Acid-base-induced association of amino-terminated polystyrenes. 1. Linear chains and ring formation

Abstract

The associating coupling process of tertiary-amino-terminated polystyrene (FS) chains with monofunctional and bifunctional dinitrophenol reagents has been studied by means of UV-vis spectroscopy and light-scattering measurements as a function of polymer concentration. The mechanism of coupling was first checked with monofunctional PS chains. The equilibrium constants of the two functional groups of the coupler were found to be slightly different from each other; but with the same average value as for the monofunctional phenol compound. The increase of molecular weight agreed well with predictions from Flory's theory. Much smaller weight average molecular weights were found, however, for the coupling of telechelic PS chains, and the deviations are stronger for the short chains than for the longer ones. The effect is explained by ring formation and three approximations were applied. These are (a) a mean field approximation, (b) the Jacobson-Stockmayer (JS) approach, and (c) the JS approach including excluded volume effect and its influence on Gaussian statistics. Molecular weights were also calculated from the weight fraction of rings and fitted to those obtained by LS where the effective bond length b was chosen to be the adjustable parameter. In the original JS treatment the effective bond length increased with the chain length of the primary chain. In treatment c this could be eliminated by consideration of excluded volume, but absolute values of b are unrealistically low.

Comparison of irreversible and reversible cluster formation

“…6). UV-VIS spectra of amino-terminated star polymer solutions of different concentration at constant coupling agent concentration (Ref 6…”

Association of Amino-Terminated Polystyrenes. 2. Dynamic Light Scattering of Associating Linear Chains

“…SLS in good solvents revealed no detectable difference in the osmotic second virial coefficient A 2 between the untagged and amino-terminated PS chains. 1 Apparently, there is no influence of the tertiary amino end group on the static properties of the chains in dilute solution. Similarly, the semidilute solution behavior of the end-tagged PS corresponded to that of the unfunctionalized PS.…”

“…Doubling of molecular weight is the only realistic possibility and was confirmed by analysis of SLS data. 1 Therefore, also the diffusion coefficient should not be lower than that of a corresponding covalent polymer of double molecular weight. This was indeed found and may directly be seen from the raw DLS data ( Figure 3b) before correction for k D .…”

“…(i) As shown previously by static light scattering (SLS), the tertiary amino end group has no detectable effect on the good solvent solution behavior. 1 Thus it is possible to characterize the polymer prior to association. (ii) Association is caused by adding the low molecular weight dinitrophenol compound I.…”

“…The number of unimers in the ring fraction could be estimated by the Jacobson-Stockmayer approach 19,20 after extending this theory to incorporate excluded volume effects. 1 The present paper considers the properties of the associates as observed by dynamic light scattering (DLS). Since the coupling of the chains is reversible, the junctions between the polymers are not permanent but open and close again according to the equilibrium process.…”