Relation between preferential solvation and intrinsic viscosity of polymers in solvent mixtures

Preferential solvation and intrinsic viscosity measurements are reported for three systems: polystyrene + benzene + methanol, polystyrene + carbon tetrachloride + methanol, and poly(2-vinylpyridine) + ethanol + cyclohexane. Plots of the coefficient of preferential solvation λ′ as a function of variation of the segment density Δ_ρ for a given ternary system, give a single curve for a large range of molecular weight and solvent mixture composition. This correlation between λ′ and Δ_ρ is verified in previously published data.     

Etude des dimensions moleculaires des polymeres dissous dans des melanges binaires de solvants polaires et non polaires—I. Polyvinyl-2 pyridine

We have studied the molecular dimensions of poly-2-vinylpyridine in solution in binary solvent mixtures consisting of a non polar and a polar component, viz. benzene-ethanol and benzene-chloroform. We have also studied the preferential solvation of the same polymer in the above mixtures using light scattering. We have observed a conformational transition of P2VP taking place in a composition region for each solvent mixture. This transition shows as a discontinuity in the unperturbed dimensions, in the long range interactions parameter and in the parameter of preferential solvation of the polymer. We think that this transition is related to the existence of two ordered structures of the polymer chain, one stable before and the other after the transition region.     

Reactive Polymers and Oligomers from Cyclic Ethers and Cyclic Sulfides

(2-Bromoethyl)oxirane is converted in 39% yield to poly-[(2-bromoethyl)oxirane] of inherent viscosity 1.99 dL/g. The AlEt₃/H₂O/AcAc system is a very effective initiator for the polymerization of (2-bromoethyl)oxirane. Poly[(2-bromoethyl)-oxirane] is a white elastomer, soluble in CHCl₃ and insoluble in CH₃OH. Polyether-urethane hydrogels are prepared by the room temperature crosslinking of poly[(3-hydroxypropyl)oxirane] with aliphatic or aromatic diisocyanates. These networks absorb 100–200% of their weights in water, and can be prepared in transparent form with potential application as biomaterials or contact lenses.     

Étude des systémes ternaires polymère-mélanges de solvants: relation entre solvatation préférentielle et viscosité

The preferential solvation of ternary systems of polymer with mixed solvents is characterized by the λ′ parameter which depends on the thermodynamic properties of the system and also on some molecular parameters of the polymer (molecular weight, index of polydispersity, index of branching etc.). The dependence of λ′ on molecular parameters can be illustrated by a unique relation between the λ′ parameter and the intrinsic viscosity [η]:λ′[η] = λ′_∝ [η] + a′ +. This representation is verified for polystyrene and polymethyl methacrylate in several mixed solvents.     

Structural features and initiating properties of the hexaadduct of polystyryllithium and fullerene C60 in tetrahydrofuran and their role in synthesis of heteroarm star-like polymers

Structural transformations of the hexaadduct of polystyryllithium and fullerene C₆₀ in the course of interaction with a proton donor or 1,1-diphenylethylene and at initiation of styrene polymerization were studied, and their role in the formation of heteroarm star-like polymers with C₆₀ center of branching and arms of polystyrene and poly-2-vinylpyridine was elucidated.     

Greffage de styrene et de styrene-acrylonitrile sur polybutadiene—comparaison des masses moléculaires

Polymerization of styrene in the presence of different types of polybutadiene leads to polystyrene (PS) grafted on to rubber and to free PS. It is shown that a difference in molecular weight exists between grafted and free PS; the molecular weight of grafted PS is systematically higher than that of free PS. A comparison to ABS systems has been made by grafting styrene and styrene-acrylonitrile in the same conditions on to polybutadiene. It appears that the difference in molecular weight between grafted and non-grafted polymer is much more pronounced in the case of ABS. These results can be explained by considering a decrease of the termination rate constant (k_t) in consequence of the local viscosity variations near the polybutadiene coils and by taking into account its preferential solvation by monomer and initiator.     

