Phase Separation of Aqueous Poly(diisopropylaminoethyl methacrylate) upon Heating.

Linda Salminen,Vladimir Aseyev,Heikki Tenhu,Erno Karjalainen

doi:10.1021/acs.langmuir.1c02224

Abstract

Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH- and thermally responsive water-soluble polymer. This study deepens the understanding of its phase separation behavior upon heating. Phase separation upon heating was investigated in salt solutions of varying pH and ionic strength. The effect of the counterion on the phase transition upon heating is clearly demonstrated for chloride-, phosphate-, and citrate-anions. Phase separation did not occur in pure water. The buffer solutions exhibited similar cloud points, but phase separation occurred in different pH ranges and with different mechanisms. The solution behavior of a block copolymer comprising poly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA was investigated. Since the PDMAEMA and PDPA blocks phase separate within different pH- and temperature ranges, the block copolymer forms micelle-like structures at high temperature or pH.

Highlights

Stimuli-responsive polymers have been the focus of many studies due to their potential applications in, e.g., drug delivery[1−5] and actuators.[6−10] Of all potential triggers, temperature and pH are of special interest
Responsive polymers are generally divided into those with the lower critical solution temperature (LCST; phase separation upon heating) behavior and those with the upper critical solution temperature (UCST; phase separation upon cooling) behavior, variations exist within the two classes.[11]
The polymers, PDPA, poly(dimethylaminoethyl methacrylate) (PDMAEMA), and PDMAEMA-b-PDPA, were synthesized with the reversible addition−fragmentation chain transfer (RAFT) polymerization method.46 4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid was used as the chain transfer agent (CTA) and azobis(isobutyronitrile) as the initiator (I)

Summary

Introduction

Stimuli-responsive polymers have been the focus of many studies due to their potential applications in, e.g., drug delivery[1−5] and actuators.[6−10] Of all potential triggers, temperature and pH are of special interest. Responsive polymers are generally divided into those with the lower critical solution temperature (LCST; phase separation upon heating) behavior and those with the upper critical solution temperature (UCST; phase separation upon cooling) behavior, variations exist within the two classes.[11]. The polymer is in a coiled form and the surrounding water molecules are in an energetically favored but ordered state. The entropic contribution overrules the energetic advantages of the ordered state and the interactions between water molecules and the polymer weaken. The hydrophobic backbone of the polymer starts to interact more strongly with other nonpolar moieties, forming a macroscopic precipitate.[12−17]

Methods

Results

Conclusion