Structural Heterogeneity in Poly(methyl methacrylate) Glasses of Different Tacticity Studied by Thermally Stimulated Current Thermal Sampling Techniques

Abstract

The thermally stimulated current thermal sampling (TSC-TS) technique was used to study the cooperative glass transition like relaxations in different tacticity poly(methyl methacrylates) (PMMAs) including iso-and syndiotactic forms. We use the high sensitivity of the TSC-TS method to study these weak and sometimes overlapping relaxations at a frequency of about 10 -3 Hz where one can resolve cooperative relaxations well below the main glass transition (Tg), even if the species are a minor fraction of the overall relaxing species. The magnitudes of the values of Ea are compared with a theoretical prediction as a function of temperature, showing that the low-temperature tail of the glass transition in conventional atactic (e.g., 45% syndiotriads) extends down to 15 °C, while in our highest syndiocontent PMMA (80% syndiotriads), the glass-transition-like relaxations only extend down to about 80 °C. Results taken from the literature also substantiate the results obtained here for atactic PMMA. The results are contrasted to those for bisphenol-A polycarbonate and other polymers and suggest that compositional heterogeneity, more specifically the presence of low Tg "pockets" of predominantly isotactic sequences, contributes to the broad glass transition extending almost 90 °C below the main glass transition in atactic PMMA.

Efficient Nonlinear Absorbing Platinum(II) Acetylide Chromophores in Solid PMMA Matrices

“…In accordance to literature PMMA should have a glass transition around 105 8C. [47] The somewhat higher T g values we recorded for neat PMMA are most likely due to the rapid heating and cooling rates (30 8C min À1 ) that were used to record the thermograms. In contrast to class I materials, the class II materials have higher glass transitions than compared to the neat PMMA due to the crosslinks caused by the Pt1-G1-methacrylate chromophore.…”

Thermally stimulated current studies on molecular relaxation and blow moulding of poly(ethylene terephthalate)

“…It is seen that both stretched samples show the relatively lower activation energy. Sauer and Kim 27 suggested that the lower values of E a indicate that the polymer chains are more homogenous in terms of their structural regularity and/or composition. This seems to agree with our results in Fig 6 that the unstretched PET shows the highest E a and the stretched PET at 95°C shows the lowest value.…”

Hybrid nanofabrication processes utilizing diblock copolymer nanotemplate prepared by self-assembled monolayer based surface neutralization

“…The PS-b-PMMA films were then annealed under a vacuum at 180°C for 24 h since the glass transition temperatures of the two polymer blocks are higher than 100°C ͑T g = 100°C for PS and T g = 105°C for PMMA͒. 18,19 After annealing, the samples were exposed to UV radiation for 90 min under vacuum to degrade the PMMA blocks. Degraded PMMA was selectively removed by sonication in glacial acetic acid for 1 min, followed by rinsing with DI water.…”