bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetik der radikalischen Copolymerisation des 3,3,3‐Trichlorpropens mit Styrol in Substanz
Authors: Szafko J. , Turska E. , Lopatina G. P. 
Published: April 2003

AbstractIn dieser Arbeit werden Untersuchungsergebnisse über die Kinetik der mit Dicyclohexyl‐peroxidicarbonat initiierten Substanz‐Copolymerisation von 3,3,3‐Trichlorpropen (TClP) mit Styrol bei 60°C mitgeteilt. Es wurde die Abhängigkeit der Copolymerisationsgeschwindigkeit von der Zusammensetzung des Monomergemisches bestimmt. Unter Annahme einer linearen Abhängigkeit der Initiierungsgeschwindigkeit vi von der Zusammensetzung des Monomergemisches wurde der Parameter Φ (relative Konstante des alternierenden Abbruchs) berechnet, wobei mit Änderung des Molenbruchs von Styrol in der Mischung von 0,136 bis 0,851 die Konstante Φ nicht monoton von 81 bis 243 ansteigt. Experimentell wurde jedoch gezeigt, daß vi keine lineare Funktion der Zusammensetzung der Monomermischung ist. Mit den experimentellen Werten für vi folgt unabhängig von der Zusammensetzung des Monomergemisches für Φ ein Wert von 72±10. Die Copolymerisationsparameter für das System TClP/Styrol betragen r1 (TClP)=0,017 und r2 (Styrol)=7,8.
Anionic polymerization of siloxanes. Mechanism of initiation with triorganosilanolates
Authors: Chojnowski Julian , Mazurek Mieczysław 
Published: April 2003

AbstractThe kinetics of initiation of the polymerization of 2,2,5,5‐tetramethyl‐1‐oxa‐2,5‐disilacyclopentane (2) with sodium phenyldimethylsilanolate 1a and two of its phenyl substituted derivatives was investigated as model reaction for studying the initiation and crosspropagation steps in anionic polymerization of cyclic siloxanes in non‐polar media.A redistribution of siloxane units between living ends of the polymer and also between living end and initiator was demonstrated to occur commonly in the siloxane anionic polymerization system affecting the initiation and crosspropagation.However, the living silethylenesiloxane polymer system 3 showed no redistribution and the initiation, followed by the dissapearance of phenyldimethylsilanolate, showed a first internal order and a fractional external order with respect to the initiator. The same fractional order was found in the propagation step with respect to the living ends. The results can be rationalized on the basis of a mechanism in which silanolate groups aggregation (cyclic or cage structures) convert active species into dormant centres. The analysis of the kinetic scheme including the formation of simple and mixed aggregate series of optional multiplicity leads to the conclusion that the scheme under some assumptions suits the kinetics observed. Solvation processes as well as the increase of the negative charge density on the silanolate oxygen by electron releasing substituents increase the reactivity of the silanolate.
Propriétés physiques et mécaniques d'un copolymère séquencé polystyrène‐polyisoprène‐polystyrène hydrogéné
Authors: Laramée André , Goursot Paul , Prud'homme Jacques 
Published: April 2003

AbstractLa séquence polyisoprénique d'un copolymère séquencé polystyrène‐polyisoprène‐polystyrène (SIS) préparé par voie anionique par le butyl‐lithium dans le benzène a été hydrogéné. Les propriétés de ce copolymère ont été étudiées par analyse enthalpique différentielle (DSC) et par tensiométrie et comparées à celles du copolymère non hydrogéné. Les deux polymères sont des élastomères amorphes présentant deux transitions vitreuses caractéristiques d'un système à deux phases. La température de transition vitreuse de la phase polyisoprène hydrogéné n'est que de 4°C supérieure à celle du polyisoprène non hydrogéné. Les courbes de traction mesurées sur des films préparés par évaporation de solvant avant et après hydrogénation montrent un comportement identique aux faibles allongements bien que la tension et l'allongement de rupture soient plus faibles dans le cas du copolymère hydrogéné. L'étude des cycles de traction montre que le copolymère hydrogéné ne présente pas les réarrangements importants observés en première traction dans le cas des copolymères SIS. A cet égard son comportement est beaucoup plus près de celui d'un caoutchouc vulcanisé. Ceci indiquerait une meilleure séparation et une plus grande rigidité des domaines de polystyrène dans le matériau hydrogéné.
Inhibition effect of 1,1,4,4‐tetraphenyl‐2‐tetrazene in the radical polymerization of styrene
Authors: Sugiyama Kazuo , Nakaya Tadao , Imoto Minoru 
Published: April 2003

