The influence of grain size on the alignment of hexagonally ordered cylinders of self-assembled diblock copolymer-based supramolecules

In situ SAXS is used to investigate the shear-induced alignment of a supramolecular system consisting of a polyisoprene-b-poly(2-vinylpyridine) diblock copolymer and octyl gallate (OG), where OG is hydrogen-bonded to the vinylpyridine block of the PI-b-P2VP copolymer. Due to microphase separation, the PI-b-P2VP(OG) system self-assembles forming a domain structure of hexagonally ordered P2VP(OG) cylinders embedded in the PI matrix. The results of the alignment showed that the orientation mobility of the cylinders, lying within the (10) planes parallel to the shear plane, is strongly dependent on the size of the cylindrical domains. Subjected to large amplitude oscillatory shear for 15 min a freshly loaded sample with a small grain size structure exhibited much better alignment compared to that of a pre-aligned/squeezed sample with a considerably larger grain size where the orientation had been first partly destroyed by squeezing.     

Reaction-induced microphase separation in thermosetting blends of epoxy resin with poly(methyl methacrylate)-block-polystyrene block copolymers: Effect of topologies of block copolymers on morphological structures

Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymers with linear and tetra-armed star-shaped topological structures were synthesized via sequential atomic transfer radical polymerization (ATRP). With pentaerythritol tetrakis(2-bromoisobutyrate) as the initiator, the star-shaped block copolymers with two sequential structures (i.e., s-PMMA-b-PS and s-PS-b-PMMA) were prepared and the arm lengths and composition of the star-shaped block copolymers were controlled to be comparable with those of the linear PS-b-PMMA (denoted as l-PS-b-PMMA). The block copolymers were incorporated into epoxy resin to access the nanostructures in epoxy thermosets, by knowing that PMMA is miscible with epoxy after and before curing reaction whereas the reaction-induced phase separation occurred in the thermosetting blends of epoxy resin with PS. Considering the difference in miscibility of epoxy with PMMA and/or PS, it is judged that the reaction-induced microphase separation occurred in the systems. The design of these block copolymers allows one to investigate the effect of topological structures of block copolymers on the morphological structures of the thermosets. By means of atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS), the morphology of the thermosets was examined. It is found that the nanostructures were formed in the thermosets containing l-PMMA-b-PS and s-PS-b-PMMA block copolymers. It is noted that the long-range order of the nanostructures in the epoxy thermosets containing l-PMMA-b-PS is obviously higher than that in the system containing s-PS-b-PMMA. However, the macroscopic phase separation occurred in the thermosetting blends of epoxy resin with s-PMMA-b-PS block copolymer.     

Functionalization of shaped polymeric nanoobjects via bulk co-self-assembling gelable block copolymers with silane coupling agents

Hairy polymer nanoobjects (PNOs) of different shapes can be easily obtained by cross-linking the discontinuous microphases of bulk block copolymers followed by dispersing in a solvent. Herein we report a general approach to functionalize the shaped PNOs by bulk microphase separation of poly(3-(triethoxysilyl)propyl methacrylate)-block-polystyrene (PTEPM-b-PS) copolymers in the presence of functional silane coupling agents. The silanes like (3-mercaptopropyl)trimethoxysilane and (3-chloropropyl)trimethoxysilane were enriched into the PTEPM discontinuous microdomains selectively. The microphase structures were characterized by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) of microtomed slices. For the PTEPM₇₈-b-PS₃₄₈ which had a lamellar structure, its blending mixtures with MMS and CMS whose content reached up to 50 wt% still remained as a lamellar structure. When small amount of MMS or CMS was added, the PTEPM₇₁-b-PS₇₈₀ as hexagonally packed cylinders remained its structure. However, the morphology changed into lamellae at higher content of the silanes. For PTEPM₄₆-b-PS₁₆₆₉, its spherical structure remained but the size distribution became broad gradually with increase of silanes. By inducing gelation and then dispersing in a good solvent of PS phases, hairy PNOs having lamellar, cylindrical or spherical shape with their cores being functionalized with the groups from co-gelated silanes were obtained.     

