N‐Isopropylacrylamide/2‐Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive Behavior

Abstract

Tri-arm star diblock copolymers, poly(2-hydroxyethyl methacrylate)-block-poly(N-isopropylacrylamide) [P-(HEMA-b-NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a twostep ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well-controlled polymerization of trifunctional macro-initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature-variable 1 H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I-(HEMA 40 -NIPAAm 320 ) 3 solutions developed into core-shell micelles with diameters of approximately 100 nm. I-(HEMA 40 -NIPAAm 320 ) 3 was used as a representative example to elucidate the mechanism underlying temperature-induced phase transition of copolymer solution. In this study we proposed a three-stage transition process: (1) separately dispersed micelles state at %17-22 8C; (2) aggregation and fusion of micelles at %22-29 8C; (3) sol-gel transition of PNIPAAm segments at %29-35 8C, and serious syneresis of shell layers.Molecular architecture of Poly(HEMA-b-NIPAAm).

Effect of Block Order of ABA‐ and BAB‐Type NIPAAm/HEMA Triblock Copolymers on Thermoresponsive Behavior of Solutions

“…It is evident that the semilogarithmic plot of the monomer concentration versus polymerization time remains linear up to about 96% conversion, which indicates a 'living character'. After 40 min, the conversion [25,28] The FT-IR spectra also confirmed the formation of the copolymers with appearance of the key bands at 3 450 (OH) and 1 730 cm À1 (C --O) attributable to HEMA units, and at 1 650, 1 538 cm À1 (-CO-NH-) assigned to NIPAAm units. [25,29] It is noted that the above NMR spectra evidenced the presence of traces of residual monomers in copolymer samples, which might influence the measurement of molecular weight and its distribution.…”

“…[25] The micellization of triblock copolymer solutions was examined by transmission electron microscopy (TEM) performed on a JEOL JEM-100CXII instrument. The aqueous solution of copolymer with a concentration above the CMC was placed on a carboncoated grid at 25 8C, and stained by phosphate-tungstic acid solution (1.5%).…”

“…In our previous work, [25] we investigated the thermoresponsive behavior of poly(2-hydroxyethyl methacrylate)-block-poly (N-isopropylacrylamide ) (PHEMA-b-PNIPAAm ) in aqueous solution and a proposed three-stage transition process: 1) dispersed micelles, 2) aggregation of micelles, and 3) sol-gel transition of PNIPAAm segments and serious syneresis of shell layers. In this study, ABA and BAB triblock copolymers based on HEMA (B block) and NIPAAm (A block) were prepared.…”

Temperature-responsive self-assembly of star block copolymers with poly(ionic liquid) segments

“…In particular, interest in the design and synthesis of star block copolymers with stimuli-responsive segments has increased because the chain architecture (topology) of block copolymers affects their self-assembling behavior and stimuli-responsive properties. [29][30][31][32][33][34][35] Herein, we report the controlled synthesis of novel star block copolymers with poly(N-vinylimidazolium salt) as a poly(ionic liquid) segment and poly(NIPAAm) as a thermoresponsive segment by RAFT polymerization. In addition to the comonomer composition and chain length of each segment, the branched structure and location of the thermoresponsive segment affected the stimuliresponsive properties and assembled structure of the material.…”

Environmental-Sensitive Hyperbranched Polymers as Drug Carriers

“…Typical LCST polymers are based on N -isopropylacrylamide (NIPAM) [33,34], N ,N -diethylacrylamide (DEAM) [35], methylvinylether (MVE) [36] or N -vinylcaprolactam (NVCl) [37] as monomers. A typical UCST system is based on a combination of acrylamide (AAm) [38] and acrylic acid (AAc) [39].…”