Effect solvatant des copolymères styrène–macromère a chaîne polyoxyéthylène. Influence du support polymère

Polyoxyethylene macromers were used to prepare functionalized linear and crosslinked copolymers with styrene and divinylbenzene. Gel or macroporous resins were prepared. These copolymers and resins were used as anionic activators for the Williamson reaction of potassium phenoxide and alkyl bromides under solid–liquid or solid–liquid–liquid (triphase) conditions. In contrast to similar resins obtained from chemical grafting of polyoxyethylene onto chloromethylated styrene–divinylbenzene polymers, the activity factors were strongly dependent on the composition of the resins and their morphology: an optimum activity was obtained for a 0.05M fraction of macromers in soluble copolymers and crosslinked resins. In addition, a macroporous resin with large pores was more efficient than a gel-type resin of similar composition. These effects are discussed in terms of accessibility of the activating group and compatibility of the support with the medium.     

Nouvelle méthode de détermination des taux de réativité des copolymères par résonance magnétique nucléaire: Application aux poly(méthacrylate de méthyle–chlorure de vinylidène)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by ¹H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.     

Analysis of fractionation of ethylene–propylene copolymers

Analysis of the solution fractionation of ethylene–propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.     

Separation of ethylene‐propylene copolymers and ethylene‐propylene‐diene terpolymers using high‐temperature interactive liquid chromatography

Ethylene‐propylene‐diene terpolymers (EPDM) are generally amorphous and, therefore, do not crystallize from solution. Consequently, fractionation techniques based on crystallization, such as crystallization analysis fractionation or temperature rising elution fractionation, cannot be used to analyze their chemical composition distribution. Moreover, no suitable chromatographic system was known, which would enable to separate them according to their chemical composition. In this study, two different sorbent/solvent systems are tested with regard to the capability to separate EPDM‐terpolymers and ethylene‐propylene (EP)‐copolymers according to chemical composition. While porous graphite/1‐decanol system is selective towards ethylene and ethylidene‐2‐norbornene, carbon coated zirconia/2‐ethyl‐1‐hexanol is preferentially selective towards ethylene. Consequently, the earlier system enables to separate both EP copolymers and EPDM according to the chemical composition and the latter mainly according to the ethylene content. The results prove that the chromatographic separation in both sorbent/solvent systems is not influenced by molar mass of a sample or by its long chain branching. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Copolymerisation radicalaire du méthacrylate de méthyle et du chlorure de vinylidène avec ou sans dérive de composition

Two sets of methylmethacrylate-vinylidene chloride copolymers were prepared via radical copolymerization in dimethylformamide. The first set is carried out in batches. Gas-chromatographic analysis of samples allows a kinetic study from which the reactivity ratios r_M - 2.73 and r_C - 0.24 are derived. For the second set a new apparatus, briefly described, has been used. It permits to keep constant the composition of the monomer mixture, through addition of methyl methacrylate, monitored by a chromatographic analysis. The two sets of copolymers are analyzed using nuclear magnetic resonance (60 MHz) leading to the triad distribution, from which the reactivity ratios are derived. Owing to the composition drift, the method cannot be applied to the first set of copolymers; but in that case, it is possible to calculate the triad distribution, the knowledge of the reactivity ratios, and the calculation fits quite well the experimental results.     

Synthèse de copolymères greffés à base de polyéthylène—1

Polyethylene macromolecular free radical initiators, obtained by ozonization, are used to prepare graft copolymers with methyl methacrylate, styrene and vinyl chloride. The reactions parameters are the number of initiator groups (found by DPPH), peroxide and hydroperoxide proportions (respectively 36 and 64%), decomposition rate (K_d at 90° 10⁻¹sec⁻¹) and monomer concentration. The molecular structure of these copolymers is defined.     

