Showing papers in "Macromolecular Chemistry and Physics in 1997"
TL;DR: In this paper, the formation of cylindrical morphologies is governed by the sum of the volume fractions of the components A and B (Φ A + Φ B ) as well as by their ratio (ϵ B /ϵ A ).
Abstract: In asymmetric ABC triblock copolymers with C being the matrix-forming majority component, the formation of cylindrical morphologies is governed by the sum of the volume fractions of the components A and B (Φ A + Φ B ) as well as by their ratio (Φ B /Φ A ). The paper describes the morphologies of various polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) and polystyrene-block-poly(ethylene-co-butylene)-block-poly(methyl methacrylate) block copolymers (SEBM) in dependence on these parameters. In addition to previously reported cylinder in cylinder (c i c, core shell) and helical (hel) morphologies, new microphase separated structures as cylinders at cylinder (c a c), undulated/perforated cylinder in cylinder (uc i c) and spheres on cylinder (s o c) are discussed. Based on a simple theoretical approach the transitions between these various morphologies are predicted. especially focusing on the transition between the c i c and c a c morphologies.
165 citations
TL;DR: In this paper, the polymerization of lactides with various D/L enantiomeric compositions using achiral Schiff's base/aluminium methoxide as initiator (SALENAlOCH 3 ) in dichloromethane solution at 70°C is reported.
Abstract: The polymerization of lactides with various D/L enantiomeric compositions using achiral Schiff's base/aluminium methoxide as initiator (SALENAlOCH 3 ) in dichloromethane solution at 70°C is reported. The conversion was kept below 70% in order to limit transesterification reactions. The polymers obtained after precipitation show a narrow molecular weight distribution (ratio of weight- to number-average molecular weights M w /M n = 1,1 - 1,2) and an optical rotation higher than that expected from the optical purity of the starting monomers. The examination of the thermal properties reveals that whatever their enantiomeric composition all the prepared polymers are crystalline. This unusual behaviour is explained by an end-chain propagation mechanism producing stereocopolymers with long enantiomeric sequences, i.e., increased isotacticity, as substantiated by an examination of the microstructure of the polymers by means of 13 C nuclear magnetic resonance. A stereocomplex formation was observed for stereocopolymers with optical purities below 40%.
150 citations
TL;DR: In this article, infrared temperature studies of a polyurea formed from 2-methylpentane-1,5-diamine and 4,4′-methylenebis(phenyl isocyanate) are presented.
Abstract: Infrared temperature studies of a polyurea formed from 2-methylpentane-1,5-diamine and 4,4′-methylenebis(phenyl isocyanate) are presented, together with those of two model diureas, 2-methylpentane-1,5-diphenylurea and ethylene diphenylurea. The main thrust of the work concerns the interpretation of the infrared changes that are observed in ordered and disordered hydrogen bonded ureas.
138 citations
IBM1
TL;DR: In this paper, a macromonomer was incorporated into the polymeric backbone to give block copolymers of controlled molecular weight and narrow polydispersities. But the graft copolymerization mixture was also used to give graft systems with a variety of functional groups attached to the backbone.
Abstract: Well defined graft copolymers have been synthesized by a nitroxide-mediated “living” free radical process using pre-formed macromonomers. Analysis of the graft systems revealed that the macromonomer was efficiently incorporated into the polymeric backbone to give block copolymers of controlled molecular weight and narrow polydispersities. An added benefit of the “living” free radical process is that macromonomers, such as polylactide or polycaprolactone, which contain reactive functional groups can be used to form novel graft systems using this approach. Functionalized monomers or polymeric initiators were also used in the copolymerization mixture to give graft systems with a variety of functional groups attached to the backbone.
116 citations
TL;DR: In this article, the effects of large amplitude oscillatory shear (LAOS) flow on the orientation behavior of lamellar polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers with emphasis on the identification of key parameters that govern the observed behavior.
