Synthesis And Characterization Of Amphiphilic Thermosensitive Poly(N-vinylcaprolactam)/Poly Ester Block Copolymer

Poly N-vinyl caprolactam (PNVCL) is a kind of thermo-responsive polymer with Lower Critical Solution Temperature(LCST). Its LCST is right at the physiological temperature range (30-40℃), which makes it enjoy an extremely wide range of applications in biology, medicine, materials and daily chemicals. A series of thermo-responsive amphiphilic copolymers were synthesized by click chemistry.First, carboxyl-terminatedpoly (N-vinylcaprolactam) (PNVCL-COOH) were synthesized via free radical chaintransfer polymerization of N-vinylcaprolactam (NVCL) with azobis isobutyronitrile as the initiator, thioglycolic acid as the chaintransfer agent. And the alkynyl-terminatedpoly (N-vinylcaprolactam) (PNVCL-≡) were synthesized by esterification with 2-methyl-3-butyn-2-ol as the Smallmolecular alcohol; the azido-terminated polycaprolactone (N3-PCL) were synthesized by ring-opening polymerization of caprolactone with the stannous octoate as the catalyst,2-azidoethanol(Azea) as the initiator. And then the final poly(N-vinylcaprolactam)-block-polycaprolactone(PNVCL-b-PCL) were synthesized by click chemistry of alkynyl-terminated poly(N-vinylcaprolactam)(PNVCL-≡) and azido-terminated polycaprolactone(N3-PCL) with (+)-sodiumL-ascorbate(SA) and Copper Ⅱ sulfatepentahldrate as the catalyst. FT-IR,1H NMR and GPC were used to demonstrate the structure and their compositions which would be adjusted by alternation of the feeding ratio of initiator and monomer. The self-assembly behavior of these copolymers in aqueous solution was studied by fluorescence technique.The results showed that these copolymers could self-assemble into nano-micelles in water. The CMC of copolymer solution and the size of micelles reduced with the increasing of the proportion of hydrophobic parts. TEM images demonstrated the micelles are all spherical. On the other hand, the UV-vis measurement showed that these diblock copolymers exhibit a reproducible temperature-responsive behavior with a lower critical solution temperature (LCST) that is tunable by the block composition.Second, azido-terminated poly(D,L-lactide) (N3-PLA) were synthesized by ring-opening polymerization of D,L-lactide with the stannous octoate as the catalyst, 2-azidoethanol(Azea) as the initiator. The poly(N-vinylcaprolactam)-block-polylactide (PNVCL-b-PLA) were synthesized by click chemistry of alkynyl-terminated poly(N-vinylcaprolactam) (PNVCL-≡) and azido-terminated poly(D,L-lactide) (N3-PLA) with (+)-sodiumL-ascorbate (SA) and Copper Ⅱ sulfatepentahldrate as the catalyst. The self-assembly behavior of these copolymers in aqueous solution was studied by fluorescence technique.The results showed that these copolymers could self-assemble into nano-micelles in water. The CMC of copolymer solution and the size of micelles reduced with the increasing of the proportion of hydrophobic parts. TEM images demonstrated the micelles are all spherical. On the other hand, the UV-vis measurement showed that these diblock copolymers exhibit a reproducible temperature-responsive behavior with a lower critical solution temperature (LCST) that is tunable by the block composition.