SWOLLEN CONFORMATIONS OF ASSOCIATING POLYMER-CHAINS

Equilibrium statistics of a single associating polymer chain are studied by means of extensive Monte-Carlo computer simulations. The chain is treated as a self-avoiding random walk. Each associating group or sticker is constrained to be adjacent to one other sticker, though stickers are free to change partners. In three dimensions chains with alternating long and short intervals between the stickers have a swollen conformation for almost all sticker placements, with the predominant association occurring between chemically nearby groups. The observed swelling is consistent with a Flory picture with an excluded volume parameter that varies linearly with the placement asymmetry x, defined as the ratio of the short interval to the sum of the long and short intervals between the stickers. A scaling analysis of the simulations is used to estimate that a chain with x = 0.496 +/- 0.004 will behave as an ideal chain in the asymptotic limit. Since the maximum x equals 0.5, in which case the stickers are equally spaced, collapsed behavior is only possible for chains with almost equally spaced stickers. In two dimensions I find swollen conformations for all sticker placements. The single chain behavior is related to the solution properties of many-chain systems.