bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stationary and non‐stationary processes in non‐classical radical polymerization with size dependent termination
Authors: Bamford Clement Henry 
Published: March 2011

AbstractKinetic analysis of non‐classical radical polymerization is discussed in terms of the Group‐Termination Procedure on the basis of the geometric mean approximation. Expressions for important kinetic functions of stationary reactions, with or without chain‐transfer, are listed and compared with their classical counterparts. In the treatment of non‐stationary reactions (with or without transfer) special attention is paid to the calculation of pre‐ and after‐effects and their applications in the evaluation of absolute rate coefficients.Nomenclature: I = rate of chain initiation. R·r = concentration of radicals of size r. R· = total concentration of radicals = ΣR· r̄ = number‐average radical size.v = mean kinetic chain‐lengthτ = mean lifetime of a kinetic chain.ω = rate of polymerization (‐dM/dt).Subscripts 1,2 applied to the above signify values at the beginning or end, respectively, of a non‐stationary period.kfL = rate coefficient for chain‐transfer to species L l = kfLL/kpMV = j/kpM + lRa = (jk)½/(kpM); b = a/(1+l).magnified imageTo simplify the presentation concentration brackets are omitted. Conventional mol, dm3, s units are assumed throughout.
Kinetics of long‐chain branching in emulsion polymerization
Authors: Mazzotti Marco , Fiorentino Stefano , Ghielmi Alessandro , Morbidelli Massimo , Storti Giuseppe 
Published: March 2011

AbstractA kinetic model suitable to deal with the case of branched polymers produced in emulsion both in the case of chain transfer to polymer and propagation to terminal double bond is briefly presented and numerically solved through the method of the moments. Thanks to the “numerical fractionation” approach, the whole molecular weight distribution of the polymer is evaluated while accounting for the compartmentalized nature of the system. The results of some illustrative calculations concerning the effects upon the molecular properties of the final polymer of starved semibatch monomer feed policies, addition of a chain transfer agent and propagation to terminal double bond are discussed.
Free‐radical polymerization kinetics in extended ranges of temperature, pressure and monomer conversion
Authors: Buback Michael 
Published: March 2011

AbstractFree‐radical polymerizations have been studied within extended ranges of pressure, temperature, and monomer conversion, including reactions in supercritical phase, where polymerization rate and polymer properties may be continuously tuned. The methods by which propagation (kp) and termination (kt) rate coefficients of homopolymerizations may be determined as a function of P and T, partly up to 3000 bar and 250 °C, are based on using pulse lasers for inducing polymerization (PLP) either in conjunction with size exclusion chromatography (SEC), for kp measurement, or in conjunction with online spectroscopic analysis of monomer conversion, for kt/kp measurement. With kp from PLP‐SEC, the kt/kp data allow to deduce also individual rate coefficients for the termination step. kp primarily depends on temperature and pressure with the values being close to each other within a monomer family, such as the acrylic ester or the methacrylic ester family. Termination rate, which refers to a radical‐radical process, depends on P, T, monomer conversion, solvent type, and on chain length. The major changes of kt with conversion are illustrated using a model that takes segmental diffusion, translational diffusion, and reaction diffusion into account.
The importance of accurate and precise molecular weight measurement in pulsed‐laser polymerization
Authors: Davis Thomas P. , Zammit Michael D. 
Published: March 2011

AbstractMolecular weight distributions generated by pulsed‐laser polymerization have been determined experimentally using multi‐detector size exclusion chromatography (SEC). The conditions for accurate and precise SEC have been defined. The importance of the inter‐detector delay (IDD) is stressed and two different methods of defining IDD are compared. In addition this work highlights the problems associated with the use of Mark‐Houwink constants in constructing a universal calibration curve. Some preliminary results obtained from matrix‐assisted‐laser‐desorption‐ionisation mass spectrometry are also presented.
Polymeric photoinitiators as a tool for clarifying mechanistic aspects of free‐radical polymerization
Authors: Carlini Carlo , Angiolini Luigi , Caretti Daniele , Corelli Elena 
Published: March 2011

