Article pubs.acs.org/Macromolecules
Regulation of Physical Networks and Mechanical Properties of Triblock Thermoplastic Elastomer through Introduction of Midblock Similar Crystalline Polymer with Multiblock Architecture Qinglong Zhang,† Wenqiang Hua,‡ Qilin Ren,† and Jiachun Feng*,† †
State Key Laboratory of Molecular Engineering of Polymers, Collaborative Innovation Center of Polymers and Polymer Composite Materials, Department of Macromolecular Science, Fudan University, Shanghai 200433, China ‡ Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 239 Zhangheng Road, Shanghai 201204, China S Supporting Information *
ABSTRACT: The physical network structure and mechanical properties of styrene-b(ethylene-co-butylene)-b-styrene (SEBS) were regulated through rational introduction of crystalline olefin multiblock copolymer (OBC). This copolymer comprised alternated crystallizable and amorphous blocks, both of which had similar composition with ethylene-cobutylene (EB) blocks of SEBS. Polarized optical microscope and atom force microscope observations revealed that OBC exhibited distinct crystalline morphologies in blends. On one hand, major OBC chains were macrophase separated with SEBS, generating bulk crystals. On the other hand, small OBC particle crystals with diameter around 10 nm could be distinguished in the SEBS matrix as well. Considering the unique multiblock architecture of OBC, particle crystals could be regarded as additional physical netpoints to SEBS networks as the corresponding amorphous blocks entangled with continuous EB blocks. Because of the interesting crystalline behaviors of OBC in the SEBS matrix, the blend exhibited dramatically elevated elongation at break at both room temperature and relatively high temperature without sacrifice of intrinsic elasticity. We believe this work sheds light on comprehending the interaction between triblock elastomers and blended polymers, and it also demonstrates the feasibility of regulating the apparent properties of triblock copolymers by the blending approach.
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INTRODUCTION Block copolymers with specific phase separation morphologies constitute an important class of thermoplastic elastomers. These materials undergo phase separation upon cooling and form ordered lattices such as spheres, cylinders, and lamellae at nanometer scales.1−6 The lattices are hard glassy minority regions, while soft components with normal entanglements connect each lattice and form physical cross-linked networks, which endow materials with elasticity of rubbers and processability of plastics. Triblock copolymers such as styrene-b-butadiene-b-styrene (SBS), styrene-b-isoprene-b-styrene (SIS), and styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) are a typical kind of thermoplastic elastomer. With regards to these microphase-separated materials, the end-blocks act as the netpoints, which are connected by highly entangled middle blocks. Owing to the formation of three-dimensional physical networks, this kind of thermoplastic elastomer exhibits outstanding mechanical properties (elasticity, strength, toughness)7−9 and has already been widely applied in adhesives, sealants, coatings, the footwear industry, automotive parts, and wire insulation, etc.10−12 Tailoring the aggregation state for desired processing and apparent properties is a topic of fundamental importance with innumerable industrial applications for block copolymers. For the triblock thermoplastic elastomer, as the physical networks are essential for its intrinsic properties, the aggregation state © XXXX American Chemical Society
should be tuned with maintenance of network structure. From this perspective, lots of investigations have explored effective regulation by changing the molecular architecture during synthesizing, such as the length, content, and relative volume fraction of each block as well as varying processing conditions.1,7,13−15 These works demonstrate the possibility of achieving balanced apparent properties. However, it is comparatively difficult and uneconomical to change the process of synthesizing, and the property regulation through changing processing conditions is quite limited due to its fixed initial compositions. Compared with above regulation method, an elegant and flexible approach to tune the morphology of block copolymers lies in blending with polymers possessing similar compositions to one of the constituent blocks.16−22 This allows targeting a multitude of bulk morphologies by simply adjusting the overall blend composition, leading to optimized end-use properties or even combined advantages of blending components. Balta-Calleja et al.22 intended to regulate the morphology as well as tensile properties and micohardness behaviors of styrene/butadiene star block copolymer through blending polystyrene (PS) homopolymer. It was found that with elevated PS content the hardness and the local yield stress Received: July 5, 2016 Revised: September 7, 2016
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DOI: 10.1021/acs.macromol.6b01441 Macromolecules XXXX, XXX, XXX−XXX
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Figure 1. DSC (a) exothermic curves and (b) endothermic curves of OBC and blends.
