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The use of phenoxy nanocomposite films as carriers of nanofillers involving multiwalled carbon nanotubes and nanoclays is successfully demonstrated for application in epoxy carbon fibers reinforced composites (CFRC) processed by RTM. Model studies on individual nanocomposite filaments embedded in epoxy precursors show that the nanofillers are passively transported by the interdiffusion gradient during heating over distance around 800 lm. A morphology gradient is generated after reaction induced phase separation and the nanofillers end up in the epoxy, despite their initial dispersion in the phenoxy. The proof of concept is extended to CFRC panels where nanocomposite phenoxy films are prepositioned between every odd carbon layer of the preform. Carbon nanotubes are filtered by the carbon fabrics, which limits their full diffusion and that of phenoxy through the preform. This has negative consequences on fracture toughness (GIc). For nanoclay, GIc is rather slightly improved although the origin is not fully clear.

We explore the influence of the interdiffusion of two thermoplastic tougheners and RTM6 epoxy resin precursors on the resulting morphologies after curing and the consequences on delamination toughness of the corresponding carbon fiber reinforced composites. Two thermoplastics with contrasting Tg and compatibility, i.e. poly(ether sulfone) (PES) and phenoxy are compared. The dramatic improvement of the interlaminar fracture toughness (GIC) found for the phenoxy-RTM6 system as compared to the pure thermoset reference can be ascribed to the broad morphology gradient only observed for that system. By contrast, the PES-RTM6 system is characterized by a steep morphology gradient and a corresponding decrease of as compared to the reference.

Toughening of epoxy thermosets with thermoplastics is an important avenue towards improved properties of high-performance systems. The main focus of the work reported was to study the complex issue of interdiffusion between thermoplastics and epoxy resin precursors, using a combination of experimental and numerical simulation methods, in order to understand the key parameters driving the process. Diameter changes of thermoplastic filaments in contact with epoxide and diamine precursors have been followed and an original approach using carbon nanotubes as tracers of the filament swelling front has been developed. This method shows that the improved mobility of low-molecular-weight resin monomers as well as the greater mobility of phenoxy of lower glass transition temperature as compared to poly(ether sulfone) control dissolution by favouring the penetration of precursors into the thermoplastic and lead to both swelling of the outer part of the filaments and reduction of the inner unaffected core. Simulation by molecular dynamics supports the idea that diffusion of polymer macromolecules remains limited compared to the dominant effect of precursor diffusion. Indeed, low diffusion coefficients have been predicted for thermoplastic oligomers compared to resin monomers. For the latter, the calculated values correlate well with the experimental data measured during interdiffusion

19NMR spectroscopy has been performed on PEEK samples in sulphuric acid, revealing that most chain ends are fluorine. Different chemical shifts have been observed on sulphonated samples due to already demonstrated long range shielding effects. The method appears suitable for Mn determination. Substitution of F chain ends, followed by 19NMR, appeared feasible leading to alkaline sulphonate end groups. Ionic chain ends associations act as seeds for nucleation. Fast crystallizing PEEK and PEK are thus obtained. This is a new demonstration of the concept of Chemical Nucleation.

BACKGROUND: Preparative successive solution fractionation (SSF) is a powerful technique for obtaining narrow-dispersity fractions on a multi-gram scale of high-density polyethylene (HDPE). in a previous paper, the operative separation mechanisms during SSF of a broad HDPE in cyclohexanone were studied. Two mechanisms, and not only one as expected from the literature, contribute to the separation of HDPE molecules according to their molar mass (MM). The very low MM chains are separated by a solid-liquid (S-L) mechanism, while the longer chains are isolated by a liquid-liquid (L-L) phase separation. In the present paper, the influence of a poorer solvent, diphenyl ether, is reported. RESULTS: It is shown that the relative importance of the S-L mechanism with respect to the L-L one is altered by the use of this solvent. The L-L temperature range is increased in diphenyl ether while the S-L transition temperature remains unchanged. Consequently, the SSF efficiency is improved. Large amounts (on a gram scale) of narrow-dispersity fractions are isolated, mainly by the L-L mechanism. Polydispersities are about 1.5 (compared to 2.0 for cyclohexanone) and a broader MM range of closer molar mass distribution fractions is available. CONCLUSION: This work demonstrates that the use of diphenyl ether, a poorer solvent than cyclohexanone (always used as SSF solvent for polyethylene in the literature), leads to an improvement of SSF efficiency for an essentially linear HDPE. The differences of behaviour during the separation with cyclohexanone or diphenyl ether are explained by the establishment of a phase diagram. (C) 2009 Society of Chemical Industry

