Synthesis of CHDM-based Polyesters

PCTG and PCTAs can all be prepared readily via standard melt-phase poly condensation processes [34, 35], The diacid can be delivered via transesterification of the dimethyl esters or via direct esterification of the diacids. Numerous conventional catalyst and catalyst combinations can be employed. The use of a catalyst or catalyst combination is important for the manufacture of polyesters via the melt-phase process and has been well reported in the literature [36-41], Appropriate catalyst systems enable the production of polyesters with high processing rates and high molecular 

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. 

When made with the normal 70/30 trans/cis CHDM isomer ratio, the melting point of PCT is about 290 °C. The melting point varies substantially with isomer 

The strong sub-rg relaxation in PCT also contributes to increased toughness of this polymer in the amorphous state. When measured on amorphous specimens, the notched Izod impact strength of PCT is greater than 1000 J/m, while that of PET is less than 100 J/m [22], 

If PCT is modified with relatively high levels of comonomer, substantially amorphous materials result (see the following sections on PETG, PCTG and PCTA). However, it is possible to maintain crystallinity at lower levels of modification. For example, replacing up to about 10mol% of the terephthalate units with isophthalate results in a polymer with reasonable crystallization rates and ultimate degrees of crystallinity. 

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