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increased correspondingly, while a higher increase rate was observed when the morphology changed from stacks of alternating PS lamellae to PS matrix. To design a membrane layers with nanometer-sized pores, Müller et al.21 achieved tetragonally perforated lamellae bulk morphology by blending a triblock terpolymer with homopolymer comprising the same composition of certain block. The pore diameter was quite regular and pore permeability could respond to pH and temperature. These pioneering works manifest that control of morphology and regulation of end-use properties can be achieved for block copolymers through the simple blending approach. However, with regards to the triblock elastomer, regulation of morphology and property through blending becomes quite complicated. The outstanding mechanical properties and elasticity of triblock elastomers mainly originate from the three-dimensional physical networks. While merely addition of polymers with similar composition as constituent blocks cannot enhance the networks or may even destroy the network structure to some extent. Therefore, although improvement of some specific properties can be achieved by the blending approach, the sacrifice of critical tenacity and elasticity is usually inevitable. In this work, we propose a novel blending approach to regulate the network structure of SEBS, a typical triblock thermoplastic elastomer, by blending olefin block copolymer (OBC) with unique multiblock architecture. OBC comprises crystallizable ethylene copolymer blocks containing low octene content (hard blocks), alternating with amorphous ethylene copolymer blocks containing high octene concentration (soft blocks).23−31 In general, both hard blocks and soft blocks of OBC have similar composition with ethylene-co-butylene (EB) blocks of SEBS, and thus they are partially miscible, indicating some chains are possible to entangle together in the melt. The unique feature of adding OBC lies in that the hard blocks can generate crystallization while soft blocks still entangle with EB blocks, which means that partial crystallization of OBC may be regarded as additional physical netpoints to SEBS simultaneously without damage to original networks. Because of this interesting morphology, the elongation at break of SEBS at room temperature or comparatively high temperature can both be elevated to a great extent, while the elasticity suffers limited influence. In addition, the rheological properties can be conveniently tuned through changing OBC content, which offers a simple method to obtain better processing ability. We believe this work sheds light on comprehending the interaction between triblock elastomers and blended polymers, and it also demonstrates the feasibility of regulating the apparent properties of triblock elastomers without sacrifice of elasticity by the blending approach.
EXPERIMENTAL SECTION
Materials. SEBS triblock copolymer (Kraton G1654) was obtained from the Kraton Polymers, Inc. The molecular weight was 1.5 × 104 with polydispersity less than 1.04, and the weight proportion of styrene block was about 31%. OBC pellets synthesized by chainshuttling technology were product from the Dow Chemical Company. The molecular parameters of the OBC are listed as follows: the content of crystallizable ethylene/octene blocks with very low octane content is 36%, while the content of amorphous ethylene/octene blocks with high octane content is 64%; the content of octene is 1.9 mol % in crystallizable segment and 21.8% in amorphous segment. The OBC granules and SEBS powders are melt-blended at 200 °C for 15 min. The OBC content in the blends was 10, 15, and 25 wt %; the corresponding samples were denoted as OBC-10, OBC-15, and OBC25. Pure SEBS and OBC experienced the same blending treatment as well. Characterizations. The thermal properties were evaluated by a Mettler DSC-821e apparatus (Mettler Toledo, Switzerland). Samples with weight of approximately 5−8 mg were sealed in aluminum pan, and all the experiments were performed in a nitrogen atmosphere. Morphologies of the blends were observed using DM2500P microscope (Leica, Germany) with Linkam-THMS600 hot stage. The crystalline morphologies were observed with polarized optical microscope (POM) at a cooling rate of 10 °C/min, and phase morphologies at 200 °C were observed with phase contrast microscope (PCM). Detailed morphologies of blends were obtained with Multimode 8 atom force microscope (AFM, Bruker, German) in PeakForce quantitative nanomechanical property mapping (QNM) mode. Under PeakForce QNM mode, the formation of images is based on difference of modulus or adhesion. Small-angle X-ray scattering (SAXS) measurements were performed by NanoStar U system (Bruker, Germany). The power is 3 kW while the detection zone is 0.2°−2.8°. The tensile testing at room temperature (23 °C) was conducted on a SANS CMT-6503 universal testing machine (Shenzhen, China) at a crosshead speed of 50 mm/min. The capacity of the load cell is 50 N in axial load. Recovery measurements were conducted on a single specimen by applying a strain 100% at a constant cross-head speed of 20 mm/min, then immediately reversing the motion of the cross-head (at the same rate) until zero stress, and repeating the process for at least five times. The strain at zero stress was recorded, while the tensile properties at 60 °C was tested with Linkam-TST350 temperature controlled tensile testing stages (UK) at a crosshead speed of 20 mm/ min. A HAAKE MARS III rotary rheometer (Thermo Fisher, Waltham, MA) with parallel plate was utilized to investigate the rheological properties of the blends. The single shear strain of 1.0% and shear frequency of 1 Hz were applied for all measurements. The dynamic frequency sweeping test was performed at 200 °C.
