The next step in precipitation polymerization of N-isopropylacrylamide: particle number density control by monochain globule surface charge modulation

Abstract

Many applications of poly( N-isopropylacrylamide) microgels necessitate robust control over particle size.

Abstract

Many applications of poly( N-isopropylacrylamide) microgels necessitate robust control over particle size. Here we derive a scaling law for the particle size in precipitation polymerization of N-isopropylacrylamide. The average particle volume in the collapsed state is proportional to the monomer ([M]) and initiator ([I]) concentration according to V̄ _p ∝ [M] ^5/3[I] ^−4/3. The derived power law agrees well with the experimentally observed particle volume. The derivation assumes the particle number density to depend on the initiation rate and the surface charge density of monochain globules generated during the nucleation phase. The model also qualitatively predicts the experimentally observed particle size trends when reaction temperature or chain transfer agent concentrations are varied. Reaction rate measurements show that the reaction proceeds initially as radical solution polymerization, therefore justifying the use of Flory–Schulz approximation for the globule surface charge density in this work.