Thermoplastic Homopolymers, PET or PBT, have been in the forefront in the thermoplastic polyester segment for the last few decades, accounting for more than 75% of the total thermoplastic polyester business. PBT, based on 1-3 butane diol, alone accounts for almost 60% of the total business, mainly on account of favourable price, easier processability and better warp resistance compared to PET based on Ethylene Glycol. PET accounts for almost 15 % of the market share, mainly due to better stiffness and higher temperature resistance. A newer hompolymer - PTT, based on 1-3 propane diol offers excellent surface finish and good rigidity. PTT is expected to gain some share of the market from PBT, mainly because of its lower cost. This significant low cost of 1-3 propane diol can be attributed to pioneering work on the catalyst carried out by Shell.

However, all these homopolymers have one major drawback : they do not provide excellent clarity, particularly in thicker sections, on account of faster crystallization behaviour. To achieve good clarity, copolyesters based on Cyclohexanedimethanol (CHMDA) are required.

Among the 3 well-known Copolyesters, PETG has already achieved almost 90% share. PETG is based on Ethylene Glycol as well CHDMA. It provides excellent clarity and high stiffness. Its usage as an environmental friendly option to PVC extrusion blow moulded container is already established. These copolyesters known as "Glass Polymer," replicate the look and feel of glass in thick-walled bottles for cosmetics and personal-care products. PETG is making new inroads in laboratory flasks and thermoformed medical packaging. Eastman recently added the Provista family dedicated to profiles for channels, signages, and medical as well as packaging tubes. Provista MP001 products use a branching agent and a broader molecular weight distribution to raise melt strength and reduce melt fracture at high throughputs, but the trade-off is lower toughness.

In addition to PETG, there are two more Copolyesters : PCTG and PCTA. PCTG contains more CHMDA compared to EG while PETG contains more EG compared to CHMDA. This change improves clarity and impact resistance. PCTA based on Isophthalic acid along with Terephthalic acid improves HDT of PETG. Both these Copolyesters cost more as compared to PETG, and therefore have a lower share compared to PETG.However both will gain some market share in the near future. Eastman is also introducing branched PETGs for medical profiles. MP002 retains the processing advantages of MP001 together with higher toughness than workhorse PETG 6763. Also new from Eastman is DN010, an injection moldable PCTG with high clarity (92% light transmission) and toughness suited to replacing acrylic. Higher toughness reduces breakage and permits snap-fit designs. Another new PCTG for injection molding is MN005 for clear medical devices and packaging. It has double the normal flow rate while minimizing trade-offs in impact strength and elongation.

SK Chemicals produces CHDM and copolyesters in Korea and is a major supplier to the Asia-Pacific region, where PETG is replacing PVC in sheet for displays, household chemical bottles and other applications.

While most of homopolymers are reinforced further with glass fibers, the copolyesters find applications without reinforcement due to the advantage of clarity.