SIS Triblock Research Articles

Synthesis of high-vinyl isoprene and styrene triblock copolymers via anionic polymerization with difunctional t-BuLi initiator

Triblock copolymers poly(styrene)-block-poly(isoprene)-block-poly(styrene) (PS-b-PI-b-PS, SIS) and poly(isoprene)-block-poly(styrene)-block-poly(isoprene) (PI-b-PS-b-PI, ISI) with different vinyl structure contents were successfully synthesized by anionic polymerization using a difunctional t-BuLi initiator. The difunctional t-BuLi initiator was prepared from tert-butyllithium (t-BuLi) and 1,3-diisopropenylbenzene, and characterized by 1H NMR, 13C NMR, DEPT135, 7Li NMR, and GC–MS analysis. According to the results of 1H NMR, 13C NMR, and 2D HSQC analysis, the contents of 1,2- and 3,4-addition (vinyl group) structures for PI in SIS and ISI were in the range of 3.7%–94.6%, and depended on the reaction temperature and amount of tetrahydrofuran (THF) added. The Mn and PDI of SIS and ISI obtained by GPC were in the ranges of 13,400–281,000 Da and 1.09–1.24, respectively. The presence of two glass transition temperatures (Tg) on the DSC curve indicated microphase separation of the PI and PS domains. The low Tg was attributed to the PI domain, which was correlated with the vinyl group content in the block copolymer. For vinyl group contents of 6.9% and 94.6% in the SIS triblock copolymer, and 6.6% and 94.2% in the ISI triblock copolymer, the corresponding Tg values of the PI block were −64 °C and 12 °C, and −62 °C and 17 °C, respectively.

Modification of bitumen emulsion via heterocoagulation with SIS triblock copolymer latex

ABSTRACTBitumen emulsions have often been modified by styrene–butadiene rubber latex. The modified bitumen can have excellent low‐temperature cracking resistance, but rutting resistance at high temperature still remains poor. In the current work, for the first time, a stable poly(styrene‐b‐isoprene‐b‐styrene) (SIS) triblock copolymer latex is synthesized by reversible addition–fragmentation transfer (RAFT) emulsion polymerization. Based on this, a simple heterocoagulation process is developed to prepare the bitumen emulsions modified by SIS. The heterocoagulation results in hybrid particles of SIS shell and bitumen core. With addition of 5 wt % SIS, a continuous polymer‐rich phase could be formed in the modified bitumen once the modified emulsion was broken down. The bitumen modified by 5 wt % SIS shows a significant increase in complex modulus at high temperature and a significant decrease in loss tangent, suggesting excellent resistance to rutting at high temperature, which is consistent with the significant increase in softening point from 41 °C for the base bitumen up to 64 °C. Meanwhile, the ductility at 5 °C of the modified bitumen is also dramatically increased from 1.4 cm for the base bitumen to 40 cm, indicating the low‐temperature cracking resistance should also be much enhanced. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45510.

Vitrification and plastic flow in transient elastomer networks

We investigate how the crossover temperature of the elastic-plastic transition, the ‘vitrification point’ Tv, changes under load for isotropic vitrimers and exchangeable liquid crystal elastomers (xLCEs), using the thermoplastic SIS triblock polymer as a reference. In all these cases, the elastic network cross-links are transient: physical micro-phase separation in SIS and covalent transesterification bonds in vitrimers. From the analysis of SIS we define Tv as the point when entropic rubber-elasticity contraction due to heating under load turns into the irreversible plastic extension due to cross-links breaking and reforming. In xLCEs, the response to mechanical stress is heavily influenced by the smectic liquid-crystalline order, which makes the material much stiffer than normal rubbery networks, and also leads to the shape-memory effect across the smectic-isotropic transition point. The vitrification in the isotropic phase of xLCE, and in isotropic vitrimers, was found to be independent of stress, which can be attributed to the thermal activity of the catalyst determining Tv and it not being mechanically coupled to the elastic network. Beyond Tv, with increasing stress the plastic extension rapidly increases with temperature, as cross-link dynamics becomes more apparent.

