Low‐frequency thermomechanical spectrometry of polymeric materials: Tactic poly(methyl methacrylates)

Abstract

SynopsisA computerized and automated torsional pendulum has been used to characterize amorphous poly(methy1 methacrylates) a t about 1 Hz in the temperature sequence 473' -93" -473°K. The effects of thermal prehistory, temperature cycling, water content, and tacticity are demonstrated. In particular, a comparison of the out-of-phase shear modulus (G") versus temperature for "syndiotactic," "atactic," and "isotactic" polymer specimens shows that the intensity of the glassy-state 6 loss peak decreases with increasing isotactic content while the temperature of its location remains the same. Extrapolation suggests that completely isotactic polymer would not display a 6 loss peak.The shape and location of the G " data a t low temperatures indicate that the basic mechanism of the 6 process is the same for the three polymer samples and support the validity of the extrapolation.The effect of tacticity is reflected also in the glass transition region; the isotactic sample has its Tx about 65°C lower with greater intensity than the syndiotactic polymer.

Dependence of the glass transition temperature of poly (methyl methacrylates) on their tacticity

“…[11] that Tg of syndiotactic PMMA does not differ too much from Tg of the atactic polymer. The Tg values reported in the literature for syndiotactic PMMA [9,12] seem to be unrealistically high.…”

Isothermal physical aging of poly(methyl methacrylate): Localization of perturbations in thermomechanical properties

“…The glass transition temperature, T, = 116°C (0.7 Hz) , is indicative of approximately 60% syndiotactic PMMA. 17 The PMMA was dissolved in tetrahydrofuran (THF, bp = 67°C) for impregnating a heatcleaned glass braid [ 0.5 g PMMA/ 2.5 mL THF] for use in torsional braid analysis experiments.…”

Automated Torsion Pendulum: Control and Data Collection/Reduction Using a Desktop Computer

“…Published superior TBA spectra obtained using the linear least squares method (8), and the peak-finding method using an analog computer (_2) , were presumably the consequence of a better basic experiment than the one used in this report to compare (as in Figure 8) the data reduction methods.…”

“…The solution is a damped sine wave: " eff) 2 ]* (8) and t is a phase angle. The shear modulus, G*, and loss modulus, G", can be derived from information in the wave:…”

“…is performed for the first minimum and the follow ing maximum, as well as for the last pair (the selection of which depends on the damping), and the period is calculated by dividing the elapsed time between the maxima by the number of cycles.The logarithmic decrement is obtained from the relation is the amplitude of the ith extremum.Least Squares Method(8). A torsion pendulum specimen has a tendency to change its rotational orientation during the course of an experiment due to an uneven distribution of stresses caused by volume expansion and contraction.This results in a drift in the baseline of the wave signal which can be represented by e = 0 o exp(-at)cos(u)t + <(>)+ Bt + C(20)where B is the drift coefficient and C is the offset.The corres ponding differential equation can be written as Downloaded by UNIV OF LEEDS on May 18, 2016 | http://pubs.acs.org Publication Date: September 24, 1982 | doi: 10.1021/bk-1982-0197.ch020 Provder; Computer Applications in Applied Polymer Science ACS Symposium Series; American Chemical Society: Washington, DC, 1982.…”