PCTAs

PCTA Copolyester. Poly(l,4-cyclohexanedimethylene terephthalic acid) (PCTA) copolyester is a polymer of cyclohexanedimethanol and terephthalic acid, with another acid substituted for a portion of the terephthalic acid otherwise required. It has the following formula ... 

CHDA CHDM DMCD EG IPA N NDA PCT PCTA PCTG PET PETG TMCD TPA cis/trans-1,4-cyclohexanedicarboxylic acid cis/trans-1,4-cyclohexanedimethanol dimethyl cis/trans-1,4-cyclohexanedicarboxylate ethylene glycol isophthalic acid dimethyl 2,6-naphthalenedicarboxylate 2,6-naphthalenedicarboxylic acid poly(1,4-cyclohexylenedimethylene terephthalate) dibasic-acid-modified PCT copolyester glycol-modified PCT copolyester poly(ethylene terephthalate) CHDM-modified PET copolyester c .S / ra .v-2,2,4,4-tetramethyl-l,3-cyclobutancdiol terephthalic acid... 

This report provides an overview of some of the newer polyester compositions based on CHDM. The basic properties and chemistries of PCT have been described in earlier reviews [9, 13]. The CHDM-based polyesters covered in this review are PCT, PCTG, PCTA, and PETG. These compositions are described in more detail in the sections that follow. 

PCTA likewise refers to an acid-modified PCT copolyester. Isophthalic acid (IPA), or alternatively the dimethyl ester of IPA, is the most commonly used modifying dibasic acid to prepare PCTA copolyesters. PCTA thus refers to PCT compositions modified with up to 50 mol% IPA. The PCTA structure is as follows ... 

PCT, PETG, 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... 

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. 

Table 7.3 Physical property comparison of amorphous PETG, PCTG and PCTA...

The crystallinity of PCT can be modified with diacids as well as with diols and these modified polyesters are often called acid-modified PCTs, or abbreviated as PCTAs. The most common diacid modifier is isophthalic acid (IPA), which can be incorporated in relatively low levels to lower the melting point of PCT to enhance processability while still maintaining crystallinity. The high Tm of PCT (295 °C) requires that the homopolymer be processed at temperatures greater than 300 °C, which is near the decomposition temperature [13]. 

Figure 7.10 Transparent toy kaleidoscopes molded from Eastman Durastar 1010 PCTA copolyester. Photograph provided by courtesy of Eastman Chemical Company...

Although the scope of this review mainly covers CHDM-based polyesters modified with isophthalic acid or ethylene glycol (i.e. PCTA or PCTG, and PETG, respectively), many other copolyesters with interesting properties have been prepared with a variety of other comonomers. 

The properties of PCTA-type structures where the modifying acid is 1,4-cyclohexanedicarboxylic acid (CHDA) have also been studied [53], The incorporation of this diacid (95 % trans) as a polyester modifier maintains the toughness, but is accompanied with significant lowering of the Tg. This is contrasted to NDA modification where the Tg is enhanced but toughness is decreased. A comparison of the properties of various PCTAs versus an amorphous PCT sample, prepared by quenching, are shown in Table 7.5. 

Table 7.5 Comparison of selected properties for various PCTA copolyesters [53]...

Thermoplastic polyesters (PET, PBT, PETG, PCT, PTMT, PCTG, PEN, PCTA, PTT)... 

Use as an anticoagulant in patients with unstable angina undergoing percutaneous transluminal coronary angioplasty (PCTA) intended for use with asprin... 

Patient controlled transdermal analgesia (PCTA) is one of the newest variations on PCA. PCTA uses a delivery system consisting of a small patch that is approximately the size of a credit card.29,45 This patch is adhered to the patient s skin, usually on the arm or upper chest. The patch is impregnated with an opioid such as fentanyl, and the patient can self-administer a... 

An analytical approach for estimating the distributions PcTA(r/)(z) of Cta(T, t ) z for nonzero t was developed in Margolin and Barkai [26, 40], To treat the problem a nonergodic mean field approximation was used, in which various time averages were replaced by the time average intensity I qj, specific to a given realization. For short t -C T the result is... 

NMR relaxometric studies of Gd(III) complexes with ligands D03A, PCTA-[12] and PCTP-[12] whose structure are given below proved interesting [78]. 

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