Engineering a sharp physiological transition state for poly(n‐isopropylacrylamide) through structural control

Abstract

Poly(N-isopropylacrylamide) (pNIPAAm), a wellstudied, biologically inert polymer that undergoes a sharp aqueous thermal transition at 32 C, has been a subject of widespread interest for possible biological applications. A major hindrance to its successful application is due to the difficulty of maintaining a sharp transition when the polymer is modified for a physiological transition temperature, especially in isotonic solutions. Current copolymer blends raise the transition temperature but also make the transition significantly broader. We have combined the use of reversible addition-fragmentation chain transfer (RAFT) polymerization with tacticity control to synthesize well-defined pNIPAAm that demonstrates sharp transitions under physiological conditions. By selecting a RAFT agent with appropriate end groups, controlling molecular weight, and increasing the racemo diad content, we were able to increase the thermal transition temperature of pure pNIPAAm to a sharp transition at 37.6 C under isotonic conditions. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: [976][977][978][979][980][981][982][983][984][985] 2012

Living Radical Polymerization by the RAFT Process – A Third Update

“…The tacticity of low molar mass NIPAm (M n 4000) prepared with trithiocarbonate (79) was found to be significantly more syndiotactic (r ¼ 58.6 %) than NIPAm produced by conventional radical polymerizations (without RAFT agent r ¼ 54.6 %). [321] This was attributed to an effect of the acid functional end-group. The syndiotacticity was further enhanced (r ¼ 61.1 %) for polymerization with 3-methyl-3-pentanol as cosolvent.…”

“…[321,322] MMA [323] MMA [324] AA [325] DMAm [326] (DMAm) [326] NIPAm [321] AA/St [327] NIPAm/ 361 [328] NIPAm/362 [328] MAA/ CHAm/NIPAm [328] MAA/BzAm/ NIPAm [328] MAA/OAm/ NIPAm [328] MAA/NIPAm/361 [328] AA/St-b-NVP [327] MAA/NIPAm/ 362 [328] MMA-b-(PEGMA/ NIPAm) [323] (NVP-b-MMA) [329,330] O I/M [285] St [285] BA [285] 81…”

RAFT preparation and the aqueous self-assembly of amphiphilic poly(octadecyl acrylate)- block -poly(polyethylene glycol methyl ether acrylate) copolymers

“…The presence of the RAFT end-group had a more significant effect on the CAC value for the amphiphilic brush diblock copolymers with a larger hydrophobic domain (i.e., 10 P(ODA) units on average), where the hydrophobic domain contributed approximately 20% of the polymer mass, compared with those with a smaller hydrophobic domain (i.e., 6 P(ODA) units on average) where the hydrophobic domain contributed approximately 10% (i.e., a tenth) of the polymer mass, as the CACs post-reduction varied only with the copolymer series with 10 P(ODA) units on average. In this case, P(ODA) 10 -b-P(PEGA-OMe) 23 The presence of RAFT end-groups has also been reported to affect the self-assembly behaviour of poly(N-isopropylacrylamide) (PNIPAM) [76,[83][84][85][86]. PNIPAM is a thermo-sensitive polymer commonly used to form hydrogels, which exhibits a phase transition at the lower critical solution temperature (LCST) around 32 • C. The LCST was reported to be influenced by the presence of additives, secondary copolymerisation monomer and modification of the end-group of the polymer chain [68][69][70][71].…”

Steric hindrance effect on thermo-responsive behaviors of well-defined water-soluble semi-rigid polymers

“…[1][2][3][4][5] They have some environmental responding properties so that they can undergo phase-separate corresponding to variation of temperature, pH, light, and ionic strength. [6][7][8][9][10] Temperature sensitivity is one of the most interesting properties in stimuli-responsive polymers.…”