MOISTURE EFFECTS ON THE GLASS-TRANSITION AND THE LOW-TEMPERATURE RELAXATIONS IN SEMIAROMATIC POLYAMIDES

The influence of moisture absorption on the primary (glass) transition (T-a or T-g) and the low temperature relaxations of semiaromatic amor phous polyamides synthesized by isomeric aliphatic diamine and metha o r para oriented phthalicdiacids has been investigated by means of diff erential scanning calorimeter (DSC) and dynamic mechanical thermal ana lyser (DMTA). The glass transition of semiaromatic polyamides was lowe red due to the water absorption, and the beta and the gamma relaxation s were as well. From the observed T-g and the difference in the heat c apacity, the calculated T-g depression per 1 wt % water content was 12 .3 K and the result was in good agreement with the experimental data. The depression of the glass transition may be expressed by the same ma nner as the plasticization of nylon 6 by water. The depressed beta rel axation observed in the specimen containing a few percent of moisture was splitted into two transitions due to the reduction of water conten t, of which one was the elevation of the T-beta and another was the si multaneous appearance of the T-gamma, and then the single T-gamma sole ly was observed for the completely dried specimen. The T-gamma seemed to be merged into or not to be observed by the large and broad T-beta transition when the sample was governed by a few percent of water, the n it was emerged from the T-beta due to water desorption. Thus, the T- beta is believed to arise from the intermolecular hydrogen bonding bet ween water molecules or between water and amide groups in wet polyamid es. In addition, the gamma relaxation originated from the peptide grou ps is attributable to the inter- and intramolecular hydrogen bonding b etween amide groups. (C) 1997 John Wiley & Sons, Inc.