Synthesis and helicity of optically active poly(N‐propargylphosphonamidates) having chiral phosphorus center

Novel chiral N‐propargylphosphonamidate monomers (HC?CCH₂NHP(?O)R? O? menthyl, 1 : R = CH₃, 2 : R = C₂H₅, 3 : R = n‐C₃H₇, 4 : R = Ph) were synthesized by the reaction of the corresponding phosphonic dichlorides with menthol and propargylamine. Pairs of diastereomeric monomers 1 – 4 with different ratios were obtained due to the chiral P‐center and menthyl group. One diastereomer could be separated from another one in the cases of monomers 1 and 2 . Polymerization of 1 – 4 with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] as a catalyst in CHCl₃ gave the polymers with number‐average molecular weights ranging from 5000 to 12,000 in 65–85%. Poly( 1 )–poly( 4 ) exhibited quantitative cis contents, and much larger specific rotations than 1 – 4 did in CHCl₃. The polymers showed an intense Cotton effect around 325 nm based on the conjugated polyacetylene backbone. It was indicated that the polymers took a helical structure with predominantly one‐handed screw sense, and intramolecular hydrogen bonding between P?O and N? H of the polymers contributed to the stability of the helical structure. Poly( 1a ) and poly( 2a ) decreased the CD intensity upon raising CH₃OH content in CHCl₃/CH₃OH. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1515–1524, 2007     

Relation entre la solvatation preferentielle et la densite en segments de polymeres: Generalisations et limitations

This paper presents results on viscosity and preferential solvation for the ternary systems: polystyrene (PS)-carbon tetrachloride-methanol, PS-benzene-cyclohexane, PS-chloroform-ethanol and poly(2 vinylpyridine)-ethanol-cyclohexane using linear and branched polymers. For a given ternary system the representation Δλ′ (variation of the preferential solvation coefficient) as a function of Δρ (variation of the segment density) already proposed gives a unique curve. This shows that this relation is not sensitive to branching or to molecular weight of the polymer when the dimensions of the polymer in the mixed solvent are lower than in the pure good solvent. However, when the dimensions of the polymer in the mixed solvent are higher than in the pure good solvent, the relation between Δλ′ and Δρ cannot be applied.     

Solvation of Na+ in N,N-dimethylformamide + methanol solutions. A nuclear magnetic relaxation study using dynamic solvent isotope effects

Inter- and intramolecular nuclear magnetic quadrupole relaxation measurements have been used to study the system methanol (CH₃OH)+ N,N-dimethylformamide (DMF)+NaI at 25°C. The dynamic behavior of the solvent molecules was investigated, throughout the composition range of the binary mixtures, by means of ¹⁴ N relaxation of DMF and ² H of methanol-d ₁ (CH ₃ OD). The intermolecular relaxation of ²³ Na⁺ in pure DMF was used to obtain information about the symmetry of the solvent electric dipole arrangement in the solvation sphere of the ion. The investigation of preferential solvation around Na⁺ in the binary mixtures was carried out by means of ²³ Na⁺ relaxation measurements using, for the first time, both the CH ₃ OH/CD ₃ OD and the DMF/DMF-d ₇ dynamic isotope effect. The results show that, throughout the composition range, there is preferential solvation by DMF. Furthermore, the use of the isotope effects of both components allowed for the first time a basic check of the reliability of the method since we obtained two independent sets of data for the composition of the Na⁺ solvation shell in the mixtures. The consistency of the two separate data sets demonstrates that the application of the dynamic isotope effect represents a powerful tool in preferential solvation studies.     

