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The molecular relaxations of poly(methyl methacrylate) (PMMA) were studied using three different techniques:  DSC, DMTA, which are sensitive to bulk properties, and the variation of fluorescence emission with temperature, a molecular sensitive method. Because this is a nonfluorescent polymer, we synthesized copolymers of methyl methacrylate with several contents of 9-methylanthryl methacrylate. The increase in the spacing between each anthryl group brought about a gradual decrease in T g of the copolymers, leveling out at about 30−40 PMMA mers, indicating that the minimum spacing to attain the PMMA glass transition was situated in this length range. The fluorescence emission of a copolymer with 98 MMA units interspersed between each chromophoric unit was proved to be mechanically equivalent to PMMA homopolymer and was used to probe macromolecular motions involving shorter segments:  apart from the main transitions commonly found for PMMA (α and β), the other two were detected at lower temperatures (γ and δ). Apparent activation energies for all relaxations using both techniques are also reported and discussed.

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