Coupling of Probe Reorientation Dynamics and Rotor Motions to Polymer Relaxation as Sensed by Second Harmonic Generation and Fluorescence

Jacob C. Hooker, John M. Torkelson*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Scopus citations

Abstract

The coupling of various rotational motions of the rotor probes 4-(tricyanovinyl)-N-(2-hydroxyethy)-N-ethylaniline (TCl) and julolidenemalononitrile (JMN) to the relaxation dynamics of poly(ethyl methacrylate), poly(isobutyl methacrylate), and an isobutyl methacrylate–TC1 labeled methacrylate copolymer has been investigated by second harmonic generation (SHG) and steady-state fluorescence in both the glassy and rubbery states. In the rubbery state, the temperature dependence of the average rotational reorientation relaxation times, 〈τ〉, of TC1, both doped and labeled, determined from SHG measurements can be fitted well to the WLF equation with reasonable C1 and C2 parameters, indicating coupling to the α-relaxation in these polymer systems. The value of 〈τ〉 at the glass transition temperature and the weaker temperature dependence of 〈τ〉 in the glassy state also support the conclusion of coupling to the α-relaxation. However, from fluorescence measurements a much weaker temperature dependence is observed for the smaller scale motions involving internal rotations and/or isomerizations of the acceptor and/or donor moieties on TC1 and JMN, indicating significant decoupling from the α-relaxation. The decoupling of these internal probe motions from the α-relaxation mechanism is discussed in terms of x, a probe-dependent parameter introduced by Loutfy, and ξ, a parameter described by Ehlich and Sillescu as indicating the degree of coupling to the α-relaxation. A consideration of the time scales and activation energies associated with the smaller scale, internal rotation of these various moieties suggests at least some coupling to sub-β-relaxations. We also note the importance of carefully considering the results of a WLF fit in order to interpret appropriately the nature of the probe coupling to the polymer relaxation.

Original languageEnglish (US)
Pages (from-to)7683-7692
Number of pages10
JournalMacromolecules
Volume28
Issue number23
DOIs
StatePublished - Nov 1 1995

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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