Preparation and stress–strain properties of SBS and SIS block polymers made with dilithium initiators

ABA-type block polymers of styrene (monomer A) and isoprene or butadiene were prepared using two commercially available dilithium adducts of isoprene as initiators. One (DiLi-1) was predominantly dilithio diisoprene and contained a small amount of dimethyl ether (ether/Li > 1.0). The second (DiLi-1 C.E.) was a higher molecular weight version of DiLi-1, containing about seven isoprene units per molecule. It contained only a trace of dimethyl ether (ether/Li < 0.1). Polymers were made by charging all of the monomers at the start of the reaction. The diene polymerized first, incorporating some styrene. When the diene was consumed, the difunctional polymer chains then added a block of nearly pure polystyrene at each end. Thus an ABA-type polymer was synthesized in one step. These polymers show the usual behavior of pseudo-vulcanized elastomers. Their stress–strain curves are given. The SBS polymers had the higher tensile strengths. None had tensile strengths as high as SBS or SIS polymers made with n- or sec-butyllithium. It was shown that the diene blocks contain appreciable amounts of styrene. This leads to more compatibility between the A and B blocks; it also shortens the styrene blocks compared to the theoretical lengths of “pure” blocks. Both effects can lead to loss of tensile strength. Microstructures of the diene homopolymers made with these initiators are also given.     

Preparation and stress–strain properties of ABA-type block polymers of styrene and isoprene or butadiene

Several series of ABA-type “tapered” block polymers of styrene (monomer A) with isoprene or butadiene were prepared with the use of n-butyllithium or sec-butyllithium as initiators in benzene solution. The stress-strain curves of the raw polymers are reported, showing that many of them behave at ambient temperature like vulcanized elastomers. These polymers consist, however, of completely linear chains, with no chemical crosslinks between them; they are thermoplastic, can be easily molded, and are soluble in common solvents. Hence, they may be classed as pseudo-crosslinked elastomers. Better stress-strain properties are obtained from polymers made with sec-butyllithium than with n-butyllithium; in turn, polymers from butadiene have better properties than those from isoprene. Stress–strain curves most closely resembling those of crosslinked elastomers are obtained in general from polymers containing about 30–45% styrene. It was found that AB-type block polymers have very poor tensile strengths and low elongations. The microstructures of polybutadienes and polyisoprenes of various molecular weights, prepared in benzene solvent with alkyllithium initiators, were also determined and compared with literature data for like polymers prepared in cyclohexane solvent.     

Effect of electron beam radiation on tensile and viscoelastic properties of styrenic block copolymers

The effect of electron beam (E‐beam) radiation on a series of styrenic block copolymers (SBCs) was investigated. These SBCs included newly developed poly(styrene‐block‐isoprene/butadiene‐block‐styrene) (SIBS), poly(styrene‐block‐butadiene‐block‐styrene) (SBS), and poly(styrene‐block‐isoprene‐block‐styrene) (SIS). The tensile properties, stress relaxation, molecular weight, and dynamical mechanical properties were studied. Generally, the crosslink density and tensile moduli of SBCs increased with increasing of E‐beam radiation dose. The tensile strength of SIBS and SIS was shown to first decrease at lower E‐beam radiation dose (<120 kGy) and then increase at higher radiation dose (>190 kGy). The tensile strength of SBS was significantly decreased at high E‐beam radiation dose (>190 kGy). This was attributed to the differences between entanglement before E‐beam radiation and the homogeneity of the crosslink network after exposure. POLYM. ENG. SCI., 54:2979–2988, 2014. © 2014 Society of Plastics Engineers     

A new difunctional anionic initiator soluble in non-polar solvents

The reaction between 1,5-diethenylnaphthalene and sec-butyllithium produces a new difunctional organolithium initiator which is soluble in non-polar solvents and effective in the synthesis of styrene-isoprene-styrene triblock copolymer. Monomodal molecular weight distributions are observed for block copolymers and styrene homopolymers. The microstructure of polyisoprene blocks is similar to those polymers initiated by butyllithium in the same solvent.     

