Temperature-responsive polymeric cross-linker

A cleavable, temperature-responsive polymeric cross-linker was utilized by Xu and cowoikers [111] to stabilize micelles from PEO-b-PAPMA-b-poly((Af,Af-diisopropylamino)ethyl methacrylate) triblock copolymer. The PNIPAm cross-linker contained activated ester end groups that were reacted with the primary amines on the PAPMA middle block. The trithiocarbonate moiety located at the middle of PNIPAm cross-linker could then be degraded by aminolysis to break the cross-links. Temperature-responsive micelles and vesicles from diblock and triblock copolymers were shell cross-linked via interpolyelectrolyte complexation [108, 112]. The cross-links formed by the electrostatic interactions of oppositely charged polyelectrolytes could be disrupted by the addition of SME. 

This chapter covers the preparation, characterization, and biomedical application of thermally sensitive particles. Thermosensitive hydrogel is prepared by precipitation polymerization of A-alkylacrylamide or A-alkylmethacrylamide as a principal water-soluble monomer, a water-soluble cross-linker (for instance, A-methylenebisacrylamide), and an initiator (such as Azobis-amidinopropane derivatives, potassium persulfate, or basically any charged initiator). The core-shell latexes are produced by a combination of emulsion and precipitation polymerization, such as the preparation of polystyrene core and poly(A-isopropylacrylamide) shell or encapsulation of coUoidal seed using alkylacrylamide derivatives. During the elaboration of such stimuli-responsive particles, various aspects should be considered (1) a water-soluble cross-linker is needed, (2) the polymerization temperature should be higher than the LCST of the corresponding linear polymer, and (3) the production of water-soluble polymer (which can be controlled by monitoring the polymerization conditions). The polymerization mechanism has been clearly discussed and well illustrated, but the nucleation step remains questionable and requires further work. 

---