Nuclear Magnetic Resonance Studies on the Polymerization of Cyclic Ethers

Abstract

High-resolution proton nmr spectroscopy was used to investigate the solution polymerization of cyclic ethers. The concentrations of secondary and tertiary oxonium ions, the propagating species, have been determined from nmr spectra. In "living" systems, where chain transfer and terminations are negligible, the kinetic molecular weight can also be monitored during the polymerization process. Molecular weight maxima were found in systems where the formation of tertiary oxonium ion is slower than the propagation. This method is generally applicable to study the Cationic polymerization of cyclic ethers which do not have proton peaks interfering with the oxonium ion signals.

Photoinduced living cationic polymerization of tetrahydrofuran. I. Living nature of the system and its application to the diblock copolymer synthesis

“…Increases in both the polymer yield and molecular weight of the polyComparison of the results at 0 and 28ЊC reveals a higher final conversion and a lower rate of polymer were observed as shown in Figure 2, revealing that the polymer chain end retains its activity merization at a lower dark reaction temperature. It is worthy to mention that the rate of polymerization to initiate the newly added monomer even after the conversion of the original monomer to the is very low when compared with that of the production of the initiating species, HPF 6 . Even at the polymer reaches its final value.…”

“…Diphenyliodonium hexafluorophosphate, a 520 FTIR (cast film) and a Bruker AN-300 NMR photocationic initiator, was synthesized by the spectrophotometer using DMSO-d 6 for poly(THF) method described elsewhere. 16 and acetic acid-d 4 for poly(THF-b-HEEI).…”

Cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols: Composition, microstructure, and properties of copolymers

“…Although polymerization of THF in the absence of HOO containing compounds can be initiated by protic acids, 6 the presence of a few % mol of alcohol or diol inhibits homopolymerization of THF; no THF homopolymerization was observed in such a system for several weeks. started only upon addition of EO into the system.…”

Bromination and Accompanying Rearrangement of the Polycyclic Oxetane 2,4-Oxytwistane

“…Both of the −CHBr− groups of 18 are flanked by two >CH− groups, which is contrary to the 1 H NMR evidence. The same argument can be made for 2,6-dibromoadamantane (19) as well as 2,4-dibromoadamantane (20), which violates all of the tenets outlined above (Chart 3). The formation of a 2-oxidotwist-4-ylium or 4-oxidotwist-2-ylium ion from oxetane 2 by two competing C−O bond heterolyses may be envisioned.…”