Surface analysis of polyethyleneterephthalate by ESCA and TOF-SIMS

PET (poly(ethylene-terephthalate)) samples provided by different suppliers were investigated with the surface-sensitive methods as electron spectroscopy for chemical analysis (ESCA) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Analysis by means of ESCA provides chemical information from a near-surface region of roughly 6 nm. Specific ESCA data on chemical shifts and on the ratio between oxygen and carbon are compared with corresponding values expected for the molecular structure of bulk PET. In addition, direct chemical information on the molecular structure at the PET surface (essentially from the first two monolayers) has been obtained by TOF-SIMS. Especially, positive and negative TOF-SIMS mass spectra were analyzed in detail and assigned with respect to characteristic polymer fragment ions. Several polymer additives as well as some contaminations present at the PET surfaces could be identified with TOF-SIMS. Dependent on the PET supplier, antioxidants and lubricants such as Irgafos 168, octylstearate, octylpalmitate, octylarachidate and PDMS (polydimethylsiloxane) found at the sample surfaces give typical positive and negative ion fragments.     

Organometallic polymers. XXV. Preparation of polyvinylferrocene

The synthetic details of solution polymerization in benzene and bulk polymerization of vinylferrocene are reported. In benzene solutions, with azobisisobutyronitrile (AIBN) as the initiator, small yields of low-polydispersity low molecular weight (M?_n ? 5000) polyvinylferrocene is obtained. However, high yields can be obtained by continuous or multiple AIBN addition. Higher molecular weight polymers and binodal polymers can be obtained as the monomer concentration is increased. In bulk polymerizations, yields of 80% can be obtained. The molecular weight increases as temperature decreases from 80 to 60°C in bulk polymerizations, and an increasing amount of insoluble polymer results. The soluble portion is often binodal, the higher molecular weight node consisting of an increasingly branched structure. Lower molecular weight polymer was readily fractionated into narrow fractions from benzene–methanol systems, but higher molecular weight polymer proved impossible to fractionate into narrow fractions due to branching.     

Development of fast atom bombardment mass spectral methods for the identification of carcinogen-nucleoside adducts

An analytical strategy using fast atom bombardment (FAB) ionization and tandem mass spectrometry has been developed to determine the molecular weight and major fragment ions, and to provide limited structural characterization of low picomole levels of carcinogen-nucleoside adducts. This strategy consists of three main components: (1) the sensitivity for analysis by FAB combined with mass spectrometry is increased via chemical derivatization; (2) the nucleoside adducts are selectively detected by using constant neutral loss scans; and (3) structurally characteristic fragments are obtained by using daughter ion scans. Trimethylsilyl derivatized arylamine-nucleoside adducts have been detected at levels as low as a few picomoles by using this approach. After experimental determination of the mass of the BH ₂ ⁺ fragment ion, daughter ion spectra have been used to probe the structure specificity associated with collision-activated decomposition of this fragment. With model C-8 substituted arylamine adducts [N-(deoxyguanosin-8-yl)-4-aminobiphenyl, N-(deoxyadenosin--yl)-4-aminobiphenyl, and N-(deoxyguanosin-8-yl)-2-aminofluorene], nucleoside-specific and carcinogen-specific fragmentation have been observed in daughter ion spectra.     

Stereochemical applications of mass spectrometry 4. Energy-resolved study of the fragmentation of esters of maleic and fumaric acids

The fragmentation of the dimethyl and diethyl esters of maleic and fumaric acids have been studied as a function of the internal energy of the molecular ions using charge exchange techniques and metastable ion studies in combination with isotopic labelling. The dimethyl ester molecular ions show distinctive behaviours at both low and high internal energies, indicating that interconversion of the molecular ions does not occur. The fumarate molecular ion fragments by elimination of CH₂O and (CO₂ + CH₃) in the metastable ion time-frame, while the maleate ester fragments primarily by loss of CH₃O. At higher internal energies both molecular ions fragment primarily by loss of CH₃O but the fragment ion from the maleate ester shows a greater stability, presumably because it assumes the cyclic cationated maleic anhydride structure. The diethyl maleate and diethyl fumarate molecular ions show identical metastable ion characteristics; in addition the [COS]⁺· charge exchange mass spectra are very similar. These results indicate that low-energy molecular ions interconvert. At higher internal energies interconversion does not occur, and, although both moiecular ions fragment by loss of C₂H₅O, the resultsint fragment ions show different stabilities and fragmentation reactions.     

