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.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 1. Kinetik,Molekulargewichtsabhängigkeit und Frage des Bruchmechanismus

The mechanical shear degradation of poly(decyl methacrylate) with weight average molecular weights 1,0·10⁶ ≤ M?_w ≤ 1,7·10⁶, and molecular polydispersity ratio M?_w/M?_n = 5 in dilute solutions is studied in turbulent flow as a function of molecular weight using a special apparatus consisting of two vessels connected by a capillary. Shear stress and shear rate remained constant during degradation. The rate of degradation was followed up by molecular weight distribution curves using gel permeation chromatography and described by ?dc_i/dt = k_i·cⁿ, i being a high molecular weight species of the distribution. The reaction was found to be of the first order (n = 1) independent of solvent and of capillary length. Rate constants k_i in the molecular weight range from 3,2·10⁶ to 13,5·10⁶ proved to be proportional to the hydrodynamic volume of the polymer molecules expressed in terms of the product of intrinsic viscosity and molecular weight [η]_i·M_i. This corresponds to a linear relationship between k_i and M_i^1,75. Additional experiments show that this type of dependence on molecular weight holds only for turbulent flow; in laminar flow the result of the literature could be confirmed that there is a linear relation between k_i and M_i¹. Both results are independent of capillary length. As to the mechanism of breakage in turbulent flow it seems that in one step each macromolecule is broken simultaneously into several smaller parts.     

Relation entre la solvatation préférentielle et la densité en segments de polymères de structure différente

This paper presents results on preferential solvation and viscosity in three ternary systems, (polystyrene (PS)-benzene-methanol, poly(2-vinylpyridine)-ethanol-cyclohexane, and PS-cyclohexane-ethanol) using linear and branched polymers. It is shown that the representation ΔΛ′ (variation of the preferential solvation coefficient) as a function of Δ_Q (variation of the segment density), gives curves which are not sensitive to branching and, therefore, caracteristic of the nature of the polymer and not of its structure. When there is an inversion in preferential solvation one can define “isosbestic” points, i.e. compositions of the solvent mixture for which Λ′ or Δ_Q are independent of the molecular weight of the polymer.     

Polymérisation anionique de l'acroléine, 2. Influence de la nature du contre-ion et de la température sur la cinétique de la réaction

In tetrahydrofuran, with Na⁺ and Li⁺ as counter-ions, the kinetic order of the anionic polymerization of acrolein is unity for monomer and for initiator. These results indicate that the living ends are not associated at the studied concentrations of initiator. The polymerization rate depends on the nature of the counter-ion. Transfer reactions to monomer do not affect the polymerization rate but greatly change the molecular weights M _n of polyacroleins. The experimental M are much lower than the theoretical M . The propagation constants k_pr and the transfer constant h_m are determined using these experimental values of M . From these results, we can conclude that with Li⁺ as counter ion, transfer reactions are much more numerous than with Na⁺. Furthermore, the polymerization rate increases with temperature. The activation energies of the propagation (E_a,pr) and transfer reactions (E_a,t) can be determined separately. When the temperature increases the propagation reaction is promoted in comparison to the transfer reaction to monomer, and simultaneously transfer reactions to polymer take place. This last phenomenon restricts the upper value of the polymerization temperature.     

Etude de la structure ramifiée du polyéthylène basse densité par viscosité et diffusion de la lumière de fractions issues de la chromatographie d'exclusion gpc

Fractions of high density polyethylene (PEhd) and low density polyethylene (PEld) obtained from gel permeation chromatography were studied by viscometry and light scattering. The variations of the intrinsic viscosity [η], the molecular weight M?_w, and the radius of gyration R_g for PEhd and PEld were compared with one another and the relationships [η] vs M and R_g vs. M for PEhd were established. The dependence of structural parameters g = (R_g²)_branch/(R_g²)_linear and g′ = [η]_branch/[η]_linear on the molecular weight was determined for three samples of PEld.     

