Typical Measurements on Poly Methyl Methacrylate PMMA

TYPICAL MEASUREMENTS ON POLY(METHYL METHACRYLATE) (PMMA) 

Thermally Stimulated Current Analysis of Thick PMMA Films 

In addition to the well-established molecular relaxations, the TSC spectrum shows a weak / relaxation, ascribed to rotation of trace amounts of absorbed water, and a weak [3 relaxation, a dielectric signal that may correspond to translational mobility of charges, hindered sidechain motions, or even structural relaxation effects [see, e.g., Muzeau et al. (1995) Kalogeras (2004). The a relaxation has a peak at = 110 °C, near the DSC Tg (Kalogeras and Neagu 2004). The intrachain effect of the stiffness of individual chain segments is—at least in the case of PMMA and some other poly(n-alkyl metharylate)s— more important than the interchain effect of the cohesive (attractive) forces 

The dielectric strength of a particular relaxation mechanism can be determined by the depolarization charge 2si, obtained from the area under the related TSC peak, by 

The area under an isolated peak is obtained by simple graphical integration of the curve. For partially overlapping bands, it is possible to obtain rough 

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Linear amorphous polymers exist in a number of characteristic physical states depending on the timescale of the measurement and temperature. These are illustrated in Fig. 5.2 in terms of an arbitrary modulus function and are classified as glassy, leathery, rubbery, rubbery flow, and viscous (Tobolsky 1960 Collins et al. 1973). All linear amorphous polymers exhibit these five physical states when they are observed over a wide range of time or temperature. Materials of this type are typical of amorphous thermoplastics, such as polystyrene (PS), poly(methyl methacrylate) (PMMA), or polycarbonate (P(i ) polymers. Polymers that are either crosslinked or crystalline do not exhibit the rubbery flow and viscous liquid responses as illustrated. Crystalline polymers, however, will exhibit a viscous response at temperatures above the melting transition. 

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