Kinetics and mechanism of oxetanes polymerization catalyzed by AlR₃. Part II. Non‐stationary polymerization and chain transfer to polymer

Abstract

Polymerization of 3.3-bis(chloromethyl)oxetane induced by (iso-CqHg)3Al/H~O catalytic system proceeds in chlorobenzene solution a t 55-95 O C in homogeneous conditions. Dilatometric study in high vacuum system permitted to establish %he following main features of the process under study : irrespectively of the [(iso-C4Hg)3Al]/[HzO] ratio or [catalyst]/[monomer] ratio a gradual acceleration at the start of reaction was observed, followed by a "linear" portion, which in turn is followed by a deceleration. The whole process can be described as the non-stationary reaction with slow initiation, fast propagation and slow degradative chain transfer to polymer. Polymerization is externally first order on [monomer] (when the influence of initiation was excluded), first order on [HzO] until [IIzO] 4 [(iso-C4Hg)3Al]. The sigmoidal dependence with saturation of rate and degree of polymerization on [(iso-C4Hg)3Al] shows, that for [(iso-C4H9)3Al] > [H20] the excess of (iso-C4H9)3Al has no important influence on both polymerization kinetics as well as on the polymer P. The low ratio of P,/Pn (lower than 1.1) indicates that the acceleration period is not due to the consumption of impurities.Approximated 10 molecules of H2O participate in the formation of one active center. This value was found by extrapolation of the plot of {Pn (theoretical)/P, (experimental)} on [HzO] to [HzO] = 0. With increasing the ratio of [catalyst]/[monomer] the percentage of the unused catalyst also increases. Solution of the kinetic scheme as described above, with a degradative chain transfer to polymer treated as an irreversible process, led to the following absolute values of the apparent rate constants, being at 7OoC equal to: ki = 1.6.10-3mole-l.l*sec-l, k,= 8.5 mole-1.l.sec-1, and kt, = 1.2.10-3mole-1.l.sec-1. The kt, was compared with the rate constants of the chain transfer to low molecular ethers (ktE). The kt, value is close to ktE found for P-chloroethyl ether of a structure close to this of a polymer segment. The plot of ktE/k, on -pK, is linear with a slope expected for a cationic process. ZUSAMMENFASSUNG:Die durch (iso-C4He)sAl/HzO als Katalysator induzierte Polymerisation von 3.3-Bis-(chlormethy1)oxetan verlauft in einer Losung von Chlorbenzol bei 55-95°C in homogener Phase. Dilatometrische Untersuchungen im Hochvakuum ergaben folgende Hauptcharakteristika der Reaktion: Ohne Riicksicht auf das Verhaltnis [ (~S O . C~H~)~A~] / H~O ] oder das Verhaltnis [Katalysator]/[Monomeres] folgt einer allmahlichen Beschleunigung bei Beginn der Reaktion ein linearer Verlauf, dem sich dann eine Geschwindigkeitsabnahme anschlieBt. Der gesamte ProzeB kann als eine nicht stationare Reaktion beschrieben werden mit langsamer Initiierung, raschem Wachstum und einer langsamen, mit Abbau verbundenen Ketteniibertragung auf das Polymere. Die Polymerisation ist in bezug auf die Komentration des Monomeren ([Monomeres]) erster Ordnung (sofern man den EinfluB der Initiierung ausschlieBt) und auch erster Ordnung in bezug auf das Wasser, solange [HzO] G [(iso-CqH9)3Al]...

Aliphatic Polyethers: Classical Polymers for the 21st Century

“…In the late 1980s, it was shown that the amount of cyclic oligomers is drastically reduced in the presence of compounds containing hydroxyl groups . In this case, the so called “activated monomer” (AM) mechanism is more likely than the conventional “active chain end” (ACE) mechanism. In case of the AM mechanism, the active centers are located on the monomer and the polymer chain is neutral thereby strongly reducing the back‐biting process (Figure ).…”

On the Statistical Nonliving Nature of the Cationic Ring‐Opening Copolymerization of Oxetane with Tetrahydropyran

“…The first needed reaction is formation of already mentioned dormant species: tertiary oxonium cations containing three copolymer chain branches (rate constant k AP , Scheme ). Such species were already suggested by Penczek and Kubisa4 to hamper homopolymerization of OXT, and these dormant species can be reactivated in reaction with monomer (slow reaction, the second of the reactions added to the reaction scheme, rate constant k PA , Scheme ). In many real OXT polymerization systems, but not in the analyzed one, the dormant species can also be reactivated with hydroxyl containing compounds (the resulted secondary oxonium cation–with the proton located on the ether oxygen atom–can start a new polymer chain, unless, as in the studied reaction, a proton trap is added).…”

“…Limiting in some way the set of equations of the general reaction scheme can be justified by the lack of cyclic oligomers in copolymerization products under certain copolymerization conditions studied. However, we think that neglecting the formation of non‐strained tertiary oxonium cations with three polymeric branches, being the product of the reaction of active species of copolymerization with polymer repeating units4 (shown on the left‐hand side of Scheme ), is not justified and led the authors to disputable conclusions as will be demonstrated below.…”

Synthesis and cationic ring‐opening polymerization of oxetane monomer containing five‐membered cyclic carbonate moiety via highly chemoselective addition of CO2

“…Several other crosslinked and linear polyoxetanes are used as amphiphilic polymers, drug delivery systems, organic semiconductors, organic light emitting diodes, organic field‐effect transistors, crosslinkable conjugated polymers, polymeric solar cells, and polymer electrolytes . In addition, trialkyl aluminum/H 2 O catalytic system gives polyoxetanes with well‐controlled molecular weights . Oxetane monomers also undergo cationic ring‐opening copolymerization with six‐ or seven‐membered heterocyclic compounds such as tetrahydropyran, ε ‐caprolactone, 1,3,2‐dioxathiepane‐2‐oxide, spiroorthoester, and spiroorthocarbonate .…”

“…[45][46][47] In addition, trialkyl aluminum/H 2 O catalytic system gives polyoxetanes with well-controlled molecular weights. 48,49 Oxetane monomers also undergo cationic ring-opening copolymerization with six-or seven-membered heterocyclic compounds such as tetrahydropyran, 50 ε-caprolactone, 51 1,3,2-dioxathiepane-2-oxide, 52 spiroorthoester, 53,54 and spiroorthocarbonate. 55 Additional supporting information may be found in the online version of this article.…”