Supramolecular Block Copolymers from Tricarboxamides. Biasing Co-assembly by the Incorporation of Pyridine Rings

The synthesis of a series of triangular-shaped tricarboxamides endowed with three picoline or nicotine units (compounds 2 and 3 , respectively) or just one nicotine unit (compound 4 ) is reported, and their self-assembling features investigated. The pyridine rings make compounds 2 – 4 electronically complementary with our previously reported oligo(phenylene ethynylene)tricarboxamides (OPE-TA) 1 to form supramolecular copolymers. C₃-symmetric tricarboxamide 2 forms highly stable intramolecular five-membered pseudocycles that impede its supramolecular polymerization into poly-2 and the co-assembly with 1 to yield copolymer poly-1-co-2 . On the other hand, C₃-symmetric tricarboxamide 3 readily forms poly-3 with great stability but unable to form helical supramolecular polymers despite the presence of the peripheral chiral side chains. The copolymer poly-1-co-3 can only be obtained by a previous complete disassembly of the constitutive homopolymers in CHCl₃. Helical poly-1-co-3 arises in a process involving the transfer of the helicity from racemic poly-1 to poly-3 , and the amplification of asymmetry from chiral poly-3 to poly-1 . Importantly, C_2v-symmetric 4 , endowed with only one nicotinamide moiety and three chiral side chains, self-assembles into a P-type helical supramolecular polymer ( poly-4 ) in a thermodynamically controlled cooperative process. The combination of poly-1 and poly-4 generates chiral supramolecular copolymer poly-1-co-4 , whose blocky microstructure has been investigated by applying the previously reported supramolecular copolymerization model.     

Salt effects on cloud points and viscosities of polymethacrylates with pendant oligo-oxyethylene chains

Comblike polymethacrylates with oligo-oxyethylene side chains were synthesized from the commercially available monomers CH₂ ? C (CH₃) COO (CH₂CH₂O)_nCH ₃, the average n being 4, 8, and 22. The three polymers exhibited lower critical solution temperatures in aqueous media. Cloud points were determined as a function of the nature and concentration of salt. For salts that destabilize the polymer solutions, the cloud points decrease linearly with salt concentration, the extent of the decrease being strongly anion dependent. Salt effects on the viscosity of the polymers were measured in water, methanol, and acetonitrile. In water the viscosity decreases on adding salt, but in methanol and acetonitrile the neutral polymers are converted to polycations as cations form stable adducts with the oligo-oxyethylene side chains. The increase in viscosity is both cation and anion dependent. The general behavior of the comblike polymers resembles that reported for aqueous or methanolic salt solutions of poly (ethylene oxide) and nonionic surfactants.     

Oligomerization of vinyl monomers 18. Stereochemistry of anionic oligomerization of 4-vinylpyridine

Oligomers of 4-vinylpyridine were prepared by reaction in vacuo of 4-vinylpyridine with lithio-4-ethylpyridine at ?78°C, followed by reaction with CH₃I(¹³CH₃I) or CH₃OH. The stereochemistry was studied by NMR and GC. Methylation and the addition of 4-vinylpyridine occurred in a stereochemically nonselective manner. The data also indicated that in contrast to the oligomerization of 2-vinylpyridine the stereoisomeric meso and racemic 4-pyridyl carbanions propagated with equal reaction rates. The stereochemistry was readily explained by an absence of coordination of the Li ion by the nitrogen of the penultimate pyridine ring observed in the corresponding oligomerization of 2-vinylpyridine.     

Reactions of living polystyrene with difunctional nitriles to produce specifically placed grafting sites

Graft polymers have been synthesized with two equal length branches and one or two branches of a different length or composition. The first step was a coupling reaction of living polystyrene with a difunctional nitrile. The product was hydrolyzed to form a ketone-containing backbone. Subsequently another sample of living polystyrene or of poly-2-vinylpyridine was added to the backbone to form the graft. Anionic polymerization was used for the synthesis of backbone and side chains, so all of the products are well defined. The products and reaction sequences also serve as models for a general synthesis of well-defined comb-shaped polymers, in which the length of the backbone, and the number, length, and spacing of the side chains may be controlled.     

