bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sequential reordering in condensation copolymers, 1. Melting‐ and crystallization‐induced sequential reordering in immiscible blends of poly(ethylene terephthalate) with polycarbonate or polyarylate
Authors: Fakirov Stoyko , Sarkissova Marianna , Denchev Zlatan 
Published: April 2003

AbstractUnlike previous attempts, the entire cycle of melting‐ and crystallization‐induced reordering is realized in binary polymer blends in the following order: two homopolymers → block copolymer → random copolymer → block copolymer. Blends of poly(ethylene terephthalate)Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).
(PET) and bisphenol‐A/polycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PET/PC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature Tg in the range between the initial two Tgs, and by solubility tests. Once randomized, annealing the samples at 235°C and 245°C, i. e., below melting of PET, results in a Tg shift toward the Tg of PET as well as in reappearance of melting. This effect is accompanied by an eight‐fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable enthropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and Tg‐values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PET/PC > 5.7/1.0. When the annealing is performed for 300 min at 165°C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.
Sequential reordering in condensation copolymers, 2. Melting‐ and crystallization‐induced sequential reordering in miscible poly(butylene terephthalate)/polyarylate blends
Authors: Denchev Zlatan , Sarkissova Marianna , Fakirov Stoyko , Yilmaz Ferdane 
Published: April 2003

AbstractA 50/50 (weight ratio (38/62 mole ratio referred to repeating units)) blend of poly(butylene terephthalate) (PBT) and polyarylate (PAr), was studied by means of thermal, solubility, X‐ray and nuclear magnetic resonance techniques after annealing procedures that enable transesterification. Prolonged thermal treatment at 290°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples at the relatively low temperature of 140°C results in the reappearance of melting endotherms in the differential scanning calorimetry curves. This effect is explained by crystallization‐induced sequential reordering from random to block copolymer by means of transreactions. In that way a PBT/PAr blend was shown to be another polymer system, along with poly(ethylene terephthalate) (PET)/polycarbonate (PC) and PET/PAr blends, in which the entire cycle is realized, from two homopolymers via a block‐ and random copolymer to a block copolymer. The unusually low temperature at which the crystallization‐induced sequential reordering to block polymers takes place is explained by the miscibility of PBT and PAr which enables transreactions to take place in the bulk.
Sequential reordering in condensation copolymers, 3. Miscibility‐induced sequential reordering in random copolyesteramides
Authors: Fakirov Stoyko , Sarkissova Marianna , Denchev Zlatan 
Published: April 2003

AbstractBinary and ternary blends of poly(butylene terephthalate) (PBT), Nylon 66 (PA66), bisphenol‐A‐polycarbonate (PC) and polyarylate (PAr) have been studied mostly by means of differential scanning calorimetry (DSC) after thermal treatment that enables transesterification. Thus, the entire cycle of sequential reordering is realized, namely: homopolymers → block copolymer → random copolymer → block copolymer. For this purpose the binary PC/PAr and PBT/PA66 blends are annealed in the molten state directly in the calorimeter until complete amorphization (as revealed by DSC). In the first blend the latter is proved by the appearance of a single glass transition temperature Tg and in the second — by the complete diappearance of the crystallization ability. At this stage a third component is added, miscible with one of the starting blend constituents — PBT for the PC/PAr and PAr for the PBT/PA66 blend. Subsequent annealing in the molten state results in amorphization of the PBT‐PC‐PAr and PBT‐PA66‐PAr terpolymers, as concluded from the loss of crystallization ability. Further annealing at 280°C and 290°C, respectively, leads to the recovery of the crystallization ability. This is documented by the reappearance of the melting temperature and the crystallinity in the DSC traces taken in heating mode. The crystallinity observed is only achieved during cooling of the melt to room temperature, i. e., crystallization‐induced sequential reordering is excluded. It is assumed that the driving force of the observed block regeneration in the melt is the trend of the PBT and PAr components of the two randomized copolymers to mix with each other. Mixing presumes the presence of longer PBT and PAr sequences. Thus, in addition to the crystallization‐induced sequential reordering in condensation copolymers, another example of transreactions is observed in the direction of an entropy decrease. It is called miscibility‐induced sequential reordering in random condensation copolymers.
Anionic polymerization of pentadecanolide. A new route to a potentially biodegradable aliphatic polyester
Authors: Jedliński Zbigniew , Juzwa Maria , Adamus Grażyna , Kowalczuk Marek , Montaudo Maurizio 
Published: April 2003