Influence of block sequence and molecular weight on morphological, rheological and dielectric properties of weakly and strongly segregated styrene-isoprene triblock copolymers

Abstract In this work, morphological, thermal, viscoelastic and dielectric properties of triblock copolymers consisting of styrene (S) and isoprene (I) blocks are discussed. SIS and ISI triblock copolymers were synthesized by sequential anionic polymerization, three of them exhibiting molecular weights below the entanglement molecular weight Me, three of them exhibiting molecular weights in the order of Me and two of them exhibiting molecular weights above Me. The objective of this work is the investigation of the influence of molecular weight and block sequence on relaxation of the block copolymer chains. Morphological investigations using small angle X-ray scattering and transmission electron microscopy studies reveal that a larger molecular weight is associated with a more pronounced microphase separation. The presence of two glass transition temperatures reveals microphase separation of the PI and PS blocks. The Fox-Flory equation was applied in order to describe the molecular weight dependence of the glass transition temperature of the polyisoprene and the polystyrene blocks. The analysis of rheological data reveals a Maxwell fluid behavior for the weakly segregated block copolymers, whereas for the strongly segregated block copolymers a pronounced elastic behavior at low frequencies of small amplitude shear oscillations was observed. In the intermediate regime of molecular weight, a complex viscoelastic behavior appears. The plateau modulus G N o is influenced by the sequence of the PS and the PI blocks (SIS or ISI). Our analysis of segmental and normal mode relaxation in dielectric spectroscopy experiments show that the relaxation processes are strongly influenced by the block sequence (PI blocks tethered at one or both ends) and the molecular weight. As a result, the block sequence in triblock copolymers influences dynamical properties in the glassy state and in the melt.

Structural origins of mechanical properties and hysteresis in SIS triblock copolymers/polystyrene blends with spherical morphology

The mechanical response and the corresponding microstructure of polymer blends composed of styrene-isoprene-styrene block copolymer and deuterated polystyrene are studied via in situ small-angle neutron scattering (SANS) measurements during intermittent uniaxial extension. The initial blend morphologies consist of spherical PS glassy domains arranged in body-centered cubic (BCC) lattices. The spheres rearrange affinely with the macroscopic deformation up to Hencky strains ~0.35. Larger deformation is mechanically characterized by yield and strain hardening. In this regime, SANS measurements reveal a transition from a BCC crystal lattice to chevron-like patterns. Using electron microscopy, we found that the chevrons arise from a real-space structure described as spheres that have been stretched along one axis and aligned parallel to one another. Such configuration is unstable and reverts to BCC structure after stress release. After unloading the blends, remnant nano-deformation is observed, which is fully relaxed only in the transverse direction after more than 10 h. Permanent damage of the internal structure along the stretching direction impedes the full recovery of the initial sphere configuration.

Functionalised SIS triblock copolymer elastomer and its nanocomposites: synthesis and characterisation

Polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer was modified into an epoxidised version (ESIS) using performic acid. The ESIS was further acrylated to prepare the acrylated version (ASIS). The nanocomposites of each sample (SIS, ESIS and ASIS) were prepared using boehmite nanofiller via solution casting, which were characterised by Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). The TEM investigations revealed that the epoxidation of the diene block enhanced the dispersion of the nanofiller in polymer matrix, which may be attributed to the improved compatibility between alkybenzene sulphonic acid coated inorganic filler and polar modified middle block of the copolymer. The segregation of the nanoparticles towards the interface of different microscopically segregated polymer domains was observed in the acrylated block copolymer based nanocomposite implying the incomplete acrylation of the block copolymer, which might segregate from the bulk unmodified or partially modified polymer.

