Cellulose acetate-graft-poly(hydroxyalkanoate)s:: Synthesis and dependence of the thermal properties on copolymer composition

Several different series of cellulose acetate-graftpoly(hydroxyalkanoate)s (CA-g-PHAs) were synthesized over a wide range of compositions by the graft copolymerization of lactic acid, L-lactide, (R,S)-beta-butyrolactone, delta-valerolactone and epsilon-caprolactone onto the residual hydroxyl positions of CA, by virtue of a suitable catalyst, solvent and procedure for each individual case. To achieve a diversity of molecular architectures of the respective graft copolymer series, the degree of acetyl substitution (acetyl DS) of the CA starting material was also varied, resulting in different levels of the intramolecular density of grafts. The CA-g-PHAs thus obtained were subjected to differential scanning calorimetric measurements and the relationship between their molecular structure and thermal transition behavior was estimated, in comparison with some semi-empirical equations available for polymer blends or comb-like polymers. In particular, the composition dependence of the T(g)s of the graft copolymers was represented well in terms of a formula proposed by Reimschuessel for comb-like polymers, when CAs of acetyl DS approximate to 2 were employed as a trunk polymer. The deviation of the glass transition data from the model function was discussed in connection with the manner of graft modification.