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.
Highlights
A typical protocol used for the synthesis of the PNAEP62−PHEA100 diblock copolymer was as follows: PNAEP62 macro-chain transfer agent (CTA) (0.250 g, 21.3 μmol), Hydroxyethyl acrylate (HEA) (0.2476 g, 2.1324 mmol; target degrees of polymerization (DP) = 100), and Ascorbic Acid (AsAc) (0.8 mg, 4.3 μmol) were weighed into a 14 mL vial charged with a magnetic flea
A typical protocol used for the synthesis of the PNAEP71−POEGA40 diblock copolymer was as follows: PNAEP71 macro-CTA (0.250 g, 21.3 μmol), oligo(ethylene glycol) methyl ether acrylate (OEGA) (0.3872 g, 853 μmol; target DP = 40), and AsAc (0.8 mg, 4.3 μmol) were weighed into a 14 mL vial charged with a magnetic flea
A typical protocol used for the synthesis of the PDEA100−PNAEP100 diblock copolymer via reversible addition−fragmentation chain transfer (RAFT) aqueous solution polymerization of NAEP was as follows: PDEA100 macro-CTA (200 mg, 10.5 μmol), NAEP (190 mg, 1.054 mmol; target DP = 100), and AsAc (0.37 mg, 2.1 μmol) were weighed into a 14 mL vial charged with a magnetic flea
Summary
Poly(N-vinylpyrrolidone) (PNVP) is a commercially important nonionic water-soluble polymer with a wide range of commercial applications.[1,2] Its high dipole moment (4.06 D)[3] enables the efficient sequestration of many fugitive dyes and its widespread use as an anti-dye transfer agent in laundry formulations.[4,5] PNVP can be utilized as a filmforming agent in hair sprays[6] and various cosmetics, and its excellent biocompatibility and relatively low cost account for its use as an excipient in drug formulations.[6,7] Bulk copolymerization with other vinyl monomers enables the production of soft contact lenses[8] while so-called “popcorn” polymerization of N-vinylpyrrolidone (NVP) produces crosslinked particles that can be used to clarify alcoholic beverages such as beer and wine.[9]. A typical protocol used for the synthesis of the PNAEP62−PHEA100 diblock copolymer was as follows: PNAEP62 macro-CTA (0.250 g, 21.3 μmol), HEA (0.2476 g, 2.1324 mmol; target DP = 100), and AsAc (0.8 mg, 4.3 μmol) were weighed into a 14 mL vial charged with a magnetic flea (reaction solution 1) This vial was immersed in an ice bath, and the solution was degassed with nitrogen for 30 min. A typical protocol used for the synthesis of the PDEA100−PNAEP100 diblock copolymer via RAFT aqueous solution polymerization of NAEP was as follows: PDEA100 macro-CTA (200 mg, 10.5 μmol), NAEP (190 mg, 1.054 mmol; target DP = 100), and AsAc (0.37 mg, 2.1 μmol) were weighed into a 14 mL vial charged with a magnetic flea (reaction solution 1) This vial was immersed in an ice bath and degassed with nitrogen for 30 min.
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