AbstractPolymeric photoinitiators, based on side‐chain benzoin methyl ether moieties differently anchored to the backbone, have been designed and applied to the UV cure of acrylic formulations for clarifying the role played by benzoyl and α‐alkoxybenzyl primary radicals in the polymerization process. Kinetic data on the photocuring processes, in the presence of the above polymeric systems, as compared with those obtained by using the corresponding low‐molecular‐weight structural models, are presented and interpreted in terms of different reactivity of the two types of primary radicals towards initiation and termination steps of the polymerization process.
Applications of the study of end‐groups. A new approach to the determination of transfer constants
Authors: Bevington John C. , Hunt Barry J. , Barson C. Anthony 
Published: March 2011

AbstractA summary is given of established procedures depending on analyses of polymers for initiator fragments incorporated as end‐groups; attention is paid to determinations of kinetic chain lengths and rates of initiation in polymerizations and also of the relative importances of combination and disproportionation during termination. Recent developments allow determination of transfer constants from information on the average number of initiator fragments in a molecule of a polymer, even in some cases where the transfer is degradative. Their applications are discussed for various transfer agents including iodoform and derivatives of propene from which allylic radicals could be produced. There is consideration of the possibilities of applying analyses for initiator fragments to study of transfer initiator, transfer to polymer and primary radical transfer.
The reactor polymer alloys: The shifting of the frontier of polymer research
Authors: Galli Paolo 
Published: March 2011

AbstractThe discovery (1968) of the high yield Ziegler‐Natta catalysts based on active MgCl2 was the beginning of a scientific and industrial revolution that has brought about the creation of superactive, isospecific, spheriform fourth generation catalytic systems. The rationalization of the polymer/catalyst replication phenomenon and the understanding of the catalyst “architecture” effects on polymer shape and morphology has led to the exploitation of the “Reactor Granule Technology”. This has made the generation of a broad range of homo, copolymers and multiphase alloys (Catalloy) possible by synthesis, most of which having a previously unobtainable spectrum of performance (Refs. 1,2,3). The reactor granule technology concept has also been the basis for the achievement of a family of polyolefin/non polyolefin alloys with engineering properties.More recently, the reactor granule approach has been extended so as to couple the advantages of both heterogeneous and homogeneous metallocene catalysts (mixed catalysis), thus allowing the synthesis of a very new family of “in situ” polyolefin alloys.
Application of equation of state theories to poly(styrene‐Co‐acrylonitrile)/poly(methyl methacrylate) blends
Authors: Rudolf Bernd , Ougizawa Toshiaki , Shimomai Ken , Higashida Noboru , Inoue Takashi , Kressler Jörg 
Published: March 2011

AbstractThe miscibility behavior of poly(styrene‐co‐acrylonitrile)/poly(methyl methacrylate) blends was described by using the equation of state theory of Flory et al. and the lattice fluid theory. The ‘surface area effect’ inherently included in the latter theory was neglected. For that case it is found that the description of the phase behavior of that theory is similar then to that obtained by using the theory of Flory et al. Without neglecting this surface area effect, however, it is not possible to describe the observed behavior with the lattice fluid theory. Moreover, for both theories it is necessary to include both, interactional and free volume effects, though the observed LSCT behavior is not solely due to free volume effects.
Calculation of miscibility behavior of multinary polymer blends
Authors: Horst Roland , Wolf B. A. 
Published: March 2011

AbstractA method for the calculation of phase diagrams (tie lines and binodal, spinodal, critical points and their stability) based exclusively on the Gibbs energy of mixing, δG, is presented which does not require the calculation of the derivatives with respect to the composition. The method is demonstrated for ternary mixtures of two homopolymers and the corresponding copolymer, and for quaternary and quinternary blends of five polymers exhibiting a closed miscibility gap. The advantages of the presented method become most obvious in the mathematical description of measured phase diagrams, where complex composition dependencies of the interaction parameter are observed.
Phase separation in thermoplastic ‐ thermoset polymer blends
Authors: Elliniadis Stavros , Higgins Julia S. , Choudhery Riaz A. , Jenkins Stephen D. 
Published: March 2011

AbstractThe effect of composition, curing temperature and curing agent on the phase separation of a blend containing poly‐ethylene‐terephalate and diglycidyl‐ether of bisphenol A was studied using a small angle light scattering(SALS) technique. The results show a wide compositional range for the spinodal decomposition mechanism and the potential for greater morphology control in this type of blends.
Morphological control of impact toughness in poly(methyl methacrylate) /acrylonitrile‐butadiene rubber blends
Authors: Lindsay C. I. , Jenkins S. D. , Emmerson G. T. , McGrail P. T. 
Published: March 2011

