bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of particle morphology in emulsion polymerization
Authors: Okubo Masayoshi 
Published: March 2011

AbstractSubmicron‐size composite polymer particles consisting of two kinds of polymers were produced by seeded emulsion polymerization. Since most polymer pairs are not compatible, phase separation of the polymers proceeds throughout the polymerization and results in unique morphologies. Factors having a great influence on the formation of such morphology were clarified. Special properties can be obtained by controlling the morphology, as demonstrated using examples. Some anomalous composite particles were produced using this method.
Kinetics and mechanism of emulsifier‐free emulsion copolymerization
Authors: Chen Show‐An , Lee Song‐Tai , Lee Shien‐Jy 
Published: March 2011

AbstractIn the emulsifier‐free emulsion polymerization of styrene/potassium persulfate (KPS) system, due to larger particle size and ionic chain ends, the polymerization only occurs in the shell part of the polymer particles (the shell‐growth mechanism). For the styrene/comonomer/KPS system, the hydrophilicity and ionic characteristic of the comonomer play a dominant role in the nucleation and growth mechanisms. If a nonionic comonomer is used, the shell‐growth mechanism also follows. If an ionic comonomer having sufficient cross‐propagation with the monomer is used, the particle size is small and the polymerization occurs uniformly within the particles as in the conventional case. If it has insufficient cross‐propagation, then shell‐growth mechanism occurs again.
Effect of alkyl substitution of dowfaxTM surfactants in styrene‐butadiene emulsion copolymerization
Authors: Dimonie Victoria L. , El‐Aasser Mohamed S. , Vanderhoff John W. , Settlemeyer Lois A. 
Published: March 2011

AbstractTypical emulsifier surface properties such as the CMC, concentration at interface saturation, the free energy of adsorption and micellization, and the efficiency in reducing interfacial tension were determined for different DOWFAXTM surfactants in the presence and absence of electrolyte. The emulsifiers' surface activity was correlated with their performance in the preparation of 50%‐solids 60:40 styrene‐butadiene latexes. The results showed that the latex particle size is dependent on the strength of emulsifier adsorption at the particle interface.
Chemical synthesis and dielectric characterisation in microwave domain of polypyrrole latexes
Authors: Epron Florence , Henry François , Sagnes Olivier 
Published: March 2011

AbstractColloidal dispersions of polypyrrole were obtained by chemical synthesis in aqueous medium, using various transition metal compounds, as initiators and dopants, and various water‐soluble polymers as steric stabilizers. The dielectric constant and the complex conductivity of the particles were determined by measurements in microwave domain. The polypyrrole latexes have conductivities ranging from 0.3 to 3 S/cm depending upon the oxidizing agent and the stabilizer. The optimum system seems to be ferric chloride/methylcellulose.
Tailored polymers by cationic ring‐opening polymerizations: Scope and limitations based on mechanistic aspects
Authors: Goethals Eric J. 
Published: March 2011

AbstractThe main‐ and side‐reactions which can occur during cationic ring‐opening polymerizations of heterocyclic monomers are discussed. Based on these general reactions these polymerizations are classified into three groups. (1) Living (or “almost living”) polymerizations provide the possibility to produce polymers with predictable molecular weight, narrow molecular weight distributions and having functional end groups (by initiation and/or end‐capping). These polymerizations also allow the production of block and graft copolymers by sequential monomer additions. (2) Polymerizations which show temporary, i.e. reversible, termination reactions may be used to produce polymers with predictable molecular weights with molecular weight distributions of ≈2. Functional end groups may be introduced by end capping or chain transfer. These polymerizations generally lead to considerable fractions of cyclic oligomers. (3) Polymerizations which show irreversible termination reactions by the formation of stable, branched or (macro)cyclic onium ions. These polymerizations stop at limited conversions and are not suitable for the synthesis of well‐defined polymers.
Branched bpa polycarbonates with high shear sensitivity from ring‐opening polymerization of cyclic carbonates
Authors: Krabbenhoft Herman O. , Boden Eugene P. 
Published: March 2011

AbstractBranched BPA polycarbonates with high shear sensitivity (i.e. having complex melt viscosity ratios as high as 8.0 or even 10.0) were prepared by ring opening polymerization of cyclic oligomeric BPA carbonates in the melt (at 275 C) with various branching agents [e.g. 1,3,5‐tris(chloromethyl)‐2,4,6‐trimethylbenzene, bis(2,4‐dihydroxyphenyl) sulfide, and 1,1,1‐tris(4‐hydroxyphenyl)ethane]. Furthermore, it was determined that the shear sensitivity is directly related to the branching agent level and inversely related to the level of initiator used in the ring‐opening polymerization.
Copolymerization of ϵ‐caprolactone and δ‐valerolactone
Authors: Storey Robson F. , Hoffman Douglas C. 
Published: March 2011