Abstract: A survey is given on the effects of large amplitude oscillatory shear (LAOS) flow on the orientation behavior of lamellar polystyrene-block-polyisoprene (PS-b-PI) diblock copolymers with emphasis on the identification of key parameters that govern the observed behavior. For LAOS at temperatures close to the order-disorder transition temperature, T ODT , three orientation regimes related to the dynamic shear viscosity of the polymers are observed: parallel orientation at high frequencies, perpendicular orientation at intermediate frequencies, and parallel orientation again at very low shear frequencies. In annealing experiments it is found that the low frequency orientation behavior depends strongly on the thermal history of the samples. In conceptually new dual frequency experiments the effect of the superposition of two deformation components with frequencies in two different orientation regimes is described. From further studies identifying strain as the control parameter in these nonequilibrium experiments an orientation diagram for the long time orientation behavior of lamellar PS-b-PI diblock copolymers is constructed as a function of strain and frequency. For intermediate time scales in the experiments it is shown that the third orthogonal orientation component, the transverse orientation, can be obtained as a transient state. For all orientation components possible orientation mechanisms are discussed.
113 citations
TL;DR: In this article, the synthesis of new functionalised macromers containing perfluoropolyether structures (PFPE) is reported, which are obtained by reaction of bis-CH 2 OH terminated PFPE with isocyanato-ethyl methacrylate (EIM).
Abstract: The synthesis of new functionalised macromers containing perfluoropolyether structures (PFPE) is reported. They are obtained by reaction of bis-CH 2 OH terminated PFPE with isocyanato-ethyl methacrylate (EIM). giving rise to the formation of perfluoropolyether bisurethane methacrylate (PFEUMA) oligomers. The products are characterised by NMR and FTIR analyses. The thermal behaviour reveals two amorphous phases, corresponding to the fluorinated and the hydrogenated moieties, while a crystalline phase can be present depending on the macromer structure. The functionalised macromers are UV-cured in the presence of a photoinitiator and the complete disappearance of the double bonds is obtained. The cured films are characterised by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) confirming the presence of a multiphasic structure. Moreover the optical properties and the surface properties of the cured systems are investigated and discussed.
108 citations
TL;DR: In this paper, experimental results on rheological characteristic properties of semi-dilute chitosan solutions in weakly acetic acid have been investigated and the most important results refer to the activation energy of viscous flow found from Arrhenius plots.
Abstract: The present work is concerned with experimental results on rheological characteristic properties of semi-dilute chitosan solutions in weakly acetic acid. The flow measurements were conducted on solutions of chitosan of various deacetylation degrees DD (62.8%-86.7%) with changing experimental conditions such as concentration (up to 5 g/100 mL), temperature (20°C-41°C) and shear rate applied (up to 10 3 s -1 ). Chitosan solutions behave generally as a typical non-Newtonian shear-thinning fluid with a characteristic n-parameter lower than 1. The rheological n-parameter decreases with decreasing deacetylation degree and increasing solution concentration but it increases with increasing temperature. Because of strong intermolecular hydrogen bonding even at low concentration the chitosan macromolecules have a tendency to entangle and to network formation. The density of the molecular entanglements in the chitosan solution depends on concentration, temperature and shear rate applied. An effect of the deacetylation degree on the Huggins viscosity constant related to polymer solvent interaction is found. The most important results refer to the activation energy of viscous flow found from Arrhenius plots. The dependence of the activation energy on solution concentration, shear rate and DD is discussed.
103 citations
TL;DR: In this article, ABC triblock copolymers of polystyrene-block poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) and poly styrene-blocks poly(4vinyl pyridine]-blockpoly (tertbutyl methyl methacylate) were synthesized by sequential living anionic polymerization in tetrahydrofuran.
Abstract: Well defined ABC triblock copolymers of polystyrene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) and polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) were synthesized by sequential living anionic polymerization in tetrahydrofuran. Triblock copolymers with narrow molecular weight distribution were obtained. Hydrolysis of the poly(tert-butyl methacrylate) block yields polystyrene-block-polyvinylpyridine-block-poly(methacrylic acid) which demonstrates pH-dependent solution properties. Interpolymer complexation of the polyvinylpyridine and poly(methacrylic acid) blocks in the micellar solution is studied in dependence of the pH in solution by potentiometric, conductometric and turbidimetric titration, and in bulk by FTIR spectroscopy.