BACKGROUND: Preparative fractionation techniques are currently used in order to obtain large amounts of polyethylene fractions. Preparative successive solution fractionation (SSF) and temperature rising elution fractionation (TREF) are compared as regards obtaining, at a multi-gram scale, low-dispersity fractions of high-density polyethylene (HDPE). The operative separation mechanisms during a SSF of a broad HDPE, which are not yet totally elucidated, are also studied in this work. RESULTS: SSF and TREF approaches lead to the separation of HDPE macromolecules according to their molar masses. If very homogeneous fractions (dispersities from 1.1 to 1.3) are isolated in TREF at the lowest elution temperature, the collected mass is too low. At higher elution temperatures, the fractions have too broad a molar mass distribution (dispersities from 2.7 to 3.7). With the SSF procedure, dispersities are not as low as for the first TREF fractions. But, the relative weight fraction is better distributed between the different extraction temperatures. The molar mass distribution exhibits a dispersity of around 1.9. CONCLUSION: The SSF method is the most suitable way to obtain large gram amounts of low-dispersity (ca 2) HDPE fractions over a wide molar mass range. Complementary gram-scale rheological characterization is thus possible enabling a better comprehension of the SSF mechanism. Liquid-liquid demixing is the main mechanism in SSF, but its relative importance depends on polymer characteristics and solvent quality. (C) 2008 Society of Chemical Industry

BACKGROUND: The surface properties of high-density polyethylene and linear low-density polyethylene were modified by grafting urethane monoacrylate monomer under UV irradiation. This graft polymerization was carried out on native substrates and on substrates pre-treated by wet oxidation, for different oxidation times. RESULTS: As the urethane monacrylate layer is crosslinked, its grafting efficiency was checked by dissolving the polyethylene substrates in hot toluene. Grafting was evidenced by Fourier transform infrared spectroscopy of the obtained residues, which showed that both the characteristic urethane acrylate (3350 cm(-1)) and polyethylene (2920, 730 and 720 cm(-1)) bands were observable for any polyethylene oxidation time. For an oxidation time longer than 10 hours, acrylate grafting was homogeneous and the grafted surface was smooth with a roughness of less than 10 nm. In addition, X-ray photoelectron spectroscopy analysis of the residues revealed that O/C had an average value of 0.19, which is lower than the value corresponding to pure acrylate (0.42), whereas N/C had an average value of 0.068, also lower than that of pure acrylate (0.09), thus confirming the grafting. CONCLUSION: A urethane monoacrylate layer was grafted on native and oxidized polyethylene films. For highly oxidized films, the grafted surfaces are smooth and homogeneous. (C) 2008 Society of Chemical Industry.

We characterize sparsely and randomly branched polycarbonate and fractions thereof by a combination of solution and rheological techniques, and we compare the observations with the results of Monte Carlo simulations as well as tube-based modeling. On-line coupling of size exclusion chromatography with intrinsic viscosity (SEC-IV) yields values for the viscosity branching index g', which deviate significantly from linear behavior above approximately 0.3 branches per chain. The experimental g' also follows closely the predictions for the geometric branching factor g calculated by Monte Carlo simulations of the polymer structure across the entire molar mass distribution (g=g'). The Monte Carlo simulations provide an explicit description of the molecular architectures present and can therefore in principle be used to test models suitable for sparsely branched polymers. Experimental dynamic moduli of unfractionated and fractionated samples are compared with predictions of a tube-based model recently published in van Ruymbeke et al. [J. Non-Newt. Fluid Mech. 128, 7-22 (2005b)]. When the model is calibrated for polydisperse linear polycarbonate, discrepancies between the predicted and measured dynamic moduli are clearly observed at levels well below the detection limit of branching by the SEC-IV coupling method. The comparison between observed and predicted moduli is therefore a very sensitive method for the detection of sparse long chain branching in poorly and moderately entangled polymers, of which polycarbonate is a good example. (c) 2006 The Society of Rheology.