Synthese d'ethers et de thioethers allyliques fluores par catalyse par transfert de phase

Several fluorinated allylic ethers, thioethers and diethers have been prepared in excellent yields by phase transfer catalysis (CTP). The used halogenated compounds are allyl chloride and bromide, p-chloromethylstyrene. The used fluorinated alcohols are aromatic pentafluorophenol and various aliphatics: CF₃CH₂OH, CF₂HCF₂CH₂OH ClCF₂CF₂CH₂OH,C₆F₁₃C₂H₄OH, HOCH₂CF₂CFClCF₂CH₂OH and HOC₆H₄C(CF₃)₂C₆H₄OH. All these new compounds have been characterized by ¹H and ¹³C NMR. We conclude that CTP is the best method to obtain allylic and diallylic compounds.     

A Molecular‐Dynamics Simulation Study of the Conformational Preferences of Oligo(3‐hydroxyalkanoic acids) in Chloroform Solution

The GROMOS96 molecular‐dynamics (MD) program and force field was used to calculate the conformations at 298 K in CHCl₃ solution of two hexakis(3‐hydroxyalkanoic acids). One consists of (R)‐3‐hydroxybutanoate (HB) residues only: H−(OCH(Me)−CH₂−CO)₆−OH ( 1 ). The other one carries the side chains of valine, alanine, and leucine: H−(OCH(CHMe₂)CH₂−CO−O−CH(Me)−CH₂−CO−O−CH(CH₂ CHMe₂)−CH₂−CO)₂−OH ( 2 ), with homochiral 3‐hydroxyalkanoate (HA) moieties. In both cases, the conformational equilibria were sampled 2500 times for 25 ns. Other than clusters of arrangements with inter‐residual hydrogen bonding (between the O‐ and C‐terminal OH and COOH groups, and with chain‐bound ester carbonyl O‐atoms; Fig. 6), there are no preferred backbone conformations in which the molecules 1 and 2 spend more than 5% of the time. Specifically, neither the 2₁‐ nor the 3₁‐helical conformation of the oligoester backbone (found in stretched fibers, in lamellar crystallites, and in single crystals of polymers PHB and of oligomers OHB) is sampled to any significant extent (Fig. 8 and 9), in spite of the high population, in both oligomers, of the (−)‐synclinal conformation around the C(2)−C(3) bond (angle ϕ₂ in Fig. 2). In contrast to β‐oligopeptides, for which strongly preferred secondary structures are found after a few ns, and for which the number of conformations levels off with time, the number of conformational clusters of the corresponding oligoesters found by our force‐field MD calculations increases steadily over the observation time of 25 ns (Fig. 5). Thus, the conclusion from biological and physical‐chemical studies, according to which the PHB chain is extremely flexible, is confirmed by our computational investigation: in CHCl₃ solution, the hexakis(3‐hydroxyalkanoate) chain samples its conformational space randomly!     

Polymer compatibility - a consequence of repulsive groups within monomer units

The majority of compatible polymer mixtures known so far has been rationalized by assuming special interactions between the different polymers or by specific repellent forces within certain types of copolymers. Thus, the compatibility of PMMA with special copolymers of styrene and acrylonitrile is explained by an intramolecular repulsion within the copolymer between the two comonomers styrene and acrylonitrile. In our opinion this phenomenon is not limited to copolymers, but also holds for explaining the compatibility of various homopolymers such as PVDF/PMMA. To this end we simply regard the homopolymer PVDF (-CH₂-CF₂-) as a copolymer of -CH₂- and -CF₂- “monomers”. By the same token it is possible to assume repellent forces within the PMMA monomer units (i.e. repulsion between the CH₂-C(CH₃) and the polar carbonyl group). Those strong repellent forces within the PVDF and PMMA homopolymers can be reduced by mixing the two species. This concept of repulsive forces within monomers as a driving force for polymer-polymer compatibility can be used to search for new classes of compatible polymers. This will be demonstrated with the polystyrene/polyalkylmethacrylate blends. Thus, with comparable geometry in the side chains, polystyrene and polymethacrylic esters will form compatible blends, as born out in the systems polystyrene/polycyclohexyl methacrylate or poly-tert-butyl styrene/poly-3,3,5-trimethylcyclohexylmethacrylate which are compatible in all proportions. Taking into account certain steric prerequisites, one can even obtain compatible blends lacking exothermic interaction.     

