Polymethyl methacrylate relaxation transitions

In Chapter 5 we cited dynamic mechanical relaxation data for polymethyl methacrylate (PMMA). There it was shown that PMMA possesses two mechanical relaxation regions over the temperature range - 50° to 160°C at low frequencies. These were labeled a for the relaxation accompanying the glass transition and / for a secondary relaxation that has generally been associated with motions of the ester side group. PMMA has a predominantly nonpolar... 

Recent developments have been in the area of microthermal analysis using thermal conductivity with thermal diffiisivity signals or AFM to visualize specific areas or domains in the material and perform localized thermal analysis studies (183,184). Relaxational behavior over time and temperature is related to changes in free volume of the material. Positron annihilation lifetime spectroscopy (PALS) measurements of positron lifetimes and intensities are used to estimate both hole sizes and free volume within primarily amorphous phases of polymers. These data are used in measurement of thermal transitions (185,186) structural relaxation including molecular motions (187-189), and effects of additives (190), molecular weight variation (191), and degree of crystallinity (192). It has been used in combination with DSC to analyze the range of miscibility of polymethyl methacrylate poly(ethylene oxide) blends (193). 

It is customary to label relaxation transitions in polymers as a, P, y, d, etc. in alphabetical order with decreasing temperature. Three of the four transitions in polymethyl methacrylate (PMMA) ... 

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