Control of Macromolecular Architecture of Polyamides by Poly‐Functional Agents, 1. Theoretic and Experimental Approaches to Star‐Branched Polyamides

In this first paper of the series, a statistical model for star‐branched polycondensation of AB type monomers in the presence of a polyfunctional agent RA_f was completely developed. The analytical expressions obtained for the number‐average (DP_n) and weight‐average (DP_w) degree of polymerization, and the dispersion index (D) for whole polymer species, linear and star macromolecular chains, were derived as a function of the conversion of the functional group of RA_f. An important molecular parameter, mole fraction of star‐branched polymer, was introduced. Numerical examples are reported on the relationship between molecular parameters and conversion of the functional group of RA_f. It is illustrated that the molecular weight properties of the linear and star‐branched polymers in the mixture of the products are very important factors for the application of this kind of polymeric materials. Polymerization of 6‐aminocaproic acid was carried out in the presence of terephthalic (T2) and trimesic (T3) acids as tri‐ and bifunctional agents. The molecular weights calculated are in good agreement with those obtained by size exclusion chromatography (SEC).     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 2. Die Abhängigkeit der Abbaugeschwindigkeit von der Polymergesamtkonzentration in guten Lösungsmitteln

Mechanical shear degradation of poly(decyl methacrylate), (viscosity average molecular weight in tetrahydrofuran M?_η = 1,3·10⁶, M?_w/M?_n = 5) in the thermodynamically good solvent tetrahydrofuran has been studied in turbulent flow through a capillary as a function of polymer concentration in the range from 0,22 to 8,9 g/100 cm³. Due to turbulent flow conditions the shear stress, shear rate and shear energy proved to be the same for all concentrations and remained constant during degradation, giving a general insight into mechanism of degradation. The rate of degradation has been followed using molecular weight distribution curves obtained by gel permeation chromatography. The reaction was found to be of first order. Rate constants determined for molecular weights from 3,2–9,5·10⁶ decreased with increasing concentration following a law of the type k_i = (K + b·c)^?1, K and b being constants for each molecular weight. Hydrodynamic volumes of polymer molecules have been calculated according to models of Rudin as function of molecular weight and concentration. It can be shown that rate constants of degradation and calculated hydrodynamic volumes are proportional for the whole range of molecular weight and concentrations up to 3,6 g/100 cm³. There is also a rather good proportionality between these rate constants and the volumes of polymer coils predicted by de Gennes. This result is an additional confirmation of the concept that hydrodynamic volume governs shear degradation of polymer solutions. Additional experiments show that this type of concentration dependence is also to be found for other polymers in other solvents.     

Étude viscosimétrique de solutions de polyélectrolytes par dilution isoionique. Effet de la densité de charge sur la conformation du polyion

The reduced viscosity η_sp/c of dilute solutions of carboxymethylcelluloses (CMC) was studied, keeping the total ionic strength of the solution constant; the variation of η_sp/c with concentration is often linear and the Huggins constant k′ increases with decreasing ionic strength. So it is possible to obtain the intrinsic viscosity [η]_{I = 0} at zero ionic strength I and to calculate the corresponding molecular dimensions. The variation of [η]_{I = 0} with the degree of substitution of CMC is explained by a progressive change from a zig-zag conformation to a rod when the linear charge of the polyion increases.     

Viscosity and intrinsic viscosity/temperature relationships for dilute solutions of poly(2-biphenylyl methacrylate) and poly(4-biphenylyl methacrylate)