Surface modification of high-density-polyethylene (HDPE) and linear-low-density polyethylene (LLDPE) films is promoted by sodium hypochlorite solutions using two different processes (I and IT). Such an oxidation system introduces limited amounts of carbonyl-carboxyl and hydroxyl groups onto the surface of hydrocarbon polymers. FTIR, XPS, and SEM were used to assess the efficiency of the oxidation. The hydrophilicity of the studied surfaces was investigated by the sessile drop technique and the Wilhelmy plate and a plausible oxidation mechanism is proposed. (c) 2006 Wiley Periodicals, Inc.

We have developed a sensitive method to detect very low levels of long chain branching in sparsely branched polymers and applied it to high-density polyethylene samples with broad molar mass distribution obtained by Ziegler-Natta, Phillips, and metallocene catalysis. We compare experimental dynamic moduli with predicted values. The predicted moduli, which are only valid for truly linear chains, are computed from a known molar mass distribution by the application of a modified time-dependent diffusion reptation model described in [van Ruymbeke et al., Macromolecules 35, 2689 (2002)]. Discrepancies between experimental and predicted moduli are observed at branching levels below the usual detection limit Of C-13 nuclear magnetic resonance (about I branch per 10000 carbon atoms). Our method is easier to implement and the results more clearcut than those obtained by the zero-shear viscosity method. The sensitivity is comparable with the activation energy spectrum method described in [Wood-Adams et al., Macromolecules 33, 7489 (2000)]. The use of our method is however not restricted to thermorheologically complex polymers. The interest of polymer fractionation is also demonstrated for the detection of extremely low levels of long chain branching. (c) 2005 The Society of Rheology.

The previously developed model [Polym Bull 2000, 44, 525] used to characterize the porous gel inside a gel permeation chromatography (GPC) column, has been extended to also include the interstitial space between the macroscopic gel particles. The hydrodynamic dimensions for 12 polystyrene (PS) standards, measured by GPC with differential refractive index (DRI), differential viscometry (VISCO), and multiangle laser light scattering (MALLS) detectors, have been used to determine the fractal parameters of the polystyrene-divinylbenzene gel corresponding to four commercial columns. The new developed model enables to predict the calibration curve for the sets of coupled columns based on the parameters of each column. (C) 2004 Wiley Periodicals, Inc.

Owing to their low polydispersity and their well controlled molecular architecture, 3-arms stars polystyrenes made by anionic synthesis are suitable models to study the solution proper-ties of long chain branched polymers. A fine characterization of such polymers by size exclusion chromatography-viscometry has shown that they often contain unwanted linear chains, leading to chromatograms presenting overlapping peaks. A mathematical procedure has been developed in order to deconvolute these chromatograms and has been validated, thanks to blends of polystyrene standards. It allows one to calculate the purity of the sample as well as the intrinsic viscosity and molar mass distribution of each component. For stars with three arms of the same length, branching parameters have also been calculated and a viscosity law has been established. (C) 2002 Elsevier Science Ltd. All rights reserved.

The sulfonation kinetics of the fluoroarylketone chain-end repeat unit of PEEK was studied. To achieve this objective, the sulfonation reactions of a trimer, a tetramer and a polymer, each fluoroarylketone ended, were followed by F-19 NMR. A general kinetic model was developed to determine the kinetic constants from F-19 NMR data. The reliability of the kinetic model and of its mathematical expression was ensured. The kinetic constants are then calculated and discussed. In particular, they were compared with the dimer rate constants previously determined. Lastly and as a conclusion of this work, a general kinetic model describing the sulfonation of main chain repeat units of PEEK is proposed. (C) 2001 Society of Chemical Industry.

The sulfonation kinetics of fluorine ended poly(ether ether ketone) (PEEK) in solution in 95.9% and 96.8% concentrated sulfuric acid was studied with the help of a model compound representative of the PEEK chain repeat unit. The reaction rate of the model compound sulfonation was found to be first order with respect to the aromatic ring to be sulfonated. Consequently, PEEK kinetic data were treated following a first order with respect to the unsulfonated repeat unit concentration. Two rate-slowing effects were detected. They were attributed to 'long range' electronic effects resulting from the inductive nature of the fluorine atom, and from the electron-withdrawing character of the grafted sulfonic acid group. (C) 2001 Society of Chemical Industry.