AbstractToughening of PMMA by in‐situ polymerisation of methyl methacrylate/acrylonitrile‐butadiene rubber solutions to give blends with a multiple‐inclusion morphology has been achieved This contrasts with the lack of impact toughening observed upon direct blending of PMMA with the same rubber. The toughened blends are analogous to HIPS in terms of the multiple‐inclusion morphology and the observed cross‐linking within the separated elastomeric phase but possess significantly larger separated phase domains.
Chemical reactions during reactive blending of polyurethanes: Fiction or reality?
Authors: Stutz Herbert , Pötschke Petra , Mierau Uta 
Published: March 2011

AbstractThe extent of reactions occurring during reactive blending of thermoplastic polyurethanes (PUR) with functionalized polyolefins or reactive compatibilizers has been studied using ethylene/acrylic acid and styrene/maleic anhydride copolymers. Due to interfacial segregation effects, no reaction was found with carboxylic groups and only little with anhydrides. Here 1–2% reaction products are generated after 30 min with preferentially multiple additions at the same molecules. Therefore, with incompatible polymers, reactive coupling is negligible with PUR under realistic blending conditions.
Reactive compatibilization of poly(styrene‐Co‐maleic anhydride)/poly(phenylene oxide) blends
Authors: Koning Cor , Bruls Willie , Buijsch Frans Op Den , Vondervoort Lizette V. D. 
Published: March 2011

AbstractPrimary amine terminated polystyrene (PS‐NH2), with Mn=12,000 g/mol and Mw=23,000 g/mol, was applied as a reactive compatibilizer for poly(styrene‐co‐maleic anhydride)/poly(phenylene oxide) (SMA/PPO) blends, in which both an impact modifier for the continuous SMA phase, viz. ABS, and the dispersed PPO phase, viz. SEBS, was incorporated. During melt blending, SMA‐g‐PS copolymers are generated at the interface between the SMA/ABS and the PPO/SEBS phases. The addition of 10 wt % of the reactive PS‐NH2 compatibilizer to a SMA/ABS/PPO/SEBS 30/30/30/10 blend results in a more significant refinement of the dispersed PPO/SEBS particles than 10 wt % of a commercially available, bulky PS‐graft‐PMMA copolymer with Mn=45,300 and Mw=293,400 g/mol. In addition, PS‐NH2 gives a more pronounced enhancement of the yield stress, the stress at break and the notched Izod Impact than the PS‐g‐PMMA. On the other hand, the elongation at break is higher in the case of the non‐reactive PS‐g‐PMMA. It was demonstrated that surface imperfections, probably introduced by an observed strongly elastic character due to partial crosslinking of the SMA/ABS phase by difunctional H2N‐PS‐NH2, are responsible for the lower elongation at break for the PS‐NH2 based blends.
Surfactant induced mesomorphic behaviour of flexible polymers
Authors: Ikkala Olli , Ruokolainen Janne , Torkkeli Mika , Serimaa Ritva , Brinke Gerrit Ten 
Published: March 2011

AbstractConditions for micro phase separated structures based on flexible polymers associated with surfactants have been investigated. Reasonably strong attractive interactions are required to oppose macro phase separation between polymer and surfactant. In order to obtain micro phase separation, additionally a sufficiently strong polar‐nonpolar repulsion has to be present. Poly(4‐vinyl pyridine), poly(2‐vinyl pyridine) and polyamide 6 have been used as model polymers in this work. Associations based on protonation, metal coordination and hydrogen bonding are presented and shown to yield micro phase separation under suitable conditions. In the charged systems, the polar‐nonpolar repulsion easily becomes large enough to render micro phase separated structures. In hydrogen bonded (i.e. noncharged) systems a more delicate balance can be achieved in which case an order‐disorder transition takes place from a homogeneous state, exhibiting nonetheless a distinct SAXS peak due to characteristic block copolymer‐like fluctuations, to a micro phase separated ordered state.
Blends of some non‐flexible and flexible polymers: Routes to molecular composites?
Authors: Cowie John M. G. , Nakata Shoichi , Adams Gordon W. 
Published: March 2011