PSA performances and viscoelastic properties of SIS‐based PSA blends with H‐DCPD tackifiers

Hotmelt pressure sensitive adhesives (PSAs) usually contain styrenic block copolymers like styrene–isoprene–styrene (SIS), SBS, SEBS, tackifier, oil, and additives. These block copolymers individually reveal no tack. Therefore, a tackifier is a low molecular weight material with high glass transition temperature (T_g), and imparts the tacky property to PSA. The SIS block copolymer with different diblocks was blended with hydrogenated dicyclopentadiene (H‐DCPD tackifier), which has three kinds of T_g. PSA performance was evaluated by probe tack, peel strength, and shear adhesion failure temperature. PSA is a viscoelastic material, so that its performance is significantly related to the viscoelastic properties of PSAs. We tested the viscoelastic properties by dynamic mechanical analysis and the thermal properties by differential scanning calorimeter to investigate the relation between viscoelastic properties and PSA performance. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2839–2846, 2006     

Morphology of pyrolyzed polystyrene–isoprene–styrene and polystyrene–butadiene–styrene block copolymers

The surface morphology of thermooxidative‐degraded polystyrene–isoprene–styrene (SIS) and polystyrene–butadiene–styrene (SBS) thermoplastic block copolymers were studied by scanning electron microscopy. Surface changes caused by heating the samples in a pyrolizer for 15 and 30 min were presented in different micrographs. The morphological changes occurring due to the formation of polar groups and their crossing linking during the thermooxidative degradation are discussed. Morphological study of these thermally degraded polymer samples show very good correlation with the thermodegradation results. The rate of thermodegradation is fast in case of SBS compared with SIS block copolymer. ©2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of styrene–isoprene–styrene,styrene–butadiene–styrene,and styrene–butadiene–rubber on the mechanical,thermal, rheological,and morphological properties of polypropylene/polystyrene blends

The mechanical, thermal, rheological, and morphological properties of polypropylene (PP)/polystyrene (PS) blends compatibilized with styrene–isoprene–styrene (SIS), styrene–butadiene–styrene (SBS), and styrene–butadiene–rubber (SBR) were studied. The incompatible PP and PS phases were effectively dispersed by the addition of SIS, SBS, and SBR as compatibilizers. The PP/PS blends were mechanically evaluated in terms of the impact strength, ductility, and tensile yield stress to determine the influence of the compatibilizers on the performance properties of these materials. SIS‐ and SBS‐compatibilized blends showed significantly improved impact strength and ductility in comparison with SBR‐compatibilized blends over the entire range of compatibilizer concentrations. Differential scanning calorimetry indicated compatibility between the components upon the addition of SIS, SBS, and SBR by the appearance of shifts in the melt peak of PP toward the melting range of PS. The melt viscosity and storage modulus of the blends depended on the composition, type, and amount of compatibilizer. Scanning electron microscopy images confirmed the compatibility between the PP and PS components in the presence of SIS, SBS, and SBR by showing finer phase domains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 266–277, 2003     

Morphology of pyrolysed polystyrene–isoprene–styrene and polystyrene–butadiene–styrene block copolymers

The surface morphology of thermooxidative degraded polystyrene–isoprene–styrene (SIS) and polystyrene–butadiene–styrene (SBS) thermoplastic block copolymers was studied by scanning electron microscopy. Surface changes caused by heating the samples in a pyrolyzer for 15 and 30 min were presented in different micrographs. The morphological changes occurring due to the formation of polar groups and their crosslinking during the thermooxidative degradation are discussed. Morphological study of these thermally degraded polymer samples shows very good correlation with the thermodegradation results. The rate of thermodegradation is fast in case of SBS when compared with SIS block copolymer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2549–2553, 2006     