The actual viscosity η and the intrinsic viscosity [η] of six fractions of poly(2-biphenylyl methacrylate) {poly[1-(2-biphenylyloxycarbonyl)-1-methylethylene], (POB); weight average molecular weight M?_w: 4,0 · 10⁴ to 1,42 · 10⁶, polydispersity ratio M?_w/M?_n ≈ 1,4} and of three fractions of poly(4-biphenylyl methacrylate) {poly[1-(4-biphenylyloxycarbonyl)-1-methyl-ethylene], (PPB); M?_w : 8,1 · 10⁴ to 5,3 · 10⁵, M?_w/M?_n ～ 1,4} in benzene have been determined at different temperatures between 20 and 60°C. Values of the apparent activation energy of the viscous flow Q and the pre-exponential term A in the expression η = A · exp[Q/(RT)] have been obtained. Q varies with M?_w and concentration c according to Moore's equation: Q = Q₀ + K_e · M · c, where Q₀ refers to the solvent and K_e depends on polymer and solvent. The numerical value of K_e for POB and PPB is 1,6 · 10^?4 (6,7 · 10^?4) and -8,1 · 10^?4 cal · dl · g^?1 (-3,4 · 10^?3 J · dl · g^?1), resp. From all polymethacrylates studied POB is the only polymer with a positive K_e value. The positive value of K_e for POB may possibly be related to the more extended form of POB in benzene and also may be connected, at least partly, with its low flexibility. The temperature coefficient of the unperturbed dimensions dln〈r₀²〉/dT for POB estimated from the viscosity data using the Burchard-Stockmayer-Fixman relation, is 0,14 · 10^?3, much lower than for PPB (2,3 · 10^?3 between 22 and 40°C and 1,2 · 10^?3 between 40 and 60°C). The positive values of dln〈r₀²〉/dT indicate that extended conformations of these polymers in benzene must be associated with higher energies.     

Study on the molecular weight dependence of dilute solution properties of narrowly distributed polystyrene in toluene and in the unperturbed state

Intrinsic viscosities [η], second and third virial coefficients A₂ and A₃, respectively, and mean square radius of gyration 〈R_G²〉 of a polymer homologous series of narrow-molecular-weight-distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 10⁶ were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 10⁴ < M_w < 24 · 10⁶, M_w/M_n ≤ 1,3): These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero-shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to M_w = 1,8 · 10⁶. A comparison of the [η]?M_w-relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K₀, 〈h²〉₀/M, the characteristic ratio C_∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard-Stockmayer-Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.     

Polymérisation de diènes conjugués aux hautes pressions. IX. Polymerisation de l'isoprène en presence de HI

Basic assumptions and theoretical approaches concerning the determination of long chain branching by experimental determination of intrinsic viscosities [η], molecular weights M_w and radii of gyration r of statistical coils of polymers with low heterogeneity of molecular weight (U_M ≈ 0,5) are examined. Neither of the two theories which are often applied makes use of the correct relation between the ratios [η]_v/[η]₁ and of branched and linear molecules of a given molecular weight in good solvents. Both theories neglect the fact that the FOX -FLORY -constant Φ of molecules with strong random branching reaches a limiting value and that certain branching mechanisms give abnormal coil shapes and hence abnormal FOX-FLORY-constants Φ. This is verified experimentally by measurements on swollen spherical gel particles and fractions of star shaped as well as statistically branched polymers and of low-density polyethylenes. Both theories furthermore use restrictive assumptions about the molecular weight distribution and partly unsuitable averages for . Model calculations show that for molecularly inhomogeneous polymers approximately the weight average n_w, of the number of branching points per molecule is obtained, if the measurements are evaluated by means of the functions derived for unimolecular polymers. A new method for the evaluation of long chain branching is given, which takes into account the different draining of linear and branched molecules.     

Poly{[(Chloro-2 éathyl)-4 phéanyl]-1 éathylène}: Synthèse,caractérisations,dégradation thermique et modifications chimiques

Poly{1-[4-(2-chloroethyl)phenyl]ethylene} ( 3 ) was synthesized by bulk polymerization of 4-(2-chloroethyl)styrene ( 6 ) in two steps from commercial products. The polymer was characterized by means of GPC (weight-average molecular weight M?_w = 85 000 and number-average molecular weight M?_n = 63 500), ¹H NMR and ¹³C NMR spectroscopy. The first stage of thermal degradation begins at 290°C and ends at about 410°C. The overall activation energy was calculated to be 43 kcal · mol^?1 (180 kJ · mol^?1). The solid residue was crosslinked and insoluble. The volatile products, identified by gas chromatography-mass spectroscopy (GC-MS), were chiefly hydrogen chloride, dichloromethane and monomer. In a strongly basic medium, nucleophilic substitution of chlorine was achieved without elimination.     