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RESULTS AND DISCUSSION The heating and cooling thermograms of SEBS/OBC blends at a rate of 10 °C/min are shown in Figure 1. The crystallization peak temperature of OBC approaches 103.5 °C, while when B
DOI: 10.1021/acs.macromol.6b01441 Macromolecules XXXX, XXX, XXX−XXX
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Figure 2. PCM micrographs of blends.
OBC is blended in the SEBS matrix, the crystallization temperature decreases to a great extent. The decrease tendency exhibits OBC content dependence; its value drops constantly from 91.9 °C for OBC-25 to 87.1 °C for OBC-10. The dramatic decrease of crystallization temperature for OBC in blends, which even drops beyond 16 °C, indicates that crystallization of OBC is confined in the initial networks of SEBS.32−34 This phenomenon can be attributed to that the molecular composition of OBC is similar to that of EB block of SEBS and thus generating strong interactions. While with regards to the melting behaviors, the difference of melting temperatures for these samples is relatively limited with maximum gap less than 4 °C. The results suggest that the difference of crystal thickness and structure for theses samples may be limited despite the distinct crystallization kinetics. The dispersion of OBC in SEBS matrix in the melt was observed by PCM; the small bright particles represented OBC phases. As shown in Figure 2, the size and dispersion of OBC phase in SEBS are quite uniform. As for OBC-10, the diameter of most OBC phases is less than 3 μm. With increase of OBC content, the size becomes larger with OBC-15 reaching 5 μm and some phases even connected to strips for OBC-25. The well-dispersed OBC demonstrates good compatibility between SEBS and OBC, which may originate from the similar molecular compositions for OBC and continuous EB blocks. We also observed the crystalline morphologies of OBC by POM. As shown in Figure 3, for pure OBC, small spherulites can be observed although they are quite imperfect after processing, while for OBC crystallized in SEBS, the morphologies exhibit dramatic contrast. Small particle or
strip-shaped crystals instead of regular spherulites are distinguished, indicating strong confined crystallization characters. The crystallization morphologies are closely correlated to the dispersion state in the melt. The OBC phases in the melt are bulk or strips with relatively small size; thus, the crystallization is confined in the formed phases and generate tiny crystals. While with elevation of OBC content in SEBS matrix, the crystals become larger and intersect into a network structure on the whole. With regards to OBC-25, bright strip crystals are distinguished, and they tend to assembled into perfect networks. The formation of networks can be attributed to the confinement of original network structure of SEBS although the network structure observed by POM possesses relatively larger size. The detailed crystalline morphologies of OBC in SEBS matrix were observed by AFM in PeakForce QNM mode. Under this mechanical mode, the formation of images is based on difference of modulus or adhesion.35−39 The phase separation morphology of SEBS is difficult to be distinguished in blends as it is too soft compared with OBC crystals (the images of pure SEBS are exhibited in Figure S1). In modulus images of pure OBC, the crystallites formed by the hard blocks are mainly needlelike structures. Meanwhile, a small amount of tiny spherical or clumpy crystallites can also be found, which may be ascribed to the crystallization confined in hard block rich domains. While in SEBS/OBC blends, the OBC crystals exhibit quite distinct morphologies. As shown in Figure 4, OBC-10 mainly generates bulk crystals with size of several micrometers, which is in consistence with the observation by POM. If the image is further magnified, we notice that a large amount of small crystal particles with diameter around 10 nm can be clearly distinguished as well. These particles possess relatively homogeneous dimension, and they exhibit a uniform distribution. With increase of OBC content in blends, more crystals with relative larger size appear, and they tend to exhibit strip morphologies, which partially resemble that of pure OBC. While in spite of OBC content, uniformly distributed crystal particles with similar dimension can be distinguished for all the blends. The coexistence of two crystalline dimensions may reveal corresponding aggregation state of OBC in blends. In combination with PCM and POM observation, we believe the crystal with larger size originate from the crystallization in OBC-rich phases. In the melt, some OBC chains in blends assemble into separated phases. With this confinement, they crystallize into bulk or strip crystals instead of perfect lamellae. With regards to the appearance of small particle crystals, it may be closely related to the strong interaction between OBC and EB blocks of SEBS. Considering the similar molecular composition for OBC and EB blocks of SEBS, partial OBC chains may entangle with EB blocks and distribute uniformly in the continuous phase of SEBS. During cooling, the
