Infrared Spectroscopic Studies of Hydrogen Bonding in Phenolic Polymers

Open Access
Author:
Choperena Guerra, Andrea
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 12, 2010
Committee Members:
  • Paul C Painter, Thesis Advisor
Keywords:
  • temperature
  • poly(vinyl phenol)
  • ethyl phenol
  • polymer
  • phenolic polymers
  • spectroscopy
  • IR
  • infrared
  • heat
  • miscibility
Abstract:
Detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of phenolic compounds are presented, including those of ethyl phenol (EtPh), poly(vinyl phenol) (PVPh) and poly(styrene-co-vinyl phenol)/poly methyl ether blends (PSVPh/PVME). This region of the spectrum of phenolic polymers is not well understood, and various issues need to be resolved in order to accomplish this work initially focused on EtPh. When this material is dissolved in cyclohexane, the band due to “free” (non-hydrogen-bonded groups) has been shown to contain overlapping contributions from both monomeric and end-group species. Other assignments are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds (as “donors” and “acceptors”, respectively), or if only the proton is acting as a donor. The strongest band in the spectra obtained at the highest concentration of ethyl phenol is due to OH groups present in linear chains of hydrogen-bonded OH groups (as recognized in numerous other studies), but a band due to cyclic trimers has also been identified. The assignment of other modes is more uncertain and various possibilities are discussed. In toluene solutions, assignments are more complicated, because bands due to OH–π hydrogen bonds are observed instead of free groups. Finally, the data from cyclohexane solutions was used to calculate equilibrium constants capable of describing the distribution of species present. A new methodology for determining the equilibrium constant describing association in the form of dimers is described. These conclusions are then used in a detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of PVPh, and their changes with temperature is presented. Bands usually assigned to “free” groups contain overlapping contributions from both monomeric and end-group species, both hydrogen-bonded to π orbitals. Assignments of bands due to hydrogen-bonded groups are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds, or whether one or the other is “free”. The assignment of other modes is more uncertain, and various possibilities are discussed. Changes in absorption coefficient with temperature appear to affect bands due to hydrogen-bonded groups in the interior of chains and monomeric species by essentially the same amount. The large change in absorption coefficient of the hydrogen-bonded band relative to a band assigned to free groups postulated in a previous study is more likely due to a change in the distribution of hydrogen-bonded and “free” species that were not resolved in previous work. Finally, a detailed analysis of the bands appearing in the OH stretching region of the infrared spectrum of PSVPh/PVME blends is presented. Bands usually assigned to “free” groups contain overlapping contributions from both monomeric and end-group species, both hydrogen-bonded to π orbitals. Assignments of bands due to hydrogen-bonded groups are made on the basis of whether the proton and oxygen in a particular OH group are both involved in hydrogen bonds, or whether one or the other is “free”. The inclusion of ether groups and OH–ether hydrogen bonds, and how they interfere with distribution of other hydrogen bonding species, is described. By using established models for predicting the extent of hydrogen bonding, it was possible to estimate the concentration of hydrogen bonds necessary for coupling of the dynamic behavior, and the size of the relevant “control volume”. In general agreement with the self-concentration model, this lengthscale was comparable to the Kuhn length.