Elongational viscosities of random and block copolymer melts

The influence of random and block copolymerized structures on the uniaxial elongational viscosity was investigated. The investigated random copolymers were poly(ethylene-random-ethyl methacrylate) with comb-branched structure and poly(styrene-random-acrylonitrile) with linear structure. The studied block copolymers were poly(styrene-block-ethylenebutylene-block-styrene) with linear structure. The elongational viscosities of random copolymers showed strain-hardening properties. The strain-hardening property was influenced little by comonomer contents and depended on whether copolymers had linear or branched structures. In contrast, the elongational viscosities of block copolymers gave strain-softening properties. The strain-softening property was not affected by strain rates and block comonomer ratios. The causes of strain-hardening and -softening properties are discussed from relaxation spectrum and damping function based on the Bernstein–Kearsley–Zapas model. The damping functions of linear and branched random copolymers agreed with those of linear and branched homopolymers, respectively. On the other hand, linear block copolymers exhibited stronger damping than linear homopolymers. It was concluded that strain-hardening and -softening properties in the elongational viscosity of random and block copolymerized structures are correlated with their damping functions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1765–1774, 1998     

Architecture dependence of thermal fluctuation effects on the order-disorder transition of block copolymer melts

Small-angle X-ray scattering has done to explore the difference in the strength of the thermal fluctuation effects between A-B diblock copolymer and (A/2)₂-B Y-shaped copolymer. SAXS profiles for both systems in their disordered states were analyzed with the Brazovskii-type non-mean field theory by Fredrickson and Helfand. The analyses yielded Ginzburg number characterizing the strength of thermal fluctuation effects. Ginzburg number of Y-shaped copolymer is larger than that of diblock copolymer, suggesting that the strength of the thermal fluctuation effects is affected by the architecture of copolymers.     

Solvation and phase separation in ABA block copolymers

A conceptual scheme is presented for classifying the phase behavior of ABA block copolymers and solvents. The effect of solvent fraction ?_S on microphase separation is described for macroscopically homogeneous systems, but more attention is focused on the limits of solubility. A “miscibility map” is developed in terms of solubility parameters δ_A, δ_B, and δ_S and used to define regions of macrophase separation, complete miscibility, and partial miscibility. Combined with known triblock molecular structure, the miscibility map can be used to predict the character of solvated systems and guide the selection of solvents for special purposes. A survey of reports in the literature shows qualitative consistency with this treatment. New observations are reported on solvation of a polystyrene–polybutadiene–polystyrene polymer in numerous solvents; these are used to infer microstructural information and define the miscibility map more realistically.     

Crystallization and coalescence of block copolymer micelles in semicrystalline block copolymer/amorphous homopolymer blends

Crystallization of two oxyethylene/oxybutylene block copolymers (E₇₆B₃₈ and E₁₅₅B₇₆) from micelles in block copolymer/amorphous homopolymer blends was studied by differential scanning calorimetry (DSC) and time-resolved small angle X-ray scattering (SAXS). Unlike the simultaneous crystallization and formation of superstructure in crystallization from an ordered structure, crystallization of block copolymer from micelles can be divided into two steps. The core of the micelles firstly crystallizes individually, with first-order crystallization kinetics and homogeneous nucleation mechanism. The SAXS revealed that crystallization-induced deformation occurs for the micelles, which strongly depends on microstructure of the block copolymers. For the shorter block copolymer E₇₆B₃₈, larger deformation induced by crystallization was observed, leading to coalescence of the micelles after crystallization, while for the longer block copolymer E₁₅₅B₇₆ the micelles show little deformation and the morphology of micelle is retained after crystallization.     