96 citations
TL;DR: In this article, a water-free ZnLac 2 L-lactide was polymerized in bulk at 120°C or 150°C and the highest number average molecular weights (M n around 70000) were obtained at monomer/initiator (M/I) ratios of 4000.
Abstract: Zn(II) L-lactate (ZnLac 2 ) was prepared either from ZnO and ethyl L-lactate or with slightly higher optical purity from ZnO and L-lactide. Using water-free ZnLac 2 L-lactide was polymerized in bulk at 120°C or 150°C. Higher yields and higher molecular weights were found at 150°C. The highest number average molecular weights (M n around 70000) were obtained at monomer/initiator (M/I) ratios of 4000. Despite the high reaction temperature the isolated poly(L-lactide)s were 100% optically pure. Analogous polymerizations were also conducted with Zn(II) L-mandelate or Zn(II) stearate with inferior results. Poor yields and molecular weights were found, when zinc glycolate salt was used as catalyst. Furthermore, numerous polymerizations were conducted with Zncl 2 , ZnBr 2 or ZnI 2 as initiators. Again poly(L-lactide)s with 100% optical purity were isolated, but most molecular weights were lower and never higher than those obtained with ZnLac 2 . Therefore, ZnLac 2 proved to be the most favorable and fully resorbable (biocompatible) initiator of this study. Finally, the combination of ZnLac 2 with a primary alcohol, which plays the role of a coinitiator, allows a broad variation of the molecular weight and the introduction and modification of an ester endgroup. This approach also allows the incorporation of bioactive alcohols such as a-tocopherol, stigmasterol or testosteron in the form of covalently bound ester endgroups.
88 citations
TL;DR: In this paper, the termination rate coefficient k t of the free radical bulk polymerization of styrene is determined between 30 and 90°C up to a maximum pressure of 2800 bar.
Abstract: The termination rate coefficient k t of the free radical bulk polymerization of styrene is determined between 30 and 90°C up to a maximum pressure of 2800 bar. The majority of polymerization experiments has been carried out at monomer conversions up to 20 per cent. In this range a single value of k t is sufficient to describe termination rate at constant pressure and temperature. Toward higher conversion, significant changes in k t are observed. The data are measured by a pulsed laser polymerization technique and partly by conventional chemically initiated experiments, both with 2,2'-azoisobutyronitrile (AIBN) as the initiator. Online spectroscopy is applied toward measurement of styrene conversion. The experimental termination rate coefficients up to 20 per cent monomer conversion are adequately represented by the expression: In[k t (p,T)/(L.mol -1 .s -1 )] = 20.785 - 1.050.10 -3 p/bar + 5.2.10 -8 p 2 /bar 2 - 753/T/K + 0.1050/T/K . p/bar. Activation volume and activation energy of k t are very close to the corresponding activation parameters that characterize the pressure and temperature dependence of the inverse of styrene monomer viscosity. Varying laser pulse repetition rate has been used to investigate a potential chain-length dependence of k t at low conversion. It turns out that effects of this kind are not sufficiently pronounced to be safely established in view of the experimental precision of ±25 per cent that is reached in the k t determinations.
87 citations
TL;DR: In this article, the gelation mechanism of aqueous solutions of methylcellulose (MC) with different molecular weights was studied by small deformation oscillation rheological measurments and differential scanning calorimetry (DSC).
Abstract: The gelation mechanism of aqueous solutions of methylcellulose (MC) with different molecular weights was studied by small deformation oscillation rheological measurments and differential scanning calorimetry (DSC). The gelation is promoted by the increase in molecular weight of MC: the elastic modulus becomes larger, the gelation occurs at lower temperatures and the DSC peaks accompanying the gel-sol transition become sharper. Cooling DSC curves split into two peaks, indicating that the gel-to-sol transition occurred via two steps.
TL;DR: In this paper, the melting behavior and the isothermal crystallization kinetics of linear and randomly branched poly(butylene terephthalate) a) (PBT) samples were investigated by differential scanning calorimetry.
