bluuebunny/crossref_metadata_2025 huggingface dataset:
Fundamentals of carbocation chemistry in alkene polymerization and alkylative or oxidative alkane condensations
Authors: Olah George A.
Published: March 2011

Some fundamental aspects of carbocation chemistry are discussed in their relationship to our better understanding of carbocationic olefin polymerization and alkane condensation reactions including those of methane. Whereas trivalent alkyl cations, i.e. R3C+ play the key role in the former, the latter is made possible through the intermediacy of five coordinate carbocations of the CH5+ type. In conventional acid catalyzed reactions carbocations are always in equilibrium with their corresponding olefins, whereas under superacidic, stable ion conditions carbocations can be generated and reacted free of such equilibria. The chemical consequences of these differences are discussed in polymerization, as well as in alkylative or oxidative alkane condensation reactions.
Kinetic and thermodynamic studies of carbenium ion additions towards alkenes
Authors: Mayr Herbert , Schneider Reinhard , Schade Christian
Published: March 2011

The ionisation (Ar2CHCl + BCl3 ⇌ Ar2CH+BCl−4) and dissociation (Ar2CH+BCl−4 ⇌ Ar2CH+ + BCl−4) equilibria of diarylmethyl chlorides in boron trichloride/dichloromethane solution have been studied by conductimetry, photometry and 1H NMR spectroscopy. Small differences in the UV‐vis spectra of diaryl‐carbenium tetrachloroborates, which have been observed in solutions of low and high tetrachloroborate concentration, can be attributed to the formation of 1:1 ion‐pairs in the more concentrated solutions. Low temperature calorimetry was used to determine the heats of addition of diarylcarbenium tetrachloroborates to 2‐methyl‐1‐pentene (Ar2CH+BCl−4 + H2C‐CRR' + Ar2CH‐CH2‐CRR'Cl + BCl3), and it is estimated that the standard free enthalpy of this reaction is greater than 0 for systems with pKR+ > −2.6. Kinetic studies have shown that paired and unpaired diarylcarbenium tetrachloroborates exhibit identical reactivity towards alkenes. A rationalisation for the different situation in carbocationic and carbanionic polymerisation is presented. The rate constants for the initiation of isobutene, styrene and isoprene polymerisation by diarylcarbenium ions have been determined, and it is shown, how propagation rate constants can be estimated from linear free energy relationships.
A new conceptualization in relation to ionic polymerizations
Authors: Saegusa Takeo
Published: March 2011

A new systematization is presented for the polymerization reactions in relation to the so‐called “Ionic Polymerizations'. The basis of the new systematization, is the concept of the reaction between “Electrophile” and “Nucleophile”. The reactants are either ions (cation or anion) or dipoles. Polymerization reactions except free radical polymerization and polycondensation are classified into three categories depending upon the reactivity characteristics (electrophilic or nucleophilic) of the propagating species.

a. Polymerization via electrophilic propagating species

b. Polymerization via nucleophilic propagating species

c. Polymerization via zwitterions

Emphasis is placed on the polymerization reactions which propagate through covalent species having nucleophilic or electrophilic reactivity. By this systematization, several polymerization systems which have been treated as unusual or exceptional cases are thus reasonably categorized.
Chain extension of oligodiols by means of cyclic acetals
Authors: Franta E. , Kubisa P. , Refai J. , Kada S. Ould , Reibel L.
Published: March 2011

We have studied the reaction of 1,3‐dioxolane with trifluoromethanesulfonic acid in the presence of α,ω‐dihydroxypolytetrahydrofurane and α,ω ‐ dihydroxypolystyrene. Besides polymerization of 1,3‐dioxolane we have observed the occurence of a fast coupling reaction between the initial oligodiols. The mechanism has been studied using a monohydroxylated polystyrene and a model compound, 3‐phenyl‐1‐butanol. We have shown that coupling takes places through transacetalization even under the mild conditions used Ethylene glycol is produced and an acetal bridge is formed between oligodiols. Conditions have been found where high‐molecular‐weight polymer is formed through this polycondensation, in the absence of homopoly(1,3‐dioxolane).
Controlled polymerization of silyl vinyl ethers by aldol group transfer polymerization
Authors: Boettcher F. Peter
Published: March 2011

Silyl vinyl ethers can be polymerized at room temperature and in high yield by initiation with electrophiles, e.g. aldehydes, in the presence of a Lewis acid catalyst. This polymerization, called aldol group transfer polymerization, is living and permits good molecular weight control. Narrow molecular weight distribution is usually obtained. The silylated polymerization products can be hydrolyzed to poly(vinyl alcohol) and coupled via the reactive end group with other functional polymers to give block copolymers. Other block and graft polymers containing the hydrophilic poly(vinyl alcohol) segment can be obtained by initiating aldol group transfer polymerization with mono‐ or multifunctional polymeric initiators.
Activated monomer mechanism in the cationic polymerization of cyclic ethers
Authors: Kubisa Przemysław
Published: March 2011

Cationic polymerization of oxiranes proceeds in the presence of hydroxyl groups containing compounds by activated monomer (AM) mechanism, competing with active chain end (ACE) mechanism. According to the AM mechanism, propagation involves reaction of activated (e.g. protonated) monomer molecules with nucleophilic sites in the growing macromolecules. Active species are located on the monomer, and growing macromolecule is neutral; thus side‐reactions, typical for active chain‐ end mechanism, are suppressed. In the polymerization of ethylene oxide (EO) ether oxygen atoms along the chain are more exposed to the attack than in the polymers of substituted oxiranes and also react with protonated monomer. The contribution of these reactions, in comparison with propagation involving hydroxyl end groups, is analysed. The participation of the polymer units is highly restrained for chains with bulky substituents. In the AM polymerization of propylene oxide (PO) and epichlorohydrin (ECH), chain growth proceeds predominantly on the terminal hydroxyl groups. Syntheses of telechelic oligomers and macromonomers, applying the AM mechanism with protonated monomers, are described.
Mathematical modelling of cationic alkene polymerization
Authors: Freyer C. V. , Nuyken O.
Published: March 2011

In recent years progress has been made in mathematical modelling of complicated chemical systems. Simulation of reactions with computational techniques offers an excellent method for testing the extent to which a reaction mechanism is indeed understood.

After considering the principles of modelling and its advantages in general we present a new type of modelling of polymerizations and its advantages in particular. This method typically involves time‐stepwise integration of kinetic equations and works at a level in between macroscopic (= conventional kinetics) and microscopic (= molecular statistics). At this “semi‐microscopic” level reactants are discriminated not only by the functional groups but also by the chain lengths. Since this method additionally provides information on molecular mass distribution, better facilities to fit experimental data and, therefore, higher confidence in the accuracy of the model are achieved.

With regard to cationic polymerization of alkenes there still is uncertainty of some mechanistic details. Showing the latest developments of our new method specially developed for polymerizations we will discuss our first results. Our objective is to apply the new method for kinetic investigations and to contribute new information on this field.
Covalent and ionic species in cationic polymerizations: Rates of exchange
Authors: Penczek Stanislaw , Szymanski Ryszard
Published: March 2011

The general kinetic scheme of simultaneous propagation on covalent and ionic species is discussed. There are a few ways of interconversion of covalent and ionic species, and at least two different modes of covalent propagation. This is either a direct inclusion with reformation of covalent species or reaction of covalent species with a monomer, giving ionic species, collapsing then into the covalent species and/or propagating ionically.

Significance of these processes for the overall kinetics is discussed; rates of exchange covalent ⇌ ionic and covalent + monomer ⇌ ionic are discussed in more detail on the basis of trityl chloride ionization and ester‐ion equilibria in the polymerization of THF and oxepane.
Liquid crystalline polymers by cationic polymerization
Authors: Percec Virgil
Published: March 2011

The synthesis of liquid crystalline polymers and oligomers containing calamitic and disc‐like mesogens by cationic polymerization and oligomerization is reviewed. Examples from ring‐opening, carbocationic, and radical‐cation polymerizations and oligomerizations are discussed.
Unsaturated telechelic oligoisobutylenes: Appraisal of the transfer efficiency of some dienes
Authors: Cheradame H. , Razzouk H. , Rousset E. , Gandini A.
Published: March 2011

Isobutylene was polymerized in the presence of 1,3‐pentadiene (BF3 initiator) and 2,5‐dimethyl–2,4‐hexadiene (AlEt2Cl initiator) in CH2Cl2. Analysis combining examination of the H (mainly 300 MHz) and C NMR spectra and oxidative cleavage by RuO4 of the copolymers obtained was carried out. Some homopolyisobutylenes (TiCl4 initiator) were synthesized for comparison. The results show that it is possible to account for the structures of macromolecular chain ends by the assumption of hydride or methide transfer. The consequences of this assumption are thoroughly discussed.
New initiators for living cationic polymerization of vinyl compounds
Authors: Higashimura Toshinobu , Aoshima Sadahito , Sawamoto Mitsuo
Published: March 2011

Living cationic polymerizations of vinyl ethers and related vinyl monomers were achieved by stabilizing the propagating carbocation either with a counteranion or with an added base. The following initiating systems, designed on the basis of these two approaches, were found to induce well‐defined living polymerizations, some of which proceeded even above room temperature (+25 to +70°C).

(a) Stabilization by a counteranion:

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(b) Stabilization by an added base:

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For the first approach, judicious matching of the stability of the growing carbocation and the nucleophilicity of a counteranion was critical. For the second approach, coordination (or solvation) of the growing end by the added base was the key to the generation of living polymers. The nature of the living propagating species is also discussed.
Synthesis of new functional polymers by living cationic polymerization
Authors: Sawamoto Mitsuo , Aoshima Sadahito , Higashimura Toshinobu
Published: March 2011

This paper covers three major areas of the synthetic applications of living cationic polymerization of vinyl ethers initiated by the hydrogen iodide/iodine (HI/I2) system; namely, the synthesis of (a) pendant‐functionalized polymers, (b) end‐functionalized polymers, and (c) amphiphilic block polymers with a unique structure. In area (a), more than 25 vinyl ethers with a functional pendant were found to undergo living polymerization to give a variety of pendant‐functionalized polymers:

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In area (b), terminally monofunctional and telechelic polymers (including macromonomers) were prepared by living polymerization using a functional initiating system (CH3‐CHI‐OCH2CH2‐X/I2) and/or by end‐capping of the HI/I2‐initiated living polymer ends with a functional nucleophile (:Nu‐X):

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In area (c), amphiphilic block polymers of vinyl ethers were obtained and characterized, the hydrophilic segment of which carried highly branched bulky substituents with a large number of hydroxyl groups (six per pendant):

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Emulsion copolymerization kinetics with polar monomers
Authors: Bartoň Jaroslav
Published: March 2011

The multi‐component polymerization of the industrially important hydrophobic and hydrophilic monomers exhibits special features in comparison to the multi‐component emulsion polymerization of hydrophobic monomers. The main difference stems from the partial or total solubility of the hydrophilic monomer in the continuous water phase and in some instances also from the formation of water‐soluble polymer. The chemical and morphological structure of the polymer particles, beside the comonomer partitioning between water and oil phases, is governed also by the reactivity ratios of comonomer pair and by the extent of the mutual miscibility or phase separation of polymeric material of the particle. Compositional (chemical) heterogeneity of the polymer particles is also influenced by different affinity of the polymer (copolymer) to the water and oil phases. Structurally inhomogeneous polymer product results from the simultaneously proceeding polymerization in the water and oil phases. The polymer product represents a mixture of homopolymer (copolymer) formed in the water phase and of the copolymer (sometimes graft copolymer) formed on the surface of the polymer particles or in the interphase surrounding the polymer particle.
Dispersion copolymerization in non‐aqueous media
Authors: Ober Christopher K.
Published: March 2011

Recent developments in dispersion copolymerization including particle formation in both polar and nonpolar media are discussed. The effects of stabilizer, reaction medium and initiation rate on particle size and distribution in homo‐ and copolymerization are described, and in particular, processes leading to the formation of monodisperse latices and the crosslinking of these microspheres will be examined.
Basic aspects and recent developments in suspension polymerisation
Authors: Brooks B. W.
Published: March 2011

In suspension processes, polymerisation occurs in a monomer‐containing phase which is dispersed in a continuous liquid phase. Controlled agitation and the presence of drop stabilisers are necessary to maintain the suspension. Temperature control is usually better than that observed in corresponding bulk processes. Polymerisation kinetics are often similar to those which apply to bulk systems but high conversions increase the probability of gel effects. Drop sizes can depend on conditions of turbulence, viscosity and interfacial tension. Correlations for maximum drop sizes are discussed. Drop segregation can affect product quality and reactor design is important. Drop sizes can change with time and particle size distributions may become bimodal. Polymeric stabilisers may be present in both the continuous and dispersed phases. If polymer precipitates inside the drops, the stabiliser can influence the particle morphology. The stabilising action of particulate inorganic solids is not well‐understood. In copolymerisation, cross‐linking may occur. Precipitation of copolymer can be promoted by the use of diluents. Stabilisers can have a role in determining porosity of the final particles. Reactivity ratios may appear to differ from those expected in bulk processes when one or more of the comonomers is appreciably soluble in the continuous phase. Relevant literature is reviewed and topics requiring further work are identified.
Hydrophilic polyelectrolyte gels by inverse suspension
Authors: Trijasson P. , Pith T. , Lambla M.
Published: March 2011

This paper is devoted to the synthesis and characterization of highly hydrophilic polymer gels based on acrylic monomers. These superabsorbant polymeric materials (SAPs) were prepared by polymerization of an aqueous solution of monomers dispersed in a continuous organic phase. This inverse suspension process (I.S) was carried out in cyclohexane, the aqueous dispersed mixture containing acrylic acid, partially neutralised, at a given crosslinker/monomer ratio. The dispersion is stabilized by the introduction of a surfactant like SPAN 80. Due to an almost complete lack of available scientific knowledge, it was necessary to perform a basic study covering the influence of the main parameters driving the behaviour of SAPs, especially maximum swelling and absorption kinetics. Further influence of crosslinking density, initial monomer concentration and process conditions have been studied on the base of a model recipe. These results led to optimisation of swelling and absorption behaviour, using various kinds of monomer species and different polymerization conditions.
Scattering studies of the morphology of copolymer colloidal particles
Authors: Bootle Ceraldine A. , Lye Jill E. , Ottewill Ronald H.
Published: March 2011

Small angle neutron scattering studies have been carried out on copolymer latices prepared using acrylonitrile and styrene. These showed that when one of the monomers was deuterated good contrast in scattering was obtained between the two polymers. In the case of poly(acrylonitrile) ‐ poly(styrene) particles evidence was obtained for a core shell morphology with the poly(acrylonitrile) forming the outer shell.
Control of particle morphology in emulsion polymerization
Authors: Okubo Masayoshi
Published: March 2011

Submicron‐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

In 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

Typical 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

Colloidal 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

The 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

Branched 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

Hydroxy‐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

1‐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

The 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

Several 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

Our 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

1H 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

Cationic 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

The 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

Synthetic 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

Blends 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

Works 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

Studies 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

The 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

Thermoplastic 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

The 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

The 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

An 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

The 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

On 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

A 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.
Stereospecific polymerization of 1‐olefins and styrene in the presence of homogeneous catalysts
Authors: Zambelli Adolfo , Pellecchia Claudio , Oliva Leone
Published: March 2011

The behaviour of several catalytic systems promoting stereospecific polymerization of α‐olefins is briefly reviewed. Syndiotactic specific polymerization of styrene is also considered and possible structures are tentatively proposed for the syndiotactic specific catalytic complexes.
Recycling of polymeric materials by pyrolysis
Authors: Kaminsky W.
Published: March 2011

As most plastics are produced from oil and as they are discussed to be an environment problem, the recycling of plastic and rubber waste is of increasing importance. A recycling of plastic wastes is costly for mixtures of polymers or even impossible as in the case of composites. Next to combustion only pyrolysis is practicable as a recycling process. Systems for the pyrolysis of plastic waste with complete exclusion of oxygen use melting vessels, rotary kilns or fluidized bed processes. The fluidized bed pyrolysis has turned out to be particularly advantageous. Under the appropriate conditions these processes could be successful on the market.
Configurational and conformational effects in the thermal degradation of poly(vinyl chloride)
Authors: Millán J. , Martínez G. , Jimeno M.L. , Tiemblo P. , Mijangos C. , Gómez‐Elvira J.M.
Published: March 2011

A series of works with the aim of clarifying the mechanisms of thermal and photochemical degradation of PVC are reviewed. They include studies on: i) degradation of PVC samples of various tacticities; ii) degradation of PVC after modification by stereoselective nucleophilic substitution; iii) influence of temperature on both kinetics of degradation and polyene distribution in degraded polymer; iv) changes in the highly resolved 13C NMR spectrum as the result of thermal degradation to low degrees; and v) degradation of PVC in blends with polymers of various degrees of compatibility. The results, yet partly unpublished, lead to the conclusion that the very labile structures are some normal local conformations, in particular the GTTG− of the isotactic triad, and allow to confirm some earlier approaches to the PVC mechanisms of degradation.
Interpolymer complexes as new materials for biomedical applications
Authors: Kabanov Victor A.
Published: March 2011

