Ethylene-styrene Interpolymers Research Articles

Novel Dinuclear Half‐Titanocene‐Producing Styrene/Ethylene Copolymers Containing Syndiotactic Styrene/Styrene Sequences

AbstractThe synthesis and characterization of a novel titanium complex, {[C5(CH3)5]ClTi}2O2C2(CH3)4(µ‐O) (2), which has two titanium metal centers linked by heteroleptic bridges, oxo and pinacolato, is described. The compound shows good stability under air. The 2/modified methylalumoxane (MMAO) catalytic system produces ethylene/styrene interpolymers (ESIs) containing syndiotactic styrene/styrene sequences (syndiotactic polystyrene blocks) with a high styrene content. To the best of our knowledge, this is the first example of a group‐4‐based catalytic system producing an ESI with syndiotactic polystyrene blocks. magnified image

Super-toughed polymer blends derived from polypropylene random copolymer and ethylene/styrene interpolymer

In this article, blends of polypropylene random copolymer (PP-R) with a novel impact modifier, namely ethylene/styrene interpolymer (ESI), were prepared to evaluate the effectiveness of ESI in toughening PP-R and the influence of ESI content on the mechanical, thermal, and rheological properties of polymer blends. Results showed that super-toughened PP-R/ESI blends (ca. Izod impact strength ≥ 500 J/m) were readily achieved with only 5 wt % ESI. The blends exhibited significant improvement in both impact strength and elongation, while small loss in tensile strength and elastic modulus when increasing ESI content. ESI had a nucleating effect that caused PP matrix to crystallize at higher temperatures, whereas PP-R/ESI blends presented lower melting temperatures (T m ) than PP-R matrix and T m decreased with the increment of ESI content. Rheology study indicated that both PP-R matrix and PP-R/ESI blends presented shear thinning behaviors during melt processing.

The compatibilization effect of ethylene/styrene interpolymer on polystyrene/polyethylene blends

AbstractIn this study, ethylene/styrene interpolymer (ESI) was used as compatibilizer for the blends of polystyrene (PS) and low‐density polyethylene (LDPE). The mechanical properties including impact, tensile properties, and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Impact measurements indicated that the impact strength of the blends increases slowly with LDPE content up to 40 wt %; thereafter, it increases sharply with increasing LDPE content. The impact energy of the LDPE‐rich blends exceeded that of pure LDPE, implying that the LDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI. Tensile tests showed that the yield strength of the PS/LDPE/ESI blends decreases considerably with increasing LDPE content. However, the elongation at break of the blends tended to increase significantly with increasing LDPE content. The compatibilization efficiency of ESI and polystyrene‐hydrogenated butadiene‐polystyrene triblock copolymers (SEBS) for PS/LDPE 50/50 was further compared. Mechanical properties show that ESI is more effective to achieve a combination of LDPE toughness and PS rigidity than SEBS. The correlation between the impact property and morphology of the ESI‐compatibilized PS/LDPE blends is discussed. The excellent tensile ductility of the LDPE‐rich blends resulted from shield yielding of the matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2136–2146, 2007

Coating solvent effects producing adhesion to molded plastic parts

While adhesion is of paramount importance to ensure durability and quality of a coating system, solvents have long been known to affect coating adhesion to molded plastics, including polyolefins. Varions research group in their characterizations of interfaces and/or adhesion to plastics, have produced much understanding of the role played by solvents in adhesion to plastics. However, the 'goodness' of a coating solvent for the plastic, defined as a small Flory interaction parameter χ12, was not indicative of the quality of the coating adhesion to the molded plastic substrates under consideration. For instance, coating adhesion to either polypropylene or ethylene–styrene interpolymer substrates, as affected by the coating solvent, was poorly related to the solvent–polymer miscibility, the magnitude of solubility parameter mismatch, or the ability of the solvent to swell the polymer bulk, except where such swelling produced a topographical change to the polymer surface. Though the topographical change was different for polypropylene compared to the interpolymer surface, if a coating solvent induced little or no change in the topography of a molded plastic then little or no coating adhesion to the plastic was observed. Polymer surface crystallinity reduced the amount of topographical change caused by a solvent and, likewise, reduced adhesion of a coating containing the solvent. The alteration of topographical features by solvent provides an adhesion mechanism and an explanation for the reported formation of diffuse interfaces and how a coating solvent could expose sub-surface domains within a polymer substrate.

