Deformation behavior of triblock copolymers based on polystyrene: an FT-IR spectroscopy study

The effect of the long range order and thermal treatment on the micromechanical deformation of two triblock copolymers was investigated, i.e. polystyrene-b-polybutadiene-b-polycaprolactone (SBC) triblock copolymer with PS as the matrix and PCL cylindrical domains and a SBS triblock copolymers with 75 wt% of styrene. FTIR spectroscopy revealed information about the molecular orientation upon deformation of the separate components in the triblock copolymers. Films of SBC possess a higher ductility when the semi-crystalline PCL cylindrical microdomains are quenched. In this case, the deformation proceeds via cavitation of the PCL domains and subsequent shear yielding. Long range order of the cylinders leads to embrittlement since crazes formation and crack propagation can proceed along the cylindrical axis. For the SBS triblock copolymers, a morphological transition from lamellar to short rod cylindrical microdomains was obtained by changing the casting solvent from toluene to MEK, while macroscopic orientation could be achieved by compression molding in a channel die. The toluene cast films were ductile and deformed in a homogeneous way. The MEK cast films behaved brittle as a result of crazing. Loading parallel to the lamellae results in yielding by propagation of a stable macroscopic neck.     

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.     

Morphology and Micromechanical Behaviour of SBS Block Copolymer Systems

By means of transmission electron microscopy (TEM) and uniaxial tensile testing, the connection between the morphology and the micromechanical properties of selected styrene-rich styrene/butadiene block copolymers was studied with respect to their molecular architecture. In particular, the structure-property correlation of a lamellae forming asymmetric linear SBS triblock copolymer was examined by systematically varying the sample preparation techniques and testing temperature. The molecular architecture was found to influence directly the morphology formation of the block copolymers. Different mechanisms such as drawing of the lamellae, shearing in the rubbery phase and rotation of the lamellar axis were observed. From room temperature down to the temperature close to glass transition temperature of the soft phase, a homogeneous plastic drawing of glassy lamellae was perceptible.     

Organization of branched rod-coil molecules into a 3-D tetragonally perforated lamellar mesophase

Tetramerization of coil-rod-coil ABC triblock copolymers to a tetrabranched molecule induces an unusual 3-D tetragonally perforated layered liquid crystalline phase as an intermediate structure between 1-D lamellar and 2-D hexagonal columnar phases.     

Unexpected consequences of block polydispersity on the self-assembly of ABA triblock copolymers

Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.     

含有十二烷基酚聚氧乙烯(10)醚的溶致液晶体系的研究

本文以非离子表面活性剂十二烷基酚聚氧乙烯(10)醚(TX-10)/苯乙烯/水组成的三元体系为研究对象, 绘制了三元相图, 选取液晶区域作为研究对象, 配制系列样品, 摄制了纹理照片, 用小角X光衍射法测定了液晶中各种组分变化时间的层间距, 并结合^2H NMR谱图和纹理照片的对照以及互为补充的分析, 为精确区分液晶结构提供了新的途径。这不仅对于基础理论研究, 同时对于日用化工和帮次采油都具有一定指导意义。     

Selective swelling blends of block copolymers for nanoporous membranes with enhanced permeability and robustness

Block copolymers (BCPs) are important precursors to produce membranes with well‐defined porosities. However, it remains challenging to prepare robust and affordable BCP‐based membranes. In this work, cheap commodity styrene‐butadiene‐styrene (SBS) elastic triblock copolymers are mixed with polystyrene‐block‐poly (2‐vinylpyridine) (SV) block copolymers in solutions, leading to macroscopically stable blend films upon casting because of the compatibilizer effect of PS existing in both copolymers. By soaking the blend films in ethanol, the microdomains of poly(2‐vinylpyridine) are selectively swollen and cavitated upon drying, resulting in a hierarchical structure with perforated SV phases interwoven with the SBS phases. The blend membranes with 30% SBS exhibit improved water permeability and mechanical robustness due to the presence of elastic SBS compared to neat SV membranes; meanwhile, the rejections of the blend membranes remain largely unchanged. Moreover, the blend membranes exhibit a pH‐responsive function, and homoporous SV regions are obtained by pre‐aligning the SV phases. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1617–1625     