Abstract: The melting behavior and the isothermal crystallization kinetics of linear and randomly branched poly(butylene terephthalate) a) (PBT) samples were investigated by differential scanning calorimetry. The multiple endotherms typical of linear PBT were observed also in branched samples and were found to be influenced both by temperature and degree of branching. The isothermal crystallization kinetic constants, obtained applying Avrami's treatment, were analysed on the basis of Hoffman's secondary nucleation theory. A decrease in the crystallization rate was observed as the content of branching units increased. This result was correlated to surface effects: the product of the surface free energies σσ e was found to increase with the ramification content. As far as the nucleation process is concerned, the induction time was determined for all the samples at different crystallization temperatures, and the results suggested that in the presence of branching points the nucleation process is favoured.
TL;DR: In this paper, the structure of the methylaluminoxane (MAO) cocatalyst of Kaminsky-Sinn catalysts was investigated by means of 27 Al, 1 H, 17 O and 13 C NMR spectroscopy.
Abstract: By means of 27 Al, 1 H, 17 O and 13 C NMR spectroscopy the structure of the methylaluminoxane (MAO) cocatalyst of Kaminsky-Sinn catalysts was investigated. We have found that the 27 Al NMR resonance line of MAO is extremely broad at room temperature (δ 60, Δω 1/2 50 ± 10 kHz). At elevated temperatures (40-120°C) MAO exhibits an 27 Al resonance at δ 110 ± 10, Δω 1/2 15 - 10 kHz, that is, within the range reported for the aluminoxane clusters [(t-Bu)Al(μ 3 -O)] 6 and [t-Bu)Al(μ 3 -O)] 9 with cage structures. The 27 Al resonance at δ 149-153, usually attributed to MAO, belongs to AlMe 3 present in MAO samples. The 17 O NMR resonance of MAO at 50°C (δ 67, Δω 1/2 1.7 kHz) is within the range typical for three-coordinate oxo ligands, but it can be attributed only to a minor part of MAO oligomers. It was shown that the intensity of 27 Al and 17 O NMR resonances of MAO increases with increasing temperature, whereas the width of both resonances is almost constant. The results obtained lead to the conclusion that at ambient conditions MAO forms oligomers (MeAlO) n with cage structure and MeAlO 3 environment. Upon increasing the temperature these oligomers reversibly break into smaller MAO units. Based on the 27 Al NMR data the average radius (R) of MAO oligomers is approximately 5.1 ± 0.3 A at 120°C. This radius corresponds to (MeAlO) n species with 9 < n < 14. At ambient conditions the predominant part of MAO forms oligomers with R = 7 < 0.5 A and 20 < n < 30.
TL;DR: In this paper, the authors show that most aspects of the perplexing flow behavior of strongly entangled melts in polymer extrusion can be depicted in terms of melt/wall interfacial interactions at a molecular level.
Abstract: This article summarizes our recent experimental studies of an important class of polymer melt rheological phenomena including flow instabilities, stick-slip transitions, interfacial melt/wall slip, gross extrudate distortion and sharkskin like surface roughening of extrudates. Our experimental results indicate that most aspects of the perplexing flow behavior of strongly entangled melts in polymer extrusion can be depicted in terms of melt/wall interfacial interactions at a molecular level. For high surface energy walls, a transition from no-slip to slip hydrodynamic boundary condition (HBC) occurs through molecular disentanglement (coil-to-stretch) of adsorbed chains from unbound chains. For weakly adsorbing walls, interfacial slip takes place through a second molecular mechanism involving a stress-induced polymer desorption process. Since the coil-stretch transition of adsorbed chains is controlled by interfacial shear stress, the HBC can be unstable throughout the die wall under the condition of a constant flow rate, where the wall stress may fluctuate in time. Unstable HBC due to the interfacial molecular instabilities is shown to be the origin of a variety of global and local flow instabilities including the oscillating flow and the sharkskin like distortion of extrudate surface. With a set of new experiments to directly probe the interfacial molecular processes, we will be able to support the unified understanding of intriguing capillary melt flow characteristics summarized in this article.
TL;DR: In this paper, a three-step anionic polymerization method was used to synthesize poly(2-vinylpyridine)-block-poly(tert-butyl acrylate) star block copolymers.
