Metallocene‐mediated cationic ring‐opening polymerization of 2‐methyl‐ and 2‐phenyl‐oxazoline

Abstract

The cationic ring‐opening polymerization of 2‐methyl‐2‐oxazoline and 2‐phenyl‐2‐oxazoline was efficiently used using bis(η5‐cyclopentadienyl)dimethyl zirconium, Cp2ZrMe2, or bis(η5‐tert‐butyl‐cyclopentadienyl)dimethyl hafnium in combination with either tris(pentafluorophenyl)borate or tetrakis(pentafluorophenyl)borate dimethylanilinum salt as initiation systems. The evolution of polymer yield, molecular weight, and molecular weight distribution with time was examined. In addition, the influence of the initiation system and the monomer on the control of the polymerization was studied. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2011

Poly(2‐oxazoline)s: A comprehensive overview of polymer structures and their physical properties

“…In the first step a nucleophilic attack of the nitrogen lone pair of the 2‐oxazoline monomer onto an electrophilic initiator forms an oxazolinium cation, initiating the polymerization reaction. Different initiator systems can be used including alkyl sulfonates such as methyl p ‐toluenesulfonate, which is most frequently mentioned in the literature, p ‐nitrobenzenesulfonates (nosylates) and trifluoromethanesulfonates (triflates), alkyl, benzyl and acetyl halides, oxazolinium salts and Lewis acids . Also functional initiators can be used as long as they do not bear any nucleophilic character that could interfere with the CROP.…”

How to Modulate the Chemical Structure of Polyoxazolines by Appropriate Functionalization

“…To date, the cationic ring‐opening polymerization of 2‐oxazolines has been accomplished using many initiators, including Lewis acids such as boron trifluoride (BF 3 ‐OEt 2 ) (column IIIa of the periodic table, Figure 2)32 zirconium/tris(pentafluorophenyl)borate,20 trihalogenobismuthine,33 and alkyl esters such as tosylates, triflates (column VIa of the periodic table, Figure 2), and halides (column VIIa of the periodic table, Figure 2). The alkyl halide initiators range from chloride34 and bromide35 to iodide,36, 37 as well as acetyl halide 38.…”

“…A lot of studies mention transfer reactions as an explanation of the limited molecular weight, but only a few of them investigate in detail this side reaction. Litt et al,19 as well as Kourti et al,20 in the particular case of an initiator based on metallocene, have proposed a monomer transfer reaction based on the abstraction of the α‐proton of the monomer and its transfer to the terminal oxazolinium species of the propagating polymer chain. Schubert et al illustrated the transfer reaction in the case of 2‐ethyl‐2‐oxazoline using matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) experiments 21…”

Ionic Polymerization

“…86,87 More recently, organometallic complexes, mainly metallocenes and half-metallocenes, after activation with suitable compounds (methylaluminoxane or fluoroarylborates) have been successfully employed for the cationic polymerization of isobutylene and other monomers. 88,89 Propagation Chain propagation is the repeated electrophilic addition reaction of the monomer to the growing polymer chain with subsequent formation of the same active species. It follows the Markonikov's rule, leading to the formation of regular head-to-tail polymers.…”