Study of fluoroalkylsilanes, a new class of amphiphilic oligomers: Determination of end groups and chain length

Abstract

Radiation-initiated polymerization of tetrafluoroethylene (TFE) in the liquid alkylsilanes Si(CH₃)₄ (I), C₂H₅Si(CH₃)₃ (II), and ClSi(CH₃)₃ (III) produces fluoroalkylsilane oligomers with the general formula R(C₂F₄)_nX, where X = H or Cl in I, II, and III and R is one of the radicals generated by the abstraction of H from the methyl and ethyl groups in I and II or Cl detachment from III. The nature of R has been determined using an NMR technique, and the molecular mass distribution (MMD) has been found from abundances in anion progressions in mass spectra and from DTG and GPC data. At initial TFE concentrations (C₀) changed from 0.4, 1, and 0.13 to 1, 2.7, and 0.7 mol/L in I, II and III, respectively, the average chain length 〈n〉 increases from 4–5 to 10–12 and the MMD changes from the unimodal to the bimodal pattern in which the proportion of oligomers with n < 6 decreases with increasing C₀. As 〈n〉 increases and the MMD changes, the homogeneous solution becomes colloidal and then turns into a gel. The colloidal particles are largely composed of long oligomers, and the number of solvent molecules per C₂F₄ unit decreases with an increase in C₀ and is 4–7 in the gel.