Figure 3. POM micrographs of blends. C
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Figure 5. AFM adhesion images of OBC and blends.
phases and particle crystals can form as well in these regions. In combination with modulus images, we believe the formation of black spheres indicates strong interaction between OBC and SEBS as they cannot be found in pure substances or separated phases, and the corresponding crystals may not only fix amorphous soft blocks but also entangle with EB blocks to some extent. Therefore, the observation of adhesion images confirms that the particle crystals are reasonable to be regarded as new netpoints for SEBS. SAXS was performed to examine the arrangement of ordered structures. The scattering peak from the arranged structure can be clearly seen as exhibited in Figure 6. The q value at the scattering peak is utilized to calculate the characteristic domain spacing or long period (d) between the adjacent lamellar layers.41,42
Figure 4. AFM modulus images of OBC and blends.
d = 2π /q
crystallization of these OBC chains is strongly confined by the networks of SEBS. Therefore, small crystal particles generate in the continuous phase of SEBS. In addition, as only hard blocks crystallize during crystallization while soft blocks are still in entanglement with EB blocks, these crystal particles may exhibit strong contact with continuous phases and can even be regarded as new netpoints for SEBS. Actually, adding new crystal netpoints has been recently achieved though rationally designing synthesizing process by Bates et al.,40 while our work demonstrates the feasibility by simply blending with unique crystalline multiblock polymers. The randomly dispersed OBC crystal spherulitic phases were further confirmed by AFM adhesion images in Figure 5. The region in Figure 5 is the same as that in the right column of Figure 4. The small crystal particles of OBC in blends exhibit black spheres with diameter around 10 nm in adhesion images, while these black spheres nearly cannot be distinguished for pure OBC, which mainly exhibits some crystal traces originating from height difference. The distinct morphologies indicate that the crystallization of OBC confined in SEBS matrix may induce different entanglement state of local regions, leading to different adhesion compared with the matrix. In contrast, the large bulk crystals cannot be distinguished in adhesion images, indicating the crystallization in OBC-rich phases does not greatly change the entanglement state. While we notice that small black spheres appear in the original bulk crystal regions, suggesting that EB blocks also exist in OBC-rich
Based on the correlation, the long period of pure OBC is approximately 20.0 nm (q = 0.313 nm−1). While after introduced into SEBS, the long period decreases obviously. As shown in Figure 6b, the peaks located at higher q represent the arrangement of OBC crystals. The long period drops to 15.1 nm (q = 0.416 nm−1) for OBC-10. With increase of OBC content, the peaks become wider and shift to lower q region to some extent. The change of peak shape and location can be closely related to the morphologies of OBC crystals. As for OBC-10, more OBC chains are strongly confined in SEBS networks and form small particle crystals. The crystal thickness is obviously smaller compared with pure substance as indicated by DSC melting points, and considering the entanglement between OBC soft blocks and EB blocks, the amorphous thickness may decrease as well. As a consequence, the long period for OBC-10 shifts to a lower value. With elevation of OBC content, more OBC chains crystallize in their rich phases, forming bulk crystals that are more similar to pure OBC. Thus, the peak shifts toward pure substance, and the peak becomes wider due to the coexistence of two distinct crystal morphologies. We also notice that the peak representing characteristic domain spacing for SEBS varies little after introduction of OBC, with q value only changing from 0.171 nm−1 for pure SEBS to 0.156 nm−1 for OBC-25. In this sense, the introduction of OBC may have limited influence on the structure of SEBS, and its original networks, which are critical for the tenacity and elasticity, can be reserved to a great extent. D
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Figure 6. (a) SAXS raw curves of OBC, SEBS, and blends. (b) SAXS fitting curves of blends.