Temperature-composition phase diagrams of binary blends of block copolymer and homopolymer

The temperature-composition phase diagrams for six pairs of diblock copolymer and homopolymer are presented, putting emphasis on the effects of block copolymer composition and the molecular weight of added homopolymers. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers having lamellar or spherical microdomains, a polystyrene-block-polybutadiene (SB diblock) copolymer having lamellar microdomains, and a series of polystyrene (PS), polyisoprene (PI), and polybutadiene (PB) were used to prepare SI/PS, SI/PI, SB/PS, and SB/PB binary blends, via solvent casting, over a wide range of compositions. The shape of temperature-composition phase diagram of block copolymer/homopolymer blend is greatly affected by a small change in the ratio of the molecular weight of added homopolymer to the molecular weight of corresponding block (M_H,A/M_C,A or M_H,B/M_C,B) when the block copolymer is highly asymmetric in composition but only moderately even for a large change in M_H,A/M_C,A ratio when the block copolymer is symmetric or nearly symmetric in composition. The boundary between the mesophase (M₁) of block copolymer and the homogeneous phase (H) of block copolymer/homopolymer blend was determined using oscillatory shear rheometry, and the boundary between the homogeneous phase (H) and two-phase liquid mixture (L₁+L₂) with L₁ being disordered block copolymer and L₂ being macrophase-separated homopolymer was determined using cloud point measurement. It is found that the addition of PI to a lamella-forming SI diblock copolymer or the addition of PB to a lamella-forming SB diblock copolymer gives rise to disordered micelles (DM) having no long-range order, while the addition of PS to a lamella-forming SB diblock copolymer retains lamellar microdomain structure until microdomains disappear completely. Thus, the phase diagram of SI/PI or SB/PB blends looks more complicated than that of SI/PS or SB/PS blends.     

Swelling behavior of ordered miktoarm star block copolymer-homopolymer blends

We report the morphological characterization of asymmetric miktoarm star block copolymers of the (PS-b-PI)_nPS type where n=2,3 (denoted 2DB and 3DB miktoarm stars, respectively) and a symmetric super H-shaped block copolymer of the (PS-b-PI)₃PS(PI-b-PS)₃ type (denoted SH) which were synthesized by anionic polymerization. The initial volume fraction of PS (φ_PS) for each copolymer was 0.51-0.56, giving a lamellar morphology. Addition of homopolystyrene (hPS) with a molecular weight lower than the respective PS blocks in the neat materials lead to a transition from the lamellar structure to hexagonally packed cylinders. Addition of low molecular weight homopolyisoprene (hPI) on the other hand, only resulted in swollen lamellae even when the overall composition was highly asymmetric (80/20). Changes in the lamellar spacing as well as in the respective PS and PI layer thickness were measured by SAXS. The transition from lamellae to cylinders with increased PS content occurred without the observation of an intervening cubic morphology for the 2DB and 3DB miktoarm stars. However, blends with 30 and 35% hPS ((φ_PS)_total=0.68-0.70) with the super H-shaped block copolymer lead to the observation of lamellar-catenoid structures.     

Synthesis and microphase separation of polystyrene‐b‐polylactide block copolymers aimed at preparation of ordered nanoparticle/block copolymer hybrid materials

A new nanoparticle/block copolymer (NP/BCP) hybrid material combining the unique properties of BCP poly(styrene)‐b‐poly(d ‐lactide) (PS‐b‐PDLA) and inorganic NP quantum dots CdSe was developed. A systematic study on the microphase separation of a series of PS‐b‐PDLAs by small‐angle X‐ray scattering showed that the degree of order of the separated microdomains depended on the initial state of the BCP and the measurement temperature and can be improved through isothermal crystallization of PDLA, thermal annealing and shear field etc. Incorporating a small amount of NPs into the BCP matrix can improve the mobility of the polymer chains and thus promote self‐assembly of the BCP, which leads to hierarchically ordered structures. Excess NPs, however, cannot be completely incorporated into the PDLA domains, resulting in the phase transformation of the BCP, destruction of the ordered structure and even macroscopic phase separation due to the aggregation of NPs. An important observation is that stereocomplexation between PDLA and poly(l ‐lactide) could provide a driving force to promote microphase separation of the BCP. The strategy presented in the current work has potential applications for developing highly ordered NP/BCP hybrid materials. © 2014 Society of Chemical Industry     

Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Polystyrene/poly(vinyl methyl ether) (PS/PVME) phase diagram was assessed by rheological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several rheological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to T_s whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing.     