Tailoring viscoelastic and mechanical properties of the foamed blends of EVA and various ethylene‐styrene interpolymers

AbstractFoamed materials (EVA/ESI) have been prepared from blends of ethylene‐vinyl acetate copolymer (EVA) and ethylene‐styrene interpolymers (ESI) in the presence of various amounts of dicumyl peroxide (DCP). Four ESIs of different compositions were employed in this study; their styrene contents ranged from 30 to 73 wt% and their Tg ranged from −2 to 33°C. It has been found that microcellular morphology, degree of crosslinking and expansion ratio were strongly affected by the DCP concentration and the type of ESI employed. A minimum degree of crosslinking was required for making good foams and the same degree of crosslinking could be achieved by employing a smaller amount of DCP for an EVA/ESI blend having a higher styrene content. In contrast to other EVA blends, such as EVA/LDPE, these EVA/ESI blends exhibited no existence of any optimum DCP concentration, and the α glass transition temperatures of the foams varied with the ESI type, covering a wide span from 0°C to 37°C. Therefore, it was possible to tailor the Tg of an EVA/ESI blend by choosing an appropriate type of ESI. Furthermore, by correctly tailoring the Tg, the EVA/ESI foam could be made into a rubbery material with a custom‐designed damping factor. Tensile strength and modulus of the EVA/ESI foams increased generally with an increase in the styrene content, with the exception that ESIs with very low styrene content will confer on the blend a high modulus at small strain and a large elongation at break.

Dimensional Stability Analysis of Foams Based on LDPE and Ethylene–Styrene Interpolymer Blends

This study extends our earlier work on the fundamental aspects ofmodeling on foam aging and dimensional stability. The thickness change of extruded polyolefin foam to the blowing agent and air counter diffusion during the postextrusion aging process is modeled. The blowing agent and air counter diffusion equations are coupled with more complicated Maxwell–Voigt fourparameter viscoelastic equations to model the foam dimensional change and recovery processes. The effects of blending ethylene–styrene interpolymer resin and adding aging modifier are investigated, respectively and altogether. The mathematical model is also compared with experimental data.

Studies of electron-beam irradiation on ethylene–styrene interpolymers

Electron-beam irradiation-induced structural and properties changes on ethylene–styrene interpolymers (ESI) have been studied at electron doses ranging from 0 to 200 kGy. The amounts of species generated by irradiation such as hydroxyls, hydroperoxides, carbonyls and unsaturated double bonds have been analyzed using ATR-FTIR. While the structural changes are minimal for ESI69 comprising 69 wt.% styrene regardless of the dose level, the changes for ESI40 comprising 40 wt.% styrene are dose dependent and reaches a maximum at a dose of 100 kGy. Gel permeation chromatography analysis indicates that macromolecular chain scission occurs at low irradiation dose and crosslinking dominates at high irradiation doses. The average molecular weights between crosslinks, M C’s, have been calculated using the Flory–Rehner equation based on data collected from solvent extraction experiments. The M C’s of ESI40 samples are much smaller than those of ESI69 samples. Irradiated ESI samples have higher glass transition temperatures as well as thermal decomposition temperatures. The electron-beam irradiation also causes an increase in the Young’s modulus of ESI69 samples and a decrease in the elongation at break of ESI40 samples.

Ethylene – Styrene Interpolymer Foam Blends: Mechanical Properties and Sport Applications

Mechanical tests were performed on foamed blends of Ethylene – Styrene Interpolymer (ESI) with low density polyethylene (LDPE). In compressive impact tests the foams, of density around 50 kg m-3, have higher initial yield stresses than Ethylene Vinyl Acetate (EVA) foam of the same density. Impact, Instron and creep tests were analysed to estimate the effective air pressure in the undeformed foam cells, and the initial yield stress. The rate dependence of the latter increases slightly with increasing ESI content. The ESI/LDPE foams have improved impact properties, compared with EVA foams of similar density, for leg protection applications. Analysis of creep tests shows that air diffuses from the cells at a similar rate to EVA foams of a greater density. The ESI/LDPE foams have potential to replace higher density EVA foams in running shoes.

Ethylene copolymers as sintering enhancers and impact modifiers for rotational molding of polyethylene

AbstractThe objective of this work was to evaluate the effect of blending minor amounts of ethylene styrene Interpolymer or ethylene vinyl acetate (EVA) with polyethylene on cycle times and impact strength in rotational molding. The blends sintered significantly faster than polyethylene. The sintering rates were primarily influenced by the melting points of the minor blend components, and not by differences in melt viscosity and/or elasticity at low shear rate. Blending Interpolymer or EVA with polyethylene resulted in improved environmental stress crack resistance and decreased flexural modulus. In rotational molding, blending Interpolymer or EVA with polyethylene generally resulted in faster bubble removal, more uniform thickness and shorter cycle times. Ductile failure was generally observed at the peak mean failure energy (MFE). The blend containing Interpolymer yielded significantly increased MFE, possibly because the Interpolymer was compatible with polyethylene and was very well dispersed.

