Alan A. Galuska

Quantitative Surface Analysis of Ethylene–Propylene Polymers using ToF-SIMS

Copolymers of ethylene and propylene (EPs) and blends of these copolymers with polypropylene (PP) are commonly used in many elastomer and thermoplastic applications. Ethylene-propylene surface and interfaces have a major effect on EP processing and are important in nearly all EP applications. Despite the importance of these surfaces and interfaces, there have been no methods for quantitatively determining the ethylene and propylene concentrations on surfaces (top 10-30 A) or in microscopic phases. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) calibrations are developed for quantitative surface analysis of EP polymers. The C 3 H 5 + /C 2 H 3 + and C 4 H 7 + /C 2 H 3 + intensity variations with EP composition are calibrated to provide quantitative (±5 wt.%) ethylene determinations. Moreover, C 5 H 9 + /C 2 H 3 + and C 8 H 13 + /C 2 H 3 + intensity variations with EP composition and sequence distribution provide quantitative (±5 wt.%) measures of propylene dyads and triads. Both ethylene and sequence distribution calibrations are then modified for micrometer analysis areas. These new capabilities are applied to a case study involving surface migratory polymer on injection-molded sheet and spunbond fibers.

ToF-SIMS determination of molecular weights from polymeric surfaces and microscopic phases

Time-of-flight (ToF) SIMS spectra were acquired from a variety of elastomer and thermoplastic molecular weight (MW) standards: polyisoprene (PIP), 1,4-polybutadiene (PBD), polyisobutylene (PIB), polyethylene (PE), polystyrene (PS), polypropylene (PP) and poly(1-butene) (P1-B). These spectra were then examined to determine any correlation between relative ion intensities and MW. In all cases, the relative intensities of protonated monomer (monomer + H) ions were particularly sensitive to MW. These monomer + H relative ion intensities were fairly constant at MWs above 20000, but increased dramatically and contiguously as the MW of the polymer decreased below 20 000. For all of the polymers examined, the variation of monomer + H ion intensities with MW could be fit using the general relationship: Relative monomer + H ion intensity = M(MW/1000) E + B, where M is the slope, B is the ion ratio intercept and E is an exponent with values between -0.5 and -0.6. Using this general relationship, ToF-SIMS MW calibration lines were developed for PIP, PBD, PIB, PE, PS, PP and PI-B. These calibration lines could be used to determine the presence and approximate MW of low-MW (≤ 20 000) polymer, but could not distinguish the MWs of high-MW (≥ 20 000) polymers. The technique was applied to the analysis of MWs on PP fibers. Moreover, the MW calibrations were shown to be useful for determining the presence of unknown low-MW waxes and additives on polymeric surfaces.

Quantitative analysis of surface ethylene concentrations in ethylene–propylene polymers using XPS valence bands

Polyolefin surfaces and interfaces can have a substantial effect on polyolefin processing and properties. Despite the importance of these surfaces and interfaces, there have been few good ways of determining the type of polyolefin on a surface. In this work, a quantitative XPS method for the determination of surface ethylene concentrations in ethylene–propylene polymers is presented. Calibration lines are created using differences in the valence band spectra of various polyethylene (PE), polypropylene (PP) and ethylene–propylene polymer (EP) standards. These lines are then used to determine surface ethylene concentrations on propylene–ethylene polymers. This procedure yields accurate ethylene determinations (±5 wt.% ethylene) when surface contamination (such as additives) is low. At higher surface contamination levels, the accuracy of the method degrades unless valence band contributions from the contamination (or additives) are accounted for. When surface additive levels are high, valence band analyses are shown to be useful in determining the nature of the additives present. Valence band spectra obtained from other polyolefins (polyisobutylene, poly-1-butene, poly-1-hexene and poly-1-octene) are also presented. The spectra for polyisobutylene and poly-1-butene are distinctly different from that obtained from PE (also PP). The spectra obtained from poly-1-hexene and poly-1-octene are similar to that obtained from PE, but are distinctly different from those obtained from polyisobutylene, poly-1-butene and PP. This valence band approach for determining surface compositions should be applicable to other mixed polyolefins that have significantly different valence bands. Case studies involving haze on injection-molded plaques and PE cling-films are presented.

Surface Characterization of EMA Copolymers Using XPS and ToF-SIMS

Semicrystalline copolymers of ethylene (CH 2 =CH 2 ) and methyl acrylate (CH 2 =CH-CO-O-CH 3 )(EMAs) are commonly used in many applications where surface properties (such as adhesion, printability, cling and sealing) are critical to polymer performance. Despite the importance of EMAs and their surface properties, the surface compositions of pristine EMAs have not been critically examined. In this work, the surface chemistries of a contiguous series of 11 pristine EMAs of varying MA content (up to 33 wt.%) have for the first time been critically examined using angle-resolved XPS and ToF-SIMS analyses. This examination has revealed the details of EMA surface chemistry, and has provided techniques for EMA identification and quantification. Below 20 wt.% bulk MA, the EMA surface is shown to consist of a thin MA-rich phase over an MA-depleted phase. This surface chemistry changes at MA levels greater than 20 wt.%. At these bulk MA concentrations, the MA is depleted from the surface and enriched in the near-surface regions. Time-of-flight SIMS analyses of these EMAs indicate that there is a great enrichment of EMA backbone (with MA branches intimately attached) associated with this MA depletion. This simultaneous backbone enrichment and MA depletion indicates that the MA-containing polymer has not been depleted from the surface. Instead, the MA branches have simply rotated away from the surface into the polymer. Upon melting, these segregation effects are removed and the surface chemistry becomes equal to that in the bulk. X-ray photoelectron spectra provide a measure of the ester and ether groups associated with MA and oxidized polyethylene, but do not provide positive EMA identification. In contrast, ToF-SIMS spectra provide positive EMA identification and detailed information on the orientation of the polymer. Time-of-flight SIMS and XPS calibrations are developed for quantitative (± 4 and 2 wt.% MA, respectively) MA determinations on surfaces (top 10-60 A). Also, these calibrations are combined with an understanding of the surface structure of EMAs to determine the bulk MA content (±2 wt.% MA) of the corresponding EMA films.

Curative Migration in Rubber Compounds Containing Brominated Poly(Isobutylene-co-4-Methylstyrene)

Abstract Blends of elastomers are widely used throughout the rubber industry. Blends are frequently used to get a balance of properties which cannot be achieved through the use of a single elastomer. For example, poly(isobutylene-co-4-bromomethylstyrene) can be blended with highly unsaturated general purpose rubbers to impart unique barrier or dynamic properties and enhanced oxidative stability. The final properties of such a blend are the result of a complex series of compounding, mixing and curing stages. These stages profoundly impact the homogeneity of the mixed components which include: the polymers, the filler, and the curatives. It is important to develop tools to monitor the changes which occur during compounding. This paper details the application of static secondary ion time-of-flight mass spectroscopy (ToF-SSIMS) imaging to simultaneously map polymer phase information with specific chemical information. The paper will highlight the utility of ToF-SSIMS for the study of the chemical and physical...