Chain Terminal Group Leads to Distinct Thermoresponsive Behaviors of Linear PNIPAM and Polymer Analogs
Xiaolong Lang, Alexander D. Patrick, Boualem Hammouda, Michael J. A. Hore
Poly(alkyl acrylamides), most notable poly(N-isopropylacrylamide) (PNIPAM), are widely studied thermoresponsive polymers. Linear PNIPAM, poly(N-n-propylacrylamide) (PNnPAM) and poly(N-cyclopropylacrylamide) (PNCPAM) were synthesized via RAFT polymerization to obtain polymers with low dispersity and varying end groups. The polymers were studied with a combination of small-angle neutron scattering (SANS), turbidimetry measurements, and dissipative particle dynamics (DPD)simulations to determine the influence of terminal group and monomer structure on assembly and thermoresponsive behavior in solution. Large scale, fractal assemblies are observed below the critical temperature for polymers terminated with short hydrophobic groups, but for long hydrophobic terminal groups, polymers formed small micelles. The two cases give rise to two distinct thermoresponsive behaviors: the fractal assemblies display the traditional coil-to-globule behavior, whereas the corona of the micelles collapsed well below the critical temperature due to n-clustering, while the micelles remained in solution. The results indicate that, despite making up only a small fraction of the polymer, the terminal groups play a large role in both the conformation and assembly of PNIPAM and its analogs below the critical temperature, and hints at the possibility of new design strategies for thermoresponsive materials.
, Patrick, A.
, Hammouda, B.
and Hore, M.
Chain Terminal Group Leads to Distinct Thermoresponsive Behaviors of Linear PNIPAM and Polymer Analogs, Polymer, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925461
(Accessed June 4, 2023)