Self-assembly in block polyelectrolytes

The self-consistent field theory (SCFT) complemented with the Poisson-Boltzmann equation is employed to explore self-assembly of polyelectrolyte copolymers composed of charged blocks A and neutral blocks B. We have extended SCFT to dissociating triblock copolymers and demonstrated our approach on three characteristic examples: (1) diblock copolymer (AB) melt, (2) symmetric triblock copolymer (ABA) melt, (3) triblock copolymer (ABA) solution with added electrolyte. For copolymer melts, we varied the composition (that is, the total fraction of A-segments in the system) and the charge density on A blocks and calculated the phase diagram that contains ordered mesophases of lamellar, gyroid, hexagonal, and bcc symmetries, as well as the uniform disordered phase. The phase diagram of charged block copolymer melts in the charge density--system composition coordinates is similar to the classical phase diagram of neutral block copolymer melts, where the composition and the Flory mismatch interaction parameter χ(AB) are used as variables. We found that the transitions between the polyelectrolyte mesophases with the increase of charge density occur in the same sequence, from lamellar to gyroid to hexagonal to bcc to disordered morphologies, as the mesophase transitions for neutral diblocks with the decrease of χ(AB). In a certain range of compositions, the phase diagram for charged triblock copolymers exhibits unexpected features, allowing for transitions from hexagonal to gyroid to lamellar mesophases as the charge density increases. Triblock polyelectrolyte solutions were studied by varying the charge density and solvent concentration at a fixed copolymer composition. Transitions from lamellar to gyroid and gyroid to hexagonal morphologies were observed at lower polymer concentrations than the respective transitions in the similar neutral copolymer, indicating a substantial influence of the charge density on phase behavior.     

共聚物组成对线形苯乙烯-丁二烯-苯乙烯嵌段共聚物粘弹弛豫与相形态的影响

研究了不同组成的苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)的相形态与粘弹弛豫.用透射电子显微镜(TEM)表征了SBS的形态,结果显示,几种SBS均呈层状结构,随着苯乙烯含量的降低,聚苯乙烯(PS)相的尺寸稍有减小,而聚丁二烯(PB)相尺寸明显增大.用动态流变学方法考察了不同温度下SBS嵌段大分子的弛豫行为,结果表明,苯乙烯含量减少,PS相玻璃化转变和有序-无序转变温度均降低;苯乙烯含量少的,在有序-无序转变过程中呈现出高且宽的损耗峰,表明有序-无序转变过程中能量的耗散主要由两相溶合时分子链间的内摩擦所决定,分子链越长,内摩擦越大,能量耗散越大.     

苯乙烯-丁二烯-苯乙烯/聚乙烯基甲基醚共混体系相容性的FT-IR及DSC研究

嵌段高聚物、均聚物共混体系相容性是近年来研究的热点。本工作以光学显微镜、DSC、FT-IR为手段,研究了三嵌段高聚物苯乙烯-丁二烯-苯乙烯(SBS);SBS-48、SBS-30,SBS-28与聚乙烯基甲基醚共混体系的相容性。DSC结果表明,随SBS中PS含量的升高,体系相容性变好,PS段分子量增大,也有助于体系相容。FT-IR结果表明PVME中COCH_3在1100cm~(-1)附近呈现的双峰的相对强度对体系的相容性十分敏感,而由于苯环C—H振动产生的698cm~(-1)峰位却不象PS/PVME体系那样随相容性的改变而有显著的改变。总而言之,嵌段高聚物SBS/均聚物PVME共混体系中,体系的相容性依赖于嵌段高聚物在体系中的组份含量及嵌段高聚物中PS的重量百分含量,PS段分子量的大小对体系相容性也有影响。     

Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers

The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25–170 °C) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27–44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/~35 °C/n/~115 °C/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above T_NI. The phase diagram is asymmetric and does not alter above T_NI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b_LC=0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.This paper is dedicated to Prof. Fischer on the occasion of his 75th birthday.     