Figure 7. Stress−strain curves of SEBS and blends at (a) room temperature and (b) 60 °C.
Figure 8. Cyclic stress−strain curves of SEBS and blends.
The large-strain tensile testing at room temperature and 60 °C is illustrated in Figure 7. In general, SEBS displays typical elastomeric characteristic with no distinctive yield point. At room temperature, the elongation at break of SEBS reaches around 550%. When incorporated with OBC, the mechanical properties of the samples changes dramatically. As for OBC-10 and OBC-15, tensile strength and elongation at break increase obviously compared with pure substance. The tensile strength reaches 14 MPa while the elongation at break increases beyond
850% for both samples, demonstrating clearly enhanced tenacity. We notice that an upturn point, which results from beginning of self-reinforcement effect, can be clearly distinguished in stress−strain curves for pure SEBS and SEBS/OBC blends. This effect mainly originates from soft-block crystallization or plastic deformation of the hard-block domains.43,44 As we know, according to some standard network theories such as neo-Hookean or Gaussian theories,45,46 more cross-linking netpoints usually correspond to a larger tensile modulus before E
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Macromolecules self-reinforcement. However, as shown in Figure 7a, the curves for SEBS and SEBS/OBC blend nearly overlap before the upturn point of SEBS, while dramatic difference emerges beyond this strain. The interesting results can be ascribed to the nature of blend system, which means that the original netpoints of PS domains and additional netpoints introduced by OBC crystals make different influence on mechanical properties. Before upturn point of SEBS, the netpoints of PS domains show a more important effect on tensile behaviors. While after beginning of self-reinforcement, the additional netpoints of OBC crystals may bear some plastic deformation of PS domains, leading to longer elongation at break, and with combination of plastic deformation of PS domains and OBC particle crystals, the ultimate tensile strength improves as a result. At 60 °C, the results are quite similar. Pure SEBS breaks at a strain of 330%, while with addition of 10% or 15% OBC, the elongation at break turns beyond 520% (the maximum testing elongation for this apparatus). The dramatically improved tenacity at 60 °C can be closely related to the additional netpoints introduced by OBC particle crystals, which make the network more stable when exposed to deformations at higher temperature. As for OBC-25, the elongation at break is lower than OBC-10 and OBC-15 at both room temperature and 60 °C. This may be ascribed to large amount of bulk OBC crystals, bringing more defects to the networks and resulting in decreased tensile property. Cyclic stress−strain tests were performed to examine the recovery behaviors and stability of dissipative capability.47−50 As shown in Figure 8, pure SEBS exhibits excellent recovery performance with only 10.6% unrecoverable strain after stretched to 100%. We also notice that the recovery behaviors are quite stable. The curves for the five continuous tests nearly superpose, and unrecoverable strain increases slightly to 13.6% after five cycles. The excellent recovery property of SEBS is reserved to a great extent after introduction of OBC. The unrecoverable strain nearly keeps unvaried for these samples. The largest unrecoverable strain is observed for OBC-25 with 11.7%, only 1% higher than pure SEBS. The stability of recovery performance is quite good for the blends as well. The unrecoverable strain increases from 11.0 to 14.5% for OBC-10 and 11.4 to 15.2% for OBC-15 after five cycles. For comparison, the stability decreases to some extent when the OBC content is elevated to 25%. The value increases to 16.5% after cyclic tests. In general, the results demonstrate that our blending approach can improve the tenacity of SEBS with