Styrene Isoprene Research Articles

Curing Behavior and Adhesion Performance of UV-Curable Styrene–Isoprene–Styrene-Based Pressure-Sensitive Adhesives

This article reports on the curing behavior and adhesion performance of ultraviolet (UV)-curable, polystyrene–polyisoprene–polystyrene (SIS)-based pressure-sensitive adhesives (PSAs) blended with di- or tri-functional monomers and a photoinitiator. The curing reaction was achieved by direct excitation of PSAs by irradiation with a 100 W high-pressure mercury lamp at different UV doses. The curing behavior of the PSAs was studied by gel fraction determination, rigid-body pendulum type physical properties test (RPT) and Fourier transform-infrared–attenuated total reflection (FT-IR–ATR) spectroscopy. The adhesion performance was determined by probe tack, peel strength and shear adhesion failure temperature (SAFT) measurements. The reaction rate and extent of UV curing reaction were found to be strongly dependent on the curing rate for the following five multifunctional monomers studied: three di-functional monomers, ethylene/glycol dimethacrylate (EGDMA), triethylene glycol dimethacrylate (TEGDMA) and poly(ethylene/glycol)(400) dimethacrylate (PEG(400)DMA), and two tri-functional monomers, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane ethoxylated (6) triacrylate (TMPEOTA). In addition, the adhesion performance was affected by the semi-interpenetrating polymer network (IPN) structure formed depending on the curing rate and degree of cross-linking.

An FTIR standard addition method for quantification of bound styrene in its copolymers

The content of bound styrene in styrenic copolymer has a great influence on its performance. In this paper, a standard addition method for quantification of bound styrene was developed to analyze styrene/butadiene rubber (SBR), styrene–butadiene–styrene (SBS) triblock copolymer and styrene–isoprene–styrene (SIS) triblock copolymer, respectively. Polystyrene with several incremental additions was dissolved with them in chloroform separately. The obtained standard addition curve of the ratio of the absorbance at 699cm−1 (styrene unit) to the one at 967cm−1 (butadiene unit) or the one at 838cm−1 (isoprene unit) versus the mass ratio of the added polystyrene to the copolymers showed good linearity (R>0.992) and accuracy (the R.S.D. for SBR, SBS and SIS was 6.38%, 3.14% and 4.07%, respectively). This developed method is universal, convenient and satisfactory.

Fundamentals of hot-melt pressure-sensitive adhesive tapes: the effect of tackifier aromaticity

We revisit the effect of varying the tackifier aromaticity on adhesive performance in a styrenic block co-polymer (SBC)-based pressure-sensitive adhesive tape. Aromaticity strongly affects the compatibility between the tackifying resin and base polymer and is defined as the relative number of protons attached to an aromatic ring. Dynamic mechanical analysis, peel resistance, tack, shear resistance and atomic force microscopy were utilized to detect changes in adhesive performance due to resin aromaticity. The results indicate that increasing the aromaticity of the tackifier enhanced the compatibility between the tackifier and styrene domains. As a consequence, the high-temperature cohesive performance measured by the shear adhesion failure temperature decreased due to plasticization of the end-blocks by the aromatic resins. However, other properties of interest such as the glass transition of the rubbery matrix, tack, peel resistance and holding power were less affected by the resin aromaticity. We note that this paper is of limited scope because we have focused this research on styrene–isoprene–styrene, which is very compatible with a wide range of tackifiers. More significant differences would be expected in formulations based on styrene–butadiene–styrene or styrene–isoprene–butadiene–styrene polymers in which the compatibility between the resin and midblock would be more sensitive to the resin aromaticity. In addition to our results, we review the literature and some fundamentals of formulating SBC-based adhesives and PSA testing.

Preparation of SIS/SBS-based UV-cross-linkable pressure-sensitive adhesives using the thiol-ene reaction

Hot-melt pressure-sensitive adhesives (HMPSAs) usually contain styrene-isoprenestyrene (SIS) or styrene-butadiene-styrene (SBS) block copolymers, tackifier, plasticizer and other additives. However, these PSAs cannot be used in high-temperature applications or where solvent and chemical resistance properties are required. We, therefore, developed UV-cross-linkable HMPSAs by the thiol-ene reaction with the aim to increase adhesion properties at elevated temperature. For effective UV cross-linking, the selection of photoinitiator and photo-cross-linker is very important for thermal stability and fast curing. Adhesion properties, such as probe tack, peel strength and shear adhesion failure temperature (SAFT), were evaluated to measure PSA performance as a function of photoinitiator type.

