Distinction entre les phénomènes d'agrégation et de micellisation présentés par des copolymères amphipathiques. Cas des copolymères polystyrène/polyvinylpyridinium en milieu aqueux

Hydrophobic-hydrophilic polystyrene/poly(4-vinyl-N-ethylpyridinium bromide) (poly-(l-phenylethylene)/poly[l-(N-ethyl-4-pyridinio)ethylene bromide]) block or graft copolymers were synthesized. These copolymers are well defined products, and are homogeneous in mole- cular weight and composition. They were obtained by quaternization, with ethyl bromide, of the nitrogen atoms of pyridine units of polystyrene/poly(4-vinylpyridine) block or graft copolymers. In dilute solution in a selective solvent for polyelectrolytic polyvinylpyridinium moities (water + salt), there is multimerization, i. e. presence of particles constituted by several macromolecules. Light scattering and ultracentrifugation measurements show that this multimerization is not the expected “micellization”, i.e. an “association” phenomenon due to the amphiphilic character of the copolymer, but corresponds Lo an “aggregation” phenomenon, resulting from incomplete dissolution of the product at the molecular scale.     

Anionic synthesis of well‐defined,poly[(styrene)‐block‐(propylene oxide)] block copolymers

Well‐defined, narrow molecular weight distribution (M_w/M_n ≤ 1.1) poly[(styrene)‐block‐(propylene oxide)] block copolymers with relatively high molecular weight poly(propylene oxide) blocks [e. g. M_n (PPO) = 10 000–12 000 g/mol] have been prepared by anionic polymerization. The polystyrene block (M_n = 5 000; M_w/M_n = 1.1) was prepared by alkyllithium‐initiated polymerization of styrene followed by chain‐end functionalization with ethylene oxide and protonation with acidic methanol. The resulting ω‐hydroxyl‐functionalized polystyrene was converted to the corresponding alkali metal salts with alkali metals (Na/K alloy, Rb, Cs) and then used to initiate block polymerization of propylene oxide in tetrahydrofuran. The effects of crown ethers (18‐crown‐6 and dicyclohexano‐24‐crown‐8) and added dimethylsulfoxide were investigated. Chain transfer to the monomer resulted in significant amounts of poly(propylene oxide) formation (50%); however, the diblock molecular weight distributions were narrow. The highest molecular weight poly(propylene oxide) blocks (12 200 g/mol) were obtained in tetrahydrofuran with cesium as counterion without additives.     

Micellisation de copolymères séquencés polystyrène-polyvinylpyridinium, 1. Méthodes d'études. Influence de la nature du solvant

The dilute solution properties of polystyrene-poly(4-vinyl-N-ethylpyridinium bromide) block copolymers (PS-PVPQ) are studied in solvents selectively solvating polyelectrolytic moieties (mixtures: water-methanol-0,1 M LiBr). For these multicomponent systems, the validity of the data given by light scattering, viscosity and sedimentation velocity measurements, is discussed. Diblock copolymers exhibit four different types of behaviours, depending on solvent composition. The macromolecules are dissolved singly in methanol, but they are associated when water is present. When the water content increases, the association degree passes through a maximum. Since the solutions may contain two species of particles, i.e. the single molecules and the multimers with a narrow weight distribution, the term of micellization for this association phenomenon is correct. Despite their high “molecular weight”, the micelles are small and hence they are very compact. Unlike results from other micellar polymeric systems, the micelle occurrence is accompanied by an increase of the intrinsic viscosity. The hydrodynamic volume of a micelle does not depend on the micellar weights; this can be explained by a star-like micellar model. Thus, the parameter determining the size of a micelle is not the number of molecules per micelle, but the length of the “branches”, i.e., the “soluble” blocks.     

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.     