AbstractHydroxy‐terminated poly(ϵ‐caprolactone‐co‐δ‐valerolactone) (PCV) copolymers were synthesized by the diol initiated bulk copolymerization of ϵ‐caprolactone (C) and δ‐valerolactone (V). The two homopolymers were semicrystalline, with almost identical melting temperatures; copolymerization significantly lowered the melting point (Tm) compared to either homopolymer. Copolymer melting points were found to decrease with decreasing molecular weight and to be dependent on composition, i.e., the incorporation of a comonomer into either homopolymer resulted in a decrease in Tm, with the maximum decrease occurring at a copolymer composition of about 60 mole‐% ϵ‐caprolactone. The molar composition of the copolyesters was determined from 13C NMR spectra. At conversions> 50 % the copolymer composition was found to be richer in ϵ‐caprolactone than predicted from the integrated form of the first‐order Markov copolymer equation, suggesting that the depolymerization of δ‐valerolactone becomes important at high conversions and the addition of ϵ‐caprolactone is greatly favored regardless of the ultimate unit.
Ring‐opening polymerization of 2‐phenyl‐4,7‐dioxaspiro[2.4]heptane
Authors: Rasoul Husam A. A. , Beam James R. , Mckinney Michael A. , Aiani Karen E. 
Published: March 2011

Abstract1‐Phenyl‐4,7‐dioxaspiro[2.4]heptane (1) was spontaneously copolymerized in bulk at 70°C with maleic and itaconic anhydride to give 1:1 alternating copolymer. Both the cyclopropyl and dioxapentyl rings were observed to open during the propagation. Copolymer yields, compositions and molecular weights are similar regardless of the presence of free radical initiator or inhibitor. A propagation mechanism via zwitterionic addition is suggested. Only homopolymers of styrene and acrylonitrile were isolated when these monomers were heated with 1 in bulk at 70°C in the presence or absence of AIBN. The cationic ring‐opening oligomerization of 1 is also discussed.
Polyoxazoline containing copolymers useful as emulsifiers for polymer blends
Authors: Sinai‐Zingde G. , Verma A. , Liu Q. , Brink A. , Bronk J. M. , Marand H. , McGrath J. E. , Riffle J. S. 
Published: March 2011

AbstractThe preparation of new block and graft copolymers containing poly (2‐alkyloxazoline)s using macroinitiator methods have been investigated. Hydroxy terminated poly(2‐alkyloxazoline) oligomers can be synthesized using alkyl iodide initiators and potassium hydroxide as the terminating reagent. Polymerizations of ϵ‐caprolactone using monofunctional poly(2‐alkyloxazoline)s as macroinitiators and Sn(oct)2 as the catalyst yield diblock copolymers of poly(2‐alkyloxazoline‐b‐ϵ‐caprolactone) with controlled molecular weights. Graft copolymers have also been prepared by first generating a poly(alkyl vinyl ether) backbone. Copolymerization of a low molar percentage of 2‐chloroethyl vinyl ether with alkyl vinyl ethers was performed using a heterogeneous cationic catalyst to yield high molecular weight random copolymers with pendent ethyl chloride groups interspersed along the chain. This pendent chlorine group, together with NaI, was used as the initiation system for 2‐alkyloxazoline grafts. Characterization of the resultant copolymers by gel permeation chromatography, intrinsic viscosity, DSC, solution and solid state 1H and 13C NMR is discussed. These materials are being evaluated as emulsifiers for polymer blends containing aliphatic polyamides as one component.
Ring‐opening polymerization of bicyclic oxalactones and oxalactams
Authors: Okada M. , Sumitomo H. , Atsumi M. , Hall H. K. 
Published: March 2011

