Crystalline structure and morphology of microphases in compatible mixtures of poly(tetrahydrofuran‐methyl methacrylate) diblock copolymer and polytetrahydrofuran

The crystalline structure and morphology of compatible mixtures of poly(tetrahydrofuran‐methyl methacrylate) diblock copolymers (PTHF‐b‐PMMA) with a polytetrahydrofuran homopolymer (PTHF) were studied with synchrotron X‐rays. Wide‐angle diffraction was used to study the crystalline structures in a confined lamellar region with a PTHF thickness ranging from 12.2 to 19.5 nm, and in a PTHF matrix with an interface distance between the PMMA cylinders ranging from 17 to 22 nm. As the above thickness values are around the long period (ca. 17 nm) of PTHF homopolymer under the crystallization condition used, the crystalline structure has been found to be very sensitive to the average thickness of the PTHF phase. The changes in the diffraction patterns with changing PTHF homopolymer content suggested a chain folding model in confined PTHF lamellae with the PTHF fiber axes being perpendicular to the thick PTHF lamella. In the case of hexagonally packed cylindrical PMMA microdomains with an interface distance ranging from 12 to 16 nm, the effects of PMMA cylinders on the crystallization morphology of PTHF in the PTHF matrix, and the effects of the PTHF crystallization on the hexagonally packed structure of PMMA cylinders were also studied. It is shown that only when the interdistance of two neighboring PMMA cylinders is comparable with the long period of the pure PTHF homopolymer, ordered PTHF stacks can be formed in the PTHF matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 779–792, 1999     

Diffusion in microstructured block copolymer solutions

This work explores the effect of heterogeneity of chemical composition on tracer diffusion, when the characteristic size of the heterogeneities approaches that of the diffusing molecule. A heterogeneous environment is created by the self-assembly of diblock copolymers in solution. The system chosen for this study is polystyrene-polyisoprene diblock copolymers in toluene, which is a common solvent for the two blocks. Above a certain critical concentration, these systems are known to microphase separate into swollen domains of polystyrene and polyisoprene. Diffusion of homopolystyrene through the microstructure is measured in this work. The characteristics of the microstructure are varied by studying block copolymers of different molecular weights and compositions. The tracer diffusion coefficients of the labelled polystyrenes are measured by forced Rayleigh scattering, while the microstructure of the matrix is inferred from small angle X-ray scattering measurements. In this paper, we report results for the diffusion of polystyrenes (molecular weights 3.2 × 10⁴ and 9.0 × 10⁴) in microstructured solutions of three copolymers. Two copolymer samples forming lamellae of alternating polystyrene and polyisoprene microphases and one sample forming polystyrene cylinders embedded in a polyisoprene matrix have been examined. The data indicate that the tracer diffusion coefficient of 3.2 × 10⁴ molecular weight polystyrene in lamellar and cylindrical solutions is comparable to that of the homopolymer in a homogeneous solution of the same concentration. In contrast, the diffusion of 9.0 × 10⁴ molecular weight polystyrene is substantially slower in the structured solutions than in unstructured solutions of the same concentration. For example, the diffusion coefficient of 9.0 × 10⁴ molecular weight polystyrene in a 47% block copolymer solution with cylindrical microstructure is lower than its value in a homogeneous solution of the same concentration by a factor of 30.     

Crystallization and structure formation of block copolymers containing a glassy amorphous component

Formation of higher‐order structure in crystallization from microphase‐separated melts was studied for polystyrene–polyethylene (PS–PE) diblock copolymers and PS–PE–PS triblock copolymers with time‐resolved synchrotron small‐angle X‐ray scattering (SR–SAXS) techniques. The PE block was crystallized at temperatures when the PS block was in the glassy state. In both crystallization and melting processes, only the peak intensity in the SR–SAXS curve changed, however, the peak positions including higher‐order peaks did not change. This means that the microphase‐structure in the crystalline state was completely the same as that in the molten state. These behaviors were observed regardless of any melt microphase structure. Also, once a stable microphase structure was formed in the molten state, the structure was not changed even if crystallization and melting were repeated. Behavior of crystallization from such microphase‐separated melts was also studied. Apparent activation energies of crystallization were high for all block copolymers, compared with that for the PE homopolymer. In particular, the triblock copolymers showed higher apparent activation energies than the diblock copolymers. Both degrees of crystallinity and Avrami indices were greatly suppressed in crystallization from the cylindrical domain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4199–4206, 2004     

