Abstract
The study was conducted on improving the performance of epoxy resins against water absorption and heat, by using 2, 3, 5-trimethylphenol (TMP) novolac as a curing agent. Firstly, on the synthesis of novolacs, the rate of reaction of TMP with formaldehyde was found to be faster than that of o-cresol (o-C) under acid conditions. Secondly, novolacs from TMP and o-C, having almost the same molecular weight distribution, were synthesized for the comparison of properties between the both resins.
The TMP novolac had larger values than those of the o-C novolac in the properties, such as Tg, thermal decomposition temperature, and melt viscosity. In comparing the behavior of these novolacs, the former made epoxy resins slower in the curing rate, and gave cured resins the properties of less water absorption and higher volume resistivity after a boiling test. The heat resistance of TMP novolac cured epoxy resins was also superior to that of resins from o-C novolac. These are caused by the property of TMP novolac which is hydrophobic in nature and is rigid in the main chain due to the existence of methyl groups in the meta-position of TMP.