Chlorinated polypropylene (CPO) is commonly used as an adhesion promoter for paint on polypropylene/ ethylene - propylene copolymer blends (PP/EP). An adhesion mechanism frequently proposed in the literature is the CPO diffusion into the substrate, leading to molecular entanglement. It is shown here that CPO and PP/EP are immiscible. On the other hand, the use of radiolabelled CPO allowed quantification of CPO diffusion into PP/EP substrates as a function of several parameters and under conditions which simulate industrial practice. Diffusion requires substrate swelling by the solvent. This explains that it increases with the EP content of the material, with the solvent ability to swell the substrate, and with the thickness of the paint. For baked samples, diffusion passes through a maximum when the delay between CPO application and baking is varied. This is due to a balance between two processes working in opposite directions, i.e. substrate swelling and solvent evaporation.

In this study we correlate parameters describing molecular structure (molar mass distribution, short chain branching content, intermolecular heterogeneity) of different ethylene-hexene Cr-catalyzed copolymers, with slow crack growth and rapid crack propagation resistances, respectively measured with Bent Strip and Charpy tests. The PTREF technique, coupled with classical techniques, was used. Two new indices were proposed to correlate mechanical properties and molecular structure. (C) 2001 John Wiley & Sons, Inc.

The mechanism and kinetics of sulfonation of two PEEK model compounds in concentrated sulfuric acid were studied. The first model compound (monomer) is representative of a PEEK repeat unit. The second one is a PEEK dimer. Because both model compounds are fluoroarylketone-ended, the sulfonation reactions were followed by F-19 NMR. The sulfonation reactions were treated following a first-order kinetics with respect to the unsulfonated PEEK repeat unit. The comparison between the monomer and dimer results showed two different types of sulfonation behaviour. If only one apparent kinetic constant is considered for monomer sulfonation, two kinetic constants were taken into account to describe the dimer sulfonation process. This is due to a rate slowing effect of a sulfonic acid group on the sulfonation of the adjacent PEEK repeat unit. Furthermore, the results also confirm the rate slowing effect of the fluorine atom on the sulfonation of the neighbouring PEEK repeat unit. (C) 2001 Society of Chemical Industry.

The purpose of this study is to propose a correlation between IR spectra and molecular structure of ethylene-propylene (EP) copolymers possibly blended with isotactic polypropylene (iPP). The method is based on the deconvolution of the spectrum in the CH2-rocking range, i.e., 800-680 cm(-1), where the bands of interest overlap. The six bands present in this region were signal averaged in position and width. The spectra were then deconvoluted (curve fitted) assuming a Lorentzian shape for the bands. The band at 1167 cm(-1) (with a shoulder at 1156 cm(-1)) corresponding to a CH3 vibration is considered as an internal standard. The method was checked by varying some fitting parameters. In order to realize some quantitative measurements, calibration curves were established with some EP samples, characterized by C-13 NMR, which were used as standards. The amounts of total -(CH2-CH2)- units (ethylene units), isolated ethylene and structural defaults in PP were determined for different iPP/EP blends. Ethylene crystallinity has also been determined. A good correlation was evidenced between infrared and C-13 NMR measurements. (C) 2000 John Wiley & Sons, Inc.

High-resolution solid-state C-13-NMR, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used to compare the very low crystalline degree and crystallite dimensions of ethylene runs in a series of isotactic polypropylene/ethylene-propylene copolymer blends exhibiting a range of properties. Results obtained from the three techniques on samples with the same thermal history are in a satisfying qualitative agreement. They show that the morphology of the polyethylene domains is only very slightly dependent on the viscosity ratio of the two blend components. On the opposite, it is largely governed by the ethylene content of the ethylene-propylene copolymer. (C) 1999 John Wiley & Sons, Inc.

The fractionation of a statistical copolyester made of poly(ethylene terephthalate- isophthalate) has been performed using Temperature Rising Elution Fractionation (TREF). TREF fractions were analyzed by size exclusion chromatography, thermal analysis, H-1-nuclear magnetic resonance and small angle X-Ray diffractometry. Results show that the fractions exhibit both interchain and intrachain defect distribution. As the intrachain defect distribution can not be determined by experimental techniques, a computer simulation based on the determination of terephthalic sequences length in a virtual polymeric distribution was performed. The simulated chains were constructed using a stochastic process. The analysis of the results obtained on the distribution of the simulated sequences in the polymer correlates quantitatively well between the new fractionation mechanism proposed for copolyesters and the experimental results.

