Synthesis, micellization, and thermally-induced macroscopic micelle aggregation of poly(vinyl chloride)-g-poly(N-isopropylacrylamide) amphiphilic copolymer

• Published in: RSC advances 2015-01, Vol.5 (115), p.94582-9459
• Main Authors: Liu, Keyong, Pan, Pengju, Bao, Yongzhong
• Format: Article
• Language: English
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c5ra16726d

A series of poly(vinyl chloride)- g -poly( N -isopropylacrylamide) (PVC- g -PNIPAM) amphiphilic copolymers with different graft lengths and densities were synthesized via the single electron transfer-living radical polymerization (SET-LRP) of NIPAM using poly(vinyl chloride- co -allyl α-bromoisobutyrate) as macroinitiator. The living nature of SET-LRP grafting copolymerization was verified by the kinetics study and narrow molecular weight distribution of PNIPAM grafts. The chemical structure, micellisation, and thermally-induced multistep aggregation of PVC- g -PNIPAMs were investigated. PVC- g -PNIPAMs form micelles comprised of a PVC core and PNIPAM corona in water at room temperature. These micelles are thermoresponsive and show a lower critical solution temperature (LCST). The micelle size and LCST of PVC- g -PNIPAM increase with increasing the graft density and length of PNIPAM. PVC- g -PNIPAM exhibits a very unique aggregation behavior above its LCST and forms a three-dimensional macroscopic aggregate with a well-defined and tunable shape at an extremely low concentration (∼0.1 wt%). The aggregate shrinks to a more compact structure with the further increase of temperature. Higher copolymer concentration, longer graft length, and lower graft density are favorable for the macroscopic micelle aggregation of PVC- g -PNIPAMs. A self-standing and superporous PVC- g -PNIPAM material having an extremely low density of ∼0.01 g cm −3 and a high porosity of >99% is attained after freeze-drying the micelle aggregate. PVC- g -PNIPAM amphiphilic copolymers with controlled graft lengths and densities are synthesized, which form unique macroscopic aggregates with well-defined 3D shapes in dilute aqueous solution above the LCST.