Phase separation in polymer blends comprising copolymers: 4. Polycarbonate/polystyrene ABCP system

An AB-crosslinked copolymer (ABCP) with polycarbonate as A-chain and polystyrene as B-chain was prepared and characterized. A series of blends of the ABCP and homopolystyrene fractions with different molecular weights were prepared and examined by electron microscopy. The results show that the miscibility between the homopolymer and the like chains in the copolymer is limited even if the molecular weight of the former is much less than that of the latter. Considering the relatively large miscibility in diblock copolymer/homopolymer blends and the limited miscibility in ABCP/homopolymer-A blends reported in literature, this study leads to an argument that the molecular architecture of a copolymer is an important factor governing its miscibility with homopolymer. The relatively complicated architecture of ABCPs causing more restriction to the chain conformation might be one of the main reasons for its low miscibility with homopolymers.     

Phase separation in polymer blends comprising copolymers: 5. Polyisoprene/poly(isoprene-g-styrene) copolymer system

As part of a programme of research into miscibility in polymer blends comprising copolymers, this paper presents the morphology of blends of polyisoprene and poly(isoprene-g-styrene) with complicated but well defined structure. The graft copolymers were prepared by polymerization of styrene initiated by metallated polyisoprene backbone and were fully characterized. All the studied blends of copolymers and polyisoprene of different molecular weights exhibit macrophase separation even when the molecular weight of the homo PI is apparently less than that of the PI segments between neighbourning junction points in the copolymers. The results provide support for the argument that the molecular architecture of a copolymer is an important factor governing its miscibility with corresponding homopolymers. Besides, it is observed that the copolymer with higher proportion of polystyrene shows apparent solubilization in polystyrene matrix of high molecular weight and solubilization varies predictably with the addition of low molecular weight polyisoprene.     

Phase separation in polymer blends comprising copolymers: 7. Statistical theory of block copolymer-homopolymer systems

The miscibility of a homopolymer in corresponding domains of a copolymer predicted by Meier's theory is far less than found experimentally. In this paper, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block copolymer-homopolymer systems. Using this model, Helfand's theory, which has been successful in explaining microphase separation of block copolymers, is extended to polymer blends of homopolymer and corresponding block copolymer with lamellar structure. The calculated free energy of mixing of the system shows that the predicted miscibility is much larger than that obtained by Meier's theory and is in good agreement with the main known experimental results. In particular, on the basis of the present theory, homopolymer can be expected to be solubilized by corresponding blocks in the whole composition range provided that the molecular weight of the former is less than that of the latter.     

Phase separation in polymer blends comprising copolymers: 5.

For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer-polymer-filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.     

Effect of polymer-filler surface interactions on the phase separation in polymer blends

For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer-polymer-filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.     

Morphology and micromechanical behavior of binary blends comprising block copolymers having different architectures

Morphology and deformation behavior of binary blends comprising styrene/butadiene block copolymers (polystyrene content, Φ_PS∼0.70) having different molecular architectures were studied by means of transmission electron microscopy and tensile testing. In contrast to the binary diblock copolymer blends discussed in literature, the phase separation behavior of the blends investigated was found to be strongly affected by asymmetric molecular architecture. The blends showed macrophase separated grains, in which the structures resembled the microphase morphology of none of the blend components. Unlike the classical rubber-modified or particle-filled thermoplastics, neither debonding at the particle/matrix interface nor the particle cavitation was observed in these nanostructured blends. The microdeformation of the blends revealed plastic drawing of polystyrene lamellae or PS struts dispersed in rubbery matrix and orientation of the whole deformation structures along the strain direction.     

Correlation of miscibility and mechanical properties of polypropylene/olefin block copolymers: Effect of chain composition

This study examines the miscibility and mechanical properties of isotactic polypropylene (iPP) and olefin block copolymer (OBC) blends (70/30 wt %). The blends exhibit phase-separated morphology. The OBC domain size decreases with increasing the 1-octene content in the soft segment. The crystallization, melting behavior, and the long spacing of the iPP component in the blends are nearly the same as those of neat iPP, while the T_g of the iPP component shifts slightly to lower temperature. “Blocky” OBC is immiscible with iPP, while the soft segment rich polymers in OBC could be partially miscible with iPP. The impact strength of the blends is greatly increased with increasing the 1-octene content in the OBC soft segment. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phase separation in blends of homopolymer and graft copolymer based on styrene and butadiene

A series of blends of homopolystyrene and styrene-g-butadiene copolymer with different combinations of molecular weights of the copolymer and graft polystyrene segments have been prepared. Phase separation behaviour of the blends has been examined by electron microscopy. The results reveal a regular change of morphology of the blends with the relative molecular weights of the free and graft polystyrene chains. The observed relationships between compatibility of the homopolymer and copolymer and the relative molecular weight are generally in agreement with that observed previously in homopolymer-block copolymer blends. Taking the inherent polydispersity of the molecular weight of the component polymers into account, some peculiarities of the morphologies of the blends have been explained.     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Compatibilization effects of styrenic/rubber block copolymers in polypropylene/polystyrene blends

