PCT-based polymers

A well-established application for extruded unreinforced PCT (copolymerized with isophthalate) is crystallized, thermoformed trays for foods. Crystallized PET is widely used for this application, but where higher-temperature performance is needed the PCT-based polymer may be chosen. Such trays are formed from extruded sheet, using a hot mold to promote crystallization. Isophthalate-modified PCT polymers are approved by the Food and Drug Administration for high-temperature food contact use. 

The good hydrolytic stability of PCT-based polymers leads to applications for monofilament in paper machine belts. Monofilament is extruded from high-molecular-weight polymer, drawn and crystallized, and then woven into a screen. Such belts are found in the drying sections of paper machines, where there is a combination of high moisture and high temperature. Because of their hydrolytic stability, PCT-based polymers provide much longer service life in this application than PET-based materials. 

The primary crystalline polymer based on CHDM is the terephthalate, poly(1,4-cyclohexylenedimethylene terephthalate) (PCT). This polyester was originally developed for fiber applications but has since found wider utility as a reinforced polymer for injection molding and (when copolymerized with a small amount of isophthalic acid) as a material for crystallized food packaging trays. The key property of PCT which sets it apart from other thermoplastic polyesters in these latter applications is its melting point. 

Cycloaliphatic LC PEAs based on commercially poly(l,4-cyclohexanedimelhylene terephthalate) (PCX) have also been synthesized with two cycloaliphatic diamines and a linear counterpart (1,6-hexamethylenediamine) (Figure 8.12) [55]. The compositions of the ester/amide units in the copolymers were varied up to 50% by the adjustment of the amounts of the diol and diamine in the feed. The introduction of amide linkages was found to induce nematic LC properties into the polyester backbone, which in turn increased the polymer chain alignment. Interestingly, the introduction of nematic LC phases into PCT was only possible when a low ratio of amide units (i.e., less than 25 mol%) was incorporated into the polymer backbone. 

Polymers in these eight groups are usually assigned source-based names, but these groups do not necessarily correspond to specific CAS poljuner classes. A CAS publication (16) cites 42 specific poljuner classes an up-to-date list may be viewed by entering CAS Registry File online and executing the command expand A/PCT. 

Ho, S. C. H. Wu, M. M. Xiong, Y. Novel cyclopolymerization polymers from nonconjugated dienes and 1-alkenes. PCT International Patent Application WO 95/06669 (Mobil Oil Corp.), March 9,1995. Hustad, P. D. Coates, G W. Insertion/isomerization polymerization of 1,5-hexadiene synthesis of functional propylene copolymers and block copolymers. J. Am. Chem. Soc. 2062,124, 11578-11579. Hustad, P. D. Tian, J. Coates, G. W. Mechanism of propylene insertion using bis(phenoxyimine)-based titanium catalysts an unusual secondary insertion of propylene in a group IV catalyst system. J. Am. Chem. Soc. 2002,124,3614-3621. 

Eastman Chemicals, based in the USA, is now the world s fourth largest producer of liquid crystal polymers. Eastman opened a 3,000 tpa plant at Tennessee, USA, in 2001. However, in March 2003, it was announced that DuPont Engineering Polymers has acquired Eastman Chemical s high-performance crystalline plastics business. The deal covers Eastman s Titan liquid crystal polymers, Thermx PCT and Thermx EG series. Under the agreement, DuPont is buying the technology rights... 

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