Stabilization capacity of PNIPAM microgels as particulate stabilizer in dispersion polymerization

The Synthesis of Narrowly Dispersed Poly(ε-caprolactone) Microspheres by Dispersion Polymerization Using a Homopolymer Poly(dodecyl acrylate) as the Stabilizer

Using dodecyl acrylate as a raw material and 2-Cyanoprop-2-yl-dithiobenzoate as a chain transfer agent, poly(dodecyl acrylate) is synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Using poly(dodecyl acrylate) as stabilizers, narrowly dispersed poly(ε-caprolactone) microspheres with particle sizes ranging from 0.5 to 1.5 μm are successfully synthesized by ring-opening dispersion polymerization. The effects of the molecular weight of poly(dodecyl acrylate), the volume proportion of mixed solvent (i.e., 1,4-dioxane/heptane), and the reaction temperature on the particle size and its distribution are investigated. With careful control of the synthesis condition, microspheres can be obtained with a particle size distribution of 1.09 (Dw/Dn). The average particle size of poly(ε-caprolactone) microspheres decreased with the increase in the molecular weight of poly(dodecyl acrylate) and increased with the increase in the relative content of 1,4-dioxane. The uniformity of microspheres decreased with the increase in the polymerization temperature.

Effect of heterogeneous and homogeneous polymerisation on the structure of pNIPAm nanogels

The choice of the polymerisation temperature and initiator in the synthesis of poly(N-isopropylacrylamide)-based nanogels can significantly influence their structure, morphology and thermoresponsive properties.

Precise regulation of particle size of poly(N-isopropylacrylamide) microgels: Measuring chain dimensions with a "molecular ruler"

HYPOTHESIS

Poly(N-isopropylacrylamide) microgels are used extensively in the design of drug carriers, surfaces for control of cell adhesion, and optical devices. Particle size is a key factor and has a significant influence in many areas.

EXPERIMENTS

In this work, precise control of the particle size of poly(N-isopropylacrylamide) microgels was achieved by controlling the separation distance of the poly(N-isopropylacrylamide) chains. Dibromoalkanes of different size were used as an adjustable "molecular ruler" to measure molecular dimensions in poly(N-isopropylacrylamide) nanoaggregates at the critical crosslinking temperature.

FINDINGS

We find that the chain separation distance decreases as the temperature increases with a sharp decrease over the 55-to-65 °C interval. Based on the observed relationships between chain separation and crosslinker, the particle size of poly(N-isopropylacrylamide) microgels can be regulated by changing the length of the "molecular ruler" (crosslinker) at the same temperature. Furthermore, for partly crosslinked poly(N-isopropylacrylamide) microgels that contain free crosslinkable sites, the particle size can be reduced still more by further crosslinking ("re-crosslinking") with crosslinkers of different size. It is shown that the particle size can be regulated by adjusting the length of "molecular ruler" and the degree of crosslinking. This work provides a "molecular level" method for precise control of poly(N-isopropylacrylamide) microgel particle size.