Cationic Polymerization of Ethylene Oxide: Iv. The Propagation Reactions

Abstract

Studies of the boron-fluoride-catalyzed reaction of ethylene oxide with simple alcohols and low molecular weight polyglycols indicate three ways in which chain growth could occur, but only one of these is considered to be important after the initial stages of polymerization. The rate of disappearance of monomer reaches a maximum a t a molecular weight of about 400. A mechanism is proposed to account for both polymerization and depolymerization and it is shown how equilibrium between these two reactions could result.The polymerization of ethylene oxide by boron fluoride is a complex process in which the propagation reaction must compete with an appareiltly independent depolymerization reaction. The depolymerization process, as discussed in the previous paper (I), breaks down the polyglycol to dioxane seemingly through a chain reaction propagated by oxonium ions acting upon the ether linkages in the polymer molecule. The polymerization on the other hand appears to occur through a stepwise addition of monomer to the terminal hydroxyls of the polymer chain. A study was therefore undertaken of the reaction of ethylene oxide with alcohols in the presence of boron fluoride in an effort to obtain a mechanism for the propagation and t o observe the transition fro111 propagation to depolymerization. This paper presents the results of these studies.. EXPERIMENTALEthylene chloride, ethylene oxide, and boron fluoride were prepared for use as previously described (2). Volatile alcohols were dried by distillation froill their magnesium alcoholates in the usual way and ethers were dried over sodium metal or calcium hydride, \ZTherever the reactants were sufficiently volatile they were stored on the vacuum system and transferred by distillation. T h e polyglycols were either stirred under high vacuum for several hours or dissolved in dry ethylene chloride and pumped free from solvent before use. Molecular weights were determined by viscosity ineasureme~lts as before, but in a few cases were confirined by freezing point depressions in benzene. Where hydroxyl content of the polynler was important, end group analysis by acetylation with acetyl chloride in pyridine, according to the nlethod of Smith and Bryant (3), was used. All three methods gave satisfactory agreement.Reactions were carried out in ethylene chloride solution a t 20° C. Rates were followed either by the decrease in vapor pressure of ethylene oxide as described in the earlier work, or by a dilatometric method. The dilatometers were so constructed that they could be dried and filled under vacuunl and then transferred to a constant temperature bath while exposing only the capillary tip t o the atmosphere. Absolute contractions were not determined but the contraction per unit of oxide appeared t o be constant over the range of the experiments. The two methods gave good agreement wherever they could be compared. 'Manuscript

Superacids and Their Derivatives. IX. Selective Cyclodimerization of Etylene Oxide to 1,4-Dioxane Catalyzed by Superacids and Their Derivatives

“…1-5), four superacid es-ters5 (No. 6-13), and a superacid anhydride (No. 14) were employed as catalysts for cyclodimerization of EO under various reaction conditions (Table I).…”

Polymerization of Ethylene Oxide

“…Eastham and coworkers have detailed the cationic polymerization of ethylene oxide using boron fluoride (41,42,43) and stannic chloride (44,45). In the coordinate anionic polymerization, good catalysts often contain metal-oxygen-metal groupings in their structure,and it appears that the propagation mechanism involves two metal atoms (46,47,48).…”

The use of Tetraalkylphosphonium-Tetrafluoroborate-Tetrafluoroboric Acid in the curing of a liquid crystalline epoxy resin

“…9 According to this mechanism, a ions. [3][4][5] The mechanism of the reactions has been proton is first transferred from the catalyst comthe subject of considerable controversy for many plex to the monomer. The activated monomer then years.…”

“…there are other ''true catalytic species.' ' Ito and Even though there is still controversy on the Okahashi observed both oxonium ion and role of BF 3 in epoxy curing, it is widely accepted (BF 3 : NHEt) 0 anion in a BF3 : N 2 C 2 H 5 (BF 3 : that some of the major catalytic species formed MEA)/epoxy system. 4,5 They concluded that the by the BF 3 complexes are tetrafluoroborate salts.…”

“…12 In some commercial epoxy / (SAA) will be investigated by DSC and Fourier amine / BF 3 : MEA / C -fiber prepregs, 13 several transform infrared spectroscopy (FTIR). The defluorine species were detected by means of provelopment of mesophase texture will be monitored ton and 19 F-NMR, which included BF 3 The liquid crystalline epoxy monomer, 4,4-diglycsystem usually assumed that the step polymeridyloxy-a-methylstibene (DOMS), and 40% tetraization caused by amine / epoxy and chain polybutylphosphonium tetrafluoroborate-tetrafluoroboric merization from epoxy / catalyst proceeded in acid complex (F2) solution were supplied by The Dow Chemical Company. The epoxy equivalent parallel.…”