Effect of architecture on the tensile properties of triblock copolymers in a lamellar phase.

We have used self-consistent field theory to calculate the tensile moduli of triblock copolymers in lamellar microstructures prepared from linear and star architectures. The extensional moduli K(33) are the main contributors to the tensile moduli, and the contribution of K(U)33 (the internal energy contribution to K(33)) is the main component of the value of K(33). We find that the tensile moduli of ABC three-miktoarm star terpolymers are smaller than those of ABC linear triblock copolymers having identical components, presumably for two main reasons. First, for the ABC three-miktoarm star terpolymers, the contributions of K(U)33 are larger than those of the linear triblock copolymers; we attribute this phenomenon to the star terpolymers having smaller lamellar domain sizes at equilibrium relative to those of the linear triblock copolymers. Second, conformational entropies play an important role in affecting the tensile moduli, mainly because of the different degrees of freedom of the various chains. In contrast, the shear moduli contribute negligibly to the tensile moduli.     

分子水平研究不同嵌段结构苯乙烯/丁二烯共聚物的表面结构

利用具有准单分子层灵敏度的和频振动光谱(SFG)、原子力显微镜(AFM)和接触角(CA)测定技术研究链结构和溶剂对苯乙烯(S)/丁二烯(B)嵌段共聚物表面准分子层化学结构形成的影响.结果表明,两嵌段共聚物SB比三嵌段共聚物SBS更有利于聚丁二烯(PB)组分在膜表面富集.利用PB的选择性溶剂环己烷做溶剂时,SB膜表面层完全由纯的PB组分组成,而SBS表面则是聚苯乙烯(PS)与PB二组分共存.利用PS的选择性溶剂甲苯做溶剂时,SB与SBS表面都是PS与PB二组分共存,其中SBS表面PS组分的含量更高.原因是由于溶剂影响嵌段共聚物分子在溶液中的构象从而影响溶剂挥发后聚合物表面结构的形成.     

ABA‐type liquid crystalline triblock copolymers via nitroxide‐mediated radical polymerization: Design,synthesis, and morphologies

We have designed and synthesized rod–coil–rod triblock copolymers of controlled molecular weight by two‐step nitroxide‐mediated radical polymerization, where the rod part consists of “mesogen‐jacketed liquid crystalline polymer” (MJLCP). The MJLCP segment examined in our studies is poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) while the coil part is polyisoprene (PI). Characterization of the triblock copolymers by GPC, ¹H and ¹³C NMR spectroscopies, TGA, DSC confirmed that the triblock copolymers were comprised of microphase‐separated low T_g amorphous PI and high T_g PMPCS blocks. Analysis of POM and 1D, 2D‐WAXD demonstrated that the triblock copolymers formed nematic liquid crystal phase. Morphological studies using TEM indicated the sample formed lamellar structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5949–5956, 2007     

Self-assembly of rod-coil-rod ABA-type triblock copolymers

Self-assembled behavior of symmetric ABA rod-coil-rod triblock copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. The phase diagram is constructed to understand the effects of the chain architecture on the self-assembled behavior. Four stable structures are observed for the ABA rod-coil-rod triblock, i.e., spherelike, lamellar, gyroidlike, and cylindrical structures. Different from AB rod-coil diblock and BAB coil-rod-coil triblock copolymers, the lamellar structure observed in ABA rod-coil-rod triblock copolymer melts is not stable for high volume fraction of the rod component (f(rod)=0.8), which is attributed to the intramolecular interactions between the two rod blocks of the polymer chain. When 0.3相似文献   

Nanostructured organic–inorganic hybrid films prepared by the sol–gel method from self‐assemblies of PS‐b‐paptes‐b‐PS triblock copolymers