Kinetically constrained block copolymer self-assembly a simple method to control domain size

In this work asymmetric polystyrene-block-polyethylene oxide (PS-PEO) diblock copolymers were blended with high and low molecular polystyrene (PS) homopolymer and spin cast, resulting in the rapid self-assembly of vertically oriented PEO cylinders in a matrix of PS. Due to the kinetically constrained phase separation of the system, increasing addition of homopolymer is shown to reduce the diameter of the PEO domains, even when the homopolymer was of significantly higher molecular weight than the PS block in the PS-PEO diblock copolymer and would be predicted to macro-phase separate from the copolymer. The outcomes of this study provide a novel method that requires the adjustment of a single variable to tune the size of vertically oriented PEO domains between 10 and 100 nm, with potential applications in a number of areas including membrane technologies.     

The influence of confinement and curvature on the morphology of block copolymers

In the bulk, at equilibrium, diblock copolymers microphase separated into nanoscopic morphologies ranging from body-centered cubic arrays of spheres to hexagonally packed cylinders to alternating lamellae, depending on the volume fraction of the components. However, when the block copolymers are forced into cylindrical pores, where the diameter of the pores are only several repeat periods of the copolymer morphology or less, then commensurability of the copolymer period and the pore diameter can impose a frustration on the microdomain morphology. In addition, due to the small pore diameter, a curvature is forced on the microdomain morphology. In combination with interfacial interactions between the blocks of the copolymer and the pore walls, the preferential segregation of one component to the walls, spatial confinement and forced curvature are shown to induce transitions in the fundamental morphology of the copolymers seen in the bulk. Lamellar morphologies transformed into torus-type morphologies, cylinders are forced into helices, and body-centered cubic arrays of spheres are force into helical arrays of spheres due to these restraints. The novel morphologies, not accesssible in the bulk, open a large array of nanoscopic structures that can be used as templates and scaffolds for the fabrication of inorganic nanostructured materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3377–3383, 2005     

Roll-Casting of block copolymers and of block copolymer-homopolymer blends

An improved technique for casting highly oriented films of block copolymers from solutions subjected to flow is presented. Polymer solutions were rolled between two counter-rotating adjacent cylinders while at the same time the solvent was allowed to evaporate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. Using this method known as ‘roll-casting’ we present in this paper a study of the morphology of polystyrene-polybutadiene-polystyrene (PS/PB/PS) triblock copolymer cast with and without additional high molecular weight homopolymers. The pure copolymer films consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix in a near single-crystal structure. Blends of copolymer with high molecular weight polystyrene and/or polybutadiene, phase separated into ellipsoidal regions of homopolymer embedded in an oriented block copolymer matrix. Annealing the films resulted in conversion of the homopolymer regions to spheres accompanied by some misalignment of the copolymer microdomains. The morphology of these films as revealed by TEM is discussed. A brief discussion of the flow field that develops in the experimental system is also presented and its similarity to the flow field of our previous work is shown. © 1994 John Wiley & Sons, Inc.     

Synthesis of poly[arylene ether sulfone-b-vinylidene fluoride] block copolymers

A series of α,ω-dihydroxy polyarylene sulfones (PAES) were synthesized comprising bisphenol A (PAES1, M_n=1800, 4900, and 9500 daltons), 4,4^′-biphenol (PAES2, M_n=4100 daltons), and hexafluorobisphenol A (PAES3, M_n=3300 daltons). These were reacted with α,ω-dibromo poly(vinylidene fluoride) (PVDF, M_n=1200 daltons) prepared by telomerization, to yield block copolymers possessing rigid and flexible segments. Block copolymers were characterized by FTIR, NMR, GPC, DSC, TGA and TEM. In several cases the block copolymers exhibited distinct thermal transitions, i.e. T_m and T_g for PVDF and PAES segments, respectively. Where observable, T_g of PAES domains in the block copolymers occurred at a temperature lower than the corresponding PAES homopolymer due to the flexible nature of the surrounding PVDF domains. Block copolymers exhibited a similar thermal stability to the corresponding PAES homopolymers but higher stability than the PVDF homopolymer, and much higher still than α,ω-dibromo PVDF. TEM analyses indicate that phase separation of PAES and PVDF domains occurs on the nanometer scale.     