AbstractThe anionic polymerization of pentadecanolide (1‐oxa‐2‐cyclohexadecanone) initiated with potassium alkoxides was investigated. Polymerization proceeds under mild conditions (tetrahydrofuran, 35°C) to form high‐molecular‐weight polymer (number‐average molecular weight M̄n up to 100 000). The formation of cyclic oligomers, via back‐biting reaction, was demonstrated by means of gel‐permeation chromatography (GPC) and matrix assisted laser desorption ionisation‐time of flight (MALDI‐TOF) analyses.
Characterization of water‐soluble polymers and aqueous colloids with asymmetrical flow field‐flow fractionation
Authors: Tank Claus , Antonietti Markus 
Published: April 2003

AbstractA study on the retention and separation of water‐soluble polymers and globular proteins by asymmetrical flow field‐flow fractionation (Asym. flow FFF) is presented. The applicability of only one carrier liquid to a great variety of samples with different charge stabilization and morphology (in order to simplify the handling and the data evaluation) is demonstrated. With this carrier liquid, the investigation of polystyrene latex beads with anionic as well as cationic surfactants, anionic polystyrene sulfonates and globular proteins in the hydrodynamic radius range 10–400 nm is presented, thus resulting in linear calibration curves as well as in the ability for the absolute determination of the diffusion coefficient as well as its distribution. The averaged plate number of the presented flow channel under the applied standard conditions is determined to be in the order of 1 500 which demonstrates the potential of this technique. Preliminary experiments with commerical, broadly distributed poly(1‐vinyl‐2‐pyrrolidone) samples show that the experiment performed at model systems can easily be extended to technical polymers of commercial interest.
Phase separation of blends of polydisperse polymers: Comparison between experiment and theory for the system poly(dimethylsiloxane)/poly(ethylmethylsiloxane)
Authors: Enders Sabine , Stammer Andreas , Wolf B. A. 
Published: April 2003

AbstractCloud point curves were measured turbidimetrically for blends (upper critical solution temperatures; UCSTs) of poly(ethylmethylsiloxane) (PEMS) and four different samples of poly(dimethylsiloxane) (PDMS); the weight average molar masses in kg/mol are 31.2 for PEMS and 10.4, 15.5, 18.1 and 24.0 for PDMS; all components have polydispersity indices D (= M̄w/M̄n) within the range from 1.82 to 2.67. Corresponding calculations on the basis of the Flory‐Huggins theory (three adjustable parameters) account for the poly‐dispersity; molecular weight distributions are represented by the generalized Schulz‐Flory equation. Calculated cloud point curves agree very well with those measured, if individual sets of parameters are admitted for each of the different mixtures. Even for an identical set of parameters the maximum deviations remain moderate. Realistic model calculations concerning the influences of D on cloud points and on critical points were performed with this set of parameters. For the present (only slightly endothermal) system, the precipitation threshold increases from 318 to 558.6 K as DPEMS is raised from 1.87 to 4.00, keeping the number average degree of polymerization constant.
Photoluminescence of a new water‐insoluble polysiloxane film containing pendant Ru(bpy) and its quenching by dioxygen
Authors: Nagai Keiji , Takamiya Nobuo , Kaneko Masao 
Published: April 2003