ABA‐based triblock copolymers of styrene as block ends and gelable 3‐acryloxypropyltriethoxysilane (APTES) as the middle block were successfully prepared through nitroxide‐mediated polymerization (NMP). The copolymers were bulk self‐assembled into films and the degree of phase separation between the two blocks was evaluated by differential scanning calorimetry (DSC). Their morphology was examined through small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), whereas the mechanical properties of the corresponding cross‐linked self‐assembled nanostructures were characterized by dynamic mechanical analysis (DMA). Acidic treatment of the triblock copolymers favored the hydrolysis and condensation reactions of the APTES‐rich nanophase, and induced a mechanical reinforcement evidenced by the increase of storage modulus values and the shift of the glass transition temperature to higher temperatures due to confinement effects. In addition, the lamellar structure of the hybrid films was retained after the removal of the organic part by calcination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Morphology and mechanical properties of binary triblock copolymer blends

The influence of the morphology on the mechanical properties of binary styrene–butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer and a thermoplastic elastomer (TPE) with different molecular architectures was studied with bulk samples prepared from toluene. Both block copolymers contained SB random copolymer middle blocks, that is, the block sequence S–SB–S. The two miscible triblock copolymers were combined to create a TPE with increased tensile strength without a change in their elasticity. The changes in the equilibrium morphology of the miscible triblock copolymer blends as a function of the TPE content (lamellae, bicontinuous morphology, hexagonal cylinders, and worms) resulted in a novel morphology–property correlation: (1) the strain at break and Young's modulus of blends with about 20 wt % TPE were larger than those of the pure thermoplastic triblock copolymer; (2) at the transition from bicontinuous structures to hexagonal structures (～35 wt % TPE), a change in the mechanical properties from thermoplastic to elastomeric was observed; and (3) in the full range of wormlike and hexagonal morphology (60–100 wt % TPE), elastomeric properties were observed, the strength greatly increasing and high‐strength elastomers resulting. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 429–438, 2005     

A new approach on the thermal stability of SDS copolymer for HMPSA, Part I: Oxidation kinetics for the whole process

The poor aging property of the styrene–diene–styrene (SDS) triblock elastomer copolymer hot-melt pressure-sensitive adhesives (HMPSAs) has raised the importance of research on the aging and anti-aging properties of SDS triblock copolymers, such as styrene–butadiene–styrene (SBS) and styrene–isoprene–styrene (SIS). A mechanistic scheme based on the standard scheme for radical chain oxidation, but taking into account the decomposition of the oxidation-induced peroxide, was built. The kinetic equation of oxygen uptake was deduced from the proposed mechanism, which is composed of a set of reasonable parameters. The relationships among the parameters to induction time, maximum oxygen uptake and the maximum oxidation rate were examined. Numerical simulation methods were established to obtain parameters from the experiment data, by which most kinetic equations of oxygen uptake of the ingredients for HMPSAs were numerically fitted and the relativity of the model to the data was discussed. The study results should prove useful for future studies on the anti-aging performance of other materials.     

聚(苯乙烯-丁二烯-苯乙烯)三嵌段共聚物链结构的研究

<正> 以丁基锂引发二步加料法制备聚(苯乙烯-丁二烯-苯乙烯)三嵌段共聚物(简称SBS),往往在共聚物的中间链段聚丁二烯段中含有少量苯乙烯,即中间链段末端含有部份无规丁苯,得不到很纯的三嵌段共聚物,本文用超导核磁共振仪(H~1-NMR)、傅立叶红外光谱仪(FT-IR)、粘弹谱仪研究了上述SBS链结构,发现非嵌段苯乙烯芳环质子共振峰由二     

High performance poly(styrene-b-diene-b-styrene) triblock copolymers from a hydrocarbon-soluble and additive-free dicarbanionic initiator

A new hydrocarbon-soluble (additive-free) dicarbanionic organolithium initiator, obtained by a simple halogen-lithium exchange reaction (Gilman's reaction) from a diarylhalide containing a side C15 alkyl chain, has been designed and used to initiate the anionic polymerization of butadiene and styrene. The dilithiated species formed afford well-defined poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers with a high percentage of 1,4-microstructure polybutadiene (91%) and excellent mechanical properties, such as ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. This represents a breakthrough in the synthesis of SBS polymers, one of the most used thermoplastic elastomers.