Copolyesters liquid crystalline type

However, interchange reactions appear to be rather slow at temperatures below Tm(15). We(50) observed that thermal treatment of some of liquid crystalline, aromatic copolyesters at the temperatures substantially lower than Tm did not lead to any changes in the comonomer sequence even after a prolonged period of time. A copolyester especially of 4-hydroxybenzoic acid, however, can undergo a special type of sequence changes below Tm, which is called the crystallization induced reaction(51). 

Two liquid crystalline copolyesters of 60 mole % PHB/PET and 80 mole % PHB/PET were used in this study. These samples were supplied by Tennessee Eastman and the properties are given elsewhere. Rheological properties were measured under various conditions of shear and thermal history using a 0.1 radian cone and plate attachment of a Rheometrics Mechanical Spectrometer (RMS). Various types of flow histories were used in this study and these are listed below ... 

A type of aromatic-aliphatic liquid crystalline copolyesters has been synthesized from 2-chlorohydroquinone, 1,4-CHDM and terephthaloyl chloride (Figure 6.14). The CHDM units act in these copolyesters as flexible spacers providing the necessary chain mobility to be thermotropic. The structure and thermal behavior of these copolyesters were characterized by hot-stage polarized light microscopy, SEM, FTIR, NMR, DSC and TGA (57). It has been reported that they are insoluble in common solvents and may form mesophases at temperatures near the melting temperature of PET (58). 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

There is a further very important class of main-chain liquid-crystal polymers that differ from those discussed above by being random copolyesters based on polymers such as poly(hydroxybenzoic acid) -fO— —C=0), where — — represents a para-disubstituted benzene ring (para-phenylene unit). The random copolymers include units of various other forms containing phenylene or naphthylene rings and their introduction reduces the crystallinity and melting point considerably without necessarily lowering the value of Polymers of these types have... 

---