Synthesis of Environmentally Responsive Polymers by Atom Transfer Radical Polymerization: Generation of Reversible Hydrophilic and Hydrophobic Surfaces

Vikas Mittal

doi:10.3390/polym2020040

Abstract

Environmentally responsive poly(N-isopropylacrylamide) brushes were grafted from the surface of polymer particles or flat surfaces in order to generate reversible hydrophilic and hydrophobic surfaces. The use of atom transfer radical polymerization was demonstrated for the grafting of polymer brushes as it allows efficient control on the amount of grafted polymer. The polymer particles were generated with or without surfactant in the emulsion polymerization and their surface could be modified with the atom transfer radical polymerization (ATRP) initiator. The uniform functionalization of the surface with ATRP initiator was responsible for the uniform grafting of polymer brushes. The grafted brushes responded reversibly with changes in temperature indicating that the reversible responsive behavior could be translated to the particle surfaces. The particles were observed to adsorb and desorb protein and virus molecules by changing the temperatures below or higher than 32 °C. The initiator functionalized particles could also be adsorbed on the flat surfaces. The adsorption process also required optimization of the heat treatment conditions to form a uniform layer of the particles on the substrate. The grafted polymer brushes also responded to the changes in temperatures similar to the spherical particles studied through water droplets placed on the flat substrates.

Highlights

Surface properties of polymer particles or flat surfaces have been one of the most important contributors to their application, especially when the application involves the interaction of these surfaces with foreign media or entities
Generation of environmentally reversible behavior on the surface can lead to a number of exciting applications of both spherical as well as flat substrates
In order to control the properties of the surfaces efficiently, it is important to control the surface functionalization processes, first with atom transfer radical polymerization (ATRP) initiator and subsequently with PNIPAAM polymer brushes

Summary

Introduction

Surface properties of polymer particles or flat surfaces have been one of the most important contributors to their application, especially when the application involves the interaction of these surfaces with foreign media or entities. These functionalized surfaces represent a novel class of materials, which at the forefront of technology can lead to revolutionary changes in conventional processes In one such approach, environmentally responsive character has been generated on the surfaces. Environmentally responsive character has been generated on the surfaces Generation of this property on the surface of the materials leads to functionalized materials in which their nature e.g., hydrophobicity or hydrophilicity can be finely controlled by environmental stimulants like temperature, salt, pH, etc. Owing to the uncontrolled nature of the process which is generally achieved by non-living conventional free radical polymerization Another important and extensively studied approach is the grafting of polymer chains ’from’ the surface. Crosslinked polystyrene particles containing a thin shell of ATRP initiator on the surface were prepared using emulsion polymerization reactions (with and without the use of surfactant) and were subsequently used for the grafting of environmentally responsible PNIPAAM brushes

Materials

Electron Microscopy

Results and Discussion

Conclusions