Swelling characteristics of block order networks prepared by styrene-ethylene/butylene ABA triblock copolymer and styrene homopolymer binary blends

Mixed networks based on polystyrene (PS) and styrene-ethylene/butylene triblock copolymer (SEBS) binary blends were synthesized via a postpolymerization Friedel-Crafts-type reaction employing styrene units and a bis-chloromethylated crosslinking agent. The swelling behavior of the produced gels was studied in relation to network densty, SEBS/PS mass ratio, and solubility parameter of the swelling media, in a range of aliphatic, chlorinated, and aromatic solvents. Swelling characteristics of the mixed macronets were found to differ markedly from those of pure homopolymer gels. Selective swelling was observed in three different regions in respect to the solvent solubility parameter, in contrast to pure PS networks where adsorption was favored in a single region of solvents. This phenomenon was found to depend primarily on the SEBS/PS constitution of gels, while the solvent holding capacity depended directly on the crosslinking density. © 1995 John Wiley & Sons, Inc.     

Association and physical gelation of ABA triblock copolymer in selective solvent

Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-PtBuA-PMMA) in 1-butanol (PtBuA selective solvent) indicated that PMMA-PtBuA-PMMA chains are molecularly dissolved above 50 °C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and PtBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9-12.0 wt%) revealed that the system was viscous sol state at 60 °C. Drastic increase of shear storage modulus (G′) occurred with decreasing temperature, and at 25 °C, G′ showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G′ indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging PtBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time-temperature superposition along the frequency axis. Just above sol-gel transition concentration (C_gel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging PtBuA chain above C_gel.     

磨盘碾磨应力场作用下苯乙烯-丁二烯-苯乙烯嵌段共聚物的结构变化

采用原子力显微镜法、傅里叶变换红外光谱法、透射电子显微镜法、差示扫描量热法和X光电子能谱法等研究了苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)在磨盘碾磨应力场作用下．其相结构和分子结构的变化。结果表明,磨盘形力化学反应器独特的剪切和挤压力场将SBS在室温下粉碎成50～100μm的微粒;在碾磨过程中,SBS分子链断裂,特性黏数下降,聚苯乙烯分散相发生畸变,其相区尺寸增加;磨盘碾磨使SBS分子链的活性增加,诱使其发生交联反应,同时在分子链中引入含氧基团．可用于SBS的改性。     

Rheological properties of melts and structure formation in polyoxymethylene-ethylene-propylene copolymer mixtures

Conclusions It has been shown that the conclusion of the Van Oene theory that the polymer with the greater melt elasticity should form a disperse type of structure and the polymer with the lower elasticity should form a stratified (laminar) structure is not fulfilled for polyoxymethylene-ethylene-propylene copolymer mixtures at ratios of 80:20 and 20:80. This means that at low content of the disperse phase polymer a disperse morphology is the most typical, regardless of the degree of elasticity of the melt.It has been found that an elevated elasticity of the disperse phase polymer does not aid specific fibre-formation.A disperse state of the polymer in a mixture and the formation of an interfacial layer lead to a decrease in the temperature (by tens of degrees) and heat effect (several-fold) of phase transitions.The interconnection between structure-formation processes and the rheological properties of the polymer mixture melt is manifested in a decrease in viscosity, an intensification of the viscosity anomaly, and an increase in the elasticity of the melt mixture as compared with these same characteristics of the starting polymers.Translated from Khimicheskie Volokna, No. 3, pp. 8–10, May–June, 1988.     

光敏感型嵌段聚合物胶束的研究进展

对聚合物结构中常见的光敏感性基团进行了介绍,并根据嵌段共聚物结构设计和光敏感基团的差异,将光敏感型嵌段聚合物胶束（BCPM）分为侧链变化型、主链断裂型、主链降解型和疏水交联型等几类,并对这几类BCPM的结构特征及其光刺激下结构的变化进行了对比分析,重点阐明了各类BCPM作为药物载体材料时对药物的光控包载或释放行为。光敏感型BCPM具有良好的结构可控性和刺激响应能力,通过结构的进一步优化和研究的不断深入将有望发展成为一类新型的药物靶向输送系统。     

Thermal conductivities of blends of polyethylene/SEBS block copolymer and polystyrene/SEBS block copolymer

