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-
A method of obtaining soluble itaconic acid (IA)–ethylene glycol (EG) unsaturated polyesters was developed. The reaction between IA and EG was conducted under moderate vacuum (50—60 mmHg) at 120 °C and stopped by nearly 85% conversion to avoid crosslinking. No isomerization of itaconate to citraconate and/or mesaconate was observed. The residual double bond contained in the polyester resin showed to be highly reactive and promoted gelification after few days. Therefore copolymerization reactions of the resin with a variety of vinyl monomers proceed without radical initiator. The synthetic method was successfully applied to reactions of IA with other glycols.
The change in the heat capacity (ACPL) at the lower glass transition (TgL) in poly(di-n-alkyl itaconates) with 7-10 carbons in the side chain has been measured. A model for a side-chain relaxation mechanism is proposed that involves hindered rotation about C-C bonds, and the relevant partition function and heat capacity contribution from this motion has been evaluated. The calculated heat capacities have been compared with the experimental values in the region of TgL, and good agreement has been found.
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