Oligomerization and copolymerization of γ-butyrolactone — a monomer known as unable to homopolymerize, 1. Copolymerization with ε-caprolactone

Copolymerization of γ-butyrolactone (γBL) with ε-caprolactone (εCL) initiated with aluminium isopropoxide trimer ([Al(OⁱPr)₃]₃, (A₃)) is described. Copolymers with molecular weights (M _n) up to 3 · 10⁴ and containing up to 43 mol-% repeating units derived from γBL are prepared. Their molecular weight is controlled by the concentrations of the consumed comonomers and the starting concentration of initiator {M _n = (86.09 · [γBL]_c + 114.14 · [εCL]_c)/3[Al(OⁱPr)₃] + 60.10}. ¹³C NMR and DSC data are indicative of a pseudoperiodic or random copolymer structure.     

Living polymerization of [o-(trifluoromethyl)phenyl]acetylene by a new catalyst system,MoOCl4–Et3Al–EtOH (1 : 1 : 4)

A new MoOCl₄-based living polymerization catalyst, MoOCl₄–Et₃Al–EtOH (mole ratio 1 : 1 : 4)/anisole, has been developed. Polymerization of [o-(trifluoromethyl)phenyl]acetylene by this catalyst in anisole at 30°C yielded a polymer having very narrow molecular weight distribution (M_w/M_n = 1,02), a four-fold excess of ethanol over MoOCl₄ was necessary to attain narrow molecular weight distributions. Multistage polymerization experiments clearly showed the living nature of the polymerization, which was maintained in the temperature range of 0 to 30°C. The absolute number-average molecular weight of the polymer measured by vapor pressure osmometry could be correlated with the number-average molecular weight measured by gel permeation chromatography as follows: M_n(VPO) = 1,48 × M_n(GPC). The propagation rate constant (k_p) at 30°C is 1,5 mol·L^–1·s^–1.     

Effet de la concentration sur la transition conformationnelle des copolymères séquencés et greffés

In this paper we have been studying the effect of concentration c on reduced viscosity η_sp/c for a triblock copolymer poly(methyl methacrylate)/polystyrene/poly(methyl methacrylate) and for a graft copolymer of the same nature. The temperature of the experiments has been chosen in the range where the conformation changes from a segregated form to a pseudogaussian one. For this temperature range η_sp/c is not a linear function of concentration but the points η_sp/c vs. c are situated on two straight line segments with a well defined intercept. We discuss the phenomenon in comparison to results obtained on mixtures of homopolymers. These results suggest a strong and anomalous dependance of molecular conformation on concentration.     

Propriétés rhéologiques à l'état fondu de mélanges binaires de polyéthylène et de polybutène-1

The dynamic rheological study on a series of binary blends obtained from low-density polyethylene and poly(1-butene) was carried out. From our results we can propose an analogical pattern which is able to simulate the rheological behaviour of the blend in the melt state. We have calculated the different parameters of the model and their variations with temperature, composition, mixing and frequency. We have demonstrated that:

• The viscosity η₀ and the mean relaxation time τ₀ decrease with increasing temperature, while the parameter h of the distribution of relaxation times remains independant of the temperature.
• Kneading operation gives rise to a drop of the τ₀, η₀ and h values compared to those products which have not been kneaded.
• The viscosity η₀ is the weighted sum of the blend components.
• The viscosity η₀ of the blend is a function of the molecular weight.

     

Polymérisation de l'ε-caprolactone par des catalyseurs dérivés du bore

The cationic polymerization of ε-caprolactone catalyzed by boron derivatives, namely acyl fluoroborates, triethyloxonium fluoroborate (Meerwein's salt), boron trifluoride etherate and boron trifluoride was investigated. The acyl fluoroborates, especially the acetyl fluoroborate, produced high molecular weight polymers with fairly poor yields, whereas triethyloxonium fluoroborate gave a high yield of a rather low molecular weight polymer. The results were compared with those obtained with the two non-ionic catalysts. It seems that the acylium or ethylium group of the catalyst initiates the molecular chain and that the fluoroborate anion serves as catalyst and keeps the activity of the reaction site at the end of the growing chain. The mechanism is that of a polymerization without termination reaction (living-polymer type). However, according to the results of the kinetic study, this is true only in the case of acyl fluoroborates. The following relation between the viscosity and the number-average molecular weight of our samples was obtained: [η] = 1,25·10^?4M?_n^0,82.     