Block polymers from isocyanate-terminated intermediates. II. Preparation of butadiene–ϵ-caprolactam and styrene–ϵ-caprolactam block polymers

Polystyrene–nylon 6 and polybutadiene–nylon 6 block copolymers have been prepared from isocyanate-terminated prepolymers. From extraction and fractionation data the products obtained were found to be mixtures of both homopolymers and pure block copolymer. The polybutadiene–nylon 6 copolymers are extremely pliable at ambient temperatures even at high ?-caprolactam contents (70–80 wt-%). This is true even though these copolymers show a crystalline melting point at 213°C similar to poly-?-caprolactam. Presumably this unusual behavior occurs because of the nature of the synthesis which renders the butadiene portion of these copolymers the continuous phase. Plasticity measurements indicate that pliability is dependent on the molecular weight of the block poly-?-caprolactam.     

Styrene–isoprene block copolymers. I. Synthesis and solution properties

Copolymers with a different degree of distribution of styrene and isoprene blocks are prepared by anionic polymerization. The products are characterized by means of ¹H-NMR spectroscopy, GPC, viscometry, and light scattering. The results show that the copolymers are homogeneous in molecular weight and chain composition. In the investigated selective solvents, cyclohexane and base lubricating oil, and equilibrium exists between micelle aggregates and individual polymer coils. The influence of the copolymer structure on the micellization is more pronounced in cyclohexane.     

Synthèse et polymérisation de monomères chlorofluorés allyliques vinyliques et acryliques

Synthesis, polymerization and copolymerization of allylic, vinylic and acrylic monomers containing chlorinated or chlorofluorinated substituents were studied. The reactivity of terminal alcohols or acids is influenced by their neighbouring group. By products and their mechanism of formation were studied.La synthèse et la polymérisation d'acrylates fluorés, a donné lieu à de nombreux travaux. Une première méthode d'obtention de ces composés consiste à faire réagir un alcool fluoré avec un chlorure d'acide insaturé. Les acrylates obtenus sont de la forme :

     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

Acrylonitrile–4-vinylpyridine copolymers effect of comonomer sequence distribution on properties

Acrylonitrile–,4-vinylpyridine copolymers were prepared in chloroform solution at 60°C with AIBN as initiator. Copolymer compositions were determined from their 15.01-MHz ¹³C-NMR spectra. Reactivity ratios of r_AN = 0.093 and r_4VP = 0.32 were calculated by the Kelen and Tudos method. The run number, number-average sequence lengths, and monomer sequence distributions were also calculated. The T_g values of the copolymers, their dye uptake, and degree of alkaline hydrolysis were influenced by the overall copolymer composition but particularly by the monomer sequence distribution in the copolymers.     

Etude par RMN 13C à 62,89 MHz des branchements éthyles dans les copolymères ethylène-butène et polyéthylène basse densité

Carbon 13 nuclear magnetic resonance spectra (at 62,89 MHz) were obtained for a series of branched heavy alcanes (12-ethyl tricosane, 11,20-diethyl tricontane, 11,18-diethyl octacosane, 11,17-diethyl heptacosane, 11,16-diethyl hexacosane, 9,12-diethyl heneicosane, 5,7-diethyl docosane, 6,7-diethyl docosane, 2 éthyl-hexyl-12 tricosane), which provide a model set for describing the ethyl branched sequences in ethylene butene copolymers and low-density polyethylene (LDPE). For ethylene-butene copolymers we do not detect any head-to-head polymerization of butene as reported recently (the existence of a 1,2-ethyl pair has not been confirmed by the low-field signal at 41,3 ppm), but only isolated ethyl and 1-3-diethyl branches. The three peaks observed in the methyl region (broad signal) of the spectrum are assigned to butene centered triads, as opposed to branches in positions having different tacticities as reported earlier. Carbon 13 nuclear magnetic resonance spectra of high-pressure polymerized low-density polyethylene have been measured at 62,89 MHz. On the basis of Willbourn's double back biting mechanism, two kinds of complex branches, the 1,3-ethyl pair and 2-ethyl-hexyl, have been assigned. Finally, these results suggest that the ethyl branches in low-density polyethylene are not isolated branches.     

