As. Merenga et al., Comparative broad-band dielectric study on poly(ester carbonate)s with 1,4-cyclohexylene linkages, MACROMOLEC, 34(1), 2001, pp. 76-81
Broad-band dielectric spectroscopy (10(-1)-10(7) Hz) has been used to study
the molecular dynamics in a set of bisphenol A poly(ester carbonate)s (BPA
-PECs) and tetramethylbisphenol A poly(ester carbonate)s (TMBPA-PECs) conta
ining 1,4-cyclohexylene dicarboxylate (CHDC) linkages. Four dielectric rela
xation processes are observed: The dynamic glass transition (a-relaxation)
being characterized by a Williams-Landel-Ferry (WLF-behavior) temperature d
ependence. Additionally three secondary relaxations (beta-, gamma'-, and ga
mma*-relaxation) exist. The beta -relaxation is related to the flip-flop mo
tion of the cyclohexylene rings and becomes dielectrically active because o
f a coupling to the neighboring carbonyl units. The gamma'- and gamma*-rela
xations originate from fluctuations of the carbonyl groups as well, either
by their own librational motions or by a coupling to the flips of the adjac
ent phenylene groups. Replacing the hydrogen atoms in the phenylene rings o
rtho to the carbonate units (BPA-PEC) by methyl groups (TMBPA-PEC) alters d
rastically the molecular dynamics below and above the calorimetric glass tr
ansition.