Characterization of Self-Association in Water of Polycations Hydrophobically Modified with Hydrocarbon and Siloxane Chains

Terpolymers of quaternized N -( N ‘, N ‘-dimethylaminopropyl)acrylamide (DMAPAA), N -dodecylmethacrylamide (C 12 MAm), and a methacrylate substituted with a poly(dimethylsiloxane) chain of a degree of polymerization of 29 (Si 29 MA), Q/C 12 ( x )/Si 29 ( y ), were synthesized by free radical terpolymerization. The self-association properties of these terpolymers were investigated in 0.1 M NaCl aqueous solutions in comparison with those of copolymers of quaternized DMAPAA with C 12 MAm (Q/C 12 ( x )) or with Si 29 MA (Q/Si 29 ( y )). In the terpolymers, the C 12 MAm contents ( f C 12 (i.e., x )) and Si 29 MA contents ( f Si 29 (i.e., y )) range from 3.6 to 26 and from 2.8 to 3.3 mol %, respectively, while in the Q/C 12 ( x ) and Q/Si 29 ( y ) reference copolymers, f C 12 and f Si 29 range from 7.4 to 31 and from 0.47 to 2.4 mol %, respectively. The following conclusions were drawn from experimental data by quasi-elastic light scattering, fluorescence, and 1 H NMR (two-dimensional nuclear Overhauser enhancement spectroscopy and spin−lattice relaxation times) studies: The Q/C 12 ( x )/Si 29 ( y ) terpolymers have a strong tendency for interchain association compared with the reference copolymers of Q/Si 29 ( y ) and Q/C 12 ( x ) when f C 12 ≥ 19 mol %. Aggregates of the Si 29 chains are “kinetically frozen”, whereas those of the C 12 chains are in a dynamic equilibrium. The C 12 and Si 29 chains in Q/C 12 ( x )/Si 29 ( y ) associate together to form mixed microdomains, and the trimethylammonium residues in the quaternized DMAPAA unit are partially incorporated into the mixed microdomain. On the basis of the experimental data, a conceptual model for aggregates formed from Q/C 12 ( x )/Si 29 ( y ) was proposed.