title: RAFT Aqueous Dispersion Polymerization ofN-(2-(Methacryloyloxy)ethyl)pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers.
abstract: RAFT solution polymerization ofN-(2-(methacryoyloxy)ethyl)pyrrolidone (NMEP) in ethanol at 70 °C was conducted to produce a series of PNMEP homopolymers with mean degrees of polymerization (DP) varying from 31 to 467. Turbidimetry was used to assess their inverse temperature solubility behavior in dilute aqueous solution, with an LCST of approximately 55 °C being observed in the high molecular weight limit. Then a poly(glycerol monomethacylate) (PGMA) macro-CTA with a mean DP of 63 was chain-extended with NMEP using a RAFT aqueous dispersion polymerization formulation at 70 °C. The target PNMEP DP was systematically varied from 100 up to 6000 to generate a series of PGMA63-PNMEPxdiblock copolymers. High conversions (≥92%) could be achieved when targeting up tox= 5000. GPC analysis confirmed high blocking efficiencies and a linear evolution inMnwith increasing PNMEP DP. A gradual increase inMw/Mnwas also observed when targeting higher DPs. However, this problem could be minimized (Mw/Mn< 1.50) by utilizing a higher purity grade of NMEP (98% vs 96%). This suggests that the broader molecular weight distributions observed at higher DPs are simply the result of a dimethacrylate impurity causing light branching, rather than an intrinsic side reaction such as chain transfer to polymer. Kinetic studies confirmed that the RAFT aqueous dispersion polymerization of NMEP was approximately four times faster than the RAFT solution polymerization of NMEP in ethanol when targeting the same DP in each case. This is perhaps surprising because both1H NMR and SAXS studies indicate that the core-forming PNMEP chains remain relatively solvated at 70 °C in the latter formulation. Moreover, dissolution of the initial PGMA63-PNMEPxparticles occurs on cooling from 70 to 20 °C as the PNMEP block passes through its LCST. Hence this RAFT aqueous dispersion polymerization formulation offers an efficient route to a high molecular weight water-soluble polymer in a rather convenient low-viscosity form. Finally, the relatively expensive PGMA macro-CTA was replaced with a poly(methacrylic acid) (PMAA) macro-CTA. High conversions were also achieved for PMAA85-PNMEPxdiblock copolymers prepared via RAFT aqueous dispersion polymerization forx≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Cunningham
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Derry
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Lee A
authors.initials: LA
authors.lastname: Fielding
authors.affiliation: Ashland Specialty Ingredients, 1005 US 202/206, Bridgewater, New Jersey 08807, United States.
authors.forename: Osama M
authors.initials: OM
authors.lastname: Musa
authors.affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Armes