Preparation and characterization of polydimethylsiloxanes with narrow molecular weight distribution

The preparation of polydimethylsiloxanes (PDMS) of narrow molecular weight distribution (MWD) by anionic polymerization of hexamethylcyclotrisiloxane (D₃) in an improved polymerization apparatus is described. Using (CH₃)₂Si(OLi)₂ as initiator and (CH₃)₃SiCl (TMCS) as terminating agent, polymers with only methyl groups were obtained with molecular weights ranging from 2 × 10³ to 2 × 10⁶. Kinetic investigations were performed only so far as necessary for controlling the polymerization under the chosen experimental conditions (solvent: n-hexane, solvating agent: hexamethylphosphortriamide (HMPT), polymerization temperature: 25°). The molecular weights of the polymers were determined by light-scattering and, after calibration, by viscometry and GPC. The non-uniformities of the samples with symmetrical MWD were estimated using the 4σ-method. The GPC apparatus had been calibrated with polystyrene and poly-α-methylstyrene samples of extremely small non-uniformity.     

Etude de la nature des especes ioniques intervenant au cours de la polymerisation anionique de la vinyl-4 pyridine

Initiation of anionic polymerization of 4-vinyl-pyridine (4-VP) in tetrahydrofuran solution, using organo-metallic compounds of Na and K, involves the same type of side reactions as the polymerization of 2-vinyl pyridine (2-VP). The living polymers of 2- and 4-VP have similar u.v. spectra. The values of the dissociation constants of ionic species of 2- and 4-VP are similar when the chain [poly(styrene-b vinyl-4 pyridine)] contains one 4-VP unit (K_n ≈ 10^?9). But when the size of 4-VP block increases, the conductivity goes up to the value observed for living polystyrene (K_D ≈ 10^?7). This phenomenon could be due to a solvation of the counter-ion by the poly 4-vinyl pyridine chain, acting as a polydentate complexing agent.     

Synthese de materiaux polymers transparents - Partie II Synthese et polymerisation d'acrylates et de methacrylates d'halogenoalkyle

Several fluorinated and chlorofluorinated acrylates and methacrylates were synthesized from the alcohols R_FCH₂OH with R_F=CCl₃, CHClCH₂CCl₃, (CF₂CFCl)_nCl, (C₂F₄)_nH, CF₃, C₇F₁₅ and C₆F₁₃CH₂. The corresponding polymers were also studied for their application as transparent polymeric materials. For this purpose the refractive indices n²⁰_D of the monomers and the polymers were measured as were the Tg values of the polymers. A study of their infrared spectra shows to what extent these products could be utilized taking into consideration their absorption in the long wavelength range between 0.85 and 1.50 m. The refractive indices of these polymers, which are reduced when increasing the number of fluorine atoms in the molecule, and that of the Tg measured between 50 and 70° C for the fluorinated methacrylates, indicate a potential use of these polymers as sheathing materials for optical fibres.     

Effets de micelles cationiques sur l'hydrolyse alcaline d'acetanilides a groupe acyle active par des substituants electro-attracteurs

Micellar effects of CTAB upon the alkaline hydrolysis of CF₃-CO-N(CH₃)C₆H₅, CHCl₂-CO-N(CH₃)C₆H₄X and CH₂Cl-CO-N(CH₃)C₆H₄X, (X=p-OCH₃H,p-Cl) are reported. Variations of k_obs, and of kinetic order of the reaction with respect to HO^? ion, are interpreted as an acceleration of HO^?-catalyzed steps, and a decrease of catalysis by water for decomposition of tetrahedral intermediates; these two effects oppose each other in HO^? and H₂O catalyzed steps. Differences between micellar and DMSO effects suggest a very small local concentration of HO^? ions in micelles.