maintenance of its critical elasticity, and this phenomenon is closely correlated to the reserved network structures. As shown by SAXS, introduction of OBC adds new physical netpoints to SEBS, while bringing little influence to the initial aggregation state of SEBS. Therefore, the intrinsic elasticity of SEBS, which originates from its physical networks, is preserved in blends. We also perform AFM observation of samples after stretching to confirm the stable recovery behaviors, and the results are exhibited in Figure 9. A large amount of small crystal particles, which can be regarded as additional netpoints for the elastomeric blends, can be distinguished for both OBC-10 and OBC-25, while there are more bulk crystals with larger size for OBC-25. Before deformation, the crystals exhibit a uniform and random distribution. After being stretched to 100% for the first time, it can be noticed that the arrangement of crystals exhibit slightly orientation from upper right to lower left as shown in Figure 9b,e. The orientation becomes more dramatic after repeated stretching to 100% for four times. Crystals clearly
Figure 9. AFM modulus images of (a) OBC-10 before deformation, (b) OBC-10 after being stretched to 100% for the first time, (c) OBC10 after being stretched to 100% for the fourth time, (d) OBC-25 before deformation, (e) OBC-25 after being stretched to 100% for the first time, and (f) OBC-25 after being stretched to 100% for the fourth time.
exhibit arrangement from upper left to lower right in Figure 9c,f. The oriented arrangement of crystals results from exposure to deformation. While we find that the deformation does not destroy or deform these crystal particles, it does not induce aggregation or segregation of these crystals as well. Although the morphology of SEBS cannot be distinguished directly, we can observe that the network composed of additional crystal netponits stays intact over many cycles, which indicates stable general network structure when exposed to deformation and repeatable recovery behaviors. The rheological behaviors of samples were explored by dynamic frequency sweeps. The strain was sufficiently small to ensure in the linear viscoelastic regime. The dynamic frequency sweeps of the samples at 200 °C are shown in Figure 10. It can be found that the storage modulus of SEBS is always much higher than loss modulus through the testing frequency, indicating largely preserved elasticity even at 200 °C. While actually, this property is unfavorable for processing and molding. With increase of OBC content, the storage modulus decreases continuously and becomes closer to the loss modulus. In this way, the plasticity of the blends increases correspondingly. The viscosity in Figure 10b confirms the results. With rise of OBC content, the viscosity decreases continuously, suggesting better fluidity and processing ability.
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CONCLUSION The crystalline morphologies and mechanical properties of SEBS were regulated by blending with OBC, which possesses unique crystalline multiblock architecture. During cooling from the melt, the hard blocks of OBC that entangle with SEBS generate small particle crystals with diameter around 10 nm. F
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Figure 10. Frequency dependence of (a) storage and loss modulus and (b) viscosity of SEBS and blends. (5) Parker, A. J.; Rottler, J. Molecular Mechanisms of Plastic Deformation in Sphere-Forming Thermoplastic Elastomers. Macromolecules 2015, 48, 8253−8261. (6) Fredrickson, G. H.; Bates, F. S. Dynamics of Block Copolymers: Theory and Experiment. Annu. Rev. Mater. Sci. 1996, 26, 501−550. (7) Adhikari, R.; Michler, G. H. Influence of Molecular Architecture on Morphology and Micromechanical Behavior of Styrene/Butadiene Block Copolymer Systems. Prog. Polym. Sci. 2004, 29, 949−986. (8) Aggarwal, S. L. Structure and Properties of Block Polymers and Multiphase Polymer Systems - Overview