Fractionation of styrene–acrylonitrile copolymers

Three types of commercial styrene–acrylonitrile copolymer were fractionated by coacervate extraction and by column-elution techniques. Both methods were studied with two different solvent–nonsolvent pairs. Glass wool was used as the support material in the column. Fractionation by the coacervate extraction method was studied with benzene–triethylene glycol as a solvent–nonsolvent system at 60°C and with dichloromethane–triethylene glycol at 25°C. Column elution was carried out with acetone–methanol as the solvent–nonsolvent system at 30°C, and with dichloromethane–methanol at 20°C. Results of excellent reproducibility were obtained by these two methods. Characterization of fractions involved determination of both the molecular weight and chemical composition. It was established that the fractionation of the samples tested was dependent upon molecular weight only. The two methods described above are compared. Each gives an efficient procedure for fractionation of styrene–acrylonitrile copolymers.     

Characterization of impact polypropylene copolymers by solvent fractionation

The compositional heterogeneity of two impact polypropylene copolymers(IPCs) was studied by a combinatory investigation of temperature rising elution fractionation(TREF) and solvent fractionation.The chain structures and composition of fractions obtained from solvent fractionation were examined in detail.The TREF results shows that there are much more E-P segmented copolymer and more uniform distribution of ethylene sequence in IPC-1,which is responsible for its better comprehensive mechanical performance.The fractions from hexane and heptane are ethylene-propylene rubber phase and E-P block copolymers respectively.The result of solvent fractionation method also shows that custom hexane or heptane extractions can not extract the E-P copolymer completely.     

Polymerization of coordinated monomers. XVIII. Sequence distribution in methyl acrylate–styrene copolymers prepared in the presence of zinc chloride

Methyl acrylate and styrene have been copolymerized in the presence of zinc chloride either by photoinitiation or spontaneously. The copolymerization mechanism is investigated by analyses of copolymers composition and monomer sequence distribution. The resulting copolymers are not always alternating, their composition being dependent especially on the monomer feed ratio. Appreciable deviation to higher methyl acrylate unit content from an equimolar composition occurs at monomer feed fractions of methyl acrylate over 0.7. The larger deviation is induced by higher temperature, by photoirradiation, and by greater dilution of the reaction mixture with toluene. The ¹³C-NMR spectrum of the alternating copolymer shows a sharp singlet at the carbonyl region, whereas the spectra of random copolymers prepared by benzoyl peroxide initiation at 60°C show a triplet splitting at the carbonyl carbon region, irrespective of copolymer composition. The relative intensities of the triplet peaks for the random copolymers are in good correspondence to the contents of triad sequences calculated by means of conventional radical copolymerization theory. These results clearly indicate that the carbonyl splitting is caused predominantly by variation of the monomer sequence and not by variation of the stereosequence. The monomer sequence distribution in the copolymers is thus directly and quantitatively measured from the split carbonyl resonance. Although the same triplet splitting appears in the spectra of methyl acrylate–rich copolymers prepared in the presence of zinc chloride at high feed ratios (>0.7) of methyl acrylate, the relative intensities of the split peaks do not fit the sequence distributions of random copolymers calculated by means of the Lewis–Mayo equation. The copolymerization yielding these peculiar sequences and the alternating sequence in the presence of zinc chloride is fully comprehended by a copolymerization mechanism proceeding between two active coordinated monomers, i.e., the ternary molecular complex composed of zinc chloride, methyl methacrylate, and styrene, and the binary molecular complex composed of zinc chloride and methyl methacrylate.     

Adsorption of polymers at the solution–solid interface. XIV. Adsorption and steric stabilization with styrene–acrylonitrile copolymers

The adsorption of random copolymers of styrene and acrylonitrile of azeotropic composition from their trichloroethylene solutions onto precipitated silica exhibits a maximum at intermediate molecular weights. These copolymers are able to stabilize dispersions of some, but not all, grades of precipitated silica; here, too, a maximum effect is found at intermediate molecular weights. Copolymers are partially desorbed by ethyl cyanide, which destabilizes silica dispersions. Block copolymers of low acrylonitrile contents do not stabilize well but, when preadsorbed, affect the behavior of subsequently adsorbed random copolymers. In particular, high molecular weight random copolymers flocculate the pretreated silica; silica with grafted polyacrylonitrile chains may also be flocculated by these copolymers.     

