Influence of Tacticity on the Retardation Mode Associated with T g in PMMA

Influence of Tacticity on the α Retardation Mode in Amorphous Poly(methyl methacrylate)

“…(ii) As expected, enthalpy rises drastically as temperature approaches T g and exhibits a maximum at T g . This behavior is generally observed in amorphous polymers investigated by thermally stimulated techniques. ,,,,− (iii) Above T g , enthalpy drops rapidly. (iv) No negative values of Δ S are obtained in the investigated PMMA samples.…”

“…For simple relaxation, relatively few cooperative motions are required, and the activation entropy is then close to zero. 4,12,13,[21][22][23][24] Complex relaxations, as R relaxation, have large positive activation entropies and involve cooperative motions of neighboring groups or molecules. 4,12,13,[21][22][23][24] The solid line in Figure 4 is calculated using eq 4 where f is the equivalent frequency of TSCR, of about (5 ( 0.2) × 10 -3 Hz, and ∆S set equal zero.…”

“…4,12,13,[21][22][23][24] Complex relaxations, as R relaxation, have large positive activation entropies and involve cooperative motions of neighboring groups or molecules. 4,12,13,[21][22][23][24] The solid line in Figure 4 is calculated using eq 4 where f is the equivalent frequency of TSCR, of about (5 ( 0.2) × 10 -3 Hz, and ∆S set equal zero. Several features can be observed for each sample: (i) The measured values of ∆H depart from the ∆S ) 0 prediction around 30 °C independent of tacticity.…”

“…This behavior is generally observed in amorphous polymers investigated by thermally stimulated techniques. 4,12,13,16,[21][22][23][24] (iii) Above T g , enthalpy drops rapidly. (iv) No negative values of ∆S are obtained in the investigated PMMA samples.…”

“…For simple relaxation, relatively few cooperative motions are required, and the activation entropy is then close to zero. ,,,− Complex relaxations, as α relaxation, have large positive activation entropies and involve cooperative motions of neighboring groups or molecules. ,,,− …”