Organic/inorganic nanoobjects with controlled shapes from gelable triblock copolymers

A functional gelable triblock copolymer, poly(2-vinylpyridine)-block-poly(3-(triethoxysilyl)propyl methacrylate)-block-polystyrene (P2VP-b-PTEPM-b-PS), was prepared by the combination of reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization and copper catalyzed click chemistry. Bulk microphase separation of P2VP₃₁₀-b-PTEPM₅₈-b-PS₃₂₂ under different conditions was studied in order to prepare organic/inorganic nanoobjects by a procedure of crosslinking PTEPM phases and dispersing in a solvent. The conditions included using different annealing solvents and adding stearic acids to form supramolecular complexes with P2VP blocks respectively. Then the packed cylinders with P2VP cores and PTEPM shells dispersed in the PS matrix, lamella with alternating PS, PTEPM and P2VP layers, and the inverse cylindrical morphology with PS cores and PTEPM shells dispersed in the matrix of P2VP/stearic acid complex were obtained respectively just from the same triblock copolymer sample. After crosslinking PTEPM microdomains by sol-gel process and dispersing in solvents, a series of organic/inorganic polymeric nanoobjects, including two types of nanofibers with inverse internal structure and one novel kind of nanoplates, were produced. Further modification of the fibers with P2VP cores has been studied.     

Mesoscopic simulation of asymmetric-copolymer/homopolymer blends: Microphase morphological modification by homopolymer chains solubilization

In this work we present the results of a mesoscopic dynamic simulation study of ordered microphases modification in asymmetric-copolymer/homopolymer binary blends, where we explore the influence of the composition, packing density and solubilization of homopolymer chains into the compatible microdomains of the asymmetric copolymer. The poly(styrene)-poly(isoprene) (PS-PI) and homopoly(styrene) (HPS) molecules were built and represented by Gaussian chain models. The pure asymmetric copolymer generates spherical microdomains of poly(styrene) (PS) in the matrix of majority component, poly(isoprene) (PI), and is taken as the base for the binary blends. The mesoscopic dynamic evolution of asymmetric-PS-PI/HPS blends display a coarse-grained system sufficiently large to determine the separation of the microphase and the formation of ordered structures. The HPS chains tend to be selectively solubilized in the PS microdomains of the asymmetric copolymer, the repulsive interaction forces between homopoly(styrene) and poly(isoprene) chains assure that essentially all the HPS homopolymer exists in the PS microdomains. As the asymmetric-PS-PI/HPS composition is varied the mesoscale simulations predict ordered structures with defined morphologies of body-centred-cubic (BCC), hexagonal packed cylinders (HPC), hexagonal perforated layers (HPL) and lamellar phases (LAM). Ordered microphases appear in reverse order when the homopoly(styrene) composition is increased in the binary blend. The agreement between our mesoscopic simulation results and available experimental outcome open a new strategy to modify the microphase morphology of asymmetric copolymers.     

Formation mechanism, chain folding, and growth behavior of the intriguing fiber-like crystal of poly (ethylene oxide-b-ε-caprolactone) block copolymer in ultrathin films

The morphologies, crystallization behavior and chain orientation of a highly asymmetric poly (ethylene oxide-b-ε-caprolactone) (PEO-b-PCL) block copolymer ultrathin films were investigated by using wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD) techniques. It is shown that the intriguing fiber-like crystal which seems to be an individual flat-on lamella was first observed in PEO-b-PCL ultrathin film according to our knowledge. The possible mechanism of forming the fiber-like crystals is chiefly ascribed to the rather low molecular weight of PEO-b-PCL and the mutual interaction between crystallization and microphase separation. At the same time, solution concentration and substrate surface energy play a crucial role. Subsequently, chain folding of the fiber-like crystal of PEO-b-PCL in ultrathin films was deduced based on the cell parameters and the lamellar thickness. Isothermal crystallization tests revealed that in the whole growth process, the crystal growths can be divided into two stages, both of which followed the diffusion-limited (DL) mechanism.     

Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA₁₁OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA₁₁OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.     

