engleski

Effect Of Structural Changes On Radiation Curing Of Unsatutrated Polyesters

In-source 60Co gamma rays induced curing of unsaturated polyester with styrene was followed directly and continuously by measuring electrical conductivity change. The results of extraction analysis proved good correlation between the change of electrical conductivity and the extent of curing. The gel content was inversely proportional to conductivity and free styrene content directly proportional to conductivity. The unsaturated polyesters contain carbonyl, carboxyl and hydroxyl groups which were likely to participate in hydrogen bonding and short-range local order could be formed. When the macromolecules achieve enough energy interactions that cause local order break and structural transitions appear. Transitions in amorphous polymers above the Tg are called liquid-liquid transition. The lower liquid-liquid transition (Tll) is the temperature at which short-range intermolecular interactions break and melt starts to flow. Its temperature is approximately 1.2 Tg (K). The intramolecular interactions mostly at polymer chain ends, break at upper liquid-liquid transition (Tlr) which is 30-50 K higher than Tll. DC-electrical conductivity has shown high sensitivity toward structural changes and enabled us to detect Tll and Tlr in unsaturated polyester. The existence and nature of Tlr we proved by additional methods: viscosity measurement, DSC, 1H NMR and Near-IR spectroscopy. The Tlr appeared in the temperature range (300-320 K) where radiation curing was performed. It could influence the rate of curing and the vitrification dose, because the intramolecular interactions influence penetration of styrene molecules to the double bonds in the polyester coil.

unstaturated polyester; radiation curing; liquid-liuid transitions; DC-electrical conducitivity

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