Kinetics and mechanism of heterogeneous polymerization of 3,3‐bis(chloromethyl)oxetane catalyzed by gaseous BF₃

Abstract

Eingegangen am 2. Oktober 1962)** S U M M A R Y :The kinetics of the cationic polymerization of 3,3-bis(chloromethyl)oxetane in methylene chloride solution was studied in the temperature range from -60' to +20°C. It was foupd that for low conversions molecular weights are independent of the conversion. The kinetics are first order with respect to monomer, catalyst, and cocatalystfor H,O/BF, ratios < 0.5. For ratios H,O/BF, near 0.5 the rate passes through a maximum and decreases rapidly a t further increase of water concentration. The same effect was previously noted by ROSE in the BF, catalyzed polymerization of trimethylene oxide. The degree of polymerization (DP) is directly proportional to [monomer], inversly proportional to [water] and does not depend on [catalyst]. The activation energies for the overall rate ( E R~) and E r p were calculated for the first time in the polymerization of @-oxides and compared with E R~ known for the ionic polymerizations of a-oxides. The mechanism of reaction is discussed and, assuming steady state conditions a simple relation for the ratio of the rate constants was derived. ZUSAMMENFASSUNG :Die Kinetik der kationischen Polymerisation von 3,3-bis(chloromethyl)oxetan in Methylenchlorid wurde im Temperaturbereich von -60 bis +20°C untersucht. Es wurde gefunden, daB das Molekulargewicht im Bereich kleiner Urnsatze unabhiingig vom Umsatz ist; die Kinetik ist 1. Ordnung in bezug auf Monomeres, Katalysator und Cokatalysator im Bereich der H,O/BF,-Verhaltnisse < 0,5. Fiir ein H,O/BF,-Verhaltnis nahe 0,5 geht die Reaktionsgeschwindigkeit durch ein Maximum und nimmt bei hoheren HzO-Konzentrationen schnell ab. Der gleiche Effekt wurde bereits von ROSE in der durch BF, katalysierten Polymerisation von Trimethylenoxyd beobachtet. Der Polymerisationsgrad ist der Monomerkonzeptration direkt und der Wasserkonzentration umgekehrt proportional; er ist unabhangig von der Katalysatorkonzentration. Die Aktivierungsenergien der Bruttoreaktion ( E R~ und E m ) wurden zum ersten Male bei der Polymerisation von P-Oxyden berechnet und mit bekannten ERp-Werten fiir die ionische Polymersation von a-Oxyden verglichen. Der Reaktionsmechanismus wird diskutiert, und unter der Annahme von Stationaritatsbedingungen wird folgende einfache Beziehung fur das Verhaltnis der Geschwindigkeitskonstanten abgeleitet.

Polymers and Sulfur: what are Organic Polysulfides Good For? Preparative Strategies and Biological Applications

“…Ether‐containing four‐membered rings (oxetanes) are generally supposed to be more prone than three‐membered ones (epoxides) to undergo ring opening through a cationic mechanism, mostly due to their higher basicity (ring strain and steric hindrance being substantially similar) 73. However, their well‐known cationic ring‐opening polymerisation74 fails when applied to thietanes,75 providing highly branched/cross‐linked materials: the active four‐membered sulfonium ions undergo not only propagation, due to the attack by monomers, but also termination due to the attack by thioethers of the polymer chains formed, which produce non‐cyclic and, therefore, unreactive sulfonium ions and short branches in the main chain (Scheme ). Therefore, other than in a few isolated cases, such as the production of core cross‐linked core‐shell block‐copolymeric structures,76 or the polymerisation of 3‐chorothietane77 (where the electron‐withdrawing effect of chlorine may reduce the nucleophilicity of the main chain sulfur atoms), this mechanism has seldom been used.…”

Photochemically Induced Cationic Photopolymerization of Vinyl Ethers and Oxetanes

“…Since ring stress is similar for oxiranes and oxetanes but basicity is higher for oxetanes we consider oxetanes an interesting family of compounds for applications in which reduced shrinkage in volume is important [28]. Ring-opening polymerization of oxetanes can be initiated by means of protonic acids [29], oxonium salts [30], hexafluorophosphates [31] and Lewis acids in the presence of coinitiators [32,33,34]. Side reactions such as ring formation and backbiting can be reduced by lowering the reaction temperature [35,36].…”

Ring‐Opening Polymerization

“…[Chien et al, 1988;Dreyfuss and Dreyfuss, 1976;Sims, 1966]. The E Rp value is 72 kJ mol À1 for 3,3-bis(chloromethyl)oxetane [Chapiro and Penczek, 1962;Penczek and Penczek, 1963]. As with ionic polymerizations of alkenes, the activation energies can vary considerably with reaction conditions.…”