Although the term denotes a phenomenon with an opposite effect to plasticization, this must not be intended in terms of increase in the glass transition temperature. Antiplasticization is a phenomenon that brings about an increase in modulus at low temperatures, as well as embrittlement at ambient temperatures. In polyvinyl chloride (PVC) this is brought about by the incorporation of small amounts of plasticizers (typically 5 – 15 parts per hundred) capable of exerting strong physical interaction, such as H- bonds with the Cl atoms in the chains. These interactions cause a depression of short time (β) relaxations, normally associated with rotational movements of side groups in a polymer chain. The effects of the addition of small amounts of plasticizer in PVC or other glassy polymers, such as polycarbonate, on the variation of modulus with temperature has shown that antiplasticization is essentially a phenomenon occurring at low temperatures and that normal plasticization takes places at higher temperatures.