Meaning
Functional chemical units located at the ends of polyester or polyamide polymer chains dictate the reactivity and stability of the material. A carboxyl terminal group consists of a carbon atom double bonded to oxygen and single bonded to a hydroxyl group. These units influence how the resin interacts with additives or glass fibre sizings during the compounding process.
Chain Architecture
Molecular structure determines the number of active sites available for further reaction or degradation. The carboxyl terminal group count is a primary metric for assessing the degree of polymerisation in resins like polyethylene terephthalate. Higher counts often indicate shorter chain lengths which results in lower melt viscosity and reduced mechanical toughness.
Degradation Pathway
Chemical breakdown in the presence of heat or water occurs more readily at specific molecular positions. In polyamides, the carboxyl terminal group can facilitate a series of reactions that lead to chain scission and the release of volatile byproducts. This mechanism is particularly active when the resin is processed without sufficient drying.
Reactivity Level
Bonding potential between the polymer matrix and reinforcements depends on the availability of these acidic end groups. A high concentration of carboxyl terminal group units can improve the adhesion to certain mineral fillers or impact modifiers. Conversely, excessive levels might lead to undesirable crosslinking or gas evolution during the extrusion phase of production.
By controlling the density of these groups, a resin manufacturer can tailor the material for specific high performance applications in the automotive sector.
