MOLECULAR MODELING OF POLYMERS .10. CHARACTERIZATION OF CONFORMATIONAL TRANSITIONS OF POLY(ACRYLIC ACID) AND POLY(METHACRYLIC ACID) USING DYAD STRUCTURES

The conformational profiles of nearest side-chain neighbors, methylene -dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic aci d), PMA, were determined as a function of tacticity, extent of ionizat ion, and presence of counterion. The dominant backbone conformer state s are quite similar for both isotactic and syndiotactic diads in a com mon charge state. Thus, the overall dimensional properties of isotacti c syndiotactic and atactic chains of PAA or PMA, based upon dyad inter actions, are predicted to be alike for a given charge state. Significa nt deviations from precise t, g+, and g- states are found for the dyad minimum energy conformations. The rod-to-coil and coil-to-rod transit ions observed in PAA and PMA, respectively, as a function of increasin g counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. ( C) 1994 John Wiley & Sons, Inc.