Synthesis of Well-Defined Pyrrolidone-Based Homopolymers and Stimulus-Responsive Diblock Copolymers via RAFT Aqueous Solution Polymerization of 2-(N-Acryloyloxy)ethylpyrrolidone

Abstract

Poly(N-vinylpyrrolidone) (PNVP) is a well-known, highly polar, nonionic water-soluble polymer. However, N-vinylpyrrolidone (NVP) usually exhibits strongly non-ideal behavior when copolymerized with methacrylic or styrenic monomers. Moreover, NVP is not particularly well-controlled under living radical polymerization conditions. For these reasons, alternative pyrrolidone-based monomers have been investigated. For example, the reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(N-methacryloyloxy)ethylpyrrolidone (NMEP) has been recently investigated using various polymerization formulations. However, PNMEP homopolymers are significantly less hydrophilic than PNVP and exhibit inverse temperature solubility in aqueous solution. In the present work, we studied the RAFT aqueous solution polymerization of 2-(N-acryloyloxy)ethylpyrrolidone (NAEP) using either AIBN at 70 °C or a low-temperature redox initiator at 30 °C. PNAEP homopolymers are obtained in high yield (>99%) with good control (Mw/Mn < 1.20) for target degrees of polymerization (DP) of up to 400 using the latter initiator, which produced relatively fast rates of polymerization. However, targeting DPs above 400 led to lower NAEP conversions and broader molecular weight distributions. 2-Hydroxyethyl acrylate (HEA) and oligo(ethylene glycol) methyl ether acrylate (OEGA) were chain-extended using a PNAEPx macro-CTA via RAFT aqueous solution polymerization, yielding double-hydrophilic acrylic diblock copolymers with high conversions (>99%) and good control (Mw/Mn < 1.31). In addition, a PNAEP95 macro-CTA was chain-extended via RAFT aqueous solution polymerization of N-isopropylacrylamide (NIPAM) at 22 °C. Dynamic light scattering (DLS) analysis indicated that heating above the lower critical solution temperature of PNIPAM led to so-called “anomalous micellization” at 35 °C and the formation of near-monodisperse spherical micelles at 40 °C. Finally, 2-(diethylamino)ethyl methacrylate (DEA) was polymerized using an N-morpholine-functionalized trithiocarbonate-based RAFT chain transfer agent and subsequently chain-extended using NAEP to form a novel pH-responsive diblock copolymer. Above the pKa of PDEA (∼7.3), DLS and 1H NMR studies indicated the formation of well-defined PDEA-core spherical micelles.

Redox-Initiated Reversible Addition–Fragmentation Chain Transfer (RAFT) Polymerization

“…[21] Armes and co-workers reported the preparation of pyrrolidone-based homo-or block-polymers via RAFT aqueous polymerization using the KPS/AsAc redox pair at 308C. [22] In all the above-mentioned studies the redox initiation systems employed for room temperature RAFT polymerization require the simultaneous addition of both reducing and oxidizing agents. An amine-containing vinylic monomer (2-vinylpyridine (2VP)) has been reported to participate in the initiation stage of an aqueous RAFT process at room temperature, as shown by Xin and co-workers.…”

Time-resolved small-angle neutron scattering studies of the thermally-induced exchange of copolymer chains between spherical diblock copolymer nanoparticles prepared via polymerization-induced self-assembly

“…monomer and solvent purification is not required). [13][14][15][16][17][18][19][20] Moreover, RAFT polymerization is well-suited for polymerization-induced selfassembly (PISA). [21][22][23][24][25][26][27] This technique involves chain extension of a soluble homopolymer precursor using a second monomer that grows to form an insoluble block on reaching a certain critical degree of polymerization (DP).…”

End-group ionisation enables the use of poly(N-(2-methacryloyloxy)ethyl pyrrolidone) as an electrosteric stabiliser block for polymerisation-induced self-assembly in aqueous media

“…11 14 In contrast, 2-(N-methacryloyloxy)ethyl pyrrolidone (NMEP) can be copolymerised with a wider range of monomers, including methacrylics and styrene. 15 19 Therefore, the synthesis of welldefined pyrrolidone-functional polymers by RAFT polymerisation is rather more straightforward using NMEP (or 2-(N-acryloyloxy)ethyl pyrrolidone 20,21 ) rather than NVP. Polymerisation-induced self-assembly (PISA) enables the rational design of block copolymer nanoparticles, including spheres, worms and vesicles.…”