Pyrrolidone-functional smart polymers via nitroxide-mediated polymerization

Modular and Substrate-Independent Grafting-To Procedure for Functional Polymer Coatings

The ability to tailor polymer brush coatings to the last nanometer has arguably placed them among the most powerful surface modification techniques currently available. Generally, the synthesis procedures for polymer brushes are designed for a specific surface type and monomer functionality and cannot be easily employed otherwise. Herein, we describe a modular and straightforward two-step grafting-to approach that allows introduction of polymer brushes of a desired functionality onto a large range of chemically different substrates. To illustrate the modularity of the procedure, gold, silicon oxide (SiO₂), and polyester-coated glass substrates were modified with five different block copolymers. In short, the substrates were first modified with a universally applicable poly(dopamine) primer layer. Subsequently, a grafting-to reaction was performed on the poly(dopamine) films using five distinct block copolymers, all of which contained a short poly(glycidyl methacrylate) segment and longer segment of varying chemical functionality. Ellipsometry, X-ray photoelectron spectroscopy, and static water contact angle measurements confirmed successful grafting of all five block copolymers to the poly(dopamine)-modified gold, SiO₂, and polyester-coated glass substrates. In addition, our method was used to provide direct access to binary brush coatings, by simultaneous grafting of two different polymer materials. The ability to synthesize binary brush coatings further adds to the versatility of our approach and paves the way toward production of novel multifunctional and responsive polymer coatings.

RAFT Aqueous Dispersion Polymerization of N-(2-(Methacryloyloxy)ethyl)pyrrolidone: A Convenient Low Viscosity Route to High Molecular Weight Water-Soluble Copolymers

RAFT solution polymerization of N-(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-PNMEP x diblock copolymers. High conversions (≥92%) could be achieved when targeting up to x = 5000. GPC analysis confirmed high blocking efficiencies and a linear evolution in Mn with increasing PNMEP DP. A gradual increase in Mw/Mn was 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 both 1H 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-PNMEP x particles 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-PNMEP x diblock copolymers prepared via RAFT aqueous dispersion polymerization for x ≤ 4000. Again, better control was achieved when using the 98% purity NMEP monomer in such syntheses.

Effect of residue structure on the thermal and thermoresponsive properties of γ-substituted poly(N-acryloyl-2-pyrrolidones)

We discuss the results of an investigation into the structure/property correlations of γ-substituted poly(N-acryloyl-2-pyrrolidