Chain extenders are usually small molecules that contain at least two functional groups capable of reacting with the hydroxyls and/or carboxyl end
groups of PET chains by formation of new covalent bonds.
The liquid-phase polymerization is commonly used in the final stage of polymerization from low molecular weight prepolymer (e.g., degree of polymerization (D[P.sub.n]) = 20-30, carboxyl end
group concentration ([COOH]) = 60-80 mmol/kg) to produce conventional PET (e.g., D[P.sub.n] = 100, carboxyl end
group concentration ([COOH]) = 20-35 mmol/kg).
The carboxyl end
then reacted with the glycine that was protected by the 9-carbonyl methoxycarbonyl group to generate an amino group by subsequent esterification , after which methoxycarbonyl protection was rapidly removed.
Alpha-helices are green cylinders; arrows point from the free amino end to the free carboxyl end
To overcome this limitation on subunit assembly, the FSH heterodimer was converted to a single chain by genetically fusing the carboxyl end
of the FSH [beta] subunit to the amino end of the a subunit by a carboxyl-terminal peptide (CTP) linker sequence (Sugahara et al., 1996).
Equations (1) and (2) are dynamic material balances on amine end groups (A), carboxyl end
groups (C) and water (W) in the molten polymer phase.
The site of binding to the ligand is the carboxyl end
and adjacent to this, the site binds to the DNA.
Moisture attacks the carboxyl end
group of the polymeric chain, causing chain cleavage and decomposition.
It has a relatively low level of carboxyl end
groups; thus, says Ticona, it has good hydrolytic stability, providing buffer tubes resistance to high heat and humidity.
The number following the delta sign indicates the location of the double bonds, counting from the carbon at the carboxyl end
of the fatty acid, (the right side of the chains in [ILLUSTRATION FOR FIGURE 1 OMITTED]) which is designated as the number 1 carbon.
In this article we will report on the result of an examination of the fatigue behavior of PET fibers having a relatively high molecular weight and different carboxyl end
groups, when spin-drawn and heat treated under conditions similar to those used in the cord-dipping process, which is essential in tire cord production.
Bisoxazolines are commonly used as chain extenders in several polymers with carboxyl end
groups such as polyamides [34-37], poly(lactic acid) [38-40], poly(butylene terephthalate) [41,42], and PET [12,34,42-48], In the case of PET, the reaction with the carboxylic acid end groups is the most important one.