Synthesis and solution behaviors of star hydrophobically modified acrylamide copolymers

Star copolymers of acrylamide and N,N-dimethyl-N-vinyl­nonadecan-1-aminium chloride (C18DMAAC) were synthesized by photopolymerization in water. Solution behaviors of these star hydrophobically modified acrylamide copolymers (SHMPAMs) with different C18DMAAC contents and the linear hydrophobically modified acrylamide copolymers (LHMPAMs) were characterized. The increase in C18DMAAC content resulted in decreased intrinsic viscosity and increased the Huggins constant for SHMPAMs. Similar results were observed for LHMPAMs. With similar intrinsic viscosity and C18DMAAC content, the Huggins constant of SHMPAMs was much higher than that of LHMPAMs, which could be due to the fact that SHMPAMs had much stronger intramolecular interaction in dilute polymer solutions. In semi-dilute solutions, the apparent viscosity of SHMPAMs was increased with increasing C18DMAAC content, which was similar to that of LHMPAMs. However, SHMPAMs exhibited higher apparent viscosity than LHMPAMs because it had more arms and thus had more chances to form three-dimensional networks in semi-dilute solutions. In the flow-induced scission experiment, SHMPAMs exhibited superior shear stability in comparison with LHMPAMs. When the strain rate was ≈40,000 s-1, the reduction ratios of the apparent viscosities of the four SHMPAMs after the scission were approximately 80%. By contrast, when the strain rate was ≈20,000 s-1, the reduction ratio of the apparent viscosity of LHMPAM-0.40 had already reached around 80%.