Tuning the Cloud-Point and Flocculation Temperature
of Poly(2-(diethylamino)ethyl methacrylate)-Based Nanoparticles via
a Postpolymerization Betainization Approach
posted on 2021-07-08, 13:08authored byMatthieu
P. J. Miclotte, Stefan B. Lawrenson, Spyridon Varlas, Bilal Rashid, Emma Chapman, Rachel K. O’Reilly
The ability to tune
the behavior of temperature-responsive polymers
and self-assembled nanostructures has attracted significant interest
in recent years, particularly in regard to their use in biotechnological
applications. Herein, well-defined poly(2-(diethylamino)ethyl methacrylate)
(PDEAEMA)-based core–shell particles were prepared by RAFT-mediated
emulsion polymerization, which displayed a lower-critical solution
temperature (LCST) phase transition in aqueous media. The tertiary
amine groups of PDEAEMA units were then utilized as functional handles
to modify the core-forming block chemistry via a postpolymerization
betainization approach for tuning both the cloud-point temperature
(TCP) and flocculation temperature (TCFT) of these particles. In particular, four
different sulfonate salts were explored aiming to investigate the
effect of the carbon chain length and the presence of hydroxyl functionalities
alongside the carbon spacer on the particle’s thermoresponsiveness.
In all cases, it was possible to regulate both TCP and TCFT of these nanoparticles
upon varying the degree of betainization. Although TCP was found to be dependent on the type of betainization
reagent utilized, it only significantly increased for particles betainized
using sodium 3-chloro-2-hydroxy-1-propanesulfonate, while varying
the aliphatic chain length of the sulfobetaine only provided limited
temperature variation. In comparison, the onset of flocculation for
betainized particles varied over a much broader temperature range
when varying the degree of betainization with no real correlation
identified between TCFT and the sulfobetaine
structure. Moreover, experimental results were shown to partially
correlate to computational oligomer hydrophobicity calculations. Overall,
the innovative postpolymerization betainization approach utilizing
various sulfonate salts reported herein provides a straightforward
methodology for modifying the thermoresponsive behavior of soft polymeric
particles with potential applications in drug delivery, sensing, and
oil/lubricant viscosity modification.