AbstractSeveral bicyclic oxalactones and oxalactams having a bicyclo[2.2.2]octane skeleton were synthesized and their ring‐opening polymerizations were investigated under various conditions. These monomers, except 2‐oxa‐6‐azabicyclo[2.2.2]octan‐5‐one (23), gave the corresponding polyesters or polyamides containing tetrahydropyran rings in their main chains. The anionic polymerization of the bicyclic oxalactam 23 afforded a dimer adduct (24) in low yield, whereas the cationic polymerization of 23 gave oligoethers (28) having six‐membered lactam rings in the main chains. The structure‐polymerization reactivity relationships for these bicyclic monomers are discussed.
New polymer architectures: Polyrotaxanes
Authors: Gibson Harry W. , Bheda Mukesh , Engen Paul T. , Shen Ya Xi , Sze Jean , Wu Chao , Joardar Saikat , Ward Thomas C. , Lecavalier Pierre R. 
Published: March 2011

AbstractOur objective is to prepare polymeric rotaxanes, materials in which many macrocycles are threaded by a linear macromolecule, in quantities sufficient to investigate the unique properties that we expect this unusual supramolecular architecture to confer. The design and synthesis of the macrocyclic components, “blocking groups” to constrain the macrocycles, and the polyrotaxanes are described. Model monomeric system has been synthesized and studied to ascertain their conformation. Step growth and chain growth approaches are described.
Initial processes in the cationic homo and copolyierization of trioxane
Authors: Lu Na , Collins G. L. , Yang N. L. 
Published: March 2011

Abstract1H NMR in situ studies of the initial processes involved in the cationic bulk homo‐ and copolymerization of trioxane indicate that the historically termed “induction period” has a kinetic rather than thermodynamic origin. The generation of cyclic acetals takes place through a process kinetically equivalent to insertion rather than back‐biting. The roles played by H2O, formaldehyde, tetraoxane and trioxepane have been further clarified.
Copolymerization of trioxane with 5‐ethyl‐5‐hydroxymethyl‐1, 3‐dioxane
Authors: Zheng Y. C. , Zhang C. L. , Yang N.‐L. , Broussard J. , Auerbach A. , Paul J. 
Published: March 2011

AbstractCationic copolymerization of trioxane with 5‐ethyl‐5‐hydroxymethyl‐1,3‐dioxane gives low‐molecular‐weight copolymer (m̌n: 2∼6×103) with methylol pendent as well as end groups. Detailed 1H NMR assignment for the copolymer has been completed. The polymer is thermally stable up to 220°C and shows a high apparent crystallinity of 69%. The methylol group of the acetal copolymer has been demonstrated to react with acyl chloride and isocyanate groups of a second compound to form graft or crosslink. The copolymerization is characterized by high level of chain transfer.
Stereospecific polymerization of cyclohexene oxide
Authors: Sepulchre M. , Kassamaly A. , Spassky N. 
Published: March 2011

AbstractThe polymerization of cyclohexene oxide with several ZnEt2‐modified initiator systems known to be stereospecific for the polymerization of chiral monosubstituted oxiranes was studied. Among chiral initiator systems only ZnEt2/(1S,2R) ephedrine system allowed us to prepare polymers with high optical activities. The sign of the latter changes with polymer conversion. Fractionation experiments and 1H and 13C NMR studies have shown that the polymers obtained with ZnEt2/(1S,2R)‐ephedrine and ZnEt2/ 1‐methoxy‐2‐propanol systems were a mixture of isotatic as well as syndiotactic polymers. A mechanism of polymerization is proposed to explain this unusual result.
Bioanalogous polymers with poly(alkylene phosphate) chains
Authors: Penczek Stanislaw , Klosinski Pawel , Narebska Anna , Wodzki Romuald 
Published: March 2011

AbstractSynthetic poly(alkylene phosphate)s with repeating units constituted of five or six atoms, i.e., (CH2)nOP(O)(OH)O‐, where n=2 or 3, mimick backbones of biopolymers: nucleic acids. (NA) and teichoic acids (TA). Progress in the synthesis of these polymers is briefly reviewed. The newly developed synthesis of ionic gels, based on reaction of H3PO4 with diepoxides, leads to products with repeating units of TA. These highly water swellable gels slowly hydrolyse at the triester knots, and convert into linear poly(alkylene phosphate)s, stable in water (containing only hydrolytically stable mono‐ and diester units). Polymers modeling TA, poly(1,2‐glycerol phosphate) and its acetate as well as poly(trimethylene phosphate) were studied in the ion transport processes ‐ one of the basic functions of TA, major component in membranes of cell walls of Gram‐positive bacteria. Transport of Mg2+ and Ca2+ ions is analysed, and dependence of the ratio of fluxes of these ions with poly(alkylene phosphate) liquid membranes on the structure of the polymer used is discussed.
Polymer blends containing copolymers
Authors: Braun D. , Yu D. , Andradi L.N. , Löwenhaupt B. , Hellmann G.P. 
Published: March 2011