Abstract1,1,4,4‐Tetraphenyl‐2‐tetrazene (1) inhibits the radical polymerization of styrene initiated by 2,2′‐azoisobutyronitrile. The inhibition period is proportional to the concentration of 1. The rate of the initiation of polymerization and the ratio of the rate constants of propagation and termination reactions k/2kt, were calculated from the consumption rate of the inhibitor. Some aromatic amines did not effect the inhibition period and the polymerization rate. Tetraphenylhydrazine showed a retarding effect.
The formation of a coloured complex of partially saponified poly(vinyl acetate) with iodine in the presence of potassium iodide
Authors: Hayashi Sadao , Takama Michihiro , Kaneko Ichiro , Hojo Nobumasa 
Published: April 2003

AbstractThe red‐violet complex which was formed from partially saponified poly(vinyl acetate) and iodine in the presence of potassium iodide was investigated by the Benesi‐Hildebrand method. The molar absorption coefficient of the complex at the absorption maximum (488 nm) was found to be 4,74.1041/(mol cm) at 10°C and to decrease with rising temperature. The concentration of units resulting from vinyl acetate (acetoxyethylene units), which can take part in the complex formation with iodine, was below 1% of the total content of acetoxyethylene units in the polymer. The changes of enthalpy (ΔH) and entropy (ΔS) were found to be −45,01 kJ mol−1 (−10,75 Kcal/mol) and −48,40 J mol−1 K−1 (−11.56 cal mol−1 K−1) at 15°C, respectively.
Studies on functional micelles, 6. Micellar effect in the preparation of poly(β‐alanine) from thio‐β‐alanine S‐alkyl esters
Authors: Kawabata Yasuziro , Kinoshita Masayoshi 
Published: April 2003

AbstractThe S‐dodecyl (1e), S‐decyl (1d), and S‐octyl esters of thio‐β‐alanine (1c) were condensed in the presence of a base in aqueous media to give poly(β‐alanine) in yields of 44, 24, und 2%, respectively. The degrees of polycondensation of the obtained poly(β‐alanine) were 13, 12, and 20, respectively. S‐hexyl ester (1b) and S‐ethyl ester (1a) gave no polymer. The process of this polycondensation reaction was explained by a proposed matrix reaction on the micelle surface.
Vinyl polymerization, 334. Polymerization of methyl methacrylate initiated with poly(styrene‐co‐acrolein) or poly(styrene‐co‐methyl vinyl ketone)
Authors: Imoto Minoru , Oishi Maku , Ouchi Tatsuro 
Published: April 2003

AbstractThe polymerization of methyl methacrylate (MMA) initiated with styrene/acrolein, [poly(St/AL)], or styrene/methyl vinyl ketone, [poly(St/MVK)] statistical copolymers was kinetically studied. The rates of polymerization, Rp, were found to obey the following equations:

The overall activation energies were 58,6 kJ/mol (14 kcal/mol) [poly(St/AL)] and 62,8 kJ/mol (15 kcal/mol) [poly(St/MVK)], respectively.Effects of several metallic ions on the polymerization rate were also studied, and thereby it was found that Fe(II), Fe(III), and Cu(II) ions at adequate concentrations are able to promote the polymerization.
Die Copolymerisation von Natriumäthylensulfonat mit Acrylnitril
Authors: Kapko Jerzy , Wegorkiewicz Ewa 
Published: April 2003

AbstractZur Klärung widersprüchlicher Angaben über Copolymerisationsparameter des Comonomerenpaares Natriumäthylensulfonat (NaAS)/Acrylnitril (AN) wurde eine Reihe von Radikalpolymerisationen in konz. Zinkchlorid‐Lösung durchgeführt. Die Berechnung der Copolymerisationsparameter zu rNaAS=0,13 und rAN=8,10 zeigte, daß beide Comonomere ein ideales System bilden (rAN. rNaAS ≈ 1).
Hydrophobic polyelectrolytes: Preparation and conformational properties of poly(styrene‐co‐methacrylic acid)
Authors: Conio Giuseppina , Patrone Eligio , Russo Saverio , Trefiletti Vincenzo 
Published: April 2003