Morphology and micromechanical behaviour of styrene/butadiene block copolymers and their blends with polystyrene

The correlation between the morphology and the deformation mechanism in styrene/butadiene block copolymers having modified architecture and in blends with homopolymer polystyrene (hPS) was studied. It was demonstrated that the morphology formation in the block copolymers is highly coupled with their molecular architecture. In particular, the micromechanical behaviour of a star block copolymer and its blends with polystyrene was investigated by using electron microscopy and tensile testing. A homogeneous plastic flow of polystyrene lamellae (thin layer yielding) was observed if the lamella thickness was in the range of 20 nm. The deformation micromechanism switched to the formation of craze-like deformation zones when the average PS lamella thickness changed to about 30 nm and more.     

聚苯乙烯-b-聚右旋乳酸二嵌段共聚物的热性能和结晶行为研究

合成了系列聚右旋乳酸(PDLA)嵌段重量分率(fw=0～0.61)的窄分子量分布聚苯乙烯-b-聚右旋乳酸二嵌段共聚物(PS-b-PDLA).运用温度调制示差扫描热分析仪(TMDSC)和热台偏振光显微镜(POM)等研究手段,对制备所得的结晶性二嵌段共聚物的热性能、结晶速率与结晶形貌等进行了研究.研究结果表明,与聚右旋乳酸均聚物相比,随着PS-b-PDLA中结晶性PDLA嵌段重量分率fw减少,无定形聚苯乙烯嵌段(PS)对PDLA嵌段链段的结晶抑制作用增强,PS-b-PDLA的热结晶性能与结晶形貌发生显著变化;相对于PDLA均聚物,PS-b-PDLA的冷结晶温度(Tcc)和结晶平衡熔点(Tm0)分别下降14℃和38℃,球晶生长速率明显降低.在无定形PS嵌段链段的玻璃化温度(Tg)附近,二嵌段PS-b-PDLA的结晶行为出现拐点,揭示PS嵌段由于相分离所形成纳米微相空间对PS-b-PDLA中PDLA链段的结晶产生影响,并且该影响作用程度与PDLA嵌段的重量分率fw和结晶温度(Tc)相关。     

Super-nucleation in nanocomposites and confinement effects on the crystallizable components within block copolymers, miktoarm star copolymers and nanocomposites

In this paper we reexamine recent results obtained by our group on the crystallization of nanocomposites and linear and miktoarm star copolymers in order to obtain some general features of their crystallization properties. Different nanocomposites have been prepared where a close interaction between the polymer matrix and the nano-filler has been achieved: in situ polymerized high density polyethylene (HDPE) on carbon nanotubes (CNT); and polycaprolactone (PCL) and poly(ethylene oxide) (PEO) covalently bonded to carbon nanotubes. In all these nanocomposites a “super-nucleation” effect was detected where the CNTs perform a more efficient nucleating action than the self-nuclei of the polymer matrix. It is believed that such a super-nucleation effect stems from the fact that the polymer chains are tethered to the surface of the CNT and can easily form nuclei. For polystyrene (PS) and PCL block copolymers, miktoarm star copolymers (with two arms of PS and two arms of PCL) were found to display more compact morphologies for equivalent compositions than linear PS-b-PCL diblock copolymers. As a consequence, the crystallization of the PCL component always experienced much higher confinement in the miktoarm stars case than in the linear diblock copolymer case. The consequences of the topological confinement of the chains in block copolymers and nanocomposites on the crystallization were the same even though the origin of the effect is different in each case. For nanocomposites a competition between super-nucleation and confinement was detected and the behavior was dominated by one or the other depending on the nano-filler content. At low contents the super-nucleation effect dominates. In both cases, the confinement increases as the nano-filler content increases or the second block content increases (in this case a non-crystallizable block such as PS). The consequences of confinement are: a reduction of both crystallization and melting temperatures, a strong reduction of the crystallinity degree, an increase in the supercooling needed for isothermal crystallization, a depression of the overall crystallization rate and a decrease in the Avrami index until values of one or lower are achieved indicating a nucleation control on the overall crystallization kinetics.     