Spurt and melt flow distorsions of linear styrene-isoprene-styrene triblock copolymers

The steady state rheological behavior of three narrow molecular weight distribution styrene-isoprene-styrene (SIS) triblock copolymers with different molecular weights and polystyrene (PS) contents was investigated by means of a capillary rheometer using the roundhole and slit die geometry. A monodisperse polyisoprene was also investigated to allow a comparison with the flow behavior of the pure elastomer. Like polyisoprene, all the copolymers exhibit spurt marked by a plateau of the shear stress versus flow rate curve and by a discontinuity of the entrance pressure when a critical shear rate is reached. Near the glass transition of the PS domains, the flow curve is mainly influenced by the PS content and exhibits, with increasing flow rate, first yield stress, and then spurt. On the contrary, at higher temperatures, yield stress and spurt disappear and the rheological behavior is qualitatively driven by the overall molecular weight as for linear polymer melts. The values of the critical stress for spurt are significantly larger than that of the polyisoprene matrix and the influence of the PS content on σspurt and the sequence of melt flow distorsions were discussed.

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

AbstractHotmelt 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 (Tg), 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 Tg. 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

Controlling the colloidal behavior of styrene–isoprene diblock copolymers by selective end functionalization

ω-Lithium poly(styrene- b-isoprene) sulfonates were synthesized by anionic polymerization. The copolymers carrying the lithium sulfonate (SuLi) end group at either the soluble or the insoluble block form a variety of different microstructures in n-decane. In the case where the SuLi group is located at the PS insoluble end block, micellar aggregates with larger aggregation number, hydrodynamic radius and thermal stability are formed, compared to the non-functionalized diblock precursor case. When the polar group is located in the soluble PI block end, the solubility of the system depends on temperature. At high temperatures where end group association primarily exists, star-like aggregates are formed. At lower temperatures PS block association also takes place, resulting in a system of highly polydisperse and interconnected aggregates. The latter materials can be considered as ABC heterotelechelic associating macromolecules presenting new ways of controlling the colloidal behavior of block copolymer systems by selective end functionalization.

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

AbstractThe effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (tb) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006

Tack and fracture energy of tackified SIS (styrene-isoprene-styrene)-based hot-melt pressure sensitive adhesives (HMPSAs)

The relationship between probe tack and fracture energy for SIS (styrene-isoprene-styrene)-based HMPSAs (hot-melt pressure-sensitive adhesives) made using various SIS and tackifiers was investigated. Generally, HMPSAs made using low-T g tackifiers have higher probe tack than using high-T g tackifiers, except in the case of Sukorez SU 100. In the case of Kraton blends, blends made using Quintone U 185, Hikorez A 1100S and Sukorez SU 100 exhibit a maximum probe tack at 60 wt% tackifier content, while the blends made using GA-100 and Regalite R 125 exhibit a maximum probe tack at 40 wt% tackifier content. In the case of the Vector blends, similar results are observed, except that those HMPSAs made using Hikorez A 1100S and Sukorez SU 100 have a maximum probe tack at 50 wt% tackifier content. Because tri-bock SIS (Vector 4111) has a higher cohesion than the diblock containing SIS (Kraton D 1107), Vector 4111/tackifier blends exhibit a maximum tack at higher tackifier contents than Kraton D 1107/tackifier blends. In terms of the fracture energy of blends, similar results were observed. Generally, the fracture energy (ω) of the SIS-based HMPSAs was closely related to the maximum probe tack. Because of the effects of failure mode on fracture energy and probe tack, there is some variation in the fracture energy between the different blends, because of their different failure modes.

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

AbstractThe 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

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

AbstractThe 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

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

AbstractThe 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

Magnetic investigations of titanium‐doped gamma iron oxides dispersed in polymers

AbstractThe preparation and characterization of titanium‐doped iron oxides–styrene isoprene styrene block copolymer composites is reported. The precursor, as‐synthesized nanoparticles, contains akaganeite, maghemite, and titanium‐doped maghemite. Hysteresis loops obtained by SQUID measurements revealed an exchange biased field assigned to the presence of akaganeite nanoparticles. It was found that the coercive field and the exchange bias field decreases as the temperature of the sample is increased. The temperature dependence of the magnetization revealed a blocking temperature of about 220 K. The ESR spectra in the temperature range 150 K to about 300 K are single broad resonance lines. It was observed that the resonance line position is strongly temperature dependent due to the combined action of the external and molecular magnetic fields. The decrease of the resonance line width as the temperature is increased is governed by the reorientation of the magnetization. Thermally activated movements of magnetic nanoparticles within the soft phase (polyisoprene) of the matrix may also contribute to resonance line narrowing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3432–3437, 2005