AbstractRandom copolymers of styrene and methacrylic acid were prepared in a wide composition range, and their conformational properties were investigated by potentiometric methods in different solvent media. A conformational transition occurs as a function of the degree of ionization (α). The Gibbs free energy change of the transition between uncharged conformers (ΔG0) was determined. The dependence of ΔG0 on styrene content as well as on the composition of the solvent mixture and the temperature, shows that the uncharged polyelectrolyte chains assume a compact conformation (globule) stabilized by hydrophobic interactions of maximum strength.Rough considerations on the electrostatic free energy of the macroion indicate that the dimensions of the compact form increase between α=0 and the transition point, so that the “globule” does not participate in the conformational change. It is suggested that this latter occurs in a one‐dimensional system, depending on the interaction of neighboring groups.
A kinetic study of the acid catalysed degradation of cellulose triacetate in chloroform/acetic anhydride solution
Authors: Bhatti Muhammad A. , Howard Peter 
Published: April 2003

AbstractThe kinetics of the degradation of cellulose triacetate in chloroform/acetic anhydride mixtures containing a perchloric or sulphuric acid catalyst was studied. The change in molecular weight with time was followed viscometrically, employing Maron's singlepoint method to evaluate limiting viscosity number values and using appropriate Mark‐Houwink constants for the chloroform/acetic anhydride mixtures. The dependence of the first‐order rate constant on concentration of catalyst, acetic anhydride, and cellulose triacetate, as well as polymer molecular weight and temperature was investigated. An explanation of the results, based on both H+ and Ac+ (acetylium ion) acting as the catalytic degradation species, is given; this is also shown to account for the degradation behaviour in similar cellulose acetate systems observed by previous workers.
Pressure dependence of the thermal conductivity of some polyamides
Authors: Andersson Per 
Published: April 2003

AbstractThe pressure dependences of the thermal conductivities of five polyamides (nylons) have been determined in a cylindrical geometry at 300K and in the pressure range 0–25 kbar. The conductivities increase strongly with pressure, the values at 25 kbar being higher by the factors 1,83, 1,90, 1,89, 2,07, and 2,03 for, respectively, nylon 66, nylon 610, nylon 6, nylon 11, and nylon 12, than those at atmospheric pressure. The results are compared with other experimental results and with theoretical calculations. The difference in conductivity response to pressure between the different varieties is discussed.
Metal complexes of poly(2‐vinylpyridine 1‐oxide), poly(4‐vinylpyridine 1‐oxide) and 2,2′‐trimethylenedipyridine 1‐oxide
Authors: Alshaikh‐Kadir Khalid , Holt Paul 
Published: April 2003

AbstractPoly(2‐vinylpyridine 1‐oxide) (3), poly(4‐vinylpyridine 1‐oxide) (4), and the dimeric analogue 2,2′‐trimethylenedipyridine 1‐oxide (2) form metal complexes with chlorides of copper(II), zinc, mercury(II), iron(III), cobalt(II), and nickel(II) salts. Due to steric reasons 4 forms two series (type 6 and 7) of complexes by intramolecular or intermolecular crosslinking in which the ratio NO/metal is 2:1 (type 6) or 1:1 (type 7), whereas 3 and its model compound 2 can form only intramolecular 2:1 complexes of type 5.
13C‐NMR‐sequenzanalyse, 5. Synthese von nylon‐5 und alternierenden copolyamiden der 5‐aminovaleriansäure aus 5‐isothiocyanatovaleriansäure
Authors: Kricheldorf Hans R. , Schilling Gerhard 
Published: April 2003

AbstractAus 5‐Aminovaleriansäure (2) wurde im Eintopfverfahren der 5‐Isothiocyanatovaleriansäure‐trimethylsilylester (1) hergestellt und aus diesem die 5‐Isothiocyanatovaleriansäure (3), welche thermisch unter verschiedenen Bedingungen zu Nylon‐5 kondensiert wurde. Über das ebenfalls aus dem Silylester 1 zugängliche 5‐Isothiocyanatovaleriansäurechlorid (4) wurde das N‐(5‐Isothiocyanatovaleryl)‐β‐alanin (5) und die N‐(5‐Isothiocyanatovaleryl)‐4‐aminobuttersäure (6) erhalten, Monomere, die sich zu alternierenden Copolyamiden der 5‐Aminovaleriansäure kondensieren lassen. Der thermische Abbau von Nylon‐3, ‐4, ‐5 und ‐6 sowie einiger alternierender Copolyamide wurde anhand der thermogravimetrischen Analyse untersucht und die Abbaumechanismen diskutiert. Die 13C‐NMR‐Spektren von alternierenden Copolyamiden des β‐Alanins, der 4‐Aminobuttersäure und der 5‐Aminovaleriansäure werden verglichen und Beziehungen zwischen den Sequenzen und der chemischen Verschiebung der CO‐Signale ermittelt.
Cationic polymerization of p‐substituted α‐methylstyrenes, 2. Crystalline polymers from p‐methyl‐ and p‐isopropyl‐α‐methylstyrene
Authors: Lenz Robert W. , Sutherland Judith E. , Westfelt Lars C. 
Published: April 2003

AbstractUnder identical conditions of cationic polymerization at low temperature 2‐(p‐tolyl)‐1‐propene (α,p‐dimethylstyrene) gave polymers with much higher syndiotactic contents than unsubstituted α‐methylstyrene. All samples of poly(α,p‐dimethylstyrene) were crystalline, but poly(α‐methylstyrene) did not crystallize even at high degrees of stereoregularity. Similarly polymers of p‐isopropyl‐α‐methylstyrene were crystalline, and the crystalline properties of copolymers of the three monomers were investigated and compared to those of the homopolymers. The rôles of stereoregularity and crystallizability in forming crystalline products were considered.
Experimenteller nachweis des molekulardispersen charakters der mischung von zwei polymeren und bestimmung des chemischen potentials in diesen mischungen
Authors: Kruse Wolfgang A. , Kirste Rudolf G. , Haas Jean , Schmitt Burghard J. , Stein Dieter J. 
Published: April 2003

AbstractMit Hilfe der Neutronenkleinwinkelstreuung wird der molekulardisperse Charakter einer glasklaren Mischung von zwei Polymeren bei Abwesenheit eines niedermolekularen Lösungsmittels in einem Fall nachgewiesen, im anderen widerlegt. Falls eine molekulardisperse Mischung vorliegt, können das chemische Potential und die Knäueldimensionen bestimmt werden. Polymethylmethacrylat und Styrol‐Acrylnitril‐Copolymere bilden für gewisse Zusammensetzungen des Copolymeren molekulardisperse Mischungen. Sie sind exotherm, besitzen eine negative Exzeßentropie und die Molekülknäuel sind gegenüber den ungestörten Knäueldimensionen expandiert. Die Theorie der Löslichkeitsparameter von Hildebrand und Scott ermöglichte zwar die Auffindung des mischbaren Systems, aber die gemessenen zweiten osmotischen Virialkoeffizienten sind in der Größenordnung verschieden von denen, die nach dieser Theorie vorausberechnet werden können.
Polymere brenzcatechin‐derivate, 2. Über die alternierende copolymerisation von 4‐propenylbrenzcatechin‐derivaten mit maleinsäureanhydrid durch tributylboran
Authors: Iwabuchi Susumu , Kojima Kuniharu , Nakahira Takayuki , Hosoya Hiromichi 
Published: April 2003

AbstractDie Copolymerisation von Maleinsäureanhydrid (MAn) und 4‐Propenylbrenzcatechin‐Derivaten, wie Eugenol (1), Isoeugenol (2), Safrol (3) und Isosafrol (4), initiiert durch Tributylboran, wurde in Cyclohexanon bei 30°C in Anwesenheit von Sauerstoff untersucht. Es wurde gefunden, daß unabhängig von den Monomeransätzen in allen Fällen 1:1‐Copolymerisate entstehen, während unter Stickstoff weder 1 noch 3, wie bereits berichtet, mit MAn copolymerisiert. Ferner wurde gefunden, daß Maleinsäureanhydrid mit den Isopropenylverbindungen bzw. Styrol‐Derivaten 2 und 4 ca. 102 mal schneller reagiert als mit den entsprechenden Allylverbindungen 1 und 3. Demnach scheint nicht nur der Sauerstoff, sondern auch die Struktur der Seitenketten eine entscheidende Rolle in diesen Copolymerisationssystemen zu spielen. Der Reaktionsmechanismus wird diskutiert. Es ist bemerkenswert, daß die 1:1‐Copolymerisate aus MAn und 2, bzw. aus MAn und 4, thermisch sehr stabil sind; sie werden erst bei Temp. > 300°C endothermisch abgebaut.
Ring‐chain equilibria in the metathesis reaction of cycloolefines
Authors: Höcker Hartwig , Reimann Walter , Riebel Klaus , Szentivanyi Zsolt 
Published: April 2003

AbstractPolyoctenylenes and polydodecenylenes prepared by the methathesis reaction exhibit a bimodal molecular weight distribution. The low molecular weight fraction consists of cyclic oligomers, the high molecular weight fraction is assumed to contain linear polymers. The distribution of cyclic oligomers together with the polymer material indicates a ring‐chain equilibrium. The slope of the plot log Kx (molar cyclization equilibrium constant) vs. log x (degree of polymerization) is close to −2,5 as predicted by the Jacobson and Stockmayer theory for unstrained macrocycles.
On the reversible crosslinking of elastomers by boranes
Authors: Schnecko Hans , Steffen Ulrich 
Published: April 2003

AbstractAttempts are reported to test the reactivity of boron‐alkyl and of boric ester bonds in polymers with regard to thermal, oxidative, or hydrolytic stability. Polymer substrates were natural rubber and low molecular weight liquid polybutadiene as well as some telechelics (OH‐functional polybutadiene, poly(ethylene glycol) and allyl‐tipped poly(ethylene glycol) or polystyrene, respectively, the latter as model compounds); as reagents, borane‐amine complexes and free borane were employed. It turned out that only with a large number of in‐chain double bonds sufficient network stability was obtained which was then irreversible. All saturated telechelics investigated revealed insufficient stability against hydrolysis and oxidation at room temperature.
Strukturbestimmung eines 1,4‐poly(1,3‐pentadien)s durch 13C‐NMR‐spektroskopie
Authors: Elgert Karl‐Friedrich , Ritter Wolfgang 
Published: April 2003

AbstractDie Polymerisation des trans‐1,3‐Pentadiens wurde mit Butyllithium als Initiator bei 80°C in Heptan durchgeführt. Die Struktur der Polymerkette wurde durch 13C‐NMR‐Spektroskopie bei 90,51 MHz bestimmt.85% 1,4‐ und 15% 1,2‐Verknüpfung wurden bestimmt. Die 1,4‐Verknüpfung setzt sich aus 70% trans‐ und 30% cis‐Verknüpfung zusammen. 50% Abweichung von der „Kopf‐Schwanz‐Verknüpfung”︁ wurden gefunden. Die Wahrscheinlichkeit einer meso‐Diade beträgt in der „Kopf‐Schwanz‐Verknüpfung”︁ m=0,5, während sie für die „Kopf‐Kopf‐Verknüpfung”︁ m=0,66 beträgt.
Microtacticity and hydrodynamic behaviour of poly(trityl methacrylate) prepared in hexamethylphosphoric triamide
Authors: Niezette Joseph , Hadjichristidis Nikos , Desreux Victor 
Published: April 2003

AbstractTrityl methacrylate was polymerized with 2,2′‐azodiisobutyronitrile at 60°C in a homogeneous hexamethylphosphoric triamide (HMPT) solution. The isotactic microstrucutre found by NMR spectroscopy was less important for this polymer than for poly(trityl methacrylate) prepared in benzene, a precipitating medium.Some aspects of the hydrodynamic behaviour of poly(trityl methacrylate) were examined in HMPT at 25°C. Relations between the intrinsic viscosity, the root‐mean‐square end‐to‐end dimension, and the weight average molecular weight were established. The unperturbed dimension 〈r〉1/2 was determined from viscosity and light scattering measurements using the well known extrapolation methods of Kurata‐Stockmayer, Stockmayer‐Fixman, Cowie, Inagaki‐Kurata, and Baumann.Poly(trityl methacrylate) adopts a moderately expanded conformation in HMPT at 25°C. The correlation of the chain rigidity with the molar volume of the side group of polymethacrylic esters shows that poly(trityl methacrylate) has a higher chain rigidity than other polymethacrylates on account of the steric hindrance of the trityl group and of the strong interactions between the aromatic rings.
Synthese und Charakterisierung sulfongruppenhaltiger Polyester
Authors: Kerber Robert , Nuyken Oskar , Pöschl Ernst 
Published: April 2003