Abstract: Heteroarm star copolymers bearing poly(2-vinylpyridine) and polystyrene arms (A n B n type) were synthesized by a three-step anionic polymerization method. Polystyrene arms are synthesized first, and they are used to initiate the polymerization of a small amount of divinylbenzene, yielding polystyrene star molecules bearing a number of active sites within its cores. In a subsequent step poly(2-vinylpyridine) arms are growing from the cores. Poly(2-vinylpyridine)-block-poly(tert-butyl acrylate) star block copolymers [(AB) n type] were also prepared using the same synthetic route. In this case, short polystyryllithium is used to build grafted poly(DVB) cores. These living plurifunctional initiators can easily polymerize 2-vinylpyridine and subsequently tert-butyl acrylate, yielding star molecules bearing diblock copolymers as arms. The short polystyrene grafts of the core can be neglected and the star molecules are considered of the (AB) n type. These star polymers have been characterized adequately and shown to exhibit rather well-defined structures. The advantages and the drawbacks of the method are discussed.
TL;DR: In this paper, a Suzuki cross-coupling reaction was used to obtain poly(1,4-phenylenevinylene) and poly( 1,4-, 1,2-dibromoethylene) with aryldiboronic acids.
Abstract: Poly(1,4-phenylenevinylene) and poly(1,4-phenyleneethynylene) were prepared from trans-1,2-dibromoethylene and 1,4-bis(2-bromoethynyl)benzene respectively with aryldiboronic acids by a Suzuki cross-coupling reaction. The polymers were synthesized in a two-phase system at room temperature using silver oxide and a Pd catalyst. 3% of biaryl formation is observed as a defect structure in the PPV polymers resulting from coupling of arylboronic acid. Soluble polymers were obtained when the aryldiboronic acid is substituted with long-chain alkoxy groups.
TL;DR: Semifluorinated diblock copolymers based on methyl methacrylate and 1H,1H, 2H,2H-perfluoroalkyl methacylates were prepared by nucleophilic catalysed group transfer polymerisation as discussed by the authors.
Abstract: Semifluorinated diblock copolymers based on methyl methacrylate and 1H,1H,2H,2H-perfluoroalkyl methacrylates were prepared by nucleophilic catalysed group transfer polymerisation. Characterisation was carried out by 1 H NMR spectroscopy, differential scanning calorimetry (DSC) and gel-permeation chromatography (GPC) in toluene. The latter method revealed the formation of micelles. The surface activity of the materials was demonstrated by tensiometry using a Wilhelmy balance. Measurements on thin polymer films showed low critical surface tensions and low dispersion force contributions to the surface energy indicating the presence of the fluorinated block at the surface.
TL;DR: In this article, Diblock copolymers of ethylene oxide and DL-lactide were prepared by sequential anionic polymerisation and characterised by gel permeation chromatography (GPC) and 13 C NMR.
Abstract: Diblock copolymers of ethylene oxide and DL-lactide (E m L n copolymers) were prepared by sequential anionic polymerisation and characterised by gel permeation chromatography (GPC) and 13 C NMR. Their association and surface properties in aqueous solution were studied by surface tension and dynamic and static light scattering. Comparison of the critical micelle concentrations (cmc) and micelle association numbers (N w ) of the E m L n copolymers with published values for oxyethylene/oxybutylene (E m B n ) copolymers indicated a slightly lower hydrophobicity for a lactide unit: i.e. L ≃ 0.75B. The temperature dependence of the cmc of copolymer E 42 L 12 was analysed to obtain a standard enthalpy of micellisation Δ mic H 0 ≃ 40 kJ.mol -1 .
TL;DR: The grafting reaction of polystyrene branches onto poly(chloroethyl vinyl ether) (PCEVE) chains, based on the deactivation of polystryl (PS) carbanionic ends onto chloroethyl ether functions has been investigated in this article.
