Online, continuous monitoring of the sensitivity of the LCST of NIPAM-Am copolymers to discrete and broad composition distributions

The lower critical solution temperature (LCST) of NIPAM/Acrylamide copolymers was monitored during synthesis using second generation ACOMP (automatic continuous online monitoring of polymerization reactions) for a series of discrete starting compositions. A full sweep of NIPAM/Am compositions was subsequently obtained in a semi-batch feed of NIPAM into Am, allowing LCST behavior to be assessed over all compositions of the two copolymers. A separate Simultaneous Multiple Sample Light Scattering (SMSLS) instrument was used to assess compositional polydispersity via the broadening of the LCST temperature transition as compositional heterogeneity of samples increases. This was achieved by combining LCST data as a function of composition and added salt into a master equation. Extended period SMSLS monitoring of the aggregates formed when the LCST is reached showed they are reversible on the short time scale of hours, but are irreversible for homopolymer NIPAM with salt and for copolymers on the scale of days.