Compatibilizing effects of styrene/rubber block copolymers poly(styrene‐b‐butadiene‐b‐styrene) (SBS), poly(styrene‐b‐ethylene‐co‐propylene) (SEP), and two types of poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS), which differ in their molecular weights on morphology and selected mechanical properties of immiscible polypropylene/polystyrene (PP/PS) 70/30 blend were investigated. Three different concentrations of styrene/rubber block copolymers were used (2.5, 5, and 10 wt %). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the phase morphology of blends. The SEM analysis revealed that the size of the dispersed particles decreases as the content of the compatibilizer increases. Reduction of the dispersed particles sizes of blends compatibilized with SEP, SBS, and low‐molecular weight SEBS agrees well with the theoretical predictions based on interaction energy densities determined by the binary interaction model of Paul and Barlow. The SEM analysis confirmed improved interfacial adhesion between matrix and dispersed phase. The TEM micrographs showed that SBS, SEP, and low‐molecular weight SEBS enveloped and joined pure PS particles into complex dispersed aggregates. Bimodal particle size distribution was observed in the case of SEP and low‐molecular weight SEBS addition. Notched impact strength (a_k), elongation at yield (ε_y), and Young's modulus (E) were measured as a function of weight percent of different types of styrene/rubber block copolymers. The a_k and ε_y were improved whereas E gradually decreased with increasing amount of the compatibilizer. The a_k was improved significantly by the addition of SEP. It was found that the compatibilizing efficiency of block copolymer used is strongly dependent on the chemical structure of rubber block, molecular weight of block copolymer molecule, and its concentration. The SEP diblock copolymer proved to be a superior compatibilizer over SBS and SEBS triblock copolymers. Low‐molecular weight SEBS appeared to be a more efficient compatibilizer in PP/PS blend than high‐molecular weight SEBS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 291–307, 1999     

聚合物共混材料中氢键的研究进展

综述了近年来国内外聚合物共混材料中氢键的研究现状,着重对影响聚合物共混材料氢键强弱的因素、氢键的研究方法、氢键对聚合物共混材料性能的影响以及基于氢键作用制备相容性聚合物共混材料的方法进行总结。指出进一步研究多组分聚合物材料的氢键相互作用,可为制备可控性聚合物共混相容材料、实现功能化材料的构筑提供理论指导。     

Studies on phase separation in polyblends of block copolymers

The morphologies of polyblends of block copolymers of styrene and butadiene with similar composition but different molecular weights have been examined with an electron microscope. The micrographs show that some supramolecular features, with different morphologies to those in the matrix, are randomly dispersed. These results, we believe, provide evidence of the incompatibility of the block copolymers in spite of their chemical identity.     

Effect of multiblock copolymers in polymer blends

The use of multiblock copolymers for the compatibilization of immiscible polymer blends is controversially discussed in the literature. Investigations have been carried out to estimate the effect of multiblock copolymers containing segments of a liquid crystalline polyester (LCP) and polysulfone (PSU) segments in blends of the based homopolymers. One goal was to determine whether multiblock copolymers provide an opportunity for compatibilizing PSU/LCP blends. By using PSU/LCP multiblock copolymers with different molecular weights of the blocks in the appropriate binary, solution-casted blends, it was shown that the interpenetration of the polysulfone phase of the block copolymer and the PSU matrix leads to an improved miscibility of the blend. This effect is retained in ternary blends of PSU, LCP, and the multiblock copolymer, assuming a certain critical molecular weight of the multiblock copolymer segments. In addition, some mechanical characteristics of PSU/LCP melt blends such as the E-modulus and fracture strength are improved by adding long-segmented multiblock copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2293–2309, 1997     

Morphology and micromechanical deformation behavior of styrene–butadiene block copolymers. IV. Structure–property correlation in binary block copolymer blends

The structure–property correlation in blends consisting of styrene/butadiene block copolymers forming alternating polystyrene (PS) and polybutadiene (PB) lamellae, and PS domains in rubbery matrix was investigated by different microscopic techniques (transmission electron microscopy, scanning force microscopy, and scanning electron microscopy), uniaxial tensile testing, and dynamic mechanical analysis. Unlike the pure lamellar block copolymer, the blends showed predominantly disordered wormlike morphology formed by the intermolecular mixing. These structures allowed a precise control of stiffness/toughness ratio of the blends over a wide range. The blends showed a gradual transition from predominantly viscoplastic to elastomeric behavior with increasing triblock copolymer content. The results demonstrated that the binary block copolymer blends provide the unique possibility of tailoring mechanical properties on the basis of nanostructured polymeric materials. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1219–1230, 2004     

Application of random phase approximation to the dynamics of polymer blends and copolymers

The dynamics of melts of homopolymer mixtures and copolymers is studied with RPA. The first cumulant and the zeroth-order time moment of the measured dynamic scattering function S(q,t) are expressed-in terms of their counterparts in the non-interacting system of bare chains. The qualitative behaviour of these quantities as function of the wave number q and the interaction parameter χ_F are obtained using Rouse dynamics for bare chains, and the results are presented graphically as a guide to the interpretation of dynamic scattering experiments on such systems. The q-dependent threshold for spinodal decomposition in the case of copolymers, and the variation of the growth rate of the mean response with q in the unstable regime are also discussed qualitatively in both systems.     