Plasticization of nano‐CaCO3 in polystyrene/nano‐CaCO3 composites

The shear rheological properties of polystyrene (PS)/nano‐CaCO₃ composites were studied to determine the plasticization of nano‐CaCO₃ to PS. The composites were prepared by melt extrusion. A poly(styrene–butadiene–styrene) triblock copolymer (SBS), a poly(styrene–isoprene–styrene) triblock copolymer (SIS), SBS‐grafted maleic anhydride (SBS–MAH), and SIS‐grafted maleic anhydride were used as modifiers or compatibilizers. Because of the weak interaction between CaCO₃ and the PS matrix, the composites with 1 and 3 phr CaCO₃ loadings exhibited apparently higher melt shear rates under the same shear stress with respect to the matrix polymer. The storage moduli for the composites increased with low CaCO₃ concentrations. The results showed that CaCO₃ had some effects on the compatibility of PS/SBS (or SBS–MAH)/CaCO₃ composites, in which SBS could effectively retard the movement of PS chain segments. The improvement of compatibility, due to the chemical interaction between CaCO₃ and the grafted maleic anhydride, had obvious effects on the rheological behavior of the composites, the melt shear rate of the composites decreased greatly, and the results showed that nano‐CaCO₃ could plasticize the PS matrix to some extent. Rheological methods provided an indirect but useful characterization of the composite structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Structural morphology and properties of star styrene–isoprene–butadiene rubber and natural rubber/star styrene–butadiene rubber blends

Star styrene–isoprene–butadiene rubber (SIBR) was synthesized with a new kind of star anionic initiator made from naphthalene lithium and an SnCl₄ coupled agent. The relationship between the structure and properties of star SIBR was studied. Star block styrene–isoprene–butadiene rubber (SB‐SIBR), having low hysteresis, high road‐hugging, and excellent mechanical properties, was closer to meeting the overall performance requirements of ideal tire‐tread rubber according to a comparison of the morphology and various properties of SB‐SIBR with those of star random SIBR and natural rubber/star styrene–butadiene rubber blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 336–341, 2004     

Grafting of N‐carbamyl maleamic acid onto a styrene–butadiene–styrene copolymer

A styrene–butadiene–styrene block copolymer (SBS) was functionalized with N‐carbamyl maleamic acid (NCMA) using two peroxide initiators with the aim of grafting polar groups onto the molecular chains of the polymer. The influence of the concentration of benzoyl peroxide (BPO) and 2,5‐dimethyl, 2,5‐diterbuthylperoxihexane (DBPH) was studied. The concentration of peroxy groups ranged between 0.75 and 6 × 10^?4 mol % while the concentration of NCMA was constant at 1 wt %. The reaction temperature was chosen according to the type of peroxide employed, being 140°C for BPO and 190°C for DBPH. FTIR spectra confirmed that NCMA was grafted onto the SBS macromolecules. It was found that the highest grafting level was achieved at a concentration of peroxy groups of about 3 × 10^?4 mol %. Contact angle measurements were used to characterize the surface of the SBS and modified polymers. The contact angle of water drops decreased with the amount of NCMA grafted from 95°, the one corresponding to the SBS, to about 73°. T‐peel strength of polymer/polyurethane adhesive/polymer joints made with the modified polymers was larger than those prepared with the original SBS. The peel strength of SBS modified with 1.5 and 3 × 10^?4 mol % of peroxy groups from BPO were five times larger than that of the original SBS. The materials modified using BPO showed peel strengths higher than the ones obtained with DBPH. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4468–4477, 2006     

Studies on the electrospun submicron fibers of SIS and its mechanical properties

The submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Grafting of maleic anhydride onto styrene–butadiene–styrene triblock copolymer using supercritical CO2 as a swelling agent

Grafting of maleic anhydride (MA) onto styrene–butadiene–styrene triblock copolymer (SBS) was carried out by free radical polymerization using supercritical carbon dioxide (SC CO₂) as a solvent of MA and swelling agent of SBS. The effect of various factors such as monomer concentration, initiator concentration, SC CO₂ pressure, and reaction time on grafting ratio was studied. SBS and the product (SBS‐g‐MA) were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). GPC data showed that the molecular weight of SBS‐g‐MA is bigger than that of SBS. DSC testing indicated that the glass transition temperature (T_g) of SBS‐g‐MA is higher than that of SBS. By SEM photo, we can observe that some particles which contain more oxygen atom grew out from the surface of SBS‐g‐MA when grafting ratio reached at 5.6%, and the amount and diameter of particles increased with increasing of grafting ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4425–4429, 2006     

