Synthetic and Physicochemical Aspects of Advanced Stimuli‐Responsive Polymers

Abstract

Although the technological and scientific importance of functional polymers has been well established over the last few decades, currently much attention has been focused on stimuli-responsive polymers. This group of materials is of particular interest owing to their ability to respond to internal and/or external chemicophysical stimuli that is often manifested by the large macroscopic responses [1]. Stimuli-responsive polymers are also referred to as smart, sensitive, or intelligent polymers [2, 3], just to name a few. These terms are loosely used under the same stimuli-responsiveness umbrella attributed to selective polymer segments or the entire polymer backbones that exhibit stimuli-responsive characteristics. Notwithstanding the scientific challenges of designing stimuli-responsive polymers, the main technological interest is in the numerous applications ranging from reactive surfaces [4] to drug-delivery and separation systems [5], or from chemomechanical actuators [6] to other applications that have been extensively explored [7, 8]. In contrast to traditional polymers, in order to incorporate responsive components, it is necessary to copolymerize responsive blocks into a polymer or copolymer backbone [8]. For this reason, the preparation of well-defined block copolymers with different architectures is essential: for example, grafting amphiphilic blocks to a hydrophobic polymer backbone [9]. Using living anionic [10] and cationic polymerizations [11] as well as controlled radical polymerizations (CRPs) techniques [12], wide ranges of block copolymers were synthesized. However, the development of the CRP based on the concept of reversible chain termination minimizes the disadvantage of the free-radical polymerization, thus permitting the synthesis of well-defined block copolymer structures [13]. The growing demand for well-defined and functional soft materials in a nanoscale range has led to a significant increase of procedures that combine architectural control with the flexibility of incorporating functional groups. In view of these considerations, there has been a significant quest for elucidating a variety of controlled polymerization strategies, which resulted in nitroxide-mediated radical polymerization (NMRP) [14–16], atom transfer