Interactions between surfactant-coated surfaces in hydrocarbon liquids containing functionalized polymer dispersant

The forces and viscosity between calcium benzene sulfonate surfactant-coated mica surfaces in various hydrocarbon liquids containing a polyamine-functionalized hydrocarbon polymer (M _W≈8000) have been measured using the surface forces apparatus technique. The polymer is found to adsorb to the substrate surfaces by displacing the surfactant layer, and to produce forces that are monotonically repulsive. The forces have a maximum range of 50–100 nm (>3R _H), indicating that tails play a particularly important role in the interaction of this relatively low molecular weight polymer. The forces become steeply repulsive below about 10 nm (∼0.6R _H), at which point a “hard-wall” repulsion comes in that can sustain pressures greater than 100 atm. Thin-film viscosity measurements indicate that the far-field positions of the slipping planes Δ_H depend on the shear rate, showing that significant shear thinning/thickening effects occur within the outermost tail regions of the adsorbed layers during shear. The position of the slipping plane, or hydrodynamic layer thickness Δ_H, varies from 0.6R _H to 2R _H away from each surface (mica and surfactant-coated mica surfaces). Beyond the hydrodynamic layer the far-field fluid viscosity is the same as that of the bulk polymer solution. At separations below D = 2Δ_H the viscosity increases as each polymer layer is compressed. The static forces exhibited various time- and history-dependent effects, which further indicate that a number of different relaxation/equilibration processes are operating simultaneously in this complex multicomponent system. The results reveal that the interactions of tails of functionally adsorbed polymers play a more important role than previously thought. This is especially true in this study where the adsorbed polymers are of low molecular weight and where the tails may represent the largest fraction of interacting segments. Received: 22 September 1998 Accepted: 11 January 1999     

Estimation of the molecular weights of noncovalent columnar polymers based on β-cyclodextrin by the measurement of the aggregation rate of their polymer inclusion complexes with polypropylene glycol

Noncovalent columnar polymers (NCPs) based on cyclodextrins (CD) are polymeric assemblies of molecules that have continuous hollow channels, the width of which is determined by the diameter of the cavity of the initial CDs. The repeating fragment in an NCP is the CD molecule. For NCPs that were obtained by the exclusion of polymer backbone macromolecule from the corresponding inclusion complexes (ICs) based on β-cyclodextrin (NCP_excl), the polymer length, expressed as the number of macrocycles in a single chain (n) is determined by the size of the included ligand, polypropylene glycol (PPG), and is the PPG polymerization degree divided by two. The determination of the molecular weight of an NCP obtained by the precipitation method (NCP_prec) is rather difficult, since they are present in the aggregated state rather than in the form of individual molecules in solution. To estimate the molecular weight of NCP_prec, an indirect method is used, which is based on the determination of the aggregation rate of the ICs formed as a result of the interaction between an NCP and polypropylene glycol with a fixed molecular weight (MW), in this case PPG 1000. The comparison of the aggregation rates of the inclusion between NCP_excb (which were synthesized using PPGs with different molecular weights) and PPG 1000 with the aggregation rate of the inclusion complex on the basis of NCP_prec provided the estimation for the MWs of single polymer chains. The fact that the samples of NCPprec contain ∼30% of the monomeric β-CD was taken into account when constructing the calibration curve. It was demonstrated that the MW of the polypropylene glycol corresponding to NCP_prec is 1320 Da. Consequently, ∼11–12 molecules of β-CD are included in the single chains of NCP_prec.     