Thermal conductivities of two series of blends of polystyrene and styrene–ethylene/butyrene–styrene block copolymer (PS/SEBS), and polyethylene and styrene-ethylene/butylene-styrene block copolymer (PE/SEBS) were measured. Here the PS part and hydrogenated polybutadiene (EB; ethylene-butene-1 copolymer) part of SEBS were confirmed to be miscible in PS and PE homopolymers, respectively, by the differential scanning calorimetry. The thermal conductivity of PS/SEBS increased, while that of PE/SEBS blends decreased monotonically, with increasing SEBS content. No significant changes in the range where microphases usually occur were noted. The thermal conductivities of PS/SEBS and PE/SEBS were explained by modifications of our equation for composites. Thermal conductivity of EB in SEBS was estimated from that of PS/SEBS blend as 4.9 × 10^?4 cal/s cm °C. Further, the thermal conductivity of PE/SEBS could be predicted by substituting the obtained value of EB into the modified equation. Therefore, the modified equations were confirmed to be applicable to thermal conductivities of PE/SEBS and PE/SEBS blends. © 1993 John Wiley & Sons, Inc.     

Stratification and phase separation in block copolymer coatings

Stratification, i.e. spontaneous formation of separate layers from a liquid coating containing inherently incompatible resinous components, provides a means of improving the adhesion of coatings. For mixtures of conventional homogeneous resins, surface and interface tensions are considered to be the driving forces for self-stratification, leading to films with separation patterns somewhere between purely spinodal decomposition textures and neatly separated A/B double layers.

Inherently domain-forming block copolymers mixed with partly compatible resins give various different separation patterns ranging from ABA-sandwich structures to physically interpenetrating networks of co-continuous phases with homogeneous layers — sometimes monomolecular ones — at film surfaces.

Besides tailoring adhesion to difficult substrates, block copolymer binders offer chances to achieve new interesting mechanical property profiles as required, e.g. for coatings for plastics or for stone chip-resistant surfacers useful in the automotive industry.

The temperature-dependence of mechanical properties is significantly reduced in comparison with conventional homogeneous coating binders.     

New extensional rheometer for elongational viscosity and flow birefringence measurements: some results on polystyrene melts

A new extensional rheometer allowing the simultaneous measurement of elongational viscosity and flow birefringence is described. Polystyrene melts have been tested at different temperatures and strain rates. It appears that the time-temperature superposition principle holds for elongational tests in the temperature range investigated, with the same shift factors as for linear shear experiments. It has been verified that the stress optical behaviour of the melts is linear for small values of the stress whereas significant deviations appear at higher stresses.     

Dynamic and steady-state rheological measurements on polymer melts

Many attempts to correlate steady-state and dynamic rheological data have been reported. Thus far, the correlations have not been convincing, particularly for polymer melts that exhibit highly non-Newtonian behavior. The purpose of this work was to provide a means for obtaining a useful correlation. The Maxwell viscoelastic model was used to correlate data from four different modes of shear—two involving steady-state deformation and two involving dynamic deformation. As certain defined requirements were met, excellent agreement was obtained for polymer melts that represent a wide range of viscoelastic behavior. One of these requirements was that the polymer molécule should have a certain degree of flexibility.     

Microstructural diagnosis of block copolymer nonlinear mechanical properties I. Uniaxial stress/strain

An earlier study on the linear dynamic properties of triblock copolymers was continued into the nonlinear property regime. Uniaxial tensile tests were performed on styrene-butadiene-styrene block copolymers. The three polymers, having polystyrene (PS) fractions 0.27, 0.29, and 0.48, also represented three molecular weights (0.49, 0.58, and 1.0 × 10⁵). Specimens were prepared by casting from three solvents (methyl ethyl ketone, MEK; cyclohexane; and a 9:1 mixture of tetrahydrofuran and MEK). This wide range of variables led to a correspondingly wide spectrum of properties, including the “plastic-to-rubber” transition in some cases. Stress-strain curves were characterized by modulus, yield stress, general elevation, and fracture stress and elongation. Results were interpreted in terms of microstructural parameters obtained from the earlier linear tests, including interphase properties, and molecular features as well. Special insight emerged from comparison of first-cycle (to 300 percent elongation) and second-cycle tests, including changes in modulus, yielding, level, and the appearance of set. Additional data on sample preparation influences and PS continuity effects on sample properties were also obtained.     