AbstractA new water‐insoluble polysiloxane containing pendant Ru(bpy) (bpy = 2,2′‐bipyridine) was studied with respect to the photoluminescence and its quenching by dioxygen. The emission was quenched by O2 in water more efficiently than in gas phase, and the Stern‐Volmer plots showed a downward deviating curve. To determine which of several quenching models can be applied to the present system, the emission decays under various O2 concentration were measured, and analyzed by a double exponential decay. From the simulations of the decay using the kinetic parameters obtained from the model analysis, it has been concluded that the quenching by O2 is caused by static quenching (model 4). The O2 concentration in the film in contact with water estimated from the quenching parameters was much higher than the solubility of O2 estimated from the solubility coefficient in a dry film. These results suggest specific affinity of the polysiloxane for O2 molecule in water.
Physical gelation of polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene copolymer in paraffinic oil. Oscillatory shear and compression measurements
Authors: Quintana José R. , Díaz Esperanza , Katime Issa 
Published: April 2003

AbstractThe thermoreversible gelation of the triblock copolymer polystyrene‐block‐poly(ethylene/butylene)‐block‐polystyrene (SEBS2) in paraffinic oil was studied. The solvent used is selective for the middle PEB block of the copolymer. The thermal behaviour as a function of copolymer concentration was investigated. The sol‐gel transition temperature increases with the copolymer concentration. The mechanical properties were examined through oscillatory shear and compression measurements. The concentration dependence of the elastic storage modulus, G′, was established. The relaxation rates observed were extremely high, indicating a considerable mobility in the gel during the measurement time.
Small‐angle X‐ray scattering on latexes
Authors: Ballauff Matthias , Bolze Jörg , Dingenouts Nico , Hickl Peter , Pötschke Dominic 
Published: April 2003

AbstractSmall‐angle X‐ray scattering (SAXS) is a tool which allows the study of the structure and the interaction of polymer latexes with great accuracy. The low electron density of the polymers used for the synthesis of latex particles as e.g. polystyrene allows the matching of the contrast by adding sucrose to the serum. Thus, scattering intensities measured at different contrast, i.e., at different excess electron densities can be evaluated (contrast variation). This yields precise information on the radial electron density of the particles. In this article recent SAXS‐investigations on latex particles are reviewed. It is demonstrated that core‐shell latexes can be analyzed precisely by contrast variation. The same method can be applied to swollen latex particles to examine the polymer concentration near the boundary to the water phase. Here it is shown that the depletion of the polymer molecules near this boundary is very small which points to a minute wall‐repulsion effect. Since the excess electron density of polystyrene latex particles in water is very small, the scattering from adsorbed layers of surfactants dominates the measured intensity in this particular system. Therefore the adsorption equilibrium of a given surfactant as well as the competitive adsorption of two different surfactants on a polystyrene latex can be assessed by SAXS.
Polymers by 1,3‐dipolar cycloaddition reactions: the “criss‐cross” cycloaddition
Authors: Maier Gerhard 
Published: April 2003

Abstract1,3‐Dipolar cycloaddition reactions have been used to prepare a large number of different heterocyclic and heteroaromatic polymers. Most of this work has been done in the 60's and 70's. Since then, interest in this field has vanished almost completely. While the number of polymer structures accessible by 1,3‐dipolar cycloaddition is very large, the high reactivity and tendency of the 1,3‐dipoles to undergo side reactions limits the successful applications in step growth polymer synthesis considerably.The “criss‐cross” cycloaddition reaction also proceeds via two consecutive 1,3‐dipolar cycloaddition steps. Its starting compounds, azines and diolefins or diisocyanates, are stable, can be purified easily, and do not undergo side reactions if the reaction conditions are chosen properly. Initially, the reaction between hexafluoroacetone azine and various diolefins was studied. This work was aimed at the preparation and structural characterization of soluble polymers. Later on, the “criss‐cross” cycloaddition between aromatic aldazines and diisocyanates was included in this research. Different azines and diisocyanates were studied to find the best compromise between reactivity of the monomers and solubility and glass transition temperature of the products. Due to the special reaction mechanism, the polymers have exclusively isocyanate end groups, independent of stoichiometry of the monomers and the conversion. Thus, this reaction is ideally suited for the preparation of telechelics. Prepolymers obtained by “criss‐cross” cycloaddition between 4‐methoxybenzaldazine and 4,4′‐diisocyanatodiphenyl ether were used as hard segments in segmented block copolymers. Those block copolymers with a hard segment content below 36% showed elastomeric behavior with ultimate elongations above 700% and tensile strengths between 2 and 6 MPa.
The influence of the comonomer in the copolymerization of ethylene with α‐olefins using C2H4[ind]2ZrCl2/methylaluminoxane as catalyst system
Authors: Quijada Raúl , Galland Griselda Barrera , Mauler Raquel Santos 
Published: April 2003