Formation of SBS thermoplastic block copolymer using hexamethyleneimine alkenyl lithium (N‐Li) initiator

Styrene and butadiene block copolymers (SBS) end functionalized with amino group at the initiating chain ends were synthesized using hexamethyleneimine alkenyl lithium (N‐Li) as initiator, tetrahydrofuran (THF) as polar modifier, and cyclohexane as solvent. By attaching a few number of butadiene molecules to N‐lithium hexamethyleneimine, a new N‐Li initiator that can effectively initiate the polymerization of SBS was obtained. ¹H NMR spectrums of the N‐Li initiator terminated by ethanol, end functionalized polystyrene, and SBS block copolymer proved the structure of N‐Li and its ability to initiate the polymerization of styrene and SBS block copolymer. Kinetics studies suggested that the polymerization rate of styrene in the first block reached the maximum when the ratio of THF/Li was increased to 5, while further increase of the ratio of THF/Li could not improve the polymerization rate. The molecular weight distribution (MWD) of SBS initiated by N‐Li varied with the ratio of THF/Li. The vinyl content of polybutadiene block increased by improving the ratio of THF/Li, while the content of cis‐1,4 and trans‐1,4 structures decreased. The vinyl content of end functionalized SBS was somewhat higher than that of SBS initiated by classical n‐butyllithium when other condition was the same. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 81–88, 2006     

In situ mid-IR and UV-visible spectroscopies applied to the determination of kinetic parameters in the anionic copolymerization of styrene and isoprene

In situ MIR and UV-visible spectroscopies have been combined in a set-up that has been used to monitor anionic (co)polymerizations of styrene and isoprene. This experimental set-up gives access to the simultaneous and real time concentrations of monomers and actives species during the polymerization, through optical fibers probes immersed in the reaction medium. This method allows fast, accurate and reproducible measurements of the rate constants of the (co)polymerizations investigated even if it does not resort to high vacuum. The influence of some experimental factors has been examined using this method. Among the kinetic parameters governing the (co)polymerization of styrene and isoprene initiated by sec-butyllithium, the influence of the nature of solvent was investigated. It appears that the only reaction to depend on the nature of the aromatic solvent (k_ss,toluene > k_{ss,ethylbenzene}) is the propagation step of styrene.     

Effect of triblock copolymers on homogeneity,mechanical properties and swelling behavior of IIR/SBR rubber blends

The present research concerns with the preparation and characterization of isobutylene isoprene/butadiene–styrene rubber (IIR/SBR) blends with different blend ratios, in the presence and absence of styrene–isoprene–styrene (SIS) and styrene–isobutylene–styrene (SiBS) triblock copolymers to be tested as compatibilizers. Effect of the triblock copolymers on the blend homogeneity was investigated with the aid of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) measurements. Characterization of the rubber blends was conducted by measuring the physico-mechanical properties after and before thermal aging, in presence and absence of the triblock copolymers. In addition, weight swell % in toluene, motor oil and brake fluid of the rubber blend vulcanizates was assessed. The incorporation of SIS and SiBS triblock copolymers improved the homogeneity of IIR/SBR blends as well as increased both tensile strength and elongation at break of the rubber blend vulcanizates. Of the entire blend ratios examined, IIR/SBR (25/75) blend containing SIS compatibilizer possessed the best physico-mechanical properties (12.6 MPa tensile strength and 425 % elongation at break) and (14 MPa tensile strength and 555 % elongation at break) after and before thermal aging, respectively. Utilization of SIS and SiBS triblock copolymers enhanced the thermal stability of IIR/SBR blend vulcanizates. Moreover, IIR/SBR blends of different blend ratios showed superior swelling resistance in the brake fluid. IIR/SBR (25/75) blend containing SIS compatibilizer and cured with CBS/ZDEC/S vulcanizing system possessed the best physico-mechanical properties (14.4 MPa tensile strength and 440 % elongation at break) and (16.5 MPa tensile strength and 610 % elongation at break) after and before thermal aging, respectively.     