Ordering of Sphere Forming SISO Tetrablock Terpolymers on a Simple Hexagonal Lattice

Hexagonally ordered spherical and cylindrical morphologies (P6/mmm and P6/mm space group symmetries) have been identified in bulk poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) (SISO) tetrablock terpolymers. These materials were synthesized by adding up to 32% by volume O blocks to a parent hydroxy-terminated SIS triblock copolymer containing 40% S by volume, and the resulting morphologies were characterized by small-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry and dynamic mechanical spectroscopy. Disordered, spherical and cylindrical phases were documented with increasing O content, where both ordered states exhibit hexagonal symmetry. Theoretical calculations based on a numerical self-consistent field theory for polymers provide crucial insights into the molecular configurations associated with these morphologies. These results offer a new approach to independently control domain shape and packing in block copolymer melts through manipulation of the ma...

Stress–Strain Behavior, Elastic Recovery, Fracture Points, and Time–Temperature Superposition of an OOT-Possessing Triblock Copolymer

The microphase-separated structures of block copolymers have been widely studied to understand the complex mechanism and the comprehensive framework of the microphase separation of the copolymers, which depended primarily upon the copolymer composition, the molecular weight, and temperature. In this work, the morphology and the mechanical properties of a SIS triblock copolymer with 18.3 wt % of polystyrene (Vector 4111) were investigated. Vector 4111 was structurally quite unique in the sense that it possessed two order–order transitions at different temperatures and an order–disorder transition at high temperature. The different microstructures in the different phases of Vector 4111 were obtained by annealing at different temperatures, confirmed by AFM and SAXS: the hexagonally aligned cylindrical phase was obtained when annealed below 185 °C, the spherical phase adopting a body-centered cubic (BCC) arrangement was formed at 185 °C < T < 215 °C, the misaligned spherical phase was obtained at 215 °C < T <...

Surface Property and Compatibility of Poly(styrene-isoprene-styrene) Triblock Copolymer/Tackifier Blend System

The frictional forces between pressure sensitive adhesives (PSAs) and a probe tip were measured with a scanning probe microscopy (SPM). A peak appeared in the scanning rate-frictional force curve shifted to a lower scanning rate with decreasing temperature. In the case of the miscible system of isoprene matrix of SIS base polymer, the tendency of a peak to shift to a lower scanning rate was observed with increasing tackifier content; however, in the case of the immiscible system of styrene domain of SIS base polymer, no remarkable shift was observed. The frictional force is influenced by viscoelastic properties of the PSA which systematically changed with miscibility. In this study, it is aimed to clarify the correlation between the observation of phase structure and the behavior of surface rheology by using two kinds of tackifiers that have different miscibility with the polyisoprene phase or the polystyrene phase of SIS triblock copolymer.

Importance of Molecular Coupling for Mechanical Performance of Block Copolymer Compounds

AbstractMixtures of polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) triblock copolymer and various styrenic block copolymers (having diblock and triblock architectures) as well as polystyrene homopolymer (PS) were prepared via solution blending to determine the influence of molecular coupling on the large strain mechanical performance of the block copolymers. The techniques used were transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) for the morphological characterization and uniaxial tensile testing for the determination of mechanical properties. In the block copolymer blends, it was possible to tailor the mechanical properties as long as the molecular coupling was present among the outer polystyrene blocks. The mechanical performance of the triblock copolymer was found to deteriorate by the presence of dangling chains in the microphase‐separated domains. In the blends comprising an SIS triblock copolymer and polystyrene homopolymers, the macrophase‐separated compounds containing PS having molar mass exceeding the entanglement molar mass showed the optimum mechanical properties. The observed mechanical behaviour has been correlated with the fracture surface morphology of the corresponding blends.