AbstractCopolymers based on ethylene with different incorporations of 1‐hexene, 1‐octene and 1‐decene were obtained. There is not any marked variation of activity when different metallocenes were tested. The type and the concentration of the comonomer in the feed do not have a strong influence on the catalytic activity of the system, but the presence of the comonomer increases the activity compared with that in the absence of it. From 13C NMR it was found that below 8% of comonomer incorporated the comonomer units appear isolated between polyethylene blocks, sequences of the type ethylene‐comonomer‐ethylene‐comonomer appear only above 8% of comonomer incorporated for all the systems studied. The reactivity of the comonomers for this particular system shows that the size of the lateral chain influences the percentage of comonomer incorporated, 1‐hexene being the highest one incorporated. The crystallinity of the copolymers exerts a linear relation with the amount of comonomer incorporated, and it is independent of lateral chain lengths. The molecular weight of the copolymers obtained was found to be dependent on the comonomer concentration in the feed, showing that there is a transfer reaction with the comonomer. The polydispersity (M̄w/M̄n) of the copolymers is rather narrow and dependent on the concentration of the comonomer incorporated.
Grafting reactions onto poly(organophosphazenes), 7. Light‐induced grafting of poly(vinyl acetate) onto catena‐poly[bis(4‐methyl‐, 4‐ethyl‐ and 4‐sec‐butylphenoxy)‐λ5‐phosphazene] and successive hydrolysis to phosphazenegrafted poly(vinyl alcohol)
Authors: Minto Francesco , Fambri Luca , Gleria Mario 
Published: April 2003

AbstractIn this paper we describe the light‐induced grafting reaction of poly(vinyl acetate) onto catena‐poly[bis(4‐sec‐butylphenoxy)‐λ5‐phosphazene], catena‐poly[bis(4‐ethylphenoxy)‐λ5‐phosphazene] and catena‐poly[bis(4‐methylphenoxy)‐λ5‐phosphazene], and the successive acid‐ (and base‐) catalyzed hydrolysis of the grafted macromolecule to poly‐(vinyl alcohol). The process was found to be dependent on the irradiation time, reaction temperature, relative monomer/methanol concentration in the reaction mixture, type of substituents present on the exploited phosphazene polymers, and on the crystallinity of these macromolecules. The new phosphazene grafted copolymers thus prepared have been characterized by IR spectroscopy, gravimetric analysis and contact angle measurements.
Synthesis of end‐functionalized polymer by means of living anionic polymerization, 5. Syntheses of polystyrenes and polyisoprenes with hydroxy and mercapto end groups by reactions of the living polymers with haloalkanes containing silyl ether and silyl thioether functions
Authors: Tohyama Mieko , Hirao Akira , Nakahama Seiichi , Takenaka Katsuhiko 
Published: April 2003

