The thermal stability of p-cresol novolac resin was studied by means o
f DSC, X-ray diffraction, thermogravimetry and SEC investigations. Aft
er 30 thermal cycles in which the same sample was heated, cooled and h
eated again, without attainment of the temperature of degradation at a
ny time in the experiment, important structural modifications are obse
rved. At the end of the experiments, the resin, which is initially hig
hly crystalline, exhibits all the characteristics of a semi-crystallin
e material.