AbstractBlends with random or block copolymers are discussed, where all components are made of one or both monomers of a given monomer pair. The critical copolymer compositions of blends of two random copolymers were determined, and phase morphologies were studied in blends close to and far from the critical point. Further, the tensile strength of blends of varying compatibility was tested. Microphase and macrophase structures of blends with one or two homopolymers and a symmetric block copolymer were characterized as a function of the chain length ratio of the components. Experiments were compared with model calculations.
New trends in polymer crystallization studies: Part I ‐ from alkanes to polyethylene: The onset of chain folding in polymer crystallization
Authors: Keller A. , Organ S.J. , Ungar G. 
Published: March 2011

AbstractWorks on strictly uniform ultra‐long n‐alkanes enabled the exploration of the onset of chain folding with increasing molecular length. It was established that folding sets in beyond a certain chain length, more specifically dependant on crystallization temperature (Tc), starting in an initially irregular chain deposition, reorganizing subsequently into a strictly quantized conformation of integral fractional fold lengths through either thickening or thinning of the crystal. In the final reorganized stage the folds are regular and sharp. The isothermal crystallization rates for extended chain crystals were found to go through a maximum followed by a minimum with decreasing Tc where chain folding takes over. This remarkable rate inversion, observed for C246 H494 and C198 H398, so far, occurs both for solution and melt crystallization and could be verified for both primary nucleation and crystal growth. We interpret it in terms of a “self poisoning” phenomenon, where chain depositions, which occur transiently in the “wrong” conformation, are blocking the nucleation and growth of the crystal, a phenomenon also reflected in the reversal of the temperature dependence of isothermal refolding on crystallization from solution. Rate reversals of all these kinds promise to be basic to our understanding and are giving rise to recent alternative explanations from elsewhere which are being quoted and discussed.
New trends in polymer crystallization studies: Part II ‐ the role of transient mesophases in polymer crystallization
Authors: Rastogi S. , Hikosaka M. , Kawabata H. , Keller A. 
Published: March 2011

AbstractStudies of crystallization of polyethylene (sharp fractions) under hydrostatic pressure revealed that the previously identified mobile hexagonal phase (h) can arise as a metastable transient even in the more customary orthorhombic (o) stability regime. In fact, it was found that crystallization in the h phase controls the crystallization process even there, at least in the portion of the P‐T phase diagram explored so far. Accordingly, crystallization (nucleation and growth) can only take place while in the h phase and ceases upon transformation into the o phase (occurring when the o phase is the stable one). Crystal growth includes both lateral and thickening growth. Thickening growth in particular involves chain refolding, envisaged by sliding diffusion, and can proceed to thicknesses far in excess to chain extension. All growth rates can be defined quantitatively and correlated with morphology. The above findings are raising wider issues such as: Are metastable transients necessary for polymer crystallization under all conditions, or alternatively are there at least two different modes of crystallization with a change‐over unspecifiable by thermodynamics? Beyond this it raises the possibility of a new source for finite uniform lamellar thickness in the form of crystal‐thickening‐induced growth limiting phase inversion, an example for which has already been found in polymer trans‐1,4‐polybutadiene.
Segmental dynamics of polymers. Influence on material properties
Authors: Monnerie Lucien 
Published: March 2011

AbstractThe segmental dynamics inside a polymer chain is described at first by considering the types of motions which can be performed and the corresponding motional models. Fluorescence Anisotropy Decay and Nuclear Magnetic Relaxation are two very convenient techniques. Results obtained on a series of polymers with low Tg's are presented and discussed. Local motions in solid polymeric materials and their influence on mechanical properties (viscoelasticity, modulus and plastic deformation) are illustrated in the case of model epoxy resins.
Processing and application of thermoplastic structural composites
Authors: Cogswell F.N. 
Published: March 2011

AbstractThermoplastic structural composites offer the designer improved damage tolerance and environmental resistance. They also offer the manufacturer the potential to translate structural composites into a mass production technology. The underpinning materials science to promote that translation is built up from the science of polymer composite product form, composite rheology and morphology, and the control of thermal stability. A range of manufacturing techniques have been developed from conventional thermoset composite processing and from metal technology. A portfolio of applications are currently being developed in the field of medicine, space and aircraft structures, marine and automotive engineering, and industrial machinery.
Rheology of liquid‐crystalline polymers. Theory and experiments
Authors: Marrucci Giuseppe , Grizzuti Nino 
Published: March 2011

