Transport of water in high T polymers: A comparison between interacting and non-interacting systems - Polyimides and Other High Temperature Polymers - page 265

Transport of water in high T g polymers: A comparison
between interacting and non-interacting systems
G. MENSITIERI, ∗ ,1 S. COTUGNO, 1 P. MUSTO, 2 G. RAGOSTA 2 and
L. NICOLAIS 1
1 Dept. of Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80,
80125 Naples, Italy
2 Institute of Research and Technology of Plastic Materials, National Research Council of Italy,
Via Toiano 6, 80072 Arco Felice (Naples), Italy
Abstract—Molecular interactions of absorbed water molecules with two different high performance
polymer matrices have been investigated using classical gravimetric analysis as well as in situ, time-
resolved FTIR spectroscopy. Sorption and desorption kinetics at several activities and equilibrium
isotherms have been evaluated by both experimental techniques, and useful information has been
gathered by comparing the results of the two approaches. These results have been discussed with re-
spect to the molecular interactions and the state of aggregation of the penetrant molecules in the two
systems. In fact, various species of absorbed water molecules have been identified spectroscopi-
cally, depending on the molecular structure of the two matrices. In the case of epoxy resin, free and
dimeric water molecules coexist with water molecules strongly bound to the polymer network
through H-bonding interactions. Conversely, in the case of polyimide, because of the absence of
strongly interacting sites along the polymer backbone, mostly free and self-associated water has
been detected. The coupled analysis of gravimetric and spectroscopic sorption isotherms has shed
light on the different sorption mechanisms operating in the two matrices. The difference in the mo-
lecular interactions between the penetrant and the polymer matrices causes a much faster water dif-
fusivity in the case of polyimide as compared to the epoxy.
Keywords : Sorption; water; epoxy; polyimide; infrared spectroscopy.
1. INTRODUCTION
Mass transport of low molecular weight compounds in polymeric materials has
caused a great scientific and technological interest in the past 40 years. There are
several engineering applications where diffusion behaviour has a major impact,
e.g. gas mixtures separation with membranes, drug delivery, barrier structures for
food packaging, environmental resistance of polymer based composites, and de-
volatilization. In this respect, the durability of high performance matrices for
composites is of considerable technological relevance. In fact these matrices,