CATIONIC POLYMERIC SURFACTANTS

An influence of polyvinyl alcohol molecular weight and acetate groups, present in the macromolecule, on adsorption and electrochemical properties of the TiO₂–polymer solution interface was studied. Calculated thickness of adsorption layers of PVA, on the surface of the oxide, allowed assume that acetate groups may have meaningful influence on the polymer chain conformation at the interface. Structure of macromolecules at titania–polymer solution interface was compared with that of bulk of solution. Obtained data allow determine the changes of the size and shape of polymer coils in the system. The results of experiments let us conclude main factors, responsible for observed zeta potential and surface charge changes of TiO₂. It was proved that change of the ion structure of Stern layer, depends on molecular weight and number of acetate groups (degree of hydrolysis) of PVA macromolecule. Possible mechanism of zeta potential changes was proposed as a function of pH of the solution and molecular weight of the polymer.     

Surface analysis of polymer materials by secondary ion mass spectrometry

Atomic as well as molecular secondary ions are emitted from the uppermost monolayer of a solid during ion bombardment. Mass analysis of these positive and negative secondary ions supplies detailed information on the chemical composition of the bombarded surface. High mass range (> 10,000 u), high mass resolution (m/Δm > 10,000), accurate mass determination (ppm range) and high sensitivity (ppm of a monolayer) are achieved by applying time-of-flight (TOF) mass analyzers. TOF-SIMS has been successfully applied to a wide variety of polymer materials, including polymer blends, chemically or plasma modified surfaces, and plasma polymerization layers. Detailed information on the composition of repeat units, endgroups, oligomer distributions, additives, as well as surface contaminants can be obtained. Basic concepts of TOF-SIMS will be described and typical analytical examples for the characterization of polymer materials will be presented.     

Effects of polymer molecular weight and temperature on case II transport

We investigated the effects of polymer molecular weight and temperature on Case II transport in the poly(methyl methacrylate)/methanol (PMMA/MeOH) system by a laser interferometric technique, using monodisperse polymer samples. Both the induction process and the steady-state front propagation were investigated. The data gave the volume fraction of MeOH in the swollen layer behind the moving front, ϕ, the steady state front speed, υ, and the characteristic induction time, t_ind. Values of ϕ separated into two groups, independent of molecular weight within each group. Significantly lower values of ϕ were found for polymers with molecular weight above the critical threshold for entanglement which can be explained by unrelaxed entanglements in the swollen layer. The Case II front velocity was independent of molecular weight for molecular weights at, or above, the critical weight for entanglement, suggesting that anelastic deformation processes other than simple viscous flow control the front propagation. Analysis of induction time data shows that the film surface properties differ from those of the bulk. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3159–3171, 1999     

Polymer decoration study in chain folding behavior of solution-grown poly(ethylene oxide) crystals

The polymer decoration method based on the vaporization and condensation-crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution-grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c-axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.     

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of polyisoprenes

Polyisoprenes (PIPs) with average molecular weights from 650 to 800,000 Da have been studied by time-of-flight secondary ion mass Spectrometry (TOF-SIMS) in the static mode. Polymer samples were bombarded by argon primary ions, and positive SIMS spectra were collected. Effects of branching and unsaturation in the polymer structure on ion formation were studied. The pendant methyl group showed little tendency to fracture as a cation. In the low mass region, C_nH _2n–1 ⁺ appeared to be more intense than C_nH _2n+1 ⁺ , attributed to the double bond structure of polyisoprene. Additionally, ion formation varied as a function of polymer molecular weight. Cationized intact oligomers and fragments dominate the high mass region. Oligomer distributions were used to calculate average molecular weights for polyisoprenes. A statistical chain scission mechanism was used to qualitatively explain the formation of five clusters within a unique fragmentation pattern. Detailed studies of the cluster structure pointed out that each cluster contained several species having varied degrees of unsaturation. It is believed that double bond rearrangements occur.     

Dependence of Polymer Chain Entanglements on the Solution Concentration

For the viscometric determination of molecular weights of polymers, sufficiently dilute solutions have to be used so that entanglements of the polymer chain are absent. The concentration of the polymer should be such that the relative viscosity (η_r) lies in the range 1.1–1.5 [1]. Similarly, for molecular weight determination by light scattering, the suggested concentration for polymer with weight-average molecular weight ( M _w ) > 10⁵ is 0.5 wt%; for those with M _w < 10⁵, up to 1% may be used [2].

