures in the polymer blends.

Internal structures of translucent poly(N-isopropylacrylamide) gel were for the first time observed by laser scanning confocal microscopy (LSCM). The observed image reflected the mesoscopic internal structures in the gel due to the “fixed concentration fluctuations” of network polymers as described in the text. Three-dimensional internal structures in the gel constructed from a series of the cross section images taken by the LSCM revealed that the gel had a bicontinuous domain structure consisting of regions dense and sparse in polymer networks.

Self-assembled structures in solvent-cast mixtures of polystyrene-block-poly(ethylenepropylene) (PS−PEP) and polystyrene-block-(partially hydrogenated polyisoprene) (PS−HPI) were investigated by small-angle X-ray scattering and transmission electron microscopy. Various self-assembled structures were observed in the solution-cast films, depending upon the degree of hydrogenation of the HPI block of the PS−HPI. The microdomain structure of PS domains and domains composed of PEP and HPI (called “rubber domains” hereafter) was first formed at relatively low polymer concentrations during the solvent-casting process over the whole range of the hydrogenation in our experiments. Subsequently, at a higher concentration during the process, phase separation between PEP and HPI in the rubber domains was observed in mixtures with medium and high hydrogenation. For mixtures with low hydrogenation, repulsive interactions between PEP and HPI become large enough to cause the segregation between PEP and HPI, which leads fi...

The influence of oscillatory shear deformation on spinodal decomposition (SD) processes in a blend of polybutadiene and polyisoprene has been investigated by in-situ observations of light scattering patterns. A large strain amplitude γ0 = 0.8, with angular frequencies ω = 0.63 and 6.3 rad/s, was imposed on the blend undergoing SD induced by a temperature jump from a homogeneous (or single phase) region to a thermodynamically unstable region. Comparing representative rates of the shear deformation (i.e., frequency ω and a maximum shear rate) with representative growth rates for SD (i.e., growth rate of concentration fluctuations in the early stage SD and that of domains in the later stage SD), the deformation used in the present study is expected to bring the system into a homogeneous state, based on an estimation in the simple shear flow case. In spite of this strong shearing criterion, SD still occurred at ω = 0.63 rad/s: the phase-separated structure is affinely deformed in harmony with the shear strai...

The morphological similarity between a phase-separated polymer blend and a one-phase bicontinuous microemulsion is discussed in detail by comparing their respective light and X-ray scattering intensity distributions with structure factors computed according to the random wave model (RWM). In the RWM, a three-parameter spectral function introduced by Lee and Chen is used in conjunction with Berk's theory and Cahn's clipping scheme to calculate the Debye correlation function for the scattering intensity. The agreement between experiment and theory is excellent. The three parameters determined by fitting the scattering intensities are then used to calculate the average Gaussian curvature of the interfaces between the two isometric phases for the first time. The RWM can also be used to generate the 3D morphologies of both the bicontinuous phase-separated polymer blend and the one-phase microemulsion. There is a striking resemblance between the morphologies of these two unrelated systems, in spite of a differe...

The effect of peroxide cross-linking on the phase diagram and the scattering function for a critical mixture of perdeuterated polybutadiene (DPB) and protonated polybutadiene (HPB) has been examined by small-angle neutron scattering as a function of temperature. The scattering curves for the cross-linked blends were essentially temperature independent. It was found that even at temperatures (T) below the critical temperature (To) of the un-cross-linked (linear) blend (e.g., T = 0 "C; T, = 99.2 "C), the cross-linked blends remained single phase and did not undergo microphase separation. The calculation of the reduced temperature, c, for the cross-linked blends also implied that the cross-linking greatly increased the single- phase region of the phase diagram. A comparison of the scattering for the cross-linked blend with that of the linear blend at the cross-linking temperature (150 "C) showed a suppression in the scattering due to the presence of the cross-links. However, it was experimentally found that the concentration fluctuations present at the temperature of cross-linking dominate the scattering, which made it rather difficult to verify the prediction on the scattering function made by de Gennes.

The miscibility of a blend of protonated polyisoprene (HPI) with the 3,4-linkage microstruc- ture in the range 7-15% and of deuterated polybutadiene (DPB) with the 1,Qlinkage microstructure in the range 12-28% was studied by small-angle neutron scattering (SANS). It was found that all blends studied here show lower critical solution temperature (LCST) type phase behaviors; i.e., the phase separation occurs by raising the temperature. It was also found that the miscibility is quite senaitive to the microstructures of the polydienes used. The effective thermodynamic interaction parameter xen per segment between two polymers was determined by fitting SANS data in the single-phase state with a theoretical scattering curve obtained on the basis of the random-phase approximation. The temperature dependence of xen showed a systematic change with the microstructure. For a given HPI, the xeff values decreased, and therefore, the blends became more miscible, with an increase in the vinyl content (Le., lI2-linkage content) in DPB. On the contrary, for a given DPB, the values increased, and therefore, the blends became more immiscible, with an increase in the vinyl content (Le., 3,4-linkage content) in HPI. We proposed an alternative explanation for the LCST phase behavior based on treatment for the random copolymer blends.

Etude de l'evolution temporelle de la difference de composition entre les 2 domaines coexistant dans les stades intermediaire et final de la decomposition spinodale d'un melange critique de polybutadiene perdeuterie et de polyisoprene protone ayant un diagramme de phase de type LCST

Determination of the three-dimensional (3D) shape of microphase-separated block copolymers (BCPs) is essential to investigate the “packing frustration” of the constituent blocks, which dominates th...

Experimental evidence of an inversion of the phase diagram from UCST to LCST with an increase of the vinyl content of protonated polybutadiene while that of perdeuterated polybutadiene is held constant