The Use of Ethylene/Styrene Interpolymers in Crosslinked Foams for the Footwear Industry

Ethylene/Styrene Interpolymers (ESI) currently under development by The Dow Chemical Company can be effectively crosslinked using current commercial equipment to produce extruded sheets, bun foams, and injection molded foams (IMF) for footwear parts providing properties that enhance and/or outperform current foams of crosslinked ethylene vinyl acetate copolymers (EVA). Crosslinked EVA foams with density ranging from 0.12 to 0.35 g/cc are becoming increasingly popular in many athletic, ladies high heel, and casual shoes for the fabrication of insoles, midsoles, and unisoles, where light weight, comfort, aesthetics, low cost, and performance are the key. ESIs can be blended with EVA or used pure to give light weight, softer foams with better compression set while maintaining or improving on resiliency, heat shrinkage, and split tear.

Toughened Blends of Polystyrene and Ethylene-Styrene Interpolymers

Ethylene-styrene interpolymer (ESI) resins prepared using a constrained geometry catalyst have been found to make toughened blends with polystyrene (PS). At a low level in the blend, an ESI resin forms dispersed micro-domains of sub-micron size in polystyrene. At 40 %, an ESI resin makes a co-continuous blend that is both stiff and ductile. The toughening effect increases as the styrene content in the ESI resin increases peaking at an approximately 70 wt % of styrene. The results indicate that ESI resins are compatible with polystyrene and the compatibility increases as the styrene content in the resin increases.

Thermodynamic Behavior of Ethylene−Styrene Interpolymers

The Dow Chemical Company has recently introduced a new family of copolymers of ethylene and styrene identified as ethylene−styrene interpolymers (ESIs). The ability of the group-contribution lattice-fluid equation of state (GCLF EoS) to predict the volumetric properties of a series of ESIs of different compositions, the solubility parameter of a given copolymer, and the solubility of toluene was tested. The two latter experiments were conducted in the temperature range 50−150 °C. On average, the error in density was less than 1.1% in the temperature and pressure ranges of 100−250 °C and 6.9−690 bar, respectively. The solubility parameter of the polymer was measured using inverse gas chromatography. The solubility parameter was found to have a strong temperature dependency that the model could not reproduce accurately. At 25 °C, however, the model predictions were found to be in the range of the literature data. The GCLF EoS gave good predictions for the solubilities of the vapors at low styrene contents. Discrepancies at high styrene contents were attributed to a less accurate description of the sorption of solvents in pure polystyrene. The investigation shows that crystallinity has an influence on the solvent solubilities even if they are treated on a crystal-free basis.

Linear Stress Relaxation Behavior of Amorphous Ethylene−Styrene Interpolymers

Amorphous ethylene−styrene interpolymers (ESIs) provide an excellent model system for testing contemporary concepts of molecular dynamics. Moreover, the results can be extrapolated to the chain reptation dynamics of amorphous polyethylene at ambient temperature which cannot be assessed by direct experimental techniques. Previous studies of creep and nonlinear stress relaxation were extended to test theoretical relaxation functions for monodisperse polymers and proposed combining rules against the linear stress relaxation behavior of ESIs in the plateau and terminal regions. Master curves were constructed by time−temperature superposition of data at temperatures from Tg to Tg + 30. The temperature dependence of the shift factor was independent of molecular weight and styrene content and was well described by the WLF equation. The master curves were satisfactorily fit by the empirical KWW equation. Relaxation master curves were modeled with theoretical relaxation functions for monodisperse polymers, appropriate combining rules, and known molecular weight distributions. The Doi−Edwards single reptation model did not give satisfactory results. However, the des Cloizeaux double reptation approach successfully described the relaxation master curves. Excellent agreement was found between the resulting plateau moduli and those from a previous study of creep in the glass transition region. The calculated entanglement molecular weight (1250−2290 g mol-1) was much closer to that of polyethylene (480−860 g mol-1) than to that of polystyrene (13 500 g mol-1) due to the unique chain microstructure of these ESIs with no head-to-tail styrene chain insertions.

Foams Made from Blends of Ethylene Styrene Interpolymers with Polyethylene, Polypropylene and Polystyrene

INSITE** Technology from The Dow Chemical Company has enabled the production of ethylene-styrene Interpolymers (ESI) by copolymerization of ethylene and styrene monomers. The properties of interpolymers vary significantly with copolymer styrene content. Interpolymers with up to about 45 weight percent copolymer styrene are semicrystalline and exhibit good low temperature toughness. Interpolymers with greater than about 45 weight percent copolymer styrene are essentially amorphous and range from those that have low modulus and high elongation to those that have higher modulus with unique stress relaxation and dead fold properties. Interpolymers have both aromatic and aliphatic functionality. Hence, they are compatible with a variety of other thermoplastics. Interpolymers have been commercially launched under the trademark "INDEXt Interpolymers" and are classified as E-Series (up to about 45 weight percent styrene) or S-series (greater than about 45 weight percent styrene). This paper describes the properties of blends of interpolymers with low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), as well as the novel and unique foams made by expanding some of these blends with physical blowing agents.

