Amorphous polymer

The degree to which a polymer's molecular chains pack into ordered, crystalline regions. Higher crystallinity generally increases stiffness, chemical resistance and melting point but also raises moulding shrinkage, as in semi-crystalline thermoplastics such as polypropylene and PEEK.

The temperature region over which an amorphous or partly amorphous polymer changes from a rigid, glassy state to a softer, rubbery one. It sets a practical upper service temperature for resins and adhesives and can be reduced by absorbed moisture or incomplete cure.

A large molecule built from many repeating chemical units joined into long chains. Polymers include thermoplastics, thermosets and elastomers, and form the matrices, adhesives, coatings and membranes used throughout the materials industry.