A block copolymer nanotemplate for mechanically tunable polarized emission from a conjugated polymer

A polymer blend system consisting of polystyrene grafted onto poly (p-phenylene ethynylene) (PS-g-PPE) and poly (styrene-block-isoprene-block-styrene) triblock copolymer (SIS) yields highly polarized emission due to the unidirectional alignment of the PPE molecules. During the roll casting, the triblock copolymer microphase separates and creates unidirectionally aligned PS cylindrical microdomains in the rubbery PI matrix. PPE, a fluorescent conjugated polymer, was grafted with polystyrene (PS) side chains that enabled sequestration and alignment of these rigid backbone emitter molecules into the PS microdomains of the SIS triblock copolymer. Deforming the thermoplastic elastomer in a direction perpendicular to the orientation direction of the cylinders causes rotation of the PS cylinders and the PPE emitter molecules and affords tunable polarized emission due to re-orientation of the PPE containing PS cylinders as well as film thinning from Poisson effect.     

Synthesis and self-assembly in bulk of six-arm star-block copolymers with a C60 core

This study focuses on the synthesis and the structural characterization of various branched star-block copolymers (polyisoprene-block-polystyrene)₆C₆₀ with a fullerene C₆₀ as a core. Well defined 6-arm stars (PI-b-PS)₆C₆₀ with a low polydispersity and a precise control of the number of branches were prepared by grafting PI-b-PS diblock copolymers through the polystyrene block onto the C₆₀ core. The self-assembled structures formed in bulk were studied by Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS) for both symmetric and asymmetric polystyrene-block-polyisoprene (PS-b-PI) diblock arms in the strong-segregation regime (65 ≤ χN ≤ 115). Various microstructures including lamellae, hexagonal packings of PS and PI cylinders as well as a gyroid phase were obtained by varying the volume fraction of polystyrene (f_PS) of the branches, leading to the formation of ordered, periodic and localized nanoscale dispersions of the C₆₀ in a polymer matrix including planes, threads and a 3D bicontinuous network of C₆₀.     

Synthesis of ABA triblock copolymer of poly(potassium acrylate-styrene-potassium acrylate) by atom transfer radical polymerization and the self-assembly in selective solvents

A series of well-defined ABA triblock copolymers of poly(methyl acrylate)-polystyrene-poly(methyl acrylate) (PMA-b-PS-b-PMA) with different molecular weights were synthesized using Cl-PS-Cl as macroinitiator, CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system via atom transfer radical polymerization (ATRP). Amphiphilic triblock copolymer poly(potassium acrylate)-polystyrene-poly(potassium acrylate) (PKAA-b-PS-b-PKAA) was obtained by hydrolyzing PMA-b-PS-b-PMA. The self-assembly behavior of the triblock copolymers in organic solutions, which is a good solvent for the PS block and in aqueous solutions, which is a good solvent for the PKAA blocks was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles obviously increases with increase in molecular weight of triblock copolymers, and the micelles in organic solutions are relatively more stable than in aqueous solutions. The effect of the length of PS block on the Z-average size of the micelles is more obvious in organic solution than in aqueous solution. The morphology of triblock copolymers PKAA-b-PS-b-PKAA in aqueous solution, which is a nearly ‘pearl-necklace’-like shape, was examined by transmission electron microscopy (TEM) at room temperature.     

Self-assembly of an A-B diblock copolymer blended with a C homopolymer and a C-D diblock copolymer through hydrogen bonding interaction

In this study, we investigated the miscibility, phase behavior, and self-assembled nanostructures formed from the immiscible crystalline-amorphous diblock copolymer poly(?-caprolactone-b-4-vinyl pyridine) (PCL-b-P4VP, A-B) when blended with the homopolymer poly(vinyl phenol) (PVPh, C) and the diblock copolymer poly(vinyl phenol-b-styrene) (PVPh-b-PS, C-D). Long-range-ordered microphase separation was difficult to achieve in the PCL-b-P4VP/PVPh (A-B/C) blend system because PVPh interacted with both the P4VP and PCL blocks simultaneously through hydrogen bonding interactions. In contrast, we observed sharp, multiple orders of diffraction in the SAXS profiles of the PCL-b-P4VP/PVPh-b-PS (A-B/C-D) blend system, indicating that perfect microphase separation occurred because the incorporation of the PS block induced the PVPh block to hydrogen bond preferentially with the P4VP block. This simple A-B/C-D (PCL-b-P4VP/PVPh-b-PS) diblock copolymer mixture exhibited self-assembly behavior (a three-lamella phase) similar to that of a corresponding ABC triblock copolymer.     