Phase Behavior of Binary Blends of High Molecular Weight Diblock Copolymers with a Low Molecular Weight Triblock

Binary blends of four different high molecular weight poly(styrene-b-isoprene) (SI) diblock copolymers with a lower molecular weight poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer were prepared, and their morphology was characterized by transmission electron microscopy and ultra-small-angle X-ray scattering. All the neat block copolymers have nearly symmetric composition and exhibit the lamellar morphology. The SI diblock copolymers had number-average molecular weights, Mn, in the range 4.4 × 105−1.3 × 106 g/mol and volume fractions of poly(styrene), ΦPS, in the range 0.43−0.49, and the SIS triblock had a molecular weight of Mn ∼ 6.2 × 104 g/mol with ΦPS = 0.41. The high molecular weight diblock copolymers are very strongly segregating, with interaction parameter values, χN, in the range 470−1410. A morphological phase diagram in the parameter space of molecular weight ratio (R = Mndiblock/1/2Mntriblock) and blend composition was constructed, with R values in the range between 14 and 43, wh...

리빙 음이온 중합법에 의한 SIS Triblock 공중합체의 제조 및 유류 고형화 특성

【SIS triblock copolymers, one of the major raw materials of oil gelling agent, were synthesized by living anionic polymerization and the resultant copolymers formed with various shapes and sizes were used to examine their oil gelling capacities. Coupling method was adapted to form final triblock products from diblock living polymers. Prior to polymerization, the impurities in monomers and solvents were throughly removed by killing technique. We experimentally investigated the effects of operating parameters of synthesis and forming of SIS triblock copolymers on oil gelling capacity. The photocatalytic decomposition of SIS triblock copolymer under ultraviolet circumstance was also investigated and it is found that the addition of P-25 enhances the photocatalytic decomposition.】

Effect of Loop/Bridge Conformation Ratio on Elastic Properties of the Sphere-Forming ABA Triblock Copolymers: Preparation of Samples and Determination of Loop/Bridge Ratio

To determine the loop/bridge ratio of an ABA triblock copolymer, dynamic viscoelastic measurements were carried out using a polystyrene-block-polyisoprene-block-polystyrene triblock copolymer (SIS), a cyclic SI diblock copolymer (cyclic-SI), and a polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) triblock copolymer (SIP), which were carefully synthesized by the anionic polymerization technique. The three copolymers show similar microphase-separated structures having spherical domains of S and/or P. By blending cyclic-SI and SIS, samples having various loop/bridge conformation ratios were prepared, and the SIP sample was also used as the 100% bridged reference sample. From the dynamic elongational measurements for a series of blended samples and SIP, it was confirmed that the storage modulus (E‘) is the highest for the SIP, and it linearly decreases with increase of cyclic-SI content. From quantitative analysis of the results, we determined that the bridge fraction, φbridge, in SIS triblock copoly...

A block copolymer nanotemplate for mechanically tunable polarized emission from a conjugated polymer

A polymer blend system consisting of polystyrene grafted onto poly ( p-phenylene ethynylene) (PS- g-PPE) and poly (styrene- block-isoprene- block-styrene) triblock copolymer (SIS) yields highly polarized emission due to the unidirectional alignment of the PPE molecules. During the roll casting, the triblock copolymer microphase separates and creates unidirectionally aligned PS cylindrical microdomains in the rubbery PI matrix. PPE, a fluorescent conjugated polymer, was grafted with polystyrene (PS) side chains that enabled sequestration and alignment of these rigid backbone emitter molecules into the PS microdomains of the SIS triblock copolymer. Deforming the thermoplastic elastomer in a direction perpendicular to the orientation direction of the cylinders causes rotation of the PS cylinders and the PPE emitter molecules and affords tunable polarized emission due to re-orientation of the PPE containing PS cylinders as well as film thinning from Poisson effect.

Effects of Triblock Copolymer Architecture and the Degree of Functionalization on the Organoclay Dispersion and Rheology of Nanocomposites

The effects of triblock copolymer architecture (ABA-type vs ABC-type) and the degree of functionalization on the organoclay dispersion in nanocomposites were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and linear dynamic viscoelasticity. For the study, a lamella-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and a homogeneous polyisoprene-block-polystyrene-block-polybutadiene (ISB triblock) copolymer were synthesized via sequential anionic polymerization. Subsequently, the polyisoprene block of the SIS triblock copolymer was hydroxylated yielding an SIOHS triblock copolymer, and the polybutadiene block of the ISB triblock copolymer was hydroxylated yielding an ISBOH triblock copolymer. The degree of hydroxylation in both SIOHS and ISBOH triblock copolymers was varied. Both the unfunctionalized (SIS and ISB) and functionalized (SIOHS and ISBOH) triblock copolymers were used to prepare nanocomposites with two different types of organ...