Compatibilization of polypropylene/polystyrene blends with poly(styrene-b-butadiene-b-styrene) block copolymer

The compatibilizing effect of the triblock copolymer poly(styrene-b-butadiene-b-styrene) (SBS) on the morphology and mechanical properties of immiscible polypropylene/polystyrene (PP/PS) blends were studied. Blends with three different weight ratios of PP and PS were prepared and three different concentrations of SBS were used for investigations of its compatibilizing effects. Scanning electron microscopy (SEM) showed that SBS reduced the diameter of the PS-dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Transmission electron microscopy (TEM) revealed that in the PP matrix dispersed particles were complex “honeycomblike” aggregates of PS particles enveloped and joined together with the SBS compatibilizer. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of crystallinity of PP/PS/SBS slightly exceeded the values given by the addition rule. At the same time, addition of SBS to pure PP and to PP/PS blends changed the orientation parameters A₁₁₀ and C significantly, indicating an obvious SBS influence on the crystallization process in the PP matrix. SBS interactions with PP and PS influenced the mechanical properties of the compatibilized PP/PS/SBS blends. Addition of SBS decreased the yield stress and the Young's modulus and improved the elongation at yield as well as the notched impact strength in comparison to the binary PP/PS blends. Some theoretical models for the determination of the Young's modulus of binary PP/PS blends were used for comparison with the experimental results. The experimental line was closest to the series model line. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2625–2639, 1998     

Phase separation in semicrystalline polymer blends and copolymers studied via thermal segregation and crystallization kinetics

The miscibility versus immiscibility in a crystalline two component system is discussed, based on phase separation and crystallization kinetics considerations. The thermal segregation was used to create or enhance the phase separation in crystalline two component systems. By comparing the crystallization kinetics before and after thermal segregation, one can distinguish two types of phase separation: (1) intrinsic phase separation in the melt for an immiscible system, or (2) phase separation induced via crystallization for a miscible system. Metallocene short‐chain branching polyethylene (SCBPE) and nylon 6/polyimide triblock copolymer systems were taken as examples, and the phase behaviour determined via this thermal segregation and crystallization kinetics method. It is evident that the crystallization kinetics after thermal segregation are substantially faster than that before thermal segregation, and become much faster after keeping the sample in the melt for some time for the SCBPE system. Our results suggest that the molecules with different SCB contents in the SCBPE system may exhibit liquid–liquid phase separation in the melt. In contrast, studies on the crystallization kinetics of the nylon 6/polyimide system showed that nylon 6/polyimide triblock copolymer exhibits lower phase separation compared with in situ or solution blends. Thermal segregation and crystallization kinetics may serve as a very useful method to study the phase behaviour in semicrystalline blends and copolymers. © 2000 Society of Chemical Industry     

Electron holography and AFM studies on styrenic block copolymers and a high impact polystyrene

Many of the artifacts of conventional electron microscopy can be avoided if the unstained polymers are studied by electron holography and atomic force microscopy (AFM). Holograms of thin sections (50–70 nm) of organic block copolymers were recorded, and the corresponding phase images were reconstructed. In this way, typical structures such as lamellae and cylinders could be imaged without any staining. In addition, we successfully recorded holograms and performed Lorentz microscopy of an impact‐modified polystyrene (high‐impact polystyrene). The results were compared with the tapping mode AFM phase images. Electron holography and AFM have been demonstrated as suitable tools to image unstained heterogeneous polymers, leading to the understanding of their structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1573–1583, 2005     

Compatibility studies on solution of polymer blends by viscometric and phase‐separation technique

Solution blending of polystyrene (PS) and natural rubber (NR) was carried out in toluene and chloroform to determine the compatibility. Experimental evidence for the compatibility of these blends was derived from viscometric and phase‐separation studies. The viscometric method was based on the intrinsic viscosities of transfer of polymer in pure and “mixed” solvents. The compatibility of these blends based on the heat of mixing was also examined theoretically. All the experimental and theoretical evidence show that the blends are incompatible at the compositions studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 880–889, 2000     

嵌段共聚物为模板合成纳米结构导电聚合物材料研究进展

简述了以嵌段共聚物为模板合成纳米结构导电聚合物材料的国内外发展状况。近年来,纳米结构导电聚合物材料作为极具研究价值的新型功能材料而成为了材料科学的研究热点。以嵌段共聚物为模板则是制备此类材料最有前途的方法之一。本文详细地总结并归纳了通过该方法制备形貌规整的纳米级导电聚合物材料的成形机理、实验方法及其影响因素等。最后总结了纳米结构导电聚合物材料相关研究中存在的诸多问题,并简要指出以嵌段共聚物为模板有助于提高导电高聚物的形貌及尺寸的可控性,进而有助于改善导电高聚物的溶解性、加工性能、电导率等各项性能,也将有利于拓宽导电高聚物在纳米科技领域中的应用前景。