Caractérisation et propriétés rhéologiques en milieu dilué et à l'état fondu des poly(téréphtalate d'éthylène)s linéaires et ramifiés

Dilute solutions of linear and branched poly(ethylene terephthalate) (PETP) samples were investigated in various solvents (or mixed solvents) by osmometry, light scattering and viscometry. Branched PETP samples were obtained with the polyfunctional comonomers trimethylolpropane (functionality f = 3) and pentaerythritol (f = 4). For the branched samples, we determined the index of branching g' and compared the experimental results with polycondensation theory in order to estimate the average number of branches per molecule. Finally, the melt viscosity (at 290°C) of branched PETP was measured and compared with the melt viscosity of linear PETP.     

Contribution à l'étude des propriétés électriques et mécaniques dynamiques de quelques polyéthylènes chlorés à saturation

Electric properties of suspension chlorinated polyethylenes (chlorine content about 73%) are investigated at the frequency of 5 MHz, within the temperature range from 20 to 80°C. The observed relaxations are dependent on the chemical structure of the polymer. In addition, dynamic mechanical properties are studied within a temperature range of ?100 to +190°C. No parallelism is noticed between electrical and mechanical properties for this rigid-chain polymer.     

Influence des traitements thermiques à l'état fondu sur les cinétiques de cristallisation du poly(oxyméthylène)

The influence of the temperature of the melt T₁ on the kinetics and the morphology of a semicrystalline polymer (poly(oxymethylene)) was investigated using thermal analysis and optical microscopy. The thermodynamic melting point T and the enthalpy of melting at thermodynamical equilibrium ΔH were determined by extrapolation of the graphs T_f = f(T_c) and ΔH_f = f(T_c); (T = 198°C, ΔH = 251 J/g). For different temperatures of the melt (T₁ = 185°C, 195°C, 205°C), isothermal and non-isothermal crystallizations were analysed using the Avrami and Ozawa equations. Nucleation and spherulitic growth in this polymer were studied by using optical microscopy at elevated temperatures. Using different analyses, we observed initial nucleation followed by spherulite growth with the following influence of the temperature of the melt on the distribution and the number of spherulites: T₁ < T produces many small spherulites; T₁ > T gives rise to few large spherulites.     

Application de la chromatographie sur gel à l'étude des polyéthylènes ramifiés

The compositions of copolymers formed by reacting butadiene or isoprene (M) with lithium in tetrahydrofuran in the presence of varying amounts of alkyl dihalides have been studied. When butadiene was reacted with dibromo-p-xylene, it was found that the dihalide predominantly dimerised by a WURTZ condensation mechanism before reacting with butadiene thus giving a copolymer of general form the value of q depending on the initial reactant ratio. Isoprene was reacted with bis(2-chloroethyl)ether and with dibromodecane. With the former reagent, and to a lesser extent with the latter, there is evidence that some initiation takes place by direct reaction of the halide with lithium. Only very low molecular weight materials were obtained with this monomer and bis(2-chloroethyl)ether. The reasons for this are discussed.     

Relation entre la structure et les propriétés mécaniques dynamiques de polyéthylènes haute pression chlorés

The dynamic mechanical properties of chlorinated polyethylenes with well determined microstructures are studied at low frequency and a temperature range between ?140°C and +240°C. An interpretation of the mechanical behaviour of these products as a function of the chemical constitution of their chains is proposed.     

Contribution à l'étude de la métallation de structures polyisoprène, 1. Mèthode de dosage

Squalene, as a model compound, and polyisoprene were metalated by the complex of sec-butyllithium (sec-BuLi) with N,N,N′,N′-tetramethylenediamine. The rate of metalation was determined indirectly by further reaction with a deactivating reagent. Amongst the various agents tested, a solution of chlorotrimethylsilane (Me₃SiCl) in diethyl ether was preferred, as deactivation by this reagent does not lead to secondary reactions. The rate of silylation of sec-BuLi by Me₃SiCl was found to be influenced by the solvent and the temperature. The presence of diethyl ether, as solvent of silylation, and a reaction temperature of 0°C are suitable conditions for the reaction between lithiated polymers and Me₃SiCl.     

Synthèse et étude des propriétés rhéologiques de polyesters stéréoréguliers à base d'acide maléique et d'acide fumarique

Pure poly(butylene maleate) and poly(butylene fumarate) of high molecular weights were synthesized by reaction of the corresponding caesium and potassium dicarboxylates with 1,4-dibromobutane in 1-methyl-2-pyrrolidone at 110°C. During the reaction a substantial amount of oligomeric products, consisting mainly of cyclic compounds, is formed. From the study of the rheological properties at high temperatures (175 to 240°C) it was concluded that some crosslinking occurs rather than isomerization.     

Les effets thermiques associés à la transition vetreuse de films de poly(téearéphatalate d'éthylène)

Differential scanning calorimetry and thermomechanical analysis are used for examining the thermal behaviour of amorphous poly(ethylene terephthalate) films in the glass-transition range. By variation of the heating rate between 0,2 and 100 K. · min^?1, it is possible to obtain either an exotherm associated with a shrinkage, or an endotherm, or both of these phenomena. It is found that very low heating rates not only give rise to a retardation mechanism but also to a molecular rearrangement.     

