Thermo-responsive polymers block copolymer

AUB Aubrecht, K.B. and Grabbs, R.B., Synthesis and characterization of thermo-responsive amphiphilic block copolymers incorporating a poly(ethylene oxide-xtoi-propylene oxide) block, J. Polym. Sci. Part A Polym. Chem., 43, 5156, 2005. 

Figure 1.6 Micelles generated by different types of thermo-responsive polymers in aqneous solutions. Block copolymers with hydrophobic blocks flanked by hydrophUic blocks.

VER Verdonek, B., Gohy, J.-F., Khousakoun, E., Jerome, R., and DuPrez, F., Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers). Polymer, 46, 9899, 2005. 

HIR Hirao, A., Inushima, R., Nakayama, T., Watanabe, T., Yoo, H.-S., Ishizone, T., Sugiyama, K., Kakuchi, T., Carlotti, S., and Deffieux, A., Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization, Eur. Polym. J., 47, 713, 2011. 

The di-block copolymers of hydrophobic-hydrophiUc PLGA-PEG also showed thermo-responsive behavior with sol-to-gel transition on increase in temperature (Choi et al., 1999). These polymers formed micelles, with a core of hydrophobic PLGA and an outer shell composed of hydrophilic PEG blocks. There is formation of bridged micelles due to interactions between PEG chains of adjacent micelles. The bridge density increases with increase in temperature, leading to aggregation and gelation. 

The di-block system of PLLA-PEG/PDLA-PEG enantiomers also showed thermo-responsive sol-gel transition. However, the solution of individual polymers does not show any gelation with temperature variation. In an aqueous solution, individual copolymers of PLLA-PEG or PDL A-PEG form micelles with a core of PLLA/PDLA and a shell of PEG chains on mixing with each other, these lead to hexagonal crystal formation of polymer chains and gelation at room temperature. With a rise in temperature, hydrophobic interactions increase, which enhances micellar aggregation. These polymers exhibit irreversible gel-to-sol conversion at 75 °C. At higher temperatures... 

Incorporating a temperature-responsive polymer structure in block copolymer architectures provides control over the solubility of a part of the copolymer structure. As such, a double hydrophilic block copolymer consisting of a permanently hydrophilic block and a LCST polymer block is converted into an amphiphilic block copolymer when the solution is heated above the LCST (Figure 22.3). This phenomenon has intrigued polymer scientists and the temperature-induced self-assembly of a large variety of different double hydrophilic thermo-responsive block copolymers into micellar structures has been extensively studied. These results have been captured in a large number of review articles and will not be further addressed here (Gil. and Hudson, 2004 Dimitrova et al., 2007 McCormick et al, 2008 Wei et al, 2009 Rodriguez-Hernandez et al, 2005 Smith et al, 2010). 

Figure 22.5 Schematic representation of modulating protein activity by conjugation with a thermo-responsive homopolymer (top) or block copolymer (bottom). (Reprinted from Progress in Polymer Science, 32, A.S. Hoffman and P.S. Stayton, Conjugates of stimuli-responsive polymers and proteins, 922-932, 2007, with permission from Elsevier.)...

Thermo-responsive polymeric micelles can be used to target adriamycin at the tumoral site. In particular, block copolymers containing hydrophobic polymers, such as poly(butyl methacrylate) (PBMA) and end-functionalized PNIPAAm [49-51], forming a micellar structure in aqueous solution below the transition temperature of PNIPAAm, act as an inert material in the hydrated form. Upon 32 °C, the polymeric chains became hydrophobic due to their dehydration and aggregation and precipitation occur. The cores of micelles then acted as a reservoir for the hydrophobic drug adriamycin. 

Plutonic analogs based on block copolymers of poly(pro-pylene oxide) and PEEP (PEEP- 7-PPO-l7-PEEP) (4) have been synthesized by ROP of EEP using commercially available PPO as the macroinitiator and Sn(Oct)2 as the catalyst. Interestingly, the aqueous solution of the polymers can form a thermo-responsive hydrogel, which can be used for sustained drug release in biomedical applications. ... 

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