R‐RAFT approach for the polymerization of N‐isopropylacrylamide with a star poly(ε‐caprolactone) core

Abstract

Reversible addition-fragmentation chain transfer (RAFT) polymerization is a more robust and versatile approach than other living free radical polymerization methods, providing a reactive thiocarbonylthio end group. A series of well-defined star diblock [poly(e-caprolactone)-b-poly(N-isopropylacrylamide)] 4 (SPCLNIP) copolymers were synthesized by R-RAFT polymerization of N-isopropylacrylamide (NIPAAm) using [PCL-DDAT] 4 (SPCL-DDAT) as a star macro-RAFT agent (DDAT: S-1-dodecyl-S 0 -(a, a 0 -dimethyl-a 00 -acetic acid) trithiocarbonate). The R-RAFT polymerization showed a controlled/''living'' character, proceeding with pseudo-first-order kinetics. All these star polymers with different molecular weights exhibited narrow molecular weight distributions of less than 1.2. The effect of polymerization temperature and molecular weight of the star macro-RAFT agent on the polymerization kinetics of NIPAAm monomers was also addressed. Hardly any radical-radical coupling by-products were detected, while linear side products were kept to a minimum by careful control over polymerization conditions. The trithiocarbonate groups were transferred to polymer chain ends by R-RAFT polymerization, providing potential possibility of further modification by thiocarbonylthio chemistry. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 571-580, 2012

Synthesis and characterization of “Living” star‐shaped poly(N‐vinylcaprolactam) with four arms and carboxylic acid end groups

“…[8][9][10][11] The core-first strategy enables two distinct synthetic routes: the Z-group approach in which thiocarbonylthio groups are linked to the core via the "stabilizing" Z-group of the chain transfer agent (CTA), [8][9][10][11][12][13][14][15][16][17][18] and the R-group approach, in which the thio entity is attached to the core via the "leaving" R-group of the CTA. [19][20][21] On the other hand, over the last decade, particular attention has been given to temperature-sensitive polymers because of their potential applications. Two of the most studied thermosensitive polymers are poly(N-isopropylacrylamide) (PNIPAM) 22 and poly(N-vinylcaprolactam) (PNVCL) 23,24 ; both polymers are water-soluble below their LCST, are nonionic, and exhibit a LCST around the physiological range (Fig.…”

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

“…In contrast, RDRP techniques are relatively robust and therefore allow for a convenient fabrication of amphiphilic star polymers. 19,21,[33][34][35][36][37][38][39] Radical addition fragmentation chain transfer (RAFT) polymerisation in particular tolerates a large variety of functional monomers and is relatively undemanding in terms of experimental setup, as only a chain transfer agent (CTA) is added to a classical FRP mixture.…”

One‐step synthesis of block copolymers using a hydroxyl‐functionalized trithiocarbonate RAFT agent as a dual initiator for RAFT polymerization and ROP

“…On the other hand, a significant shortening of the induction period and an increase in the apparent propagation rate in the RAFT polymerization of MMA were observed, resulting in higher mole fractions of the PMMA block than those of the PLA block. Bian et al 21 reported a similar phenomenon from the RAFT polymerization of NIPAM at 100 C using star-shaped PCL macro-RAFT agents (SPCL-RAFTs). The RAFT polymerization rate of NIPAM using SPCL 25 -RAFT was higher than that using SPCL 10 -RAFT.…”