Control of the morphology of linear and cyclic PS-b-PI block copolymer micelles via PS addition

We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.     

Composite ultrafiltration membranes with tunable properties based on a self‐assembling block copolymer/homopolymer system

Composite ultrafiltration membranes were fabricated by coating a thin film of self‐assembling polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) block copolymers and poly(acrylic acid) homopolymers on top of a support membrane. Block copolymers self‐assembled into a nanostructure where the minority component forms cylinders, whereas homopolymers reside in the core of the cylinders. Selective removal of the homopolymers led to the formation of pores. The morphology of the polymer layer was controlled by varying the content of homopolymers or polymer concentration of the coating solution, which led to membranes with different molecular weight cutoffs (MWCOs) and permeabilities. Uniform pores were obtained using low homopolymer contents, whereas high homopolymer contents caused macrophase separation and resulted in large polydisperse pores or craters at the surface. The thickness of the block copolymer film also influenced the structure and performance of the membranes, where a thicker film results in a strong decrease in permeability but a lower MWCO. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1546–1558     

Preparation and properties of phenylene oxide–aryl ether sulphone block copolymers and their blends

We have prepared triblock copolymers of poly(phenylene oxide) (PPO) and polysulphone (PSF) of the form PPO–PSF–PPO in order to assess their intrinsic mechanical properties and their potential as interfacial compatibilizers in polystyrene/PSF blends. For sufficiently long polysulphone block lengths, we observed microphase separation both in the triblock copolymers and in their blends with polystyrene. The triblock polymers, nevertheless, showed very similar microdeformation behavior to the PPO homopolymer, suggesting the phase separation to play a minor role. On the other hand, the compatibility of the poly(phenylene oxide) blocks and polystyrene ensured a high degree of interphase adhesion in blends containing both polystyrene and free PSF, even for relatively high homopolymer molecular weights. © 1996 John Wiley & Sons, Inc.     

Crystallization and melting behaviors of polystyrene-b-poly(ethylene-co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature (T_c), melting temperature (T_m) and fusion enthalpy (ΔH_f) increase rapidly with PEB volume fraction (V_E) for block copolymers with V_E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature (T_g) of the PSt block and order-disorder transition temperature (T_ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent (n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V_E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt-b-PEB block copolymers with V_E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T_c, but confined at lower T_c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.     

Morphologies and domain sizes of microphase-separated structures of block and graft copolymers of different types

Well-defined block and graft copolymers of different types with different compositions and molecular weights, such as styrene(S)-2-vinylpyridine(P) diblock copolymers, SP star-shaped block copolymers, PSP triblock copolymers, styrene(S)-isoprene(I) multiblock copolymers of the (SI)_n type, ISP triblock copolymers, SPP graft copolymers and their deuterated samples were prepared. Variations of the morphologies with compositions, molecular weight dependences of the lamellar domain sizes and conformations and distributions of block chains in the lamellar domains were studied in the strong segregation limit. Besides typical morphologies such as spherical, cylindrical and lamellar structures, ordered bi- and tri-continuous structures were found between cylindrical and lamellar structures for SP diblock copolymers, PSP and ISP triblock copolymers, respectively. The composition ranges of morphologies are different for the block and graft copolymers of different types. The molecular weight dependences of lamellar domain sizes are about the same, but their magnitudes are not always the same for the block and graft copolymers of different types. These results are well explained by the theories of Helfand-Wasserman and Semenov. Block chains in lamellae are extended along the direction perpendicular to lamellae, but they are contracted along the parallel direction. The former result is well explained by the theories, but the latter is not. Chains adjacent to the junction points between different block chains are localized near the domain interface, but chains at the free-ends of block chains are widely distributed in the domain with the maximum at the center of domain.     

