Heat capacity measurements on polymers and copolymers of itaconic acid ester exhibiting two glass transitions

Abstract

Differential scanning calorimetry has been used to establish the heat capacity (C") as a function of temperature for a series of itaconic acid based random copolymers in which the content of n-neptyl, n-octyl, and n-nonyl ester side chains varies from 0 to 100%. Two separate inflections in the Cp-T behavior are observed when the concentration of the long side chain comonomer is ca. 30 mol % and greater. The two processes are also observed as separate relaxations in the dynamic mechanical spectra of the copolymers. The higher temperature inflection is associated with the conventional glass-rubber transition (Fgu). The temperature of the lower, subambient, inflection (TgL) is essentially independent of copolymer composition, and its magnitude (ACpL) is a function of the concentration of n-alkyl side chains in the copolymer. TgL is assigned to a separate relaxation process of the n-alkyl side chains.In our previous work on comb-branched polymers it was reported that poly(di-n-alkyl itaconates) with side-chain lengths from 7 to 11 carbons exhibit two glass transitions.1•2 These were observed in both dynamic mechanical measurements and differential scanning calorimetry (DSC). In the former technique, the two glass transitions, designated Tgu and TgL (where u refers to the higher temperature), are evidenced by two major damping peaks, whereas in the latter technique, two distinct inflections in the DSC thermograms are seen. TgL has been ascribed to inde-

Investigation of local chain dynamics in poly(di-n-alkylitaconate)s

“…At the same time, the side chains are becoming less flexible, which explains the parallel evolution of T L g reported by Cowie et al [4]. These interpretations are in agreement with the existence of a microphase separation in PDAI's, as proposed by Cowie et al [5].…”

“…1, have a rather sterically hindered backbone with one of the two main-chain carbons in the repeat unit bearing two side chains whose length is defined by the number of carbons, n, in each of the alkyl groups. As shown by their mechanical and dielectrical properties and by their thermal transitions in bulk [1][2][3][4][5], PDAI's exhibit a complex relaxational behavior which strongly depends on the alkyl side-chain length. Their different sub-glass and glass relaxation processes have been recently revisited by dielectric spectroscopy [6], which clearly confirms the existence of an additional low-temperature glass-transition, a L , in derivatives with six carbon atoms at least in the alkyl part.…”

Laminin chains in rat and human peripheral nerve: Distribution and regulation during development and after axonal injury

“…These polymers show important changes in their properties, both in solution and the solid state 15–17. The thermal stability and dielectric and viscoelastic properties of several series of poly(itaconates) and copolymers containing itaconate units have been assessed by several researchers 8–14, 16, 18–23. In the case of poly(di‐ n ‐alkyl itaconates), there is an important increase of the steric hindrance because of the presence of two side groups per repeating unit.…”

Order in amorphous di‐n‐alkyl itaconate polymers, copolymers, and blends

“…The mechanical spectra of these higher alkyl itaconates (7 < n < 11) show a major sub‐ T g relaxation ascribed to the independent motion of the side chains 14. This relaxation is also evidenced by a step change in the heat capacity,15, 16 and so it has the characteristic of a conventional glass transition. It has been proposed that the main chain and side chains are constrained to occupy different regions of space and are thus separated into domains with different conformational freedoms that can relax independently.…”