The limits of polymer concentration for such measurements are not clearly known. On dissolution, the polymer molecules adopt a more or less extended configuration whose shape depends on the structure and molecular weight of the polymer, the properties of the solvent, and the temperature

[3]. The molecules of flexible linear polymers acquire a coiled configuration due to free rotation about the C-C bonds. When a dilute solution satisfies theta conditions, the polymer molecules are free from all kinds of interaction and move freely. Then their solution properties could possibly be related to their end-to-end distance. Based on this concept, our attempt to establish the permissible limits of polymer concentration for dilute solutions of several polymers of different molecular weights is reported here.     

Ammonia Chemical Ionization Mass Spectra of Sydnones

The mass spectra of twenty-nine sydnones were measured by using NII₃ as a reagent gas. The [M + H + NH₃]⁺ ions are the base peaks for the entire series. Very few fragment ions were observed except for the derivatives of 4-hydroxymethylenesydnones (XXI-XXIX). Only the relatively stable sydnonyl-methylene cations are formed. With consistent formation of [M + 18]⁺ ion as the base peaks with simple spectra, the NH₃ CI-MS can be an excellent method for the molecular weight determination.     

Photo-controlled/living radical polymerization mediated by 2,2,6,6-tetramethylpiperidine-1-oxyl in inert atmospheres

The photo-controlled/living radical polymerization of methyl methacrylate using a nitroxide mediator was established in an inert atmosphere. The bulk polymerization was performed at room temperature using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator and (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) as the initiator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the accelerator by irradiation with a high-pressure mercury lamp. The photopolymerization in a N₂ atmosphere produced a polymer with a comparatively narrow molecular weight distribution; however, the experimental molecular weight was slightly different from the theoretical molecular weight. The Ar atmospheric polymerization also provided a polymer with the molecular weight distribution similar to that of the polymer obtained by the N₂ atmospheric polymerization. These inert atmospheric polymerizations more rapidly proceeded to produce polymers with narrower molecular weight distributions than the vacuum polymerization. The livingness of the Ar atmospheric polymerization was confirmed on the basis of the first-order time–conversion plots and conversion–molecular weight plots.     

Molecular Weight Distributions of Polymer Solutions: Combination of Field Flow Fractionation (FFF) and Analytical Ultracentrifugation (AUC)

Molecular weight, distribution, as well as other molecular characteristics are important drivers in determining the potential behaviors and hence applications of polymeric materials. Out of different methods available for the determination of molecular weight and its distribution, field flow fractionation (FFF) provides absolute molecular weight values and accurate molecular weight distributions. Analytical ultracentrifugation (AUC), on the other hand, relies on the exact density of the polymer materials in solution to determine the accurate molecular weight and its distribution and in the absence of knowledge of exact density, AUC is less accurate than the FFF method. However, combination of the two methods can be achieved to gain insights into the other molecular characteristics of swollen polymer chains. One such example is the determination of the exact density of the swollen polymer chains by the incorporation of the molecular weight information from FFF into AUC analysis. Based on the comparison of the optimized polymer chain density with the bulk density, it was observed that the polyacrylic acid and polyacrylamide chains were swollen in the range of 27 to 29%. Moreover, the FFF and AUC can also complement each other in enhancing the range of characterization possible with the two methods when used separately.     

Effect of the remaining lanthanide catalysts on the hydrolytic and enzymatic degradation of poly-(ϵ-caprolactone)

Poly-(ϵ-caprolactone) is a biodegradable polymer, which can be used for both medical and environmental applications. Due to its multiple applications the synthesis of such a polymer has been attracting an increasing attention in the past few decades. In our work, the polymers were synthesised by bulk polymerisation, using different lanthanide halides as initiators. The lanthanide derivatives are known as very active catalysts in the ring-opening polymerisation of cyclic esters. Moreover, they are not toxic in comparison of catalysts, which are usually used for this synthesis. In this paper, the influence of the lanthanides on both the hydrolytic and enzymatic degradation of the PCL obtained by ring-opening polymerization of ϵ-caprolactone with different lanthanide-based catalysts such as: lanthane chloride (LaCl₃), ytterbium chloride (YbCl₃) and samarium chloride (SmCl₃) was assessed. Samarium seems to slightly accelerate the hydrolytic degradation of the polymer and to slow down or inhibit its enzymatic degradation, mainly when the molecular weight of the polymer is high. The behaviour of PCL containing another lanthanide like lanthane is dependent on the nature of the metallic ion. Complete degradation, by the Lipase PS from Pseudomonas cepacia, is achieved only with Ytterbium.     