Polymer networks which can be “de‐crosslinked” in a controlled way, i.e. at a given moment and under chosen experimental conditions, have a number of potential applications such as temporary protective coatings and erodable bio‐materials. If the de‐crosslinking occurs by scission of bonds which differ from those that form the branching points of the network, soluble star‐shaped polymers are formed, the analysis of which gives information about the functionality of the branching points.
De‐crosslinkable networks
Authors: Goethals E.J. , Trossaert G. , De Vos R. , De Clercq R.
Published: March 2011

Recent extensive studies have distinguished a special class of polymers which are able to form thermotropic mesophases despite the absence of mesogenes in their chemical structure [1]. In the most striking form the tendency to form such mesophases is displayed by polymers with flexible inorganic backbone, such as poly(diethylsiloxane)/PDES/. In this presentation recent results concerning mechanical and thermomechanical behaviour of a series of PDES mesophase elastomers are considered. Three types of PDES elastomers were studied: crosslinked samples prepared by peroxide vulcanization [2,3], crosslinked samples vulcanized by a multifunctional siloxane resin [4] and block copolymers with ladder polysilsesquioxane as the hard block and PDES as the soft block [5].
Intermolecular interactions and properties of bulk polymers
Authors: Rutledge Gregory C. , Suter Ulrich W.
Published: March 2011

Interaction of molecular self organization and molecular recognition leads to formation of functional supramolecular systems. They combine order and mobility, and their function is based on their organization1. These fascinating phenomena ‐ and the living cell is only the most perfect example ‐ can help to mimic biomembrane processes as well as to develop new synthetic materials.
Synthesis in the future of polymer science
Authors: Bikales Norbert M.
Published: March 2011

This presentation asserts the importance of synthesis in the creation of new materials, the discovery of new phenomena, and the development of new or improved materials for high‐technology industries. It points to the neglect of synthesis and processing in American universities, and the response of the National Science Foundation to overcome this shortcoming in the future.
New synthetic routes towards polyphosphazenes
Authors: Matyjaszewski Krzysztof , Cypryk Marek , Dauth Jochen , Montague Robert , White Michael
Published: March 2011

Two new methods for the synthesis of polyphosphazenes are described. The first is based on the catalyzed polycondensation of phosphoranimines using various catalysts and initiators. Certain mechanistic aspects of this process with reactive intermediates are discussed. Linear polymers are formed quantitatively at temperatures around 100 °C in a few hours (the thermal process requires a few days at 200 °C). The second method is based on the direct reaction between phosphonites and phosphinites with silyl azides. This reaction proceeds by phosphine azide intermediates and provides new polyphosphazenes.
New initiating systems for living cationic polymerization: Design and mechanism
Authors: Sawamoto Mitsuo , Higashimura Toshinobu
Published: March 2011

This paper concerns the recent progress in our search for new initiating systems for living cationic polymerization and the mechanisms involved therein, specifically focusing on:

(a) Protonic acid/Lewis acid initiating systems for vinyl ethers;

(b) Initiating systems for living cationic polymerization of styrene;

(c) Multi‐functional initiating systems.

In area (a), the design of counteranions was discussed relative to the principles of living cationic polymerization; in area (b), the first truly living cationic polymerization of styrene is described; and in area (c), the multi‐functional initiating systems led to tri‐armed polymers of vinyl ethers and p‐alkoxystyrenes with amphiphilic arm chains of uniform lengths.
Cationic bulk polymerization of vinyl ethers in the liquid crystalline phase
Authors: Jonsson Haakan , Percec Virgil , Gedde Ulf W. , Hult Anders
Published: March 2011

Cationic bulk polymerization of liquid crystalline phenyl benzoate and biphenyl vinyl ethers was performed using either thermal or photochemical initiation by onium salts. High molecular mass polymers having narrow molecular mass distribution were produced in high yields at very high temperatures (i.e., ≤ 120°).

Seemingly, the polymerization system could stabilize the growing species and thus reduce the amount of chain transfer reactions. Thin films of the monomers were oriented in their liquid crystalline state by the use of conventional ordering techniques used for low molar mass liquid crystals. On subsequent polymerization the orientation was preserved giving liquid crystalline thin films having a very high degree of order.