Experimental and Self-Consistent-Field Theoretical Study of Styrene Block Copolymer Self-Adhesive Materials

This work addresses thermodynamic and mechanical properties of styrene block copolymer (SBC) self-adhesive materials. Mixtures of polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymers with resin and their blends with polystyrene-block-polyisoprene (SI diblock) copolymers were investigated experimentally and theoretically. The experiments involved small-angle X-ray scattering, atomic force microscopy, and tensile measurements, while the theoretical analysis invoked a mesoscopic representation of SBC materials combined with a continuum, 3D real-space self-consistent-field (SCF) approach. The calculations predict that the SBC systems should become microphase separated, with PS-rich spherical domains forming a bcc lattice in SIS triblock/SI diblock blends and in SIS triblock/resin systems with low resin content (20 wt %), while at high (60 wt %) resin content a disordered structure of PS-rich domains is expected. Extensive comparisons of SCF predictions concerning the type and the geometric characteristics of the morphologies obtained, the composition profiles, and the effect of diblock and resin content on the long-range space ordering of the PS-rich domains are performed against the experimental data. SCF theory predicts that approximately 79% of SIS molecules are connecting different PS-rich domains (i.e., are forming bridges) in SIS/SI blends, almost independently of the SI diblock content. The SCF results are combined with a slip tube model of rubber elasticity to predict the elastic behavior of SBC materials. In particular, the bridging properties are used to estimate the PS-rich domain cross-linking contribution, Gc, to the total shear modulus. The entanglement contribution, Ge, is evaluated from experimental and theoretical results reported in the literature concerning the properties of entanglements. The predicted stress−strain curves are in good qualitative agreement with the tensile experimental data for small values of strain.

Effects of Sample Preparation Method and Thermal History on Phase Transition in Highly Asymmetric Block Copolymer: Comparison with Symmetric Block Copolymers

Symmetric and highly asymmetric polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymers were synthesized via sequential anionic polymerization using difunctional initiator, and symmetric and highly asymmetric polystyrene-block-polyisoprene (SI diblock) copolymers were also synthesized using monofunctional initiator. The molecular weight of the triblock copolymer was approximately twice that of the diblock copolymer. The phase transition temperatures of the SIS triblock and SI diblock copolymers were determined using oscillatory shear rheometry and small-angle X-ray scattering (SAXS), respectively. It has been found that the sample preparation methods (solvent casting vs compression molding) and annealing conditions employed have a profound influence on the “apparent” phase transition temperatures of the highly asymmetric block copolymers that undergo order−disorder transition (ODT) involving lattice disordering/ordering transition (LDOT) followed by the demicellization/micellization tra...

Phase Transition in End-Functionalized Polystyrene-block-polyisoprene-block-polystyrene Copolymers

Phase transition in polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymers end-capped with carboxylic acid group (-COOH) or sodium carboxylate group (-COONa) was investigated using oscillatory shear rheometry and transmission electron microscopy (TEM). For the study, three SIS triblock copolymers having almost an equal block length ratio, but varying molecular weights, were synthesized via sequential anionic polymerization. The number-average molecular weights of the three block copolymers synthesized were 1.8 x 10 4 g/mol (SIS1), 2.3 x 10 4 g/mol (SIS2), and 3.4 x 10 4 g/mol (SIS3). It was found that both SIS1 and SIS2 were homogeneous block copolymers, while SIS3 had lamellar microdomains, and it had an order-disorder transition temperature (T ODT ) of 180 °C. Each of the triblock copolymers was end-capped with a -COOH group to obtain SIS-COOH using high-purity, gaseous carbon dioxide. Subsequently, part of the SIS-COOH was neutralized with sodium hydroxide to obtain SIS-COONa. It was found that SIS1-COOH, SIS1-COONa, and SIS2-COOH remained homogeneous, while SIS2-COONa microphase-separated into a lamella-forming triblock copolymer, as determined from TEM, which has a Tool of 123 °C as determined from oscillatory shear rheometry. The T ODT of lamella-forming SIS3 was found to increase from 180 to 182 °C after it was end-capped with a -COOH group and to 228 °C after it was end-capped with a -COONa group. Cloud point measurements show that (i) the upper critical solution temperature (UCST) of the mixtures composed of polyisoprene (PI) and polystyrene (PS) end-capped with a -COONa group, PI/(PS-COONa) mixtures, is much higher than that of the mixtures composed of PI and PS end-capped with a -COOH group, PI/(PS-COOH) mixtures, and PIPS mixtures, and (ii) the UCST of PI/(PS-COOH) mixtures is only slightly higher than that of PI/PS mixtures. It is concluded that the formation of lamellar microdomains in SIS2-COONa from homogeneous SIS2 after it was end-capped with a -COONa group and a very high T ODT observed for SIS3-COONa are attributable to strong ionic associations and significantly increased repulsive segment-segment interactions between the PI and PS-COONa phases in the block copolymers.

Phase Transition from Disordered Sphere to Hex-Cylinder via Transient Ordering into Bcc-Sphere in SIS Triblock Copolymer

We have investigated the ordering processes from the disordered-sphere phase (designated hereafter disordered sphere), where spherical microdomains exist but they have only a short-range liquidlike order, to the phase of hexagonally packed cylindrical microdomains (designated hereafter hex-cylinder), induced by the temperature drop (T-drop). The block copolymer studied is a compositionally asymmetric polystyrene-block-polyisoprene-block-polystyrene triblock copolymer and forms disordered sphere above the order−disorder transition temperature involving the lattice disordering−ordering transition temperature, TODT or TLDOT, spheres in a body-centered-cubic lattice (designated hereafter bcc-sphere) below TLDOT but above the order−order transition (OOT) temperature, TOOT, and hex-cylinder below TOOT. The ordering processes induced by T-drop were explored in situ and at a real time by using time-resolved small-angle X-ray scattering, and the transient microdomain structures developed during the ordering processes were observed by a transmission electron microscope and a polarized optical microscope for specimens rapidly frozen below the glass transition temperature at particular times in the ordering processes. We confirmed that the freeze-in process does not change the long-range order of the system. When the specimen is deeply quenched into the temperature range below TOOT, hex-cylinder is directly formed from disordered sphere. However, when the specimen is shallowly quenched below TOOT, bcc-sphere is first formed from disordered sphere and fills the whole sample space. Then bcc-sphere is transformed into hex-cylinder. This striking ordering process first involves the ordering into a metastable structure followed by the OOT into a stable structure.

Phase Transitions in Sphere-Forming Polystyrene-block-polyisoprene-block-polystyrene Copolymer and Its Blends with Homopolymer

Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shear rheometry, transmission electron microscopy, and small-angle X-ray scattering (SAXS). For the investigation, a commercial grade of high-molecular-weight SIS triblock copolymer (Vector 4113, Dexco Polymers) and a low-molecular-weight SIS triblock copolymer (SIS-100) synthesized in our laboratory were used. It is found from oscillatory shear rheometry and SAXS that both Vector 4113 and SIS-100 undergo order−disorder transition (ODT) having a characteristic feature of lattice disordering/ordering transition (LDOT) of spheres, giving rise to a phase consisting of micelles with short-range liquidlike order at thermal equilibrium above ODT and demicellization/micellization transition (DMT), as a pseudo phase transition, giving rise to a micelle-free phase with only thermal composition fluctuations. The LDOT temperature (TLDOT...