Fluorescence Spectroscopic Study of the Aggregation Behavior of Non-Cross-Linked and Cross-Linked Poly(alkylmethyldiallylammonium bromides) Having Decyl, Octyl, and Hexyl Side Chains in Aqueous Solution

Abstract

The conformational state of a series of non-cross-linked and cross-linked poly(alkylmethyldiallylammonium bromides) bearing decyl, octyl, and hexyl side chains ((CL)-CopolC1-10, (CL)-CopolC1-8, and (CL)-CopolC1-6, respectively) in aqueous solutions were investigated by fluorescence spectroscopy using pyrene as a probe. Photophysical studies show that the conformational transition of random coil non-cross-linked and cross-linked copolymers to compact coils is strongly side chain length dependent. (CL)CopolC1-10 with sufficient n-decyl side chains was found to form hydrophobic microdomains in compact coil conformations in aqueous solution. Much less efficient intramolecular micellization was observed for (CL)-CopolC1-8 in a similar concentration range. No conformational transition to compact coils was found in the case of(CL)-CopolC1-6 as indicated by the absence of pyrene binding to the macromolecule. The presence of sodium bromide facilitates the formation of compact coil conformations for (CL)-CopolC1-10 in aqueous solution. There are significant effects of side chain length and alkyl group content on the critical aggregation concentration(cac). The cac for (CL)-CopolC1-10 in aqueous solution decreased strongly with increasing total hydrophobicity of the n-decyl side chains in the polysoaps. The cross-linked copolymers CL-CopolC1-10 exhibited lower cac's than the corresponding non-cross-linked copolymer analogues. A minimum in the cac for (CL)-CopolC1-10 in aqueous solution was found at about 0.20%(w/w) cross-linking agent.