Morphological reorientation by extensional flow deformation of a triblock copolymer styrene–isoprene–styrene

An oriented morphology has been generated by shear aligning a triblock copolymer SIS below its order–disorder transition (ODT) temperature. Elongational flow deformation was conducted on a polystyrene-block–polyisoprene-block–polystyrene (SIS) triblock copolymer having soft spherical microdomains composed of polyisoprene block chains in a hard matrix of polystyrene block chains with extensional rheometer (RME). The triblock copolymer has an equilibrium microphase-separated morphology of spheres (body centered cubic, BCC) of polystyrene in a polyisoprene matrix. The evolving structure was investigated with rheology, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The structure related to various condition of elongational flow deformation has been determined from SAXS patterns by considering separately changes in the single particle scattering, which influence the scattering patterns. The TEM and SAXS data of the film samples show that the spherical PS-domain was deformed and reoriented along the direction of elongation. It was found that the spheres microdomains are transformed into cylinder microstructures with short-range order.

Rheological Properties of Hot Melt Pressure Sensitive Adhesives (HMPSAs) Based on Styrene–Isoprene Copolymers, Part 3: Rheological Behavior of Different Block Copolymers With High Diblock Content

ABSTRACT The processing and application properties of hot-melt pressure-sensitive adhesives (HMPSA) are governed, to a large extent, by their rheological properties. Coating of the HMPSA is performed at high temperatures in the molten state. At room temperature, the adhesive satisfies the Dahlquist criterion and, consequently, has permanent tack. We have particularly studied the full formulations based on triblock and diblock copolymers, and also those based on newly designed molecules, such as tetrablock or radial copolymers. We have demonstrated in the previous articles of this series that, for these systems, the volume fraction of the free polyisoprene is the most important parameter that drives the tack performances by controlling the level of the secondary elastic plateau modulus observed in the low-frequency range. To improve the end-user properties, we have increased the diblock content in the blends. We describe here the dynamic mechanical properties, at room temperature, of the pure copolymer blends (i.e., without addition of a tackifying resin) and the full HMPSA formulations. We focus particularly in this article on blends that contain a high diblock content. The effect of the morphology of the diblock copolymer on the rheological behavior of the adhesive is discussed in detail. Finally, we propose a model, based on molecular dynamics concepts, which describes the rheological behavior in a very wide range of frequencies for all copolymers and full formulations of the study.

Collaborative studies of thermo-oxidative degradation of styrene–isoprene diblock copolymer

Mechanisms and dynamics of thermo-oxidative degradation of styrene- co-isoprene (SI) diblock at a temperature above the order–disorder transition temperature, T odt, have been investigated both experimentally and theoretically. The structural development of SI during degradation was monitored by optical microscopy, and the reduction of molecular weight and molecular weight distribution during the degradation was determined by gel permeation chromatography (GPC). The degradation process was modeled in the framework of a kinetic model based on the framework of the Flory principle. The theoretical predictions were compared with the GPC results. Fourier transformed infrared spectroscopy (FTIR) experiment was conducted in situ during the thermo-oxidative degradation of the SI copolymers, to gain further insight into the chemical modification mechanisms, the reduction of unsaturated double bonds and the formation of carbonyl and hydroxyl groups.

Relaxation Properties of Pressure-sensitive Adhesives upon Withdrawal of Bonding Pressure

ABSTRACT Relaxation properties of pressure-sensitive adhesives (PSA) have been studied with the squeeze-recoil tester used in the regime of parallel-plate dilatometer under conditions imitating the removal of compressive force in the course of adhesive bond formation. The relaxation properties of PSAs are compared with their adhesive behavior measured using the 180-Deg Peel Test. Two classes of PSAs are considered: 1) conventional rubbery adhesives based on the mixtures of styrene-isoprene-styrene (SIS) block copolymer with a tackifier resin and a plasticizer, and butyl rubber plasticized with low-molecular-weight polyisobutylene, and 2) hydrophilic PSAs composed of the blends of high-molecular-weight poly(N-vinyl pyrrolidone) (PVP) with oligomeric polyethylene glycol (PEG). By comparing the adhesive and relaxation behaviors of different PSAs, the relaxation criteria for pressure-sensitive adhesion have been stated. Relaxation behavior of the examined PSAs demonstrates two values of retardation time: the shorter retardation time of 10–70 sec and the longer time of 300–660 sec. These times can be associated, respectively, with small- and large-scale mechanisms of strain recovery. By comparing the relaxation and adhesive properties of PVP-PEG blend (which involves the formation of a hydrogen-bonded network through both terminal hydroxyl groups in PEG short chains) with the properties of covalently crosslinked copolymers of vinyl pyrrolidone (VP) with PEG-diacrylate and comb-like VP copolymers with PEG-monomethacrylate, the contributions of covalent crosslinking and H-bonding network have been characterized.

