engleski

INVESTIGATION OF UPPER LIQUID-LIQUID TRANSITION IN UNSATURATED POLYESTER BY NEAR-INFRARED SPECTROSCOPY

It has been shown that there exists short range order in polymer melts based on inter- and intramolecular interactions. These interactions break at temperatures labeled liquid-liquid transitions. At the moment this type of transitions is proven in many different polymers and by a number of methods although the changes at these transitions are weak. Spectroscopic methods are of particular importance in elucidating their structural origin. Near infrared spectroscopy is sensitive to structural changes, especially if changes of hydrogen bonding are involved. It is possible to record spectra of thicker samples what increase possibility of detecting weak changes so this method was chosen to investigate liquid liquid transitions. In unsaturated polyester resins liquid liquid transitions have already been detected by electrical conductivity measurements and differential scanning calorimetry. Short range order is pronounced in polar polymers capable of forming hydrogen bonds such as resins. Previous results implied changes in hydrogen bonding. The near infrared spectra were recorded at different temperatures. Absorptions at 1429 nm and between 1900 nm and 2000 nm changed significantly at transition temperature. These absorptions are caused by hydrogen bonded and free hydroxyl and carbonyl groups and it confirmed the assumption that transitions are caused by changes in hydrogen bonding. All other absorptions changed in the manner characteristically for polymer melt with no structural transformation as well as absorptions at 1429 nm and between 1900 nm and 2000 nm changes with temperature.

unsaturated polyesters; upper liquid-liquid transition; short-range order; near-infrared spectroscopy; hydrogen bonding

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