Fluoropolyethers end-capped by polar functional groups. II. Effect of catalyst and reagents concentration, solvent nature, and temperature on reaction kinetics of ?,?-bis(hydroxy)-terminated fluoropolyethers with cycloalyphatic and aromatic diisocyanates

Abstract

A comparative kinetic study of the dibutyltin dilaurate (DBTDL) and 1,4-diazabicyclo[2,2,2]octane (DABCO) catalyzed reactions of α,ω-bis(hydroxy)-terminated fluoropolyethers (FPEs)—Z-DOLs and Z-DOL TXs—of various molecular weights and purity, with 4,4′-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI) and 2,4-toluene diisocyanate (TDI) was carried out in different solvents. An analytical method was used to follow the kinetics of the reactions at four different temperatures. The rate of NCO disappearance measured by two independent methods—IR spectroscopy and chemical titration were found to be very close. Straight proportionality between rate constants kcat and catalyst concentration was found. But in some cases for the DBTDL catalyzed reactions effect of catalyst saturation along with appearance of the limiting DBTDL concentration Clim below which the rate of reaction was close to zero were observed. Reactivity of Z-DOLs in the tin-catalyzed urethane reactions was found to decrease with their storage time at RT due to the slow hydrolysis of the end COOR groups impurities, which give the corresponding acids that act as a strong inhibitor of the DBTDL activity. These acid admixtures have no influence on the DABCO catalyzed reactions. For the DBTDL and DABCO catalyzed reactions of Z-DOLs with IPDI the dependence of effective rate constants keff (where keff = kcat · 0.01/[DBTDL] and catalyst concentration is taken in mol % based on IPDI) on total reagents concentration were found to be described by curves with a maximum. Critical reagents concentration, after which the relationship keff = f (C) changes from proportional to inverse proportional, seems do not substantially depend on the solvent nature. Hydrogenated analog poly(ethylene glycol) MW 400 (PEG-400) differs greatly from Z-DOLs: only steady decrease of keff was observed with increase of reagents concentration C from 5 up to 95 wt %. Activation energies for all the studied reactions are within the range of 10.8–16.7 kcal/mol. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2579–2602, 2000