Theoretical representation of shear and pressure influence on the phase separation behavior of PVME/PS mixture

In the framework of lattice fluid model, the Gibbs energy and equation of state are derived by introducing the energy (E_s) stored during flow for polymer blends under shear. From the calculation of the spinodal of poly(vinyl methyl ether) (PVME) and polystyrene (PS) mixtures, we have found the influence of E_s on equation of state in pure component is inappreciable, but it is appreciable in the mixture. However, the effect of E_s on phase separation behavior is extremely striking. In the calculation of spinodal for the PVME/PS system, a thin, long and banana miscibility gap generated by shear is seen beside the miscibility gap with lower critical solution temperature. Meanwhile, a binodal coalescence of upper and lower miscibility gaps is occurred. The three points of the three-phase equilibrium are forecasted. The shear rate dependence of cloud point temperature at a certain composition is discussed. The calculated results are acceptable compared with the experiment values obtained by Higgins et al. However, the maximum positive shift and the minimum negative shift of cloud point temperature guessed by Higgins are not obtained. Furthermore, the combining effects of pressure and shear on spinodal shift are predicted.     

Phase separation of polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) deposited on polystyrene thin films

Phase separation of a triblock copolymer, polystyrene-b-(ethylene-co-butylene)-b-styrene (SEBS) on the thin films of a homopolymer, polystyrene (PS), was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The final morphology after phase separation was found to be greatly dependent on the relation between the molecular weight of the PS block and homo-PS. Dispersed spherical and worm-like micelles of SEBS were observed when the molecular weight of homo-PS is smaller than the PS block in SEBS, while large structures with inner micro-phase separation of SEBS was found when the molecular weight of homo-PS was much higher than that of the PS block. The origin of such a change in morphology is attributed to the difference of structure and interfacial tension at the interface between the matrix homo-PS and the PS block in SEBS triblock copolymer assembly.     

Phase separation in polystyrene-poly(vinylmethylether) blends: a a fluorescence emission analysis

Fluorescence emission of labels appears to be a new technique for the investigation of the LCST behaviour of polystyrene-poly(vinylmethylether) (PS-PVME) blends. Indeed, heating ternary blends of PVME/PS/labelled PS results in sharp increases in the fluorescence intensity, which occur simultaneously with their phase separation. Specific interactions between the anthracenic units of the labelled PS and the ether functions of PVME, are responsible for the fluorescence quenching, which occurs in the compatible blends. Quenching drops as phase separation proceeds, because of the lowering of the probability for label-PVME interactions in the two-phase state. By relating the phase separation curves obtained in this way to those acquired by the classical light scattering method, it is shown that fluorescence experiments may allow determination of both spinodal and binodal curves, provided that heating rate is appropriate.     

三嵌段共聚物PS-b-PEG-b-PS与聚苯乙烯共混薄膜的表面形貌与性能研究

使用原子转移自由基聚合(ATRP)制备三嵌段共聚物PS-b-PEG-b-PS.通过红外光谱、核磁共振氢谱(1H-NMR)和凝胶渗透色谱(GPC)对嵌段共聚物结构及分子量进行表征.将嵌段共聚物与聚苯乙烯溶液共混成膜,使用原子力显微镜(AFM)和接触角测试仪(CA)对不同含量嵌段共聚物共混膜的表面形貌和性能进行了分析表征.PEG链段与PS链段在共混膜中发生了微相分离,由于PEG链段对PS链段的热力学排斥作用以及PS的硬链段特性,PS不能在PEG微区上方形成覆盖,因而在薄膜表面形成大量孔洞,PEG微相区位于孔洞底部.随嵌段共聚物含量增加,孔洞(PEG微区)尺寸增大.当嵌段共聚物含量增加10％以后,孔洞内出现PS微相区,导致形成“胞状”结构.嵌段共聚物含量增加使得共混薄膜的亲水性和表面张力增大.     

Phase diagram for polystyrene/poly(vinylmethyl ether) blends by 13C-NMR

Summary The composition of each phase separated domain, thus the phase diagram, has been determined by ¹³C NMR methods for thermally phase separated polystyrene (PS)/poly(vinylmethyl ether) (PVME) blends. Even in compatible PS/PVME blend T ₁ ^H at –5°C, determined indirectly via ¹³C intensities show microheterogeneity at an estimated 20 Å level if the PVME content is greater than 50%.