Diffusion of p-aminoazobenzene in SBS block copolymer

The temperature dependence of p-aminoazobenzene diffusion in a styrene–butadiene–styrene (SBS) triblock copolymer film, prepared from a toluene or ethyl acetate solution, was investigated in the temperature region from 40° to 110°C by using a sublimative desorption method. Parallel studies on the mechanical relaxations of this copolymer were carried out in the same temperature range to be compared with the diffusion data. The penetrant-diffusion characteristics were interpreted in terms of Fujita's free-volume theory with due consideration of the different SBS domain morphology. The value of B_d, defined as the diffusional volume ratio of a penetrant molecule to a segment, was then estimated as 0.45–0.55 above the T_g of the polystyrene phase or 0.7 below that temperature. Interestingly, sigmoidal desorption appeared in the range under the T_g of the polystyrene phase for film cast from ethyl acetate; the anomalous behavior was considered to reflect the slow relaxation process of the copolymer chain ascribable to the predominant exposure of the polystyrene phase on the film surface.     

丁苯嵌段共聚物结构与性能研究

以苯乙烯（St）、丁二烯（Bd）为单体,正丁基锂为引发剂,通过阴离子聚合合成了丙烯腈-丁二烯-苯乙烯（ABS）改性用丁苯嵌段共聚物（LBS）。探讨了聚合温度、加料工艺对产品分子结构及性能的影响规律。详细分析了相对分子质量及其分布、结合St质量分数、分子结构参数、St序列分布与产品性能的关系,探讨了影响产品生胶门尼粘度（MV）的关键因素。合成出了可用于连续本体ABS改性的LBS新产品,并进行了连续本体ABS改性性能评价实验。     

嵌段共聚物的合成及其组装行为

嵌段共聚物在选择性溶剂中可逆缔合形成以不溶性链段为核 ,溶解性链段为壳的胶束。广泛用作表面活性剂、增溶剂、药物载体和纳米材料等。综述了嵌段共聚物的合成方法 ,着重分析了浓度、温度、嵌段长度、溶剂、添加物及电荷等因素对嵌段共聚物在选择性溶剂中组装行为的影响及其形成机理。展望了嵌段共聚物组装行为的应用前景     

Toughening isotactic polypropylene and propylene-ethylene block copolymer with styrene-ethylene butylene-styrene triblock copolymer

Dynamic mechanical properties, low-temperature impact behavior, flexural modulus and heat distortion temperature (HDT) of isotactic polypropylene (i-PP) and propylene-ethylene block copolymer (Co-PP) toughened with styrene-ethylene butylene-styrene triblock copolymer (SEBS), at blending ratios of 0–30 phr, were studied and compared. A scanning electron microscopic morphology study of the impact-fractured surfaces demonstrated the changes in fracture mechanisms at various temperatures and SEBS contents. SEBS remarkably improves the impact endurance in the lower-temperature range when blended with Co-PP in comparison with i-PP, due to the increased compatibility in the interface between SEBS particles and the Co-PP matrix.     

Fibrillation in the flow of polyoxymethylene melts

The phenomenon of specific fibrillation from melts of polymer mixtures is considered (using mixtures of polyoxymethylene with copolyamide as an example) when, in contrast to conventional fibre spinning methods, a complex thread consisting of hundreds of thousands of ultrafine fibrils oriented along the extrusion axis is obtained as a result of compressing the melt mixture through a single orifice (or upon extension of one stream of the polymer melt mixture). Here we deal with a radically new process of fibrillation of one of the polymers of the mixture (under the effect of the rheological forces at the capillary inlet) in the matrix of the other, when the number of the filaments in the thread is not determined by the number of the orifices in the die.After solvent extraction (from the solidified extrudate) of the polymer forming the matrix the other component remains as a bundle of fine fibrils less than 1 μm in diameter. The microstructure of mixture extrudates depends on the rheological properties of the melt, the mixture composition, the conditions of mixing and extrusion. Capillary viscometry methods have revealed a drastic difference in the viscoelastic properties of melt mixtures as compared with the separate components.