Synthèse et caractérisation de copolymères coordinés par des sels métalliques

The anionic block copolymerisation of isoprene and 2-vinylpyridine (2VP) followed by a coordination with iron (III) chloride, leads to thermoreversibly crosslinked copolymers. These copolymers are character+ed by a low polydispersity (M?_w/M?_w≈1,1) between the coordination nodules of poly(2-vinylpyridine). The study of the swelling ratio at the equilibrium in benzene shows that such a polymeric network does not reach the equilibrium state expected from the thermodynamic analysis of the system. The presence of 2VP in the copolymer induces a screening effect which prevents the solvent diffusion through the polyisoprene network.     

Effect of the End‐Positioning of a Lithium Sulfonate Group on the Aggregation and Micellization Behavior of ω‐Lithium Sulfonate Polystyrene‐block‐polyisoprenes

Summary: ω‐Lithium sulfonate polystyrene‐block‐polyisoprenes were synthesized by anionic polymerization high vacuum techniques and a post‐polymerization reaction with 1,1‐diphenylethylene and 1,3‐propane sultone. The solution properties of ω‐lithium sulfonate block copolymers were studied in a low polarity solvent (CCl₄) which is a good solvent for both blocks. The study revealed the formation of aggregates due to the association of the lithium sulfonate groups (SuLi). The mass, size and shape of the aggregates were studied by static and dynamic light scattering and viscometry. The aggregation number decreased as the length of the chain increased and the aggregates showed a behavior similar to that of star polymers. The micellization of ω‐functionalized block copolymers was also studied in a polar selective solvent for polystyrene, N,N‐dimethylacetamide (DMA). Micelles formed from block copolymers containing the sulfonate group at the polyisoprene end exhibited an association number which was about 80% of that of the neutral block copolymer and had a higher critical micelle concentration. The samples having the polar group at the PS end showed a similar behavior.

The structures of the end‐functionalized block copolymers studied.     

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.     

Synthèse de polyglutarimides à partir de PMMA,de la cyclohexylamine et de la méthylamine, 3 Etude du mécanisme d'imidification sur des modèles macromoléculaires

In order to check the mechanism of intramolecular cyclization to obtain glutarimide rings, we have prepared various homo and copolymers: homo N‐methyl‐ and homo N‐cyclohexylmethacrylamide and the corresponding copolymers with MMA and MAA. This first study showed that methacrylamides are less reactive than other methacrylic derivatives as shown by the r₁ and r₂ values of MMA and N‐cyclohexylmethacrylamide. The cyclization at 250°C in xylene proves that in the case of N‐cyclohexyl derivatives, the following reactivity is obtained: amide‐acid ≫ amide‐amide ≫ amide‐ester. On the contrary with N‐methyl derivatives, the reactivity of each complex is higher although amide‐acid remains the more reactive. The steric hindrance may account for this phenomenon.     

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.     

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.     

SynthèSe de copolymères triséquencés polybutyramide-polystyrène et polybutyramide-polyisoprène

The synthesis of triblock copolymers with crystalline outer blocks of polybutyramide and a central block of polystyrene or polyisoprene was performed. First polystyrene (or polyisoprene) fitted at both ends with acyllactam functions were obtained. In a second step these endstanding functions promote the lactame polymerization to yield the polyamide blocks. A careful characterization of the resulting samples was carried out. The behaviour of these block copolymers is typically that of a thermoplastic elastomer, whereby the crystalline blocks constitute the physical crosslinks in the samples.     

Catalyse de transformation des oléfines par les complexes du tungstène. II. Télomérisation des oléfines cycliques en présence d'oléfines acycliques

A computer program has been adapted for use with the Sofica Light Scattering Photometer and extended for application to block copolymer studies. In the first part of the program, which is equally suitable for homopolymers and copolymers alike, the apparent molecular weight, M_app, radius of gyration 〈S²〉^1/2, and the virial coefficients A₂, A₃ are obtained in individual solvents. In the second part, M?_w and the parameters characterizing the heterogeneity in composition of the copolymer are calculated. This is achieved by solving three simultaneous equations from all combinations of experiments in six or more solvents with different refractive index increments. The first stage has been tested using data from a sample of polystyrene. The complete program has been applied to data originally treated by the usual graphical methods. Finally, the parameters derived by the two techniques are compared and discussed.     