AbstractThe definition of a molecular composite is a blend of a rigid rod polymer and a flexible coil polymer that is miscible at the molecular level. This concept has been tested using systems in which the chain flexibilities differ as widely as possible as judged by the difference in glass transition temperatures (δTg). The biggest variation (δT ∼360°C) was obtained by mixing poly benzimidazole with copolymers of poly(vinyl acetate‐ran‐vinyl alcohol). It was observed that the blends were distinctly two phase when the hydroxyl content was less than 50 mol %. Above this value clear blends were obtained with finely dispersed phases although it is doubtful if mixing at the molecular level takes place.Miscible blends could be obtained from combinations of the sodium salt of poly(phenylene terephthalamide) with poly(4‐vinylpyridine) and mixtures of poly(phenyl imino‐1,4‐phenyleneoxyterephthalate) with poly(styrene‐stat‐hydroxylstyrene) where coulombic interactions and hydrogen bonding respectively promoted the miscibility.
On the extension of polysoaps: The Gaussian approximation
Authors: Borisov Oleg V. , Halperin Avraham 
Published: March 2011

AbstractPolysoaps are linear hydrophilic chains that incorporate, at intervals, covalently bound amphiphilic monomers. In water, the amphiphilic monomers self assemble into intrachain micelles thus endowing the chain with a secondary structure. The relaxation of the secondary structure upon deformation qualitatively modifies the elastic behaviour of polysoaps in accordance with the LeChatelier principle. For long polysoaps a regime in which the tension in the chain, f, is independent of the end to end distance R, f ˜ R° is predicted. The extension of long polysoaps is analysed for the particularly simple case when the backbone obeys Gaussian statistics and excluded volume interactions are neglected.
ABC and BAC triblock copolymers ‐ morphological engineering by variation of the block sequence
Authors: Abetz Volker , Stadler Reimund 
Published: March 2011

AbstractDifferent morphologies and phase transitions of ternary triblock copolymers with different block sequences (ABC and BAC) are discussed qualitatively. The interplay between interfacial energies and elastic energies of the different blocks leads to various morphologies and enhances or prevents mixing of different blocks, depending on composition and topology.
Electrooptical properties of mesogenic chain molecules in solution and in nematic state
Authors: Tsvetkov Victor N. , Tsvetkov Nikolay V. , Kant Rama 
Published: March 2011

AbstractElectrooptical characteristics of mesogenic chain molecules in solution and in mesophase can be described in terms of intra‐ and intermolecular orientational orders. The value and sign of electric birefringence δn in a solution of kinetically rigid chain molecules are determined by the combination of two factors: intramolecular orientational order which depends on the dipolar and anisotropic architecture of the molecule and intermolecular orientational order caused by the action of the external electric field E. The value and sign of the dielectric anisotropy δε of the polymer nematic phase are also determined by the combination of intra‐ and intermolecular orders. However, in this case the latter is not maintained by the external field but by the nematic potential of the mesophase. Therefore, comparative investigations of electrooptical properties of polymers in solutions and in nematic melts make it possible to obtain information about the intra‐ and intermolecular orientational orders of the molecules under investigation in these two states. These investigations were carried out using the method of electric birefringence in solutions and the method of orientational deformations of nematic textures in an electric field. The objects being investigated were nematogenic dimers and trimers. Experimental data obtained for these compounds showed the presence of intramolecular order in their molecules, which is manifested in the odd‐even oscillations of the value and sign of Kerr constant K≈δn/E2 in solution and δε in the nematic phase when the number of C‐C bonds in the methylene spacers of these molecules is varied. This effect is particularly dramatic in the mesophase where it is enhanced by intermolecular nematic potential.
Fluctuation, relaxation and “super‐structure” in liquids the conformon model
Authors: Kilian Hanns‐Georg 
Published: March 2011

AbstractThe conformon model of liquids postulates a heterogeneous dynamic superstructure in liquids. The model predicts a universal reduced energy‐ and entropy‐density distribution (Planck distribution) which typify together the thermodynamics of fluctuations. The mean reduced energy‐ and entropy density distributions are identical and invariant at all temperatures, independently of the type of molecules the liquid is comprised of. The model predicts therefore a unique superstructure at the quasi‐static glass‐transition temperature. Tapping‐mode atomic force experiments on monolayers of bottle‐brush molecules reveal a type of a superstructure which is, in fact, in good accord with the conformon model. Relaxation experiments can be described as superposition of a broad set of intra‐conformon Debye‐processes which is consequently related to the heterogeneous equilibrium structure. Principal aspects of the results are reflected in the paper.
Nuclear magnetic relaxation in solutions of poly(fluoromethylene) and poly(vinyl fluoride); segmental mobility of fluorinated ethylene polymers
Authors: Stockmayer Walter H. , Yang Henry W.‐H. , Matsuo Keizo 
Published: March 2011