Contribution à l'étude de la métallation de structures polyisoprène, . Etude sur polymères

Metalation of polyisoprene by the complex sec-butyllithium-N,N,N′,N′-tetramethylethylenediamine (secBuLi-TMEDA) is strongly affected by the conditions of reaction. In certain cases, a first order rate constant with respect to each reagent is observed. The mole ratio secBuLi/TMEDA has a preponderant effect on the rate of metalation. A maximum yield is observed when the mole ratio secBuLi/TMEDA is 1/0,5. Addition of a cocomplexing reagent, potassium tert-butoxide (tertBuOK), to the complex secBuLi-TMEDA yields a higher rate of metalation. A good yield can be obtained when polysioprene is treated with the metalating complex secBuLi-TMEDA-tertBuOK in a mole ratio of 1/0,5/1.     

Nouveaux copolymères alternés préparés à partir du dicyanure de propène-1 ylidène-1 avec le styrène et la vinyl-1 pyrrolidone-2

A trisubstituted ethylene, 1-propene-1-ylidene dicyanate has been prepared via Knoevenagel reaction of acetaldehyde and malonitrile with β-alanine as a catalyst. This product has been copolymerized in bulk — with 2,2′-azoisobutyronitrile as an initiator — with styrene and 1-vinyl-2-pyrrolidone. Preliminary ¹H and ¹³C NMR studies of the copolymers are in good agreement with an alternating structure besides minor proportions of homopolymers of styrene or 1-vinyl-2-pyrrolidone. The propagation mechanism has also been studied with ¹H-¹H correlation spectroscopy.     

Synthèse de diamines aromatiques macromoléculaires à basicité controlée à partir de poly(tétraméthylène glycol)

This study describes the synthesis of poly(tetramethylene glycol) with amino end-groups on both sides by chemical end modification. For this purpose, α-hydro-ω-hydroxypoly(oxytetramethylene) and α-propyl-ω-(3-aminopropoxy)poly(oxytetramethylene) are converted into aromatic diamines with controlled basicity. For this, different chemical reactions are performed in order to obtain different links between aromatic amines and poly(oxytetramethylene). This method leads to products which present pK_a values between 2,8 and 5,26 in accordance with theoretical values.     

Volumes spécifiques de polystyrènes en étoile à l'état liquide

Specific volume measurements carried out on linear and star-shaped liquid polystyrene versus the number average molecular weight, M_n scaling between 5000 and 2.10⁶, are in good agreement with a review of the experimental results of others. These results confirm the occurrence of a loss of volume per monomeric unit above a molecular weight of 10000 already observed for polystyrene in solution. We attribute the influence of this specific volume variation against M_n on the thermal dilatometric coefficient α = (1/v)dv/dT and the temperature of vitrous transition. We also attempted to give an explanation for this phenomenon.     

Etude comparée des propriétés mécaniques dynamiques des formes I et II du polybutène-1. Cinetique de transformation II → I

The behaviour of the molecular motion in synthetic cis- and trans-1,4-polyisoprenes was studied by nuclear magnetic resonance. The line-widths (ΔH_pp), second (M₂) and fourth moments (M₄) of the absorption curves were measured at 77, 4.2, and 1.3 K. The obtained values of ΔH_pp and M₂ for cis-polyisoprene indicate that the molecular motions are apparently not completely quenched at 77 K since there is a further increase in the values of M₂ and ΔH_pp when decreasing the temperature from 77 to 4.2 K. It was found also that the value of M₂ at 4.2 and 1.3 K (? 20 G²) was larger than the previously computed one for a rigid lattice (18.5 G²). The temperature dependence of M₂ and ΔH_pp for trans-polyisoprene is different from that for cis-polyisoprene. The values of M₂ are constant in the range from 77 to 1.3 K (? 19.5 G²), which suggests that the molecular motion is presumably stopped in this polymer already at 77 K.     

Photo-oxydation et photolyse de copolymères d'éthylène et d'acétate de vinyle à courte et grandes longueurs d'onde

Analytical and kinetic aspects of the photooxidation and photolysis in the solid state of various ethylene-vinyl acetate (EVA) copolymers (0 < VA (in mol-%) < 26) are described. At long wavelengths (λ > 300 nm), the photooxidation is independent of the vinyl acetate content. The acetate groups, which are not preferential sites for the photo-induced hydroperoxidation, are photoconverted into chain ketones similar to those formed in the photooxidation of low density polyethylene (LDPE). As the content of monomeric units of vinyl acetate increases, associations between alcohols formed and the acetate groups are observed, based on the appearance of the 3530 cm^?1 absorption band. The rate of the formation of vinyl-type insaturations is a decreasing function of the content of monomeric units of vinyl acetate. At short wavelength (λ = 254 nm) direct photolysis of the acetate groups is observed through the formation of alcohols and ketones again similar to those found in LDPE photooxidation. The rate of the EVA photolysis varies linearly with the vinyl acetate content. Oxygen reacts with the primary radicals formed at 254 nm. Alcohols and ketones are formed faster than through photolysis, although no stoichiometry change is observed.     