The fracture toughness of PP-EP (Polypropylene-Ethylene-Propylene) blends is studied at room temperature using the "essential work of fracture" (EWF) method. The results obtained by applying this method are compared with those of puncture and tensile tests. Whereas the classical puncture tests do not allow classifying the rubber-toughened PP-EP blends, the EWF method proves to be a sensitive technique to monitor the effect of composition and morphology of the blend on fracture toughness. Moreover, the application of the EWF method allows monitoring how the fracture toughness of a material depends on its ability to deform extensively before fracturing and on its capacity to bear some load. A good combination of these two properties thus yields materials presenting an optimal fracture toughness.

Characterization of high-temperature poly(ether sulfone) (HTPES) molar mass was performed using light scattering, viscometry and size-exclusion chromatography (SEC). In pure N-methyl-2-pyrrolidone (NMP), a large increase of the reduced viscosity at low concentration was observed. By addition of a salt such LiBr, this effect was suppressed. Using the viscosity laws of HTPES and poly(methyl methacrylate) (PMMA) in NMP + LiBr the SEC method was standardized via the universal calibration established with PMMA standards. The Mark-Houwink-Sakurada (MHK) relationship for HTPES in NMP containing 0,1 mol/L LiBr at 25 degrees C with the intrinsic viscosity [eta] and molecular weight M afforded the MHK constants K = 33,8 . 10(-5) dL . mol(a) . g(1+a) and a = 0,70. The weight-average molar masses obtained from SEC were very close to those obtained from light scattering. A comparison of number-average molar masses obtained from H-1 NMR, potentiometric titration of chain-ends, and from SEC has shown more discrepancy for high molar masses. The study of dilute solution properties of HTPES macromolecules has shown the marked decrease of anisotropy with the number of repeating units, the low values of the characteristic ratio and of the Kuhn segment. All these conformational properties are similar to those of freely rotating chains.

HTX, a poly(aryletherketone-co-sulfone), is characterized in solution in concentrated sulfuric acid. Upon dissolution in concentrated H2SO4, HTX is chemically modified by sulfonation of phenyl rings. The modification of the chemical structure is studied with a model compound by means of IR spectroscopy. The increase of the molar mass corresponding to a complete sulfonation is determined by means of mass spectrometry. Light scattering and F-19 NMR measurements are performed in order to obtain the weight- (M(w)BAR)s and number-average (M(n)BAR)s molar masses of sulfonated HTX samples. (M(w)BAR)s values allow the determination of the Mark-Houwink-Sakurada relationship for HTX in 99,5% H2SO4 at 25-degrees-C.

A new method for poly(ether ether ketone) (PEEK) molecular-mass characterization by room-temperature (r.t.) size (steric) exclusion chromatography (s.e.c.) based on a derivatization procedure that improves the polymer solubility is described. Upon dissolution in 99.5% sulfuric acid at room temperature, PEEK is chemically modified by sulfonation of phenyl rings without polymer degradation. As complete sulfonation is achieved, the reproducibility of the chemical modification is ensured as well as the increase of molecular mass. Sulfonated PEEK is soluble at room temperature in different solvents suitable for s.e.c. N-Methyl-2-pyrrolidine (NMP) is selected as PEEK s.e.c. solvent. Owing to the polyelectrolyte nature of sulfonated PEEK, a salt (0.1 M LiBr) is added to NMP. Various broad-dispersity PEEK standards are used to establish specific and universal calibrations. The viscosity laws of sulfonated PEEK in NMP + LiBr (0.1 M), in methanesulfonic acid (MSA) and in 99.5% H2SO4 are determined. As sulfonated PEEK is a hygroscopic polymer, some spectroscopic methods are developed to determine the absolute concentration of the standards in order to perform accurate viscometric experiments giving the Mark-Houwink-Sakurada parameters in NMP-salt and in MSA. The s.e.c. universal calibration curve is constructed with poly(methyl methacrylate) narrow-dispersity standards.