CONTROLLED SYNTHESIS OF AMPHIPHILIC BLOCK POLYMERS HAVING GLUCOSE RESIDUES AND THEIR STRUCTURE FORMATION

Vinyl ether (VE)-based amphiphilic block copolymers with D-glucose residues as hydrophilicpendants were synthesized by CH_3 CH(OiBu)Cl/ZnI_2-initiated sequential living cationic copolymerization of3-O-(vinyloxy)ethyl-1, 2:5, 6-di-O-isopropylidene-D-glucofuranose (IGVE) and isobutyl VE (IBVE ) andsubsequent deprotection. The precursor block copolymers had a narrow molecular weight distribution(M_w/M_n～1.1) and a controlled segmental composition. The solubility characteristics of the amphiphiliccopolymer depended strongly on composition. Their solvent-cast thin films were examined, under atransmission electron microscope, and could be seen to exhibit various microphase-separated surfacemorphologies such as spheres, cylinders, and lamellae, depending on composition. The amphiphiliccopolymers with the appropriate segmental composition were found to form a stable monolayer at the air-water interface, which was successfully transferred onto a substrate by the Langmuir-Blodgett (LB)technique. The layered strucfure of the built-up LB films was controlled by blending the homopolymer.     

Evolution of the “knitting pattern” morphology in ABC triblock copolymers

A new morphology of ternary ABC triblock copolymers is presented which results from the asymmetric interaction between a centre block (poly(ethylene-co-butene)) to different end blocks (polystyrene and poly(methyl methacrylate)). This morphology with the appearance of a “knitting pattern” can be described as an intermediate of a morphology of A, B and C lamellae and a morphology of A and C lamellae with B cylinders at the A/C interface.     

Preparation and Morphologies of AB6¯ Block‐Graft Copolymers

Microphase‐separated structures of a series of AB₆ block‐graft copolymers were studied by TEM and SAXS. Ten copolymers with the same polystyrene (S) backbone and six polyisoprene (I) grafts on the average but with different graft chain lengths were carefully synthesized by living anionic polymerization, covering the range 0.21 ≤ ?_S ≤ 0.90, where ?_S denotes polystyrene compositions. From TEM observation of the AB₆ block‐graft copolymers, it turns out to be clear that they show four microphase‐separated structures, S‐spheres, S‐cylinders(S‐prisms), alternative lamellae, and I‐cylinders. Among them, for example, the samples with 0.54 ≤ ?_S ≤ 0.58 shows prism structures whose cross sections of the S domains are close to hexagons, not circles, due to packing frustration of grafts. Composition dependence of morphologies of the present AB₆ block‐graft copolymers reveals their phase diagram is extremely asymmetric with respect to ?_S = 0.5. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 952–960     

Poly(3-alkylthiophene) diblock copolymers with ordered microstructures and continuous semiconducting pathways

Conjugated rod-coil diblock copolymers self-assemble due to a balance of liquid crystalline (rod-rod) and enthalpic (rod-coil) interactions. Previous work has shown that while classical block copolymers self-assemble into a wide variety of nanostructures, when rod-rod interactions dominate self-assembly in rod-coil block copolymers, lamellar structures are preferred. Here, it is demonstrated that other, potentially more useful, nanostructures can be formed when these two interactions are more closely balanced. In particular, hexagonally packed polylactide (PLA) cylinders embedded in a semiconducting poly(3-alkylthiophene) (P3AT) matrix can be formed. This microstructure has been long-sought as it provides an opportunity to incorporate additional functionalities into a majority phase nanostructured conjugated polymer, for example in organic photovoltaic applications. Previous efforts to generate this phase in polythiophene-based block copolymers have failed due to the high driving force for P3AT crystallization. Here, we demonstrate that careful design of the P3AT moiety allows for a balance between crystallization and microphase separation due to chemical dissimilarity between copolymer blocks. In addition to hexagonally packed cylinders, P3AT-PLA block copolymers form nanostructures with long-range order at all block copolymer compositions. Importantly, the conjugated moiety of the P3AT-PLA block copolymers retains the crystalline packing structure and characteristic high time-of-flight charge transport of the homopolymer polythiophene (μ(h) ~10(-4) cm(2) V(-1) s(-1)) in the confined geometry of the block copolymer domains.     

嵌段共聚物受限自组装的实验研究进展

嵌段共聚物有着丰富的相行为,在本体中会发生微相分离形成球形、柱形、双连续形和层状结构.当嵌段共聚物被限制在一定的空间几何中且空间几何特征尺寸与嵌段共聚物的平衡周期相近时,自组装过程会受到强烈的影响而形成与本体不同的自组装结构.本文从实验研究方面总结了限制因素和边界条件对嵌段共聚物受限自组装过程的影响,并指出了当前存在的一些问题以及今后的发展方向.