Semi-Aromatic Homo-Polyesters

153 °C for isosorbide and 155 °C for isoidide. The synthesis of isomannide-based polyesters was unsuccessful. 

Braun et al. reported the synthesis of a broad range of polyesters from isosor-bide/isomannide and acid dichlorides via melt condensation [12], The acid chlorides used include linear C4-C16 alkanoyl, ortho/iso/terephthaloyl, and 1,8- and 2,6-naphthalenoyl. Relatively high aliphatic polyesters were obtained, with up to 60 000 (GPC) for poly(isosorbide sebacate). Contrary to the aliphatic polyesters, the semi aromatic polyesters are highly viscous at high temperatures, hampering polycondensation. The TgS recorded for polyesters obtained by melt polymerization of isosorbide or isomannide with terephthaloyl chloride were 147 and 156 °C, respectively. 

Storbeck and Ballauff prepared polyesters from isohexides and terephthaloyl dichloride by solution polymerization in pyridine, giving colourless, fibrous materials [13]. Isomannide and isoidide yielded semi-crystalline materials however, crystallinity could not be recovered after annealing since their glass transition temperature and melting temperature are too close to each other for them to be crystallized from the melt. Thermogravimetric analysis (TGA) of poly(isosorbide terephthalate) (PIT) showed thermal stability up to 360 °C under a nitrogen atmosphere. 

Kricheldorf reported PIT synthesis by transesterification with dimethyl terephthalate, giving a polymer with a Tg of 197.5 °C [14] (Table 9.1). 

Despite the broad range of molecular weights obtained with the different polymerization methods, and hence the spread in observed Tg values, it is clear that poly(isosorbide terephthalate), or PIT, is a high Tg amorphous material. 

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The first papers on isohexide based semi-aromatic homo-polyesters were published by Thiem et al. in 1984 [10,11]. They prepared polyesters from all three isohexides by melt condensation with terephthaloyl chloride at elevated temperatures (Figure 9.3). Colourless, brittle oligomers were obtained with Mn 3000-8000. These materials exhibited very high TgS - that is. 

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