Moisture Effects on the Glass Transition and the Low Temperature Relaxations in Semiaromatic Polyamides YOUNGSOO PARK, 1 JAEYOUNG KO, 2 TAE-KWANG AHN, 1 SOONJA CHOE 1 1 Department of Chemical Engineering, Institute of Polymer Science and Engineering, Inha University, Inchon, 402-751, Korea 2 Keum-Ho Petroleum Chemical Co., Ltd., Yu-Chun, Chun-La Namdo, 555-210, Korea Received 11 March 1996; revised 30 October 1996; accepted 1 November 1996 ABSTRACT: The influence of moisture absorption on the primary ( glass ) transition ( T a or T g ) and the low temperature relaxations of semiaromatic amorphous polyamides synthesized by isomeric aliphatic diamine and metha or para oriented phthalicdiacids has been investigated by means of differential scanning calorimeter ( DSC ) and dynamic mechanical thermal analyser ( DMTA ) . The glass transition of semiaromatic polyam- ides was lowered due to the water absorption, and the b and the g relaxations were as well. From the observed T g and the difference in the heat capacity, 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 manner as the plasticization of nylon 6 by water. The depressed b relaxation observed in the specimen containing a few percent of moisture was splitted into two transitions due to the reduction of water content, of which one was the elevation of the T b and another was the simultaneous appearance of the T g , and then the single T g solely was observed for the completely dried specimen. The T g seemed to be merged into or not to be observed by the large and broad T b transition when the sample was governed by a few percent of water, then it was emerged from the T b due to water desorption. Thus, the T b is believed to arise from the intermolecular hydrogen bonding between water molecules or between water and amide groups in wet polyamides. In addition, the g relaxation originated from the peptide groups is attributable to the inter- and intramolecular hydrogen bonding between amide groups.  1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 807–815, 1997 Keywords: moisture effect; glass transition; low temperature relaxations; semiaro- matic amorphous polyamides; hydrogen bonding; molecular analysis INTRODUCTION the glass transition temperature in diluted sys- tems was often expressed to a contribution of an additional free volume provided by the diluent, It has been reported that low molecular weight which allows high segmental mobility at low tem- materials such as water, solvent, or plasticizer, peratures. The behavior of the glass transition called diluents, influence the glass transition tem- temperature of plasticized systems was suggested perature of a polymeric system. A depression of as a critical volume fraction at the glass transition by Kelley and Bueche 1 or Williams et al. 2 Based on the theory of configurational entropy Correspondence to: S. Choe in glass formation by Gibbs and DiMarzio, 3 Gor- Contract grant sponsor: Inha University  1997 John Wiley & Sons, Inc. CCC 0887-6266/97 / 050807-09 den et al. have derived an expression for the com- 807 9603021 / 8Q28$$3021 02-27-97 16:06:41 polpas W: Poly Physics