Supercritical carbon dioxide foaming of elastomer/heterocyclic methacrylate blends as scaffolds for tissue engineering

This study reports on the supercritical carbon dioxide (scCO2) foaming of rubber toughened heterocyclic methacrylates for potential applications as non-degradable scaffolds in tissue repair and engineering. Porous blends of styrene–isoprene–styrene copolymer elastomer (SIS) and tetrahydrofurfuryl methacrylate (THFMA) at three SIS/THFMA compositions that ranged from methacrylate to elastomer rich were foamed and characterised in terms of their morphological, mechanical and biological properties. The results showed that the foaming factor (FF) was dependent on blend composition and the foaming conditions demonstrating that the process was tuneable. A greater FF, resulting in higher open and total porosities, was obtained for THFMA rich formulations, which were demonstrated by a predominantly open pore structure. Quasi-static and dynamic mechanical analysis (DMA) showed that the foamed SIS/THFMA blends gave distinct behaviours according to their compositions which were in the range of mechanical properties of soft tissues. The loss modulus and mechanical loss tangent through DMA gave two transition regions associated with the glass transition temperatures of poly(THFMA) and polystyrene components in the blends, along with a reduction in storage modulus. Cell adhesion and spreading in terms of neuroblastoma (human neuron-like SH-SY5Y) cells and ovine meniscal chondrocytes were demonstrated for scaffolds with THFMA rich formulations confirming their suitability for tissue engineering.

Effect of substrate and tackifier on peel strength of SIS (styrene-isoprene-styrene)-based HMPSAs

SIS (styrene–isoprene–styrene)-based hot-melt pressure-sensitive adhesives (HMPSAs) have high tack, high cohesion (at ambient temperature), and good adhesion to various substrates. In this study, we investigated the effects of the properties of the substrates and tackifier on the characteristics of the SIS-based HMPSAs. SUS (stainless steel), PE, PP, PVC, Bakelite, Teflon, and glass were used as the substrates. The substrates used in this study were classified into three groups (high, medium, and low peel). A similar classification was obtained using surface tension as the distinguishing factor. The maximum peel strength of the HMPSAs made with high softening point (SP) tackifier shifts to lower tackifier content than those made with low SP tackifier. This may be due to blends made with high SP tackifiers that have higher G′ at use temperature than those made with high SP tackifiers.

RHEOLOGICAL PROPERTIES OF HOT-MELT PRESSURE-SENSITIVE ADHESIVE (HMPSAs) BASED ON STYRENE–ISOPRENE COPOLYMERS. PART 2: INNOVATIVE MOLECULAR DESIGN FROM PREDICTIVE FORMUlATION

This article is the second in a series that deals with the viscoelastic properties of Hot-melt pressure-sensitive adhesives (HMPSAs) based on formulations of block copolymers and tackifying resins. The viscoelastic properties of HMPSAs govern, to a large extent, their adhesion, processing, and end-use properties. In the first part of this article, we present a brief description of the rheological behavior of styrene isoprene styrene–styrene isoprene [SIS–SI] copolymer blends at room temperature. We then present an original approach that may lead to the design of new block copolymers (tetrablock and radial copolymers) that mimic the rheological behavior at room temperature of optimized SIS–SI blends used in adhesive formulations. We describe the concept and calculations that lead to the design of the characteristics of these new molecules. In the third part of this article, we discuss in detail the rheological behavior of these new block copolymers compared with the observed behavior of equivalent SIS–SI. In the last part we also demonstrate how the molecular model of the rheological behavior developed in the first article of this series can be applied to these new molecules. We propose, in particular, to apply the blending law (presented in the first article) on the complex shear modulus instead of the relaxation modulus, which simplifies calculations and even leads to a better agreement with experimental data. As a conclusion, we show how this original approach can bring really innovative solutions for the formulation of adhesives with specific properties by using molecular concepts of viscoelasticity.