Synthesis of poly(9-hexyl-3,6-carbazolyleneethynylene) and its model compounds

The novel conjugated polymer poly(9-hexyl-3,6-carbazoylyleneethylene) ( 16 ) was prepared by palladium-catalyzed polycondensation of 3,6-diiodo-9-hexylcarbazole and 3,6-diethynyl-9-hexylcarbazole. The polymer has a number-average molecular weight (M?_n) of 3 100. By fractionation a polymer with M?_n of 6 400 was obtained. Besides polycondensation, a palladium-catalyzed bond-opening polymerization of the triple bonds occurs as a side reaction which can be partially suppressed by lowering the reaction temperature to 60°C. Two well-defined model compounds of the title polymer, a dimer and a trimer, were synthesized by stepwise reaction. The mass spectra of both model compounds demonstrate the remarkably high stability of the radical cations of the dimer and trimer. Since the trimer forms a stable glass it is ideally suited for the investigation of its photoconductive properties. First experiments carried out by the Time-of-Flight technique showed remarkably high carrier mobilities up to 2 · 10^?4 cm²/(V · s) for the trimer.     

Etude de la télomérisation de l'acide acrylique par les mercaptans, 1 Télomérisation de l'acide acrylique par l'acide thioglycolique; Influence de la nature du solvant sur la valeur de la constante de transfert et de kp/√kte

The telomerization of acrylic acid (AA) with thioglycolic acid (TGA) initiated with 2,2′‐azoisobutyronitrile (AIBN) was first investigated in organic medium (THF, 65°C). The kinetic study of this telomerization led to the determination of the TGA transfer constant (C_T = 3.2) and to the ratio k_p/√k_te equal to 0.48 L^1/2·mol^–1/2·s^–1/2. Then, the same study was performed both in aqueous medium and in water/THF mixture in order to investigate the solvent effect on the transfer constant. From these works it is emphasised that the nature of the solvent plays an important role on the kinetics parameters. First, this research underlined an increase of the k_p/√k_te value by raising the water proportion in water/THF mixtures. Then, the kinetic study showed the highest value for the k_p/√k_te constant, equal to 2.48 L^1/2·mol^–1/2·s^–1/2 when the telomerization proceeded in water. Consequently, the value of C_T, which is directly influenced by the k_p/√k_te constant, presented a decrease from C_T = 3.2 in THF to a value equal to 0.5 in water. By this way, the « ideal » case of telomerization (C_T = 1) was reached for a mixture of solvents; 80% water/20% THF (v/v).     

Beiträge zur polymerisation von 2-isopropenylnaphthalin, 3. Anionische homopolymerisation von 2-isopropenylnaphthalin

The anionic homopolymerization of 2-isoprenylnaphthalene with butyllithium in tetrahydrofuran at –78°C is described. The refractive index increment amounts to dn/dc = 0,2084 ml/g for these polymers in toluene at 25°C and wavelength λ = 436 nm. Determination of the molecular weights by light scattering yielded values between 13 000 and 270 000. The second virial coefficients also determined by light scattering measurements are comparable with the corresponding data of poly(α-methylstyrene). A calibration curve is given for gel permeation chromatography of the poly(2-isoprenylnaphthalene)s, whose polymolecularity indexes M_w/M_n lie between 1,06 and 1,2. Their intrinsic viscosity/molecular weight relationship is [η] = 1,43·10^?2 M^0,663. From ¹H NMR of the α-methyl group fractions of isotactic triads between 30 and 55% are evaluated. The glass transition temperature extrapolated to infinite molecular weight is T_g∞ = 221°C. Above 300°C fast degradation by monomer formation is observed.