AbstractThe rheological behaviour of liquid crystalline polymers differs considerably from that of ordinary polymers as well as of low‐molecular‐weight liquid crystals. The only theoretical approach which has reached a significant development is based on the rigid rodlike model of the polymer molecule. In spite of the crudity of the model, the theoretical predictions based on it prove able to qualitatively describe the most peculiar features of the observed rheological behaviour. A comparison between the relevant experimental peculiarities and the qualitative predictions of the theory is presented.
Dual phase continuity in polymer blends
Authors: Lyngaae‐Jørgensen J. , Utracki L.A. 
Published: March 2011

AbstractThe literature on formation of immiscible polymer blends with dual phase continuity is shortly reviewed. When the volume fraction of one phase is low, nearly spherical discrete domains may be formed in flow fields. The critical volume fraction for formation of infinite structures: φcr = 0.156, predicted by percolation theory for monodisperse spherical domains, is in reasonable accordance with experimental data for samples with spherical domains. In simple shear flow and low volume fraction the coalescence and break up processes may lead to the coexistence of long nearly cylindrical domains (large) oriented in the flow direction and (small) spherical domains. A hypothesis predicting a decrease of the percolation threshold value when φL* · φS* · P · 4 is large, is shown to be in accordance with experimental observations. φL* and φS* are the relative volume fraction of large and small domains, respectively, and P is the aspect ratio of the elongated (cylindrical) drops. The applicability of general (scaling) relations based on percolation theory are discussed.
Toughening in polymer composites. Preliminary results of a micromechanical analysis of yielding in particulate‐modified glassy polymers under multiaxial stresses
Authors: Pavan A. , Mercante L. 
Published: March 2011

AbstractAn elementary model of particulate composite material, comprising one or more spherical particles embedded in an infinite matrix of glassy polymer, is examined. A micromechanical analysis of the stress field, as modified by the inclusions, is first carried out in different, significant applied‐stress states (encompassing those occurring at the tip of a crack during fracture), and the relevant yield criteria are then applied. The results are discussed in view of their relevance to the fracture phenomenon, so as to exploit the toughening potential of the composite material.
The chemistry of magnesium chloride supported catalysts for polypropylene
Authors: Albizzati Enrico , Galimberti Maurizio , Giannini Umberto , Morini Giampiero 
Published: March 2011

AbstractThe reactions between the components of high activity catalysts for polypropylene, aluminum alkyls, magnesium chloride, titanium halides and Lewis bases, are discussed with particular reference made on their influence on the activity and stereospecificity of the catalytic system.
The polymerization of conjugated dialkenes to isotactic and syndiotactic polymers. Effect of ligands on the stereospecificity
Authors: Porri Lido , Giarrusso Antonino , Ricci Giovanni 
Published: March 2011

AbstractOn the basis of the results obtained with various substituted dialkenes, including deuterated monomers, an interpretation is presented of the mechanism of formation of the following polymers: 1,2 iso‐ and syndiotactic polybutadiene; cis‐1,4 iso‐ and syndiotactic polypentadiene; 1,2 syndiotactic poly(5‐methyl‐1,3‐pentadiene); trans‐1,4 threo diisotactic poly(2,4‐hexadiene). Evidence is given that the ligands bonded to the transition metal of the catalyst are important in determining the orientation of the incoming monomer.
Metallocene/polypropylene structural relationships: Implications on polymerization and stereochemical control mechanisms
Authors: Ewen John A. , Elder M. J. , Jones R. L. , Haspeslagh Luc , Atwood Jerry L. , Bott Simon G. , Robinson Kerry 
Published: March 2011

AbstractA series of group 4 metallocenes possessing chiral ligand environments have been characterized and their structures are compared with their propylene polymerizations. Isotactic, syndiotactic, hemiisotactic, and atactic polypropylenes are produced selectively with chiral monoalkyl metallocene cations paired with perfluorotetraphenyl borate; analogous to the results obtained using methylaluminoxane as a cocatalyst. The relative catalyst stereospecificities suggest specific π‐face selectivities and nonbonded contacts. Trends with solvents, temperatures, and catalyst structures are consistent with contact ion pairing for iPr[CpFlu]Zr‐P(+) in liquid propylene. The specificities of differently structured metallocenes imply chain‐migratory monomer addition reactions.