Hydroperoxydation primaire de terpolymères d'éthylène/propylène/éthylidene-5 norbornène-2

Ethylene/propylene/5-ethylidene-2-norbornene terpolymers (1) are very sensitive to photooxidation. In the early stages, hydroperoxidation occurs specifically at the carbon atom in α-position to the ethylidene group. Isolated and hydrogen-bonded hydroperoxides can be detected by IR spectrophotometry at 3550 and 3380 cm^?1, respectively. In post-thermolysis experiments at temperatures above 60°C the associated hydroperoxides were found to be less stable than the isolated hydroperoxides. Saturation of the ethylidene groups is concomitant with the decomposition of associated hydroperoxides, which are transformed thermally and photochemically into alcohols and cyclic saturated ketones. The lack of vinyl groups shows that hydroperoxidation proceeds only at the norbornene cycle.     

Photo-oxydation de polyéther-bloc-polyamides, 3. Propriétés des hydroperoxydes dans les homopolym`res de polyéthers correspondants

The photooxidation of poly(tetramethylene glycol) (PTMG), poly(propylene glycol) (PPG) and poly(ethylene glycol) (PEG) was studied at 60°C applying wavelengths longer than 300 nm. Hydroperoxy groups were found to accumulate in high photostationary concentration in PTMG and were decomposed essentially into formate groups. Hydroperoxides were observed in low photostationary concentration in PEG and PPG. Decomposition of the PPG hydroperoxides into formate groups showed that hydroperoxidation occurs, surprisingly, at the secondary carbon atom of the propylene glycol monomeric unit, rather than at the tertiary carbon. These results account for the large variation in the properties of hydroperoxides observed throughout the photooxidation of polyether-block-polyamides of various composition.     

Application de la spectrométrie mécanique et diélectrique à i'analyse du comportement du poly(téréphtalate d'éthylène). Influence de la cristallinité

In order to correlate crystallinity and dynamic mechanical properties, poly(ethylene terephthalate) (PETP) samples were prepared and subjected to viscoelastic measurements. The evolution of the glass-rubber transition is analyzed for samples annealed at different temperatures. Multiplexing analysis allows to draw the Cole-Cole plot and to develop a rheological model for the polymer behaviour. In the case of the amorphous PETP, the asymmetric Cole-Cole plot may be represented by a “biparabolic” rheological model. On the other hand, for the semi-crystalline polymer, the Cole-Cole plot is symmetrical and the corresponding rheological model is the “liquid Cole” one. Dielectric spectroscopy experiments are in good agreement with the previous method. Particularly, the Cole-Cole plot for semi-crystalline samples is perfectly symmetric. The previous rheological models with, in addition, a static modulus are applicable to glass-fibre reinforced PETP. These new models are called “limited biparabolic” and “Zener parabolic” model, respectively.     

Formation et propriétés élastiques de réticulats radicalaires préparés à partir d'esters méthacryliques

The preparations of the following methacrylic esters were investigated: 2,2-dimethyl-1,3-dioxolan-4-yl methylmethacrylate ( 1a ), 4-(2,2-dimethyl-1,3-dioxolan-4-yl)-3-oxabutyl methacrylate ( 2a ), and 2,3-epoxypropyl methacrylate ( 1b ). Using radical copolymerization, the corresponding networks were synthesized with ethylene dimethacrylate ( 5 ) as bifunctional monomer and with bis(4-tert-butylcyclohexyl) percarbonate as initiator in tetrahydrofuran. The acidic hydrolysis of the acetal or epoxy ring yields hydrophilic polymer networks. The networks prepared from 1a are characterized both by the equilibrium volume swelling degrees and by their elastic moduli. By coupling of the two techniques and with some assumptions, the determination of the molecular parameters of the system was carried out applying the theory of the rubber elasticity. The results obtained are discussed and it is shown that the networks are close to ideality.     

Propriétés physiques et mécaniques d'un copolymère séquencé polystyrène-polyisoprène-polystyrène hydrogéné

Differential scanning calorimetry (DSC) and stress-strain measurements have been made on a polyisoprene hydrogenated polystyrene-polyisoprene-polystyrene (SIS) elastomeric block copolymer and compared with those of the corresponding nonhydrogenated copolymer. The SIS copolymer was prepared by anionic polymerization with butyllithium in benzene. Both polymers are two-phase amorphous elastomeric materials displaying two glass transition temperatures. The transition temperature of the hydrogenated polyisoprene phase is only 4°C higher than that of the polyisoprene phase in the unhydrogenated material. Stress-strain curves measured on solvent cast films before and after hydrogenation show identical behaviors at low elongation. Both the tensile strength and elongation at break are smaller for the hydrogenated polymer. Comparison between the stress-strain curves measured in successive extension cycles shows that this polymer does not exhibit the “leathery” behavior generally observed for SIS elastomeric block copolymers, but behaves more like a typical vulcanized elastomer. This would indicate more rigid and much better separated polystyrene particles in the hydrogenated system.