HTX, a poly(aryletherketone-co-sulfone), is characterized by size exclusion chromatography (SEC) at room temperature. As HTX is not soluble in any solvent compatible with the SEC instrumentation, a derivatization procedure is applied in order to prepare a modified copolymer with improved solubility properties. This derivatization consists in a sulfonation by concentrated sulfuric acid. The derivative polymer is soluble in N-methyl-2-pyrrolidone (NMP), a classical SEC solvent. Sulfonated HTX (HTXS) is a polyelectrolyte. Consequently, a salt is added to NMP to perform reliable viscometric and SEC analyses. The SEC method is standardized with the establishment of the universal calibration with poly(methyl methacrylate) standards and the determination of the Mark-Houwink-Sakurada relationship of HTXS in NMP-salt at 25-degrees-C. Finally, the reliability of the derivatization procedure and of the SEC method is confirmed by comparison with molecular masses from NMR.

Some poly(ether ether ketone) (PEEK) samples were analysed by light scattering (l.s.) before and after complete sulfonation. Afterwards, the average molecular masses and molecular-mass distribution of the same PEEK samples are determined by high-temperature size (steric) exclusion chromatography (s.e.c.) for unmodified PEEK and by room-temperature s.e.c. (r.t.s.e.c.) for totally sulfonated PEEK. From this work, it appears that l.s. and s.e.c. measurements using sulfonated or unsulfonated PEEK sample give identical results within the limit of the s.e.c. and l.s. accuracy. This verification assesses the reliability of the derivatization method used to perform r.t.s.e.c. It is also shown that number-average molecular masses ((M) over bar(n)) of fully fluoroarylketone-terminated PEEK determined by F-19 nuclear magnetic resonance experiments agree very well with (M) over bar(n) values from s.e.c. These results support the validity of both s.e.c. methods used in this work. Finally, a PEEK-carbon fibre composite is characterized. The fibre content is evaluated. The derivatization process is applied to the matrix and the molecular parameters are obtained by r.t.s.e.c.

The solution properties of poly(methylphenyl)silane are studied in tetrahydrofuran at room temperature. Combined measurements by gel permeation chromatography (g.p.c.) and light scattering indicate that the absolute molecular-weight values of poly(methylphenyl)silane do not differ from the g.p.c. values obtained using a classical g.p.c. calibration with polystyrene standards. Some calculations are performed on the molecular-weight values using the theory of Yamakawa and Fujii. These results allow one to conclude that the behaviour in solution of poly(methylphenyl)silane can be described using a model based on rigid-rod-like elements involving about 40 Si atoms.

Fast-crystallizing poly(ether ether ketone) (PEEK) and poly(ether ketone) (PEK) samples have been prepared by substitution of the F chain ends, leading to alkaline sulphonate groups. Ionic chain-end associations act as seeds for nucleation. The concept of chemical nucleation already demonstrated with poly(ethylene terephthalate) is shown to apply to PEEK and PEK.

The purpose of this paper is to provide a correlation between lambda(max) and molecular weight for poly(methylphenyl)silane by the use of fractionated samples and by on-line coupling of a GPC chromatograph with a u.v. diode-array detector.

For decades, kieselguhr has been the most common filter aid for beer filtration. However, costs for disposal are severely increasing and brewers today are concerned about replacing kieselguhr filtration by a greener technology. Filtration trials were carried out with the regenerable filter aid oxidized high-density polyethylene (OxPE) on a pilot-scale candle filter using green lager beer from settling tanks. OxPE has an average particle size distribution of 37 μm and its outer surface presents nodular structures. The porosity of the OxPE media is 0.6 compared with 0.85 for kieselguhr. OxPE retains a good amount of haze and yeast cells without clogging; however, the expected clarity was reached only when using Brewtan. The use of polyvinyl-polypyrrolidone (PVPP) mixed with the OxPE filter aid (25/75%) showed the best results for filtration because of the shape of PVPP particles and their slight compressibility. Regeneration is one of the most important steps to achieve because the filter aid has to be reused as many times as possible while keeping its properties of retention toward haze and yeast cells. OxPE proved to have very good resistance to aggressive regeneration conditions, and filtration trials carried out after such an operation confirmed this. © 2012 American Society of Brewing Chemists, Inc.

