Author/Authors :
Cao, Zhifeng Chinese Academy of Sciences - Chengdu Institute of Organic Chemistry, China , Cao, Zhifeng The Graduate School of the Chinese Academy of Sciences, China , Jin, Yong Chengdu Institute of Organic Chemistry - Chinese Academy of Sciences, China , Zhang, Biao Chinese Academy of Sciences - Chengdu Institute of Organic Chemistry, China , Zhang, Biao The Graduate School of the Chinese Academy of Sciences, China , Miao, Qing Chinese Academy of Sciences - Chengdu Institute of Organic Chemistry, China , Ma, Chunyan Chinese Academy of Sciences - Chengdu Institute of Organic Chemistry, China , Ma, Chunyan The Graduate School of the Chinese Academy of Sciences, China
Abstract :
Asort of novel stimuli-responsive water-soluble polymer-biomolecule conjugate,casein-g-poly(N-isopropylacrylamide) (PNIPAAm), was synthesized by freeradical graft copolymerization of N-isopropylacrylamide (NIPAAm) from casein.The graft polymerization was induced by a small amount of t-butyl hydroperoxide(TBHP) in water under general condition. Free radicals on the amino groups of caseinand t-butoxy radicals were generated concurrently, which initiated the graft copolymerizationand homopolymerization of NIPAAm, respectively. The graft copolymers andhomopolymer of NIPAAm were isolated and the chemical structure of the graftcopolymer was characterized by Fourier transform infrared spectroscopy (FTIR) anddifferential scanning calorimetry (DSC). The phase-transition behaviours of the graftcopolymers in aqueous solutions were investigated by the turbidity measurements.Casein-g-PNIPAAm did not precipitate at around the isoelectric pH (IP) of casein at25°C and the lowest transmittance was changed as the pH changed. These resultssuggest that the PNIPAAm offers a greater hindrance to the aggregation of casein at25°C and the casein offers a hindrance to the aggregation of PNIPAAm at thetemperature of lower critical solution temperature (LCST) and at the pH apart from theIP. In addition, casein almost has no effect on LCST. The graft copolymer is stimulisensitivewith respect to both temperature and pH in aqueous solutions and thepolymeric micelles with different structures can be obtained simply by changing theenvironmental conditions. It associates into core-shell micelles in aqueous solution withcollapsed PNIPAAm as a core as well as inverse core-hair micelles with expandedcasein as a core on changing temperature or pH, indicated by transmission electronmicroscopy (TEM). With the casein being a nature protein and the graft copolymers aremetal ion-free therefore, they may have great potential for biomedical and biomaterialapplications.
Keywords :
biopolymers , conjugated polymers , core , shell polymers , stimuli , sensitive polymers , water , soluble polymers.
