Molecular Mobility of the Interface in a Model Polymer Composite: A NMR Study


The interface of a model polymer composite has been probed using solid-state NMR techniques. The adsorption of (aminoalkyl)silane coupling agents onto silica surfaces and the interaction of these functional silanes with a bis(maleimide) resin were studied. Carbon-13 CP/MAS NMR was used to confirm the bonding between the silane and bis(maleimide) (BMI) resin and elucidate the nature of the cross-linking reaction of BMI. Deuterated coupling agents were synthesized, adsorbed, and reacted on silica surfaces. The deuterium labels on the coupling agents allowed their dynamics to be probed independently of the other organic materials present through the use of 2H solid-echo NMR. The experimental results were consistent with motions where the alkyl portion of the coupling agent undergoes gauche migration (gtt ↔ ttg) and pair gauche production (ttt ↔ gtg) conformational isomerizations plus slow anisotropic rotation. The room-temperature spectra were simulated with a model that included hopping between two discrete sites on the tetrahedral lattice with a jump rate of 8 × 105 s-1 and rotational diffusional constants of R∥ = 7 × 104 s-1 and R⊥ = 1 × 104 s-1. Polymerizing BMI resin over the chemisorbed coupling agent resulted in a line shape that could be modeled as a simple two-site jump with occupational probabilities of 0.7 and 0.3 and a jump frequency of 1.7 × 105 s-1. The anisotropic rotation was no longer required to simulate these spectra. The types of motions of the coupling agent were not affected significantly over the temperature range -100 to +85°C, although the exchange rate was changed. © 1992 American Chemical Society.



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© 1992 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 1992