Macroreticular resins. III. Formation of macroreticular styrene–divinylbenzene copolymers

Experimental evidence is presented that describes the mechanism of formation of macroreticular styrene–divinylbenzene copolymers in which phase separation occurs during a suspension polymerization. The mode of formation of the macroreticular structure is described as a three-stage process in which each droplet of the organic phase behaves as an individual in a bulk polymerization that results in a bead of copolymer. Macroreticular structure formation is described by changes in copolymer swelling ratios, infrared absorption spectra of vinyl groups pendent to the polymeric matrices, surface area, total porosity, and pore-size distribution. The proposed mechanism of formation is also substantiated by electron micrographs of the copolymers during various stages of the copolymerization.     

Agglomération contrôlée de latex par formation de complexes tensioactifs anioniques : copolymères à blocs à base de poly(oxyde d’éthylène)

For polystyrene–poly(ethylene oxide) (PS–PEO) diblock copolymers, as micellar dispersions in aqueous medium, the formation of complexes with anionic surfactants, such as sodium dodecylsulfate (SDS) could be confirmed. The number of SDS molecules fixed per EO unit is close to the values reported for the SDS–PEO homopolymer interaction. Advantage of this type of complexation was taken to develop a controlled agglomeration process for SDS stabilized PS and PVC latexes by using as agglomerants ‘hairy’ latexes of PS and PVC that have been synthesized in the presence of PS–PEO block copolymers and that carry therefore a fringe of PEO sequences on their surface. The complexation of SDS by these surface-anchored PEO chains leads to the destabilization of the anionic latex, which has a tendency to precipitate onto the surface of the agglomerant latex. The average particle size and the size distribution of the agglomerated particles were studied as a function of the weight and number ratio of the two types of latexes involved in the agglomeration process, as well as in function of the surface coverage by SDS and PEO respectively. By adjusting these parameters, it was possible to obtain, with an efficiency of almost 100%, latex agglomerates with a monomodal distribution in the size range of 1 to 40 μm. An agglomeration mechanism could be outlined taking into account the complexation capacity and the specific surface of the agglomerating ‘hairy’ latex. To cite this article: P. Peter et al., C. R. Chimie 6 (2003).     

Adsorption of polymers at the solution–solid interface. XIII. Adsorption and steric stabilization with styrene–2-vinylpyridine copolymers

Random and block copolymers of styrene and 2-vinylpyridine, covering the full range of composition, have been synthesized. The adsorption of these polymers from trichloroethylene solution on to precipitated silica has been studied and their ability to impart colloidal stability to the silica dispersions also investigated. Estimates of the layer thickness of adsorbed copolymers have been made. Polystyrene is not adsorbed from trichloroethylene and does not stabilize dispersions of precipitated silica. A random copolymer having 1% 2-vinylpyridine units is adsorbed but shows very little steric stabilization. Random copolymers of 2-vinylpyridine content greater than 10% and AB block copolymers of more than 6% 2-vinylpyridine behave very similarly in respect both of the quantity adsorbed and in their ability to stabilize silica suspensions. Layer thickness does not seem to depend on copolymer composition. Random copolymers with low to intermediate 2-vinylpyridine contents are better steric stabilizers in trichloroethylene than are the corresponding copolymers of methyl methacrylate with styrene: this is attributed in part to the longer sequences of adsorbable units in the vinylpyridine copolymers.     

An experimental and numerical study on crystallization analysis fractionation (Crystaf)

Crystallization analysis fractionation (Crystaf) is a new technique used to estimate the chemical composition distribution (CCD) of semi-crystalline copolymers. In this study, the effect of chain microstructure and operation parameters on Crystaf profiles was investigated using a series of ethylene/1-hexene copolymers and their blends. The Crystaf profiles were also modeled via stochastic simulation based on the distribution of average ethylene sequence lengths.