Block copolymers by transformation of living anionic polymerization into controlled/“living” atom transfer radical polymerization

A method for the transformation of living anionic polymerization (LAP) to controlled/“living” atom transfer radical polymerization (ATRP) is reported and utilized for the preparation of block copolymers. The macroinitiators, polystyrene and polystyrene-block-polyisoprene containing the 2-bromoisobutyryl end group (PS-Br, M_n = 12 200, M_w/M_n = 1.04; PS-b-PIP-Br, M_n = 16 800, M_w/M_n = 1.03), were prepared by LAP of styrene and styrene/isoprene, correspondingly, and suitable termination agents. These compounds were used as macroinitiators for controlled/“living” ATRP to prepare block copolymers with methyl acrylate (PS-b-PMA), butyl acrylate (PS-b-PBA), methyl methacrylate (PS-b-PMMA), a mixture of styrene and acrylonitrile (PS-b-P(S-r-AN)) and also chain extension with styrene (PS-b-PS and PS-b-PIP-b-PS). The block copolymers were characterized by means of size exclusion chromatography, ¹H NMR and FT-IR spectroscopy.     

Block copolymers with controlled interphase width. Effects of interphase and composition on domain dimensions

Ultrathin osmium tetroxid stained sections of solution cast block copolymer films were studied by electron microscopy. Two morphological systems were prepared from diblock copolymers containing 80 wt.-% styrene and 20 wt.-% isoprene: Systems with asymmetric lamellar morphology cast from cyclohexane, a preferential solvent for PI; and spherical morphology of rubber spheres in a continuous PS matrix, cast from tetrachloromethane, a non-selective solvent. For the two morphologies the variation of domain dimensions was studied in dependence of molecular weight in the range from 70 000 to 600 000 g/mol. Two types of block copolymers were investigated: Unmodified block copolymers and block copolymers containing 10 wt.-% of a random interblock between the pure polystyrene and polyisoprene blocks. For both kinds of morphologies the domain dimensions of the unmodified systems vary with M_n^2/3 as predicted by Helfand's theory. In the modified block copolymers a much weaker increase with M_n is found for both morphological systems. The results can be understood in terms of equilibrium domain dimensions controlled by an interfacial tension depending on both composition and sequence structure of the block copolymers.     

Tuning Dispersity in Diblock Copolymers Using ARGET ATRP

Poly(methyl acrylate)‐b‐polystyrene with controlled molecular weight distribution of each block was synthesized via activators regenerated by electron transfer atom transfer radical polymerization. Polymers with tunable dispersity, in the range of M _w/M _n 1.32 to 2.0, were achieved by adjusting the concentration of the copper catalyst and reaction temperature, thereby controlling the rate of reversible deactivation reaction as well as the number of monomer units added during each activation cycle. Regardless of the increased dispersity, high chain‐end functionality was retained and the livingness of the macroinitiators was confirmed by chain extension, resulting in diblock copolymers with controlled dispersity in each block. Liquid chromatography under critical conditions was employed to determine if any macroinitiator remained in the final product.     

Syndiotactic styrene‐butadiene block copolymers synthesized with CpTiX3/MAO (Cp = C5H5, X = Cl,F; Cp = C5Me5, X = Me) and TiXn/MAO (n = 3, X = acac; n = 4, X = O‐tert‐Bu)

Copolymers sPS‐B consisting of blocks of syndiotactic polystyrene (sPS) and polybutadiene (B) have been prepared using CpTiX₃ (Cp = C₅H₅, X = Cl, F; Cp = C₅Me₅, X = Me) and TiX_n (n = 3, X = acetylacetonate (acac); n = 4, X = O‐tert‐Bu) activated with methylaluminoxane (MAO). If proper conditions are used, copolymers containing a range of styrene and butadiene molar fractions can be prepared. Structural analysis of these copolymers by means of ¹³C NMR spectroscopy allowed the assignment of different monomer diads (SS, SB, BB; S = styrene, B = butadiene) and the calculation of reactivity ratio products r₁·r₂. Differential scanning calorimetry (DSC) analysis further confirmed the block‐like structure of these copolymers. The melting points (T_m) of syndiotactic styrene sequences decrease as the styrene molar fraction decreases, whereas the glass transition temperature (Tg) increases with decreasing butadiene molar fraction in the copolymer. The polydispersity values (M_w/M_n) determined by GPC suggest that these copolymers are produced by a single site catalyst.     