Abstract: The grafting reaction of polystyrene branches onto poly(chloroethyl vinyl ether) (PCEVE) chains, based on the deactivation of polystyryl (PS) carbanionic ends onto chloroethyl ether functions has been investigated. The selectivity of the coupling is very high and allows the almost complete substitution of the chloride group of the CEVE units by PS chains with molar masses up to 15 000. The main side reaction observed is the deactivation of some PS chains, at the very beginning of the reaction. It is attributed mainly to impurities present in the PCEVE solution. Since the PCEVE polymer backbone and the PS grafts can be prepared by both living cationic and anionic polymerization, it is possible to synthesize poly(CEVE-g-styrene) copolymers possessing both a backbone with controlled dimensions and an adjustable number of branches having precise length and narrow molar mass distribution. The synthesis and the characteristics of comblike poly[(chloroethyl vinyl ether)-g-styrene]s are described.
TL;DR: In this paper, the effect of the variation of the amount and the structure of cocatalyst and of polarity of the solvent on propene/l-hexene copolymerization with the isospecific catalyst rac-[ethylenebis(l-indenyl)lzirconium dichloride (rac-(EBI)ZrCl 2 ) was performed.
Abstract: An investigation on the effect of the variation of the amount and the structure of cocatalyst and of polarity of the solvent on propene/l-hexene copolymerization with the isospecific catalyst rac-[ethylenebis(l-indenyl)lzirconium dichloride (rac-(EBI)ZrCl 2 ) was performed. A noticeable enhancement of copolymerization activity and a moderate increase of the molecular weights were observed with increasing MAO/Zr ratio as well as upon mixing methylaluminoxane (MAO) and AliBu 3 , while isotacticity and comonomer composition are not affected by such variations. On the other hand, a gradual increase in CH 2 Cl 2 content in the CH 2 Cl 2 /toluene solvent mixture, which greatly increases the copolymerization activity, noticeably influences the molecular weight and sensibly enhances the l-hexene comonomer content. The formation of cationic active species, separated from their counterions, might be the cause of the better accessibility of the active sites for the bulkier comonomer.
TL;DR: In this article, a potentiometric and viscometric analysis of the interpolymer complexation between polyacrylamide (PAAM) and poly(N-isopropylacrylide) (PNIPAAM) with poly(acrylic acid) (PAA) in dilute aqueous solution is presented.
Abstract: We present potentiometric and viscometric results on the interpolymer complexation between polyacrylamide (PAAM) and poly(N-isopropylacrylamide) (PNIPAAM) with poly(acrylic acid) (PAA) in dilute aqueous solution. A potentiometric procedure for the determination of the complex stoichiometry in monomeric units has been proposed. The temperature dependence of the strength of the complexes formed has been investigated. From the results obtained it has been concluded that hydrogen bonding is the main factor stabilizing the PAAM/PAA complex, strengthened by decreasing the temperature while the much stronger PNIPAAM/PAA complex, strengthened by increasing the temperature, is stabilized by hydrophobic intcraction.
TL;DR: In this paper, the thermally reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) and D,L-lactide (L), E 42 L 12, E 38 L 16, E 39 L 20, E 4 L 26, E 78 L 14 and E 77 L 26, was studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy.
Abstract: The thermally-reversible gelation of aqueous solutions of diblock copolymers of ethylene oxide (E) and D,L-lactide (L), E 42 L 12 , E 38 L 16 , E 39 L 20 , E 4 L 26 , E 78 L 14 and E 77 L 26 , has been studied using gelation temperature measurements, polarised light microscopy and NMR spectroscopy. The solutions showed a high temperature gel-sol boundary but no low temperature gel-sol boundary. Polarised light microscopy showed that the gel phase was isotropic, and the dependence of sol-gel temperature on concentration suggested that the micelles were prolate ellipsoidal, rather then spherical. NMR spectroscopy showed that below ca. 60°C, the L block in the micelle core became highly restricted. It is tentatively suggested that this is due to the L blocks forming an ordered structure, thus explaining the absence of a low temperature gel-sol boundary.
TL;DR: In this paper, a high increase in the bulk polymerization rate of L,L-lactide and racemic D,L -lactides is observed when aluminium isopropoxide is added with an equimolar amount of a Lewis base, such as triphenylphosphine (P(Φ) 3 ) and better 4-picoline (C 6 H 7 N).