A New Generation of Materials for the Calendering Industry

While polyvinyl chloride (PVC) has been employed in the calendering industry for many years, other polymers have not been as widely used. Ethylene styrene interpolymers (ESI) demonstrate the requisite rheological properties and thermal stability to be successfully used in the calendering process. Commercial scale validations were performed on ESI based formulations. Examples of the applicability of ESI to calendering are discussed.

Synthesis and properties of copolymers of ethylene/carbon monoxide with styrene/carbon monoxide

The terpolymerization of ethylene, styrene, and carbon monoxide was accomplished by two different palladium-based catalysts: a phosphine-based ligand system and a nitrogen-based ligand system. The range of possible compositions and the composition dependence of the properties of the resulting polymers were determined. These polymers were essentially carbon monoxide versions of the ethylene styrene interpolymers recently presented by Dow. A comparison between the two families of polymers is attempted. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 752–757, 2000

Synthesis and properties of copolymers of ethylene/carbon monoxide with styrene/carbon monoxide

The terpolymerization of ethylene, styrene, and carbon monoxide was accomplished by two different palladium-based catalysts: a phosphine-based ligand system and a nitrogen-based ligand system. The range of possible compositions and the composition dependence of the properties of the resulting polymers were determined. These polymers were essentially carbon monoxide versions of the ethylene styrene interpolymers recently presented by Dow. A comparison between the two families of polymers is attempted. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 752–757, 2000

Extruded Non-Crosslinked Foams Made from Ethylene-Styrene Interpolymers and Blends with Polyethylene

Ethylene-styrene Interpolymers (ESI) are a new class of polymers made by copolymerisation of ethylene and styrene monomers using INSITE® Technology, the patented constrained geometry single site catalysts and proprietary solution process of The Dow Chemical Company. The tradename of the Interpolymers is INDEX®. Foams with novel and unique properties have been made by expanding these polymers using physical blowing agents. This paper describes the properties of foams made from Interpolymers and blends with polyethylene.

Large Strain Stress Relaxation and Recovery Behavior of Amorphous Ethylene−Styrene Interpolymers

Ethylene−styrene interpolymers (ESIs) are viewed as random copolymers of ethylene and ethylene−styrene dyads. The amorphous ESIs offer an approach to characterizing polyethylene without the constraints imposed by the inevitable crystallinity. Large strain, nonlinear stress relaxation and recovery of ESIs were studied at temperatures above the glass-transition temperature (Tg). The nonlinear stress relaxation curves superposed on the double-logarithmic scale by vertical shifting after a characteristic time τk that increased as the molecular weight increased and the testing temperature approached Tg. The experimental shift factors were independent of molecular weight and styrene content and correlated well to the damping function obtained in the tube theory. The instantaneous recovery after stress relaxation increased as the molecular weight increased or as the testing temperature decreased approaching Tg. Instantaneous recovery was correlated with stress relaxation in terms of mechanisms of molecular dynamics. The success of this approach led to a generalization of the model of two coexisting networks used previously.

Creep behavior of amorphous ethylene–styrene interpolymers in the glass transition region

The viscoelastic behavior of amorphous ethylene–styrene interpolymers (ESIs) was studied in the glass transition region. The creep behavior at temperatures from 15°C below the glass transition temperature (Tg) to Tg was determined for three amorphous ESIs. These three copolymers with 62, 69, and 72 wt % styrene had glass transition temperatures of 11, 23, and 33°C, respectively, as determined by DMTA at 1 Hz. Time–temperature superposition master curves were constructed from creep curves for each polymer. The temperature dependence of the shift factors was well described by the WLF equation. Using the Tg determined by DMTA at 1 Hz as a reference temperature, C1 and C2 constants for the Williams, Landel, and Ferry (WLF) equation were calculated as approximately 7 and 40 K, respectively. The master curves were used to obtain the retardation time spectrum and the plateau compliance. The entanglement molecular weight obtained from the plateau compliance increased with increasing styrene content as 1,600, 1,870, and 2,040, respectively. The entanglement molecular weight of the ESIs was much closer to that of polyethylene (1,390) than to that of polystyrene (18,700); this was attributed to the unique chain microstructure of these ESIs with no styrene–styrene dyads. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2373–2382, 1999