of Present Status and Future Potential. Polymer 1976, 17, 938−956. (9) Sierra, C. A.; Galan, C.; Fatou, J. G.; Parellada, M. D.; Barrio, J. A. Thermal and Mechanical Properties of Poly-(styrene-b-ethylene-cobutylene-b-styrene) Triblock Copolymers. Polymer 1997, 38, 4325− 4335. (10) Ghosh, S.; Khastgir, D.; Bhowmick, A. K. Phase Modification of SEBS Block Copolymer by Different Additives and Its Effect on Morphology, Mechanical and Dynamic Mechanical Properties. J. Appl. Polym. Sci. 1998, 67, 2015−2025. (11) Kim, J. K.; Paglicawan, M. A.; Balasubramanian, M. Viscoelastic and Gelation Studies of SEBS Thermoplastic Elastomer in Different Hydrocarbon Oils. Macromol. Res. 2006, 14, 365−372. (12) Grein, C.; Gahleitner, M.; Bernreitner, K. Mechanical and Optical Effects of Elastomer Interaction in Polypropylene Modification: Ethylene-Propylene Rubber, Poly-(ethylene-co-cctene) and Styrene-Butadiene Elastomers. eXPRESS Polym. Lett. 2012, 6, 688− 696. (13) Matsen, M. W. Equilibrium Behavior of Asymmetric ABA Triblock Copolymer Melts. J. Chem. Phys. 2000, 113, 5539−5544. (14) Adhikari, R.; Godehardt, R.; Lebek, W.; Weidisch, R.; Michler, G. H.; Knoll, K. Correlation between Morphology and Mechanical Properties of Different Styrene/Butadiene Triblock Copolymers: A Scanning Force Microscopy Study. J. Macromol. Sci., Part B: Phys. 2001, 40, 833−847. (15) Adhikari, R.; Michler, G. H.; Goerlitz, S.; Knoll, K. Deformation Behavior of Styrene-Butadiene Block Copolymers. III. Binary Blends of Asymmetric Star Block Copolymer with General-Purpose Polystyrene. J. Appl. Polym. Sci. 2004, 92, 1208−1218. (16) Higuchi, T.; Sugimori, H.; Jiang, X.; Hong, S.; Matsunaga, K.; Kaneko, T.; Abetz, V.; Takahara, A.; Jinnai, H. Morphological Control of Helical Structures of an ABC-Type Triblock Terpolymer by Distribution Control of a Blending Homopolymer in a Block Copolymer Microdomain. Macromolecules 2013, 46, 6991−6997. (17) Abetz, V.; Goldacker, T. Formation of Superlattices Via Blending of Block Copolymers. Macromol. Rapid Commun. 2000, 21, 16−34. (18) Tureau, M. S.; Rong, L.; Hsiao, B. S.; Epps, T. H. Phase Behavior of Neat Triblock Copolymers and Copolymer/Homopolymer Blends near Network Phase Windows. Macromolecules 2010, 43, 9039−9048. (19) Hashimoto, T.; Tanaka, H.; Hasegawa, H. Ordered Structure in Mixtures of a Block Copolymer and Homopolymers. 2. Effects of Molecular-Weights of Homopolymers. Macromolecules 1990, 23, 4378−4386.
With corresponding soft blocks still entangled with EB blocks, these particles can be regarded as new netpoints for the networks of SEBS. It is also found that the introduction of OBC does not greatly changes the original structure of SEBS as shown by SAXS. Because of the interesting interaction between OBC and SEBS, the blend exhibits dramatically elevated elongation at break both at room temperature and comparatively high temperature, while the elasticity suffers limited influence. In addition, the rheological properties could be conveniently tuned through changing OBC content as well. This work may provide a new direction to regulate the morphology and property of triblock elastomers with physical network structure by the blending approach.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.6b01441. Figure S1 (PDF)
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AUTHOR INFORMATION
Corresponding Author
*Tel +86 21 65643735; Fax +86 21 6564 0293; e-mail jcfeng@ fudan.edu.cn (J.F.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the Natural Science Foundation of China (21574029, 51373042) and the Science and Technology Planning Project of Guangdong Province of China (2014B090901009). The experiments are partially carried out in Shanghai Synchrotron Radiation Facility (Project No. Z14sr0051).
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DOI: 10.1021/acs.macromol.6b01441 Macromolecules XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.macromol.6b01441 Macromolecules XXXX, XXX, XXX−XXX