Abstract: A high increase in the bulk polymerization rate of L,L-lactide and racemic D,L-lactide is observed when aluminium isopropoxide is added with an equimolar amount of a Lewis base, such as triphenylphosphine (P(Φ) 3 ) and better 4-picoline (C 6 H 7 N). Polylactide of high molecular weight and narrow molecular weight distribution is accordingly prepared in a controlled manner when the Al(OiPr) 3 . C 6 H 7 N combination is used as an initiator over a large temperature range from 110 to 180°C. A secondary alcohol, such as 2-propanol, has proved to be an efficient transfer agent, which allows the amount of Al per kg of polylactide to be advantageously reduced. All the alcohol molecules participate in the ring-opening polymerization even at an [iPrOH] 0 /[Al] ratio as high as 10 3 .
TL;DR: In this article, a supported zirconocene catalysts with bisindenyl, bisfluorenyl, and bis(1,2,3,4-tetramethyl)cyclopentadienyl side groups were synthesized by condensation of the corresponding dichlorosilane compounds and water to obtain supported Zirconian catalysts.
Abstract: Polysiloxanes with bisindenyl, bisfluorenyl, and bis(1,2,3,4-tetramethyl)cyclopentadienyl side groups were synthesized by condensation of the corresponding dichlorosilane compounds and water to obtain supported zirconocene catalysts. The polymerization of ethene was conducted over these catalysts combined with methylalumoxane. The polymerization activity depends markedly upon the substituents and decreases in the order: bisindenyl >> bisfluorenyl >> bis(1,2.3,4-tetramethylcyclopentadienyl). All the supported catalysts give linear polyethene with fairly high molecular weights. The catalyst with bisindenyl groups was found to be composed of a toluene-soluble and a toluene-insoluble fraction. The polymerization profile (activity versus time curve) was analyzed with the toluene-soluble and -insoluble fraction as well as the corresponding homogeneous system. The homogeneous system, which exerts the highest activity in the initial phase, was completely deactivated after several hours whereas the activity of the supported catalyst, especially of the toluene-insoluble fraction, was unchanged during 12 h even at 70°C. Polysiloxanes with different content of bisindenyl groups were also synthesized via the co-condensation with dimethyldichlorosilane and applied as the carrier. However, the activity per Zr atom decreases remarkably with an increase in dimethylsilane units.
TL;DR: In this paper, atom transfer radical polymerization (ATRP) was applied to the homopolymerization of glycidyl acrylate (GA) to obtain high conversions and high molecular weights using halogenated initiators.
Abstract: Atom transfer radical polymerization (ATRP) was applied to the homopolymerization of glycidyl acrylate (GA). This functionalized monomer can be polymerized to high conversions and high molecular weights using halogenated initiators and CuBr/4,4'-bis(5-nonyl)-2,2'-bipyridine (dNbipy) as the catalyst. The polymerizations exhibit first order kinetics and molecular weights increase linearly with conversion. The M n of the products is controlled by the ratio Δ[M] 0 /[I] 0 . The polymers obtained showed narrow molecular weight distributions, M w /M n = 1.25.
TL;DR: In this article, the authors characterized the cocatalytic ability of these characterized MAOs in ethylene polymerization catalyzed by rac-Et(ind) 2 ZrCl 2 (ind = indenyl) and the influence of the AlMe 3 content, the type and the aging of MAO is correlated to the cocaratalytic performance.
Abstract: Methylaluminoxane (MAO) solutions containing known amounts of AlMe 3 and solutions of different MAO samples were characterized by several methods: a) low temperature 13 C NMR analysis; b) determination of the molecular weight of the MAO samples by cryoscopy in benzene; c) titration of AlMe 3 using 31 P NMR analysis of the AlMe3-PPh 3 complex (PPh 3 = triphenylphosphine) formed after addition of defined amounts of PPh 3 to the MAO solutions. The results confirm the disproportionation reaction caused by AlMe 3 addition. The MAO molecular weights are shown to decrease after the AlMe 3 addition according to a linear relationship. The cocatalytic ability of these characterized MAOs was tested in ethylene polymerization catalyzed by rac-Et(ind) 2 ZrCl 2 (ind = indenyl) and the influence of the AlMe 3 content, the type and the aging of MAO is correlated to the cocatalytic performance.
