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Characterization of stimuli‐sensitive polymers for biomedical applications
Author(s) -
Yoo Mi Kyong,
Seok Won Kyung,
Sung Yong Kiel
Publication year - 2004
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.200450316
Subject(s) - polyelectrolyte , comonomer , self healing hydrogels , lower critical solution temperature , cloud point , polymer chemistry , polymer , acrylic acid , copolymer , isoelectric point , materials science , cationic polymerization , titration , chemical engineering , chemistry , aqueous solution , organic chemistry , composite material , engineering , enzyme
Stimuli‐sensitive polymers were synthesized by copolymerizing varying ratios of N‐isopropyl acrylamide(NIPAAm) and acrylic acid(AAc). The influence of polyelectrolytes on the lower critical solution temperatures(LCSTs) of these temperature/pH sensitive polymers was investigated in the pH range of 2‐12. Polyelectrolyte complexes were prepared by mixing poly(NIPAAm‐ co ‐AAc) as anionic polyelectrolyte with poly(allyl amine)(PAA) or poly(L‐lysine)(PLL) as cationic polyelectrolytes, respectively. Back titration was performed to determine the pK a values of PAAc in poly(NIPAAm‐ co ‐AAc) and to study the effect of comonomer ionization on the cloud point temperature. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). The swelling ratio of poly(NIPAAm‐ co ‐AAc) hydrogels as a function of pH at various temperature was obtained by measuring the weight of the hydrogels in buffer solutions. The LCSTs of the poly(NIPAAm‐ co ‐AAc) were strongly affected by pH, polyelectrolyte solutes, AAc content, and charge density. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm/water in the copolymer was stronger than that of poly(allyl amine)(PAA). Indomethacin was loaded into these hydrogels, and controlled release of this molecule from the hydrogel was determined under various temperature and pH conditions using UV/Vis spectrophotometry.