Synthesis, characterization and application of dual thermo- and solvent-responsive double-hydrophilic diblock copolymers of N-acryloylmorpholine and N-isopropylacrylamide

Abstract

A series of double-hydrophilic diblock copolymers of N-acryloylmorpholine (NAMO) and N-isopropylacrylamide (NIPAm) with varying degree of polymerization were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. Structures and average molecular weights of these diblock copolymers were determined through 1H NMR spectra and SEC methods. Thermo-sensitivities and solvent-responsiveness of these copolymers were studied at varying temperatures in ethanol/water mixtures with different ethanol content. Beyond that, thermal behaviors during phase transitions were monitored by means of transmittance methods and DSC measurements, and the variation of aggregating structures in the interim was deduced basing on the results from DLS and TEM tests. Due to the cononsolvency effect of PNIPAm block along with the alcohol-insolubility of PNAMO block, thermo-responsive behaviors of copolymer chains would keep changing with the gradual addition of ethanol. Considering the thermo-responsive and the polar solvent-sensitive properties, we introduced the copolymers into a heavy oil/water mixing system, which possessed both changes of temperature and the attendance of polar groups. Tests results showed that the copolymer solutions did a quite good job on heavy oil viscosity reduction at the target temperature. The stimuli-response behavior of these copolymers endowed the polymer solution with the ability to interact with polar groups in heavy oil and form heavy oil/water emulsions, and made it possible to be used as a novel heavy oil viscosity reducer.