Abstract1H and 19F spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for solutions of poly(fluoromethylene) in DMSO, and for poly(vinyl fluoride) in DMF. These results, together with literature values for other fluorinated ethylene polymers, show that substitutions of F for H on the chain backbone produce only mild changes in segmental mobility.
Reversible thermothickening of aqueous solutions of polycations from natural origin
Authors: Desbrières Jacques , Rinaudo Marguerite , Chtcheglova Lilia 
Published: March 2011

AbstractThis paper concerns our first set of experimental data on alkyl chitosans in acidic medium allowing to compare the roles of the degree of alkylation and that of the length of the alkyl chains on their physicochemical properties in aqueous solution. The balance between electrostatic repulsion (related to the fraction of ‐NH3+) and the hydrophobic attraction is discussed on the CC12 sample, a chitosan modified with a C12 aliphatic chain. A phase diagram is established separating the conditions for gel‐like structure formation and phase separation. The roles of the net charge and that of the temperature on the formation of hydrophobic aggregates are examined.
Spreading of polymer molecules on solid surfaces
Authors: Stuart Martien A. Cohen , van Eijk Marcel C.P. , Dijt Jaap C. , Hoogeveen Nynke G. 
Published: March 2011

AbstractWhen a homopolymer adsorbs from dilute solution onto a solid surface it first attaches and then maximises its number of contacts with the substrate by means of a spreading process. Evidence for this spreading process can be obtained from experiments on the adsorption kinetics. We report on a case where the adsorption kinetics depend on the rate at which the polymer was supplied to the surface (a protein adsorbing onto silica). Also, we discuss competitive adsorption experiments in which one kind of chain molecule attempts to displace another one from the surface. In these experiments, the desorption rate of the displaced species reflects the spreading rate of the displacer. When this rate is slower than the supply of displacer molecules, oversaturated layers result that spontaneously eject polymer. We have measured the rate of these displacement‐driven desorption processes in various cases and conclude that it depends strongly on the energy of the segment‐surface bond. A model involving the diffusion of defects over the surface may account for this finding.
Interfaces between coexisting phases of polymer mixtures: Comparison between Monte Carlo simulations and theoretical predictions
Authors: Binder Kurt , Müller Marcus 
Published: March 2011

AbstractLarge scale Monte Carlo investigations of the interface between A‐rich and B‐rich phases of symmetric binary (AB) polymer mixtures are presented, using the bond fluctuation model of flexible chains with NA=NB=N=32 effective monomers. The temperature range studied, 0.144<T/Tc0.759, includes both the strong and the weak segregation limit. Interfacial free energy and interfacial structure are studied, and compared to predictions based on the selfconsistent field theory. Also the broadening of the interfacial width due to capillary waves is considered, and finite size effects due to the confinement of interfaces in thin films of polymer blends are discussed.
Structures of “crew‐cut” aggregates of polystyrene‐b‐poly(acrylic acid) diblock copolymers
Authors: Zhang Lifeng , Eisenberg Adi 
Published: March 2011

Abstract“Crew‐cut” aggregates of polystyrene‐b‐poly(acrylic acid) block copolymers can be prepared by dissolving the copolymers in N,N‐dimethylformamide (DMF) and adding water to the solution to induce aggregation of the styrene segments of the copolymer chains. The aggregates are formed at near‐equilibrium conditions, and their structures are subsequently frozen by isolating them into aqueous solution by dialysis. Aggregates of a number of different morphologies have been prepared. The morphologies, identified by transmission electron microscopy, consist of spheres, rods, vesicles, lamellae, large compound vesicles, large compound micelles, etc. The formation of aggregates of different morphologies can be controlled by varying the copolymer composition, by changing the initial copolymer concentration in DMF, by adding ions (e.g. NaCl, CaCl2, HCl and NaOH, etc), or by adding homopolystyrene.