This contribution concerns poly(methylphenyl)silane and, involves three topics: the first one is the calibration of the GPC technique by LS measurements. The second one is the study of the solution properties of that polysilane by LS technique and the last one, the calibration of a UV-M W relationship. The PSi GPC calibration is close to the PS one despite its behavior in solution can be described using a model based on rigid rod-like elements involving about 40 Si atoms.

In order to assess the reliability of absolute molecular weights of bisphenol-A polycarbonate samples measured by size exclusion chromatography, the results obtained from two experimental systems and two calibration methods are compared with each other as well as with data provided by light scattering determinations. The interest of coupling a light scattering detector to the chromatographic system is discussed.

The changes in the molecular composition of purified commercial polystyrene following thermal degradation were analyzed by gel permeation, reverse phase liquid and gas chromatography. Three major low molecular weight compounds were identified: styrene monomer, a dimer, and a trimer. The composition, the molecular weight, and the structure of the two oligomers were determined by elementary analysis, mass spectroscopy, nuclear magnetic resonance, and infrared spectroscopy. A linear structure with an ethylene end group is proposed for the two oligomers. The appearance of these degradation compounds is explained on the basis of an intramolecular mechanism involving chain-end folding and transfer of a labile tertiary hydrogen.

19F n.m.r. spectroscopy of poly(ether ether ketone) (PEEK) and related model compounds has been performed in various solvents including sulphuric acid. Different chemical shifts have been observed on sulphonated samples and long range shielding effects are discussed. An alternative method for the M n evaluation of PEEK is proposed.

Attempts have been made to determine the weight average molecular weight ( M W ), the radius of gyration ( R G ) and the second virial coefficient (A2) of five samples of poly(ether-ether-ketone) (PEEK) by light scattering (LS) in concentrated sulphuric acid. Account has been taken of the sulphonation of the polymer. Correlations between LS-molecular weights, melt viscosities and intrinsic viscosities in sulphuric acid or in a 50 50 phenol-trichlorobenzene mixture have been established. Gel permeation chromatography (g.p.c.) analyses at 115°C have been performed in this latter solvent and two calibration methods were compared.

The separation of polycarbonate (PC) oligomers is achieved by high-performance size-exclusion chromatography (h.p.s.e.c.) with styrene-divinylbenzene microparticulate gel as stationary phase and methylene chloride as mobile phase. Oligomers were separated up to ten repeating units. H.p.s.e.c. is also shown to be useful for analysing the low-molecular-weight content of commercial PC samples. Retention times are significantly influenced by the nature of the end-groups (O or OHO), indicating that adsorption occurs with hydroxy-terminated oligomers. H.p.s.e.c. separations are compared with results obtained by reverse-phase h.p.l.c. A simple method for determining the u.v. molecular absorption coefficient of the oligomers is proposed.

Two polypropylenes, PP1 and PP2, produced with different heterogeneous Ziegler-Natta catalytic systems were studied in this work. Preliminary characterization of the non-fractionated materials showed that a low difference in their average tacticity (PP2 > PP1) leads to an important modification of their rigidity properties. In order to establish correlation between the molecular structure parameters and the rigidity properties of these polymers, fractionation of the materials according to crystallizability was performed by means of temperature rising elution fractionation (TREF). Analysis of the fractions of both PP1 and PP2 was carried out by means of C-13 NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results first showed that TREF does not strictly fractionate PP according to tacticity, but according to the longest crystallizable sequence in a chain. C-13 NMR, SEC and DSC analysis of the fractions demonstrated that the inter-chain tacticity distributions of the polypropylenes is affected by the change of the polymerization conditions, which, in turn, modifies the rigidity properties of the materials. Some results also seem to indicate that the intrachain tacticity distributions are different for the two PP. An AFM study of the elastic modulus was carried out for the first time on the TREE fractions. It showed that the rigidity or the fractions strongly increases as the TREF elution temperature increases in accordance with a concomitant increase of isotacticity and the crytallinity of the fractions. PP2 TREE fractions were, moreover, found to exhibit a higher elastic modulus than PP1 TREF fractions at all elution temperatures. This study allowed us to further identify the TREF fractions that were responsible for differences in rigidity. To summarize, it is shown how the experimentally observed increase of the average rigidity of one of these two polypropylenes can be rationalized via information collected from a TREF fractionation. (C) 2000 Published by Elsevier Science Ltd.