AbstractAus Dimethyl‐3,3′‐sulfonyldipropionat (1) und Äthylenglykol (2) wurden Polyester mit einem mittleren Molekulargewicht von ca. 104 hergestellt. Der Sulfongruppengehalt der Polymeren ließ sich durch systematischen Austausch der Esterkomponente 1 gegen Dimethylterephthalat (4) in der Ausgangsmischung gezielt verändern. Spektroskopische Methoden (1H‐NMR, IR), Schwefelanalyse, die mittels Dampfdruckosmometer und Ultrazentrifuge bestimmten Molekulargewichte sowie die Viskositätszahlen dienten zur Charakterisierung der erhaltenen Produkte. Kurzzeitige Behandlung der sulfongruppenhaltigen Polymeren mit wäßriger Natriumhydroxid‐Lösung oder alkoholischer Natriummethanolat‐Lösung spaltet diese in niedermolekulare Bestandteile.
Dilute solution properties of alternating copolymers from methacrylonitrile and styrene and methacrylonitrile and α‐methylstyrene
Authors: Cincu Cornel , Uglea Constantin V. 
Published: April 2003

AbstractKuhn‐Mark‐Houwink‐Sakurada relations were obtained in various solvents for alternating copolymers from methacrylonitrile and styrene, (MAN‐ST), and from methacrylonitrile and α‐methylstyrene, (MAN‐αMST).The values of the unperturbed dimensions, Kθ or A=(r/M)1/2 and conformational parameter σ were determined using usual extrapolation techniques.The values of the unperturbed dimensions are dependent on the solvent nature and are quite different from the “ideal” values calculated on the basis of additivity rules from the unperturbed dimensions of the parent homopolymers.
On the thermal degradation of poly‐ε‐caprolactone
Authors: Iwabuchi Susumu , Jaacks Volker , Kern Werner 
Published: April 2003

AbstractThe thermal degradation of poly(oxycarbonylpentamethylene), (poly‐ε‐caprolactone), (3), was investigated at 220°C and 80 mm Hg under nitrogen. 3 was found to be thermally much more stable than poly(oxycarbonylethylene), (poly‐β‐propiolactone), (1), although it decomposed faster than poly(oxycarbonyl‐1,1‐dimethylethylene), (polypivalolactone), (2). The reaction was of the first order with a rate constant of k=6,2.10−4 min−1 and proceeded via a “zipper mechanism” to yield monomeric ε‐caprolactone.
Polymerization of β‐aminopropionitrile
Authors: Ree Keiu , Minoura Yuji 
Published: April 2003

AbstractThe polymerization of β‐aminopropionitrile (β‐APN) was carried out by using basic catalysts such as sodium sec‐butoxide in organic solvents and gave polyamidine which was converted to poly‐β‐alanine by hydrolysis. Poly‐β‐alanine was identified by IR and 1H ‐NMR spectra and elemental analysis. The degree of polymerization was determined to 9,1 by vapor pressure osmometry. Free β‐alanine was obtained by hydrolysis of the poly‐β‐alanine. From a kinetic study of this polymerization, it was found that the rate of polymerization was

The polymerization mechanism of β‐APN is discussed.
Cationic polymerization of styrenes by protonic acids and their derivatives, 2. Two propagating species in the polymerization by CF3SO3H
Authors: Sawamoto Mitsuo , Masuda Toshio , Higashimura Toshinobu 
Published: April 2003

AbstractThe bimodal molecular weight distribution (MWD) of the polymers and the polymerization rate in the cationic polymerization of styrene by CF3SO3H were studied under a variety of conditions. Both the decrease of the dielectric constant of the reaction mixture and the addition of a common‐ion salt (Bu4N+SO3CF) reduced the polymerization rate and the formation of the higher molecular weight portion of the polymers (the high polymer). It appears that of the two propagating species the one which forms the high polymer is more ionically dissociated and more reactive in propagation. Salt effects indicate that in nitrobenzene the propagating species is a solvent‐separated ion pair and/or a free ion. The effects of monomer concentration on the bimodal MWD have shown that there are different chain‐breaking reactions for the two propagating species. The possibility that the monomer is complexed with one of the growing species is also discussed.