RAFT Polymerization of N‐Isopropylacrylamide and Acrylic Acid under γ‐Irradiation in Aqueous Media

Abstract

Summary: The ambient temperature (20 °C) reversible addition fragmentation chain transfer (RAFT) polymerization of N‐isopropylacrylamide (NIPAAm) and acrylic acid (AA) conducted directly in aqueous media under γ‐initiation (at dose rates of 30 Gy · h−1) proceeds in a controlled fashion (typically, $\overline M _{\rm w} /\overline M _{\rm n}$ < 1.2) to near quantitative conversions and up to number‐average molecular weights of 2.5 × 105 g · mol−1 for PNIPAAm and 1.1 × 105 g · mol−1 for PAA via two water‐soluble trithiocarbonate chain transfer agents, i.e., S,S‐bis(α,α′‐dimethyl‐α″‐acetic acid)trithiocarbonate (TRITT) and 3‐benzylsulfanylthiocarbonylsulfanyl propionic acid (BPATT). The generated polymers are successfully chain extended, which suggests that the RAFT agents are stable throughout the polymerization process so that complex and well‐defined architectures can be obtained.An increase of the monomer/CTA ratio leads to an increase of the molecular weight for the RAFT polymerization of NIPAAm under γ‐radiation in water using TRITT at ambient temperature.imageAn increase of the monomer/CTA ratio leads to an increase of the molecular weight for the RAFT polymerization of NIPAAm under γ‐radiation in water using TRITT at ambient temperature.

In Situ Formation of Protein–Polymer Conjugates through Reversible Addition Fragmentation Chain Transfer Polymerization

“…Above 60 %, the increase in the molecular weight was much less, which might be due to the effect of increased steric hindrance of growing polymer chains on the accessibility of the RAFT groups. [25,31,32] The nondenaturing PAGE of the dialyzed polymerization mixtures showed clearly the formation of the polymer conjugates with molecular weights higher than the molecular weight of BSA (Figure 2 D).…”

“…The large polydispersity index (PDI) values of the samples might be due to the hindrance of the RAFT end groups by the growing polymer chain on the protein. [25,31,32] Furthermore, the presence of low-molecular-weight peptide fragments formed by the cleavage of BSA might have also caused the lowermolecular-weight tails on GPC traces and hence increased the PDI values.…”

“…g Radiation has been employed previously to initiate RAFT-mediated polymerizations. [24][25][26][27] It was reported that there is no difference in the mechanism of the RAFT process between g ray and thermally initiated polymerizations. The advantage of using g radiation to initiate a polymerization reaction is that the polymerizations can be performed at room temperature in a variety of solvents including water.…”

Living Radical Polymerization by the RAFT Process—A First Update

“…Quinonoid species are well known as excellent hydrogen atom donors. The effect on kinetics would be similar to the Buback-Vana proposal [144] but would lead to the formation of a new RAFT agent 99 which might be detectable under appropriate conditions but, for the case of acrylate polymerization, may not be readily distinguished 47 [104] HPMAM [104] NIPAM [104] 48 DMA [105] 49 [106] MA [106] C [12] MMA [4,12] 51 [30] (S) [30] 52* [106] AA [107] AN [108] MA [106] 53 [31] BA [31] 54* BA [31] MA [71] MMA [109] 55 [31] AA [110] BA [31] NIPAM [110] C 56 [111] NIPAM [111,112] 57 [111] NIPAM [111] [31] (BA) [31] 60 [31] BA [31] 61* AA [110] BA [31,109] MA [71] NIPAM [110] [30] BA [56] NIPAM [56] (NVP) [56] 63 [30] S [30] 64 ...…”

“…[71] The paper emphasizes the importance of selecting an irradiation wavelength, the RAFT agent, and the photoinitiator (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, to avoid side reactions such as photodissociation of the RAFT agent. [71] Gamma-initiated RAFT polymerizations of MA in the presence of various dithioesters (including 20, 21, 42, 43b), [87] xanthates [146] and dithiocarbamates, [147] of MMA in the presence of 32, [91] and of NIPAM and AA in the presence of 55 or 61 in aqueous media [110] have been reported.…”