AbstractAnionic living polystyrene and polyisoprene were allowed to react with six tert‐butyl‐dimethylsilyl ethers of ω‐halo‐1‐alkanols 1–6, the trimethylsilyl ether of bromohydrin (7), the tert‐butyldimethylsilyl ether of 4‐bromophenol (8), and tert‐butyldimethylsilyl 3‐chloropropyl sulfide (9), followed by acid‐catalyzed cleavage of SiO and SiS bonds to afford polystyrene and polyisoprene, respectively, with hydroxy or mercapto end groups. The alcoholic hydroxy groups were introduced quantitatively to the polymer chain end regardless of the kind of halogen atom, length of methylene spacer separating the protected hydroxy group from the halogen, and structure of protecting groups. The tert‐butyldimethylsilyl ether of 4‐bromophenol (8) was not suitable for this reaction, since most (≈90%) of the original living polyisoprene was dimerized due to metal‐halogen exchange followed by the coupling reaction of the polymeric allyl bromide derivatives thus formed with remaining living polyisoprene. Polystyrene and polyisoprene with tert‐butyldimethylsilyl sulfide end group were obtained quantitatively by the reaction of their anionic living polymers with 9. Generation of mercapto groups through deprotection was confirmed by I2 oxidation and reaction with acrylonitrile.
Synthesis of end‐functionalized polymer by means of living anionic polymerization, 7. Reaction of anionic living polymers with perfluoroalkyl halides
Authors: Sugiyama Kenji , Hirao Akira , Nakahama Seiichi 
Published: April 2003

AbstractReactions of anionic living polymers of styrene, tert‐butyl methacrylate, and 2‐(trimethylsiloxy)ethyl methacrylate with perfluoroalkyl (Rf) halides, such as C4F9(CH2)3I(1), (CF3)2CF(CF2)6I (2), C4F9(CH2)2I (3), C8F17(CH2)2O(CH2)4Br (4), were investigated to synthesize well‐defined polymers with Rf groups at the chain end. Nucleophilic attack of living polystyryl anions on 1 and 4 quantitatively proceeds to give the Rf‐terminated polystyrenes with predictable molecular weights and narrow molecular weight distributions, while low functionalities (0–50 mol‐%) were obtained in the cases of 2 and 3, on account of electron transfer and ß‐proton elimination. The anionic propagating ends of the methacrylates with potassium countercation react with 1 and 4 to afford the Rf‐terminated poly(methacrylate)s in high efficiency. Poly[2‐(trimethylsiloxy)ethyl methacrylate] produced was deprotected under acidic conditions to give poly(2‐hydroxyethyl methacrylate) bearing the Rf‐terminal group. However, the reactions of the propagating enolate with lithium countercation with 1 and 4 result in low yields of the Rf‐terminated polymers. From the surface analyses of the Rf‐terminated polymer films by X‐ray photoelectron spectroscopy and contact angle measurements, a remarkable enrichment of the Rf group at the dry surface and a surface restructuring corresponding to the environmental change are indicated.
The effect of terminal alkyl chains on hyperbranched polyesters based on 2,2‐bis(hydroxymethyl)propionic acid
Authors: Malmström Eva , Johansson Mats , Hult Anders 
Published: April 2003

AbstractA hyperbranched hydroxyfunctional polyester based on 2,2‐bis(hydroxymethyl)propionic acid as AB2‐monomer and a tetrafunctional polyol as core was end‐capped with five different alkylacyl chlorides. Alkyl chain lengths ranging from three to sixteen carbons were used. Short alkyl chains (3–6 carbons) decrease the glass transition temperature from around 30°C for the hydroxyterminated polyester to temperatures well below zero. With a sufficiently long alkyl chain (12–16 carbons) the polymers tend to crystallize. The polyesters with C16‐chains as terminal groups exhibit several different crystalline phases as revealed by differential scanning calorimetry. From X‐ray data it was possible to suggest that the crystallization for the C16‐terminated samples occurs in a non‐interpenetrating fashion for the larger sample and in an interpenetrating way for the smaller polymers.