TL;DR: In this article, a new procedure for the determination of the amounts of phases in samples of isotactic poly(propylene) quenched at different cooling rates from the same melted polymer is described.
Abstract: A new procedure for the determination of the amounts of phases in samples of isotactic poly(propylene) quenched at different cooling rates from the same melted polymer is described. According to the procedure, all the patterns corresponding to the same quenching series are simultaneously analyzed for the amounts of phases so that reliable phase fractions relative to the different samples of the series are achieved. The analysis of the results points out that for increasing cooling rates above 30°C/s a remarkable increase of the mesomorphic phase settles, mainly at the expense of the α-monoclinic one.
TL;DR: Oligomers of 2,5-dialkyl-1,4-phenylenevinylenes (DR-OPV, R = C 4 H 9, C 7 H 15, C 10 H 21 and C 6 H 11 (CyH) were prepared via metathesis polycondensation of the respective 2,6-dimethylphenylbenzenes as mentioned in this paper.
Abstract: Oligomers of 2,5-dialkyl-1,4-phenylenevinylenes (DR-OPV, R = C 4 H 9 , C 7 H 15 , C 10 H 21 and C 6 H 11 (CyH) were prepared via metathesis polycondensation of the respective 2,5-dialkyl-1,4-divinylbenzenes The synthesis of the monomers is described The highly active metal-alkylidene complex Mo(NAr Mc2 )(CHCMe 2 Ph)[OCMe(CF 3 ) 2 ] 2 (Ar Me2 = 2,6-dimethylphenyl) serves as a catalyst The degree of polymerization can be controlled by variation of the solvent and by the length of the side chains, since the reaction proceeds as a precipitation polycondensation The DR-OPVs are bilious-green products and, depending on the molecular weight, soluble in various solvents like toluene, THF and CHCl 3 The solutions are highly fluorescent and coloured The DR-OPVs have vinylic end groups The vinylene double bonds are of all-trans configuration Due to their rigid-rod structure, the DR-OPVs synthesized have a distinct tendency to crystallize in a highly ordered state, forming a sanidic layer structure
TL;DR: In this article, commercial FeCl 2 and Fe(II) glycolate were used as initiators for the polymerization of L-lactide, and the results showed that viscosity average molecular weights (M V ) around 50000 and yields above 90%.
Abstract: Commercial FeCl 2 and Fe(II) glycolate, Fe(II) L-lactate or Fe(II) L-mandelate were used as initiators for the polymerization of L-lactide. All polymerizations were conducted in bulk at 150°C, because no conversion was observed in bulk at 121J°C. The Fe(II) lactate was found to be more reactive than FeCL 2 , and it yielded slightly higher molecular weights than all other initiators. Under the optimum conditions, viscosity average molecular weights (M V ) around 50000 and yields above 90% were obtained. However, slight racemization (2-5%) of the isolated poly(L-lactide) was also observed under most circumstances. Characterization of unreacted monomer proved that the racemization mainly involves the monomeric lactide due to its higher C-H acidity.
TL;DR: In this paper, the first biodegradable regular poly(ester urethane) was synthesized by polycondensation of di-p-toluenesulfonic acid salts of bis(phenylalanine) α,ω-alkylene diesters 1 with di-(p-nitrophenyl trimethylenedicarbonate (4) under mild conditions in organic solvents in the presence of triethylamine as acid acceptor.
Abstract: Novel biodegradable regular poly(ester urethane)s 2 (η red ≤ 0,62 dL/g) were synthesized for the first time by polycondensation of di-p-toluenesulfonic acid salts of bis(phenylalanine) α,ω-alkylene diesters 1 with di-p-nitrophenyl trimethylenedicarbonate (4) under mild conditions in organic solvents in the presence of triethylamine as acid acceptor. The first synthesis of homopoly(ester urea)s 3 (q red ≤ 0,33 dL/g) was carried out by polycondensation of 1 with di-p-nitrophenyl carbonate (5) under the same conditions. Preliminary in vitro evaluation of specific and nonspecific hydrolysis of the polymers obtained has been brought about using potentiometric titration.