M. Konas et al., MOLECULAR-WEIGHT CHARACTERIZATION OF SOLUBLE HIGH-PERFORMANCE POLYIMIDES .1. POLYMER-SOLVENT-STATIONARY PHASE INTERACTIONS IN SIZE-EXCLUSION CHROMATOGRAPHY, Journal of polymer science. Part B, Polymer physics, 33(10), 1995, pp. 1429-1439
Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides
based on several anhydride/diamine monomers were prepared in N-methyl
pyrrolidine (NMP) and cyclized by solution imidization to controlled m
olecular weight. The polyimides and a polyamic acid precursor were suc
cessfully analyzed by size exclusion chromatography (SEC) utilizing on
line parallel coupled refractive index and differential viscometer det
ectors. The calculated ($) over bar M(n) values were varied from 3,000
to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF),
and chloroform served as mobile phases for the cross-linked polystyren
e gel packings. Normal retention behavior of the polyimides was observ
ed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over
P2O5 before use. Values of Mark-Houwink-Sakurada exponents for narrow
distribution linear polystyrene indicate that pure NMP and NMP with 0
.06 M LiBr are good solvents for polystyrene standards at 60 degrees C
. In contrast, SEC behavior of polyimides in pure NMP leads to splitti
ng of the peaks with the major portion observed to pass through the co
lumns at the exclusion limit. In contrast to strong polymeric chain ex
pansion of the polyamic acid in dilute solution, presumably due to a p
olyelectrolyte effect, no increase of intrinsic viscosity of polyimide
samples in pure NMP was observed. This exclusion effect of polyimides
analyzed in NMP is discussed in terms of possible ion-exclusion from
pores of the stationary phase. Differences in polystyrene calibration
in NMP with of without additives and the temperature dependence of cal
ibration curves in these mobile phases is discussed as well. (C) 1995
John Wiley & Sons, Inc.