Étude de la polymérisation du styrène en émulsion inverse

The polymerization of reversed emulsions water in styrene prepared with polystyrene-polyethyleneoxide block copolymers (Cop PS-POE) has been studied. The kinetics of this polymerization has been studied as a function of the parameters: type and concentration of initiator, phase ratio water/styrene, concentration of Cop PS-POE, molecular characteristics of Cop PS-POE. The type of the emulsion can be regulated by the characteristics of the Cop PS-POE and by the phase ratio water/styrene. The initiation of the polymerizations can be achieved by water soluble initiators (K₂S₂O₈). Correlations could be established between the rate of polymerization and the initiator concentration, the amount of water in the reversed emulsions and the concentration of Cop PS-POE. It was shown furthermore that the rate of polymerization increases with the POE content of two-block copolymers and that three-block copolymers are more appropriate for the polymerization in reversed emulsions. Finally the main influence of the water/styrene interface was demonstrated which regulates the transfer of radicals from the aqueous into the organic phase.     

Synthesis and characterization of new ABA triblock copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] and poly(ethylene oxide) blocks

ABA type block copolymers with poly[3(S)-isobutylmorpholine-2,5-dione] (PIBMD, A) and poly(ethylene oxide) (M_n = 6 000, PEO, B) blocks, PIBMD-b-PEO-b-PIBMD, were synthesized via ring-opening polymerization of 3(S)-isobutylmorpholine-2,5-dione in the presence of hydroxytelechelic poly-(ethylene oxide) with stannous octoate as a catalyst. M_n of the resulting copolymers increases with increasing 3(S)-isobutylmorpholine-2,5-dione content in the feed at constant mole ratio of monomer (M) to catalyst (C) (M/C = 125). No racemization of the leucine residue takes place during both homopolymerization of IBMD and polymerization of IBMD in the presence of PEO and Sn(Oct)₂. The melting temperature of the PIBMD segments in the block copolymers depends on the length of the PIBMD blocks. The melting temperature of the PEO blocks is lower than that of the homopolymer, and the crystallinity of the PEO block decreases with increasing length of the PIBMD blocks. The PIBMD block crystallizes first upon cooling from the melt. This leads to only imperfect crystallization or no crystallization of the PEO blocks.     

Comportement de copolymères greffés en milieu solvant sélectif des greffons. Cas des copolymères poly(styrène-g-bromure de vinyl-4 N-éthylpyridinium)

The dilute solution properties of amphiphilic graft copolymers with an “insoluble” polystyrene backbone (PS) bearing “soluble” poly(4-vinyl N-ethylpyridinium bromide) grafts (PVPQ), were studied in water-methanol-LiBr (0,1 mol/l) mixtures. In contrast to block copolymers with an identical chemical nature and in the same solvents, graft copolymers do not present intermolecular association. Viscometric data clearly show that a single graft molecule (or “monomolecular pseudo-micelle”), has a structure similar to that of a “plurimolecular micelle” of a block copolymer, and exhibits a compact star-like structure.     

Micellisation de copolymères séquencés polystyrène-polyvinylpyridinium, 2. Influence des caractéristiques moléculaires des copolymères

The influence of the molecular characteristics of polystyrene-poly(4-vinyl-N-ethylpyridinium bromide) block copolymers (PS-PVPQ) on their dilute solution properties is investigated in a solvent selective for polyelectrolytic moieties (water-methanol-0,1 mol/1 LiBr mixtures). It is shown that the association degree depends much more upon the length of the insoluble hydrophobic part of the macromolecule than on the length of the soluble hydrophilic part. Micelle dimensions could not be determined from light scattering measurements because of the compactness of the particles. Attempts for the calculation of micelle size were made using a star-like micellar model.