“Living” radical polymerization of methyl methacrylate with diethyl 2,3-dicyano-2,3-diphenylsuccinate as a thermal iniferter

The bulk polymerization of methyl methacrylate (MMA) initiated with diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS) was studied. This polymerization showed some “living” characteristics; that is, both the yield and the molecular weight of the resulting polymers increased with reaction time, and the resultant polymer can be extended by adding MMA. The molecular weight distribution of PMMA obtained at high conversion is fairly narrow (M_w/M_n = 1.24≈1.34). It was confirmed that DCDPS can serve as a thermal iniferter for MMA polymerization by a “living” radical mechanism. Furthermore, the PMMA obtained can act as a macroinitiator for radical polymerization of styrene (St) to give a block copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4610–4615, 1999     

Synthesis of well-defined, polymer-grafted silica nanoparticles via reverse ATRP

The surface grafting onto ultrafine silica via reverse ATRP of methyl methacrylate initiated by peroxide groups introduced onto the surface and conventional ATRP of Styrene initiated by the hybrid nanoparticles were investigated. The introduction of peroxide groups onto the silica surface was achieved by the reaction of hydrogen peroxide with chlorosilyl groups, which were introduced by the treatment of silica with thionyl chloride. Well-defined polymer chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polymer layer. The polymerization was closely controlled in solution at quite low temperature such as 70 °C. In both cases, linear kinetic plots, linear plots of molecular weight (M_n) versus conversion, in hydrodynamic diameter with increasing conversion, and narrow molecular weight distributions (M_w/M_n) for the grafted polymer samples were observed. Hydrolysis of silica cores by hydrofluoric acid treatment enabled characterization of cleaved polymer using GPC. Ultrathin films of hybrid nanoparticles were examined using TEM and AFM.     

Quantitative analysis of styrene‐pentafluorostyrene random copolymers by ToF‐SIMS and XPS

Poly(styrene) (PS), poly(2,3,4,5,6‐pentafluorostyrene) (5FPS) and their random copolymers were prepared by bulk radical polymerization. The spin‐cast polymer films of these polymers were analyzed using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The surface and bulk compositions of these copolymers were found to be same, implying that surface segregation did not occur. The detailed analysis of ToF‐SIMS spectra indicated that the ion fragmentation mechanism is similar for both PS and 5FPS. ToF‐SIMS quantitative analysis using absolute peak intensity showed that the SIMS intensities of positive styrene fragments, particularly C₇H₇⁺, in the copolymers are higher than the intensities expected from a linear combination of PS and 5FPS, while the SIMS intensities of positive pentafluorostyrene fragments are smaller than expected. These results indicated the presence of matrix effects in ion formation process. However, the quantitative approach using relative peak intensity showed that ion intensity ratios are linearly proportional to the copolymer mole ratio when the characteristic ions of PS and 5FPS are selected. This suggests that quantitative analysis is still possible in this copolymer system. Copyright © 2005 John Wiley & Sons, Ltd.     

Cationic polymerization of styrene by acetyl perchlorate. II. Steric structure of the polymer and nature of the propagating species

Cationic polymerization of styrene initiated by acetyl perchlorate in CH₂Cl₂ yields a polymer having a bimodal molecular weight distribution. The high molecular weight and the low molecular weight portions of the polymer were separated by thin-layer chromatography, and the steric structure of these separated polymers was investigated by ¹³C NMR spectra. The high molecular weight polymer had a larger racemic dyad content than the low molecular weight material. From the dependence of the steric structure of the polymer on the polarity of a solvent, it was estimated that the propagating species producing the high molecular weight material was a loose ion pair or a free ion, and that producing the high molecular weight material was a loose ion pair or a free ion, and that producing the low one was a nondissociated species.