Stimuli-responsive copolymers

Zhang, Y., Yarin, Ai., 2009. Stimuli-responsive copolymers of n-isopropyl acrylamide with enhanced longevity in water for micro- and nanofluidics, drug delivery and nonwoven applications. Journals of Materials Chemistry 19, 4732—4739. 

Kelley, E. G., Albert, J. N. L., Sullivan, M. O., Epps, 1.1.1. T. H. (2013). Stimuli-responsive copolymer solution and surface assemblies for biomedical applications. Chemical Society Reviews, 42, 7057-7071. 

In the sections that follow, amphiphilic block copolymers prepared via CRP techniques will be discussed. Representative examples of reports from the literature are briefly described to demonstrate solution properties and applications of stimuli-responsive copolymers. 

De las Heras Alercon, C., Pennadam, S., and Alexander, C. (2005) Stimuli responsive copolymers far biomedical applications. Chemical Society Reviews, 34,276-285. 

Christo B. Tsvetanov is full professor of polymer science at the Institute of Polymers, Bulgarian Academy of Sciences and head of the Scientific Council of the Institute of Polymers. A major focus of his research concerns controlled polymerization methods, water-soluble polymers and hydrogels, stimuli-responsive copolymers, and their self-assembly to polymeric nanopartides. He is well known for his contributions to the area of anionic coordination polymerization ofoxiraneandthe role of donor and acceptor additives on the mechanism of anionic polymerization. Since 2004, he has been a corresponding member of the Bulgarian Academy of Sdences. 

Deen, G. and Gan, L. 2008. Study of microemulsion polymerization conditions on the preparation of stimuli responsive copolymer nanogels of N-acryloyl-A/ -methyl piperazine and methyl methacrylate. J. Disper. Sci. Technol. 29 431-435. 

In 2000, the first example of ELP diblock copolymers for reversible stimulus-responsive self-assembly of nanoparticles was reported and their potential use in controlled delivery and release was suggested [87]. Later, these type of diblock copolypeptides were also covalently crossUnked through disulfide bond formation after self-assembly into micellar nanoparticles. In addition, the encapsulation of l-anilinonaphthalene-8-sulfonic acid, a hydrophobic fluorescent dye that fluoresces in hydrophobic enviromnent, was used to investigate the capacity of the micelle for hydrophobic drugs [88]. Fujita et al. replaced the hydrophilic ELP block by a polyaspartic acid chain (D ). They created a set of block copolymers with varying... 

ELP-based triblock copolypeptides have also been used to produce stimulus-responsive micelles, and Chaikof and coworkers envisioned the possible application of these micelles as controlled drug delivery vehicles. These amphiphilic triblock copolymers were constructed from two identical hydrophobic ELP endblocks and a hydrophilic ELP midblock. Below the transition temperature, loose and monodispersed micelles were formed that reversibly contracted upon heating, leading to more compact micelles with a reduced size [90]. 

Selected examples of block copolymer micelles in both aqueous and organic media will then be presented in Sects. 3 and 4. Section 4.3 emphasizes stimulus-responsive micellar systems from double-hydrophilic block copolymers. Prediction of the dimensional characteristic features of block copolymer micelles and how it varies with the composition of the copolymers will be shortly outlined in Sect. 5, with a consideration of both the theoretical and experimental approaches. Tuning of micellar morphology and triggering transitions between different morphologies will then be discussed in Sect. 6. 

Stimulus-responsive ABC triblock micelles were also investigated by Patrickios et al. for copolymers containing insoluble PEVE blocks, thermore-sponsive PMVE midblocks, and water-soluble PMTEGVE outer blocks with varying block sequences [277]. While in aqueous solutions only unimers were found, and the addition of salt led to aggregates. 

Li C, Madsen J, Armes SP, Lewis AL (2006) A new class of biochemically degradable, stimulus-responsive triblock copolymer gelators. Angew Chem Int Ed 45 3510-3513... 

Eloi J-C, Rider DA, Cambridge G, Whittell GR, Winnik MA, Manners I (2011) Stimulus-responsive self-assembly reversible, redox-controlled micellization of polyferrocenylsilane diblock copolymers. J Am Chem Soc 133 8903-8913... 

Due to the relative ease of control, temperature is one of the most widely used external stimuli for the synthesis of stimulus-responsive bmshes. In this case, thermoresponsive polymer bmshes from poly(N-isopropylacrylamide) (PNIPAM) are the most intensively studied responsive bmshes that display a lower critical solution temperature (LOST) in a suitable solvent. Below the critical point, the polymer chains interact preferentially with the solvent and adopt a swollen, extended conformation. Above the critical point, the polymer chains collapse as they become more solvophobic. Jayachandran et reported the synthesis of PNIPAM homopolymer and block copolymer brushes on the surface of latex particles by aqueous ATRP. Urey demonstrated that PNIPAM brushes were sensitive to temperature and salt concentration. Zhu et synthesized Au-NPs stabilized with thiol-terminated PNIPAM via the grafting to approach. These thermosensitive Au-NPs exhibit a sharp, reversible, dear opaque transition in solution between 25 and 30 °C. Shan et al. prepared PNIPAM-coated Au-NPs using both grafting to and graft from approaches. Lv et al. prepared dual-sensitive polymer by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from trithiocarbonate groups linked to dextran and sucdnoylation of dextran after polymerization. Such dextran-based dual-sensitive polymer is employed to endow Au-NPs with stability and pH and temperature sensitivity. 

Besides the heavily studied pH-, temperature-, redox-, and light-responsive nanoassemblies, some other stimulus-responsive nanoassemblies such as magnetic field and ultrasound-responsive systems have also been explored and are reviewed." In addition, many multiresponsive nanoassemblies have been explored to achieve multiple functionalities. For example, many nanoassemblies dually responsive to both pH and temperature have been synthesized using copolymers containing pH- and temperature-responsive components. 

Q. Yuan, R. Venkatasubramanian, S. Hein, and R. Misra, A stimulus-responsive magnetic nanoparticle drug carrier Magnetite encapsulated by chitosan-grafted-copolymer, Acta Biomaterialia, 4 (4), 1024-1037, 2008. 

Y-shaped double-hydrophilic block copolymers, with a poly(EO-co-PO) sequence and two blocks of various hydrophilic methacryKc polymers, were synthesized by an elaborated ATRP technique by Armes and co-workers [239]. pH and thermal stimulus-responsive micelles could be obtained by these authors. 

Cai, Y., Tang, Y. and Armes, S.P. (2004) Direct synthesis and stimulus-responsive micellization of Y-shaped hydrophilic block copolymers. Macromolecules, 37,972S-97 i7. 

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