Daniel Daoust

On the Molecular-weight Determination of a Poly(aryl-ether-ether-ketone) (peek)

Abstract 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.

A sensitive method to detect very low levels of long chain branching from the molar mass distribution and linear viscoelastic response

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.

Characterization of the molecular structure of two highly isotactic polypropylenes

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

F-19 Nmr End-group Analysis of a Poly(aryl Ether Ether Ketone) (peek)

Abstract 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.

Diffusion of adhesion promoter (CPO) into polypropylene/ethylene-propylene (PP/EP) copolymer blends: mechanism

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.

Chemical Modification of Poly(ether Ether Ketone) for Size-exclusion Chromatography At Room-temperature .2. On the Reliability of the Derivatization Procedure for Peek Molecular-mass Determination-application To Peek-carbon Fiber-composite

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.

On the Molecular-weight Determination of Bisphenol-a Polycarbonate

Abstract 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.

Chemical Modification of Poly(ether Ether Ketone) for Size-exclusion Chromatography At Room-temperature .1. Absolute Molecular-mass Determination for Sulfonated Peek

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.

Solution Properties of Poly(methylphenyl)silane

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.

Characterization of ethylene in EP and in iPP/EP systems by deconvolution of IR spectra

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