Blends of i‐PP and SBS. II. Influence of in situ compatibilization on the mechanical properties

This article concerns the in situ compatibilization of immiscible isotatic polypropylene/styrene–butadiene–styrene triblock copolymer blends (i‐PP/SBS) by use of a reactive mixture. For this purpose, maleated PP (PP–MAH) and SBS (SBS–MAH) were used as functionalized polymers and 4,4′‐diaminediphenylmethane was used as a coupling agent between maleated polymers, resulting in a graft copolymer. Binary blends of i‐PP/SBS, nonreactive ternary blends of i‐PP/PP–MAH/SBS, and reactive ternary blends of i‐PP/PP–MAH/SBS–MAH with varying diamine/anhydride molar ratios were prepared. The mechanical properties of the blends were determined by tensile and impact‐resistance tests. The optimum improvement in the mechanical properties was found when the diamine/anhydride molar ratio in the ternary reactive blends was 0.5/1. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 516–522, 2003     

High‐speed photocrosslinking of thermoplastic styrene–butadiene elastomers

Photoinitiated thiol/ene polymerization was used to crosslink a triblock styrene/butadiene/styrene (SBS) polymer of low vinyl content (8%). The crosslinking process was followed by infrared spectroscopy (loss of unsaturation), insolubilization, swelling, and hardness measurements. The photogenerated thiyl radicals react with both the vinyl and the 2‐butene double bonds of the copolymer. Concentrations of less than 1 wt % in the trifunctional thiol crosslinker and in the acylphosphine oxide photoinitiator proved to be sufficient to create, within 0.5 s, a permanent chemical network in the elastomeric phase. This UV‐curing technology was successfully applied to crosslink rapidly commercial SBS–Kraton® thermoplastic elastomers. It proved also effective in the case of the much less reactive triblock styrene/isoprene/styrene (SIS) polymer which contains no vinyl double bonds. The thiol/ene polymerization was shown to be a much more efficient process to crosslink SBS and SIS thermoplastic elastomers than was the copolymerization of the rubber double bonds with a diacrylate monomer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1902–1912, 2000     

Morphology and rheological behavior of maltene–polymer blends. I. Effect of partial hydrogenation of poly(styrene‐block‐butadiene‐block‐styrene‐block)‐type copolymers

Because of the importance of the maltene–polymer interaction for the better performance of polymer‐modified asphalts, this article reports the effects of the molecular characteristics of two commercial poly(styrene‐block‐butadiene‐block‐styrene‐block) (SBS) polymers and their partially hydrogenated derivatives [poly{styrene‐block[(butadiene)_1?x–(ethylene‐co‐butylene)_x]‐block‐styrene‐block} (SBEBS)] on the morphology and rheological behavior of maltene–polymer blends (MPBs) with polymer concentrations of 3 and 10% (w/w). Each SBEBS and its parent SBS had the same molecular weight and polystyrene block size, but they differed from each other in the composition of the elastomeric block, which exhibited the semicrystalline characteristics of SBEBS. Maltenes were obtained from Ac‐20 asphalt (Pemex, Salamanca, Mexico), and the blends were prepared by a hot‐mixing procedure. Fluorescence microscopy images indicated that all the blends were heterogeneous, with polymer‐rich and maltene‐rich phases. The rheological behavior of the blends was determined from oscillatory shear flow data. An analysis of the storage modulus, loss modulus, complex modulus, and phase angle as a function of the oscillatory frequency at various temperatures allowed us to conclude that the maltenes behaved as pseudohomogeneous viscoelastic materials that could dissipate stress without presenting structural changes; moreover, all the MPBs were more viscoelastic than the neat maltenes, and this depended on both the characteristics and amount of the polymer. The MPBs prepared with SBEBS were more viscoelastic and possessed higher elasticity than those prepared with SBS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

五嵌段热塑性弹性体SISIS的合成

本文首先对目前工业化产品热塑性弹性体SBS和SIS的工艺问题、分子结构、生产成本和产品性能等作了详细评述,最终确定了SISIS的配方设计和完成路线,继而以改性萘锂为引发剂,经三步加料法,依次加入苯乙烯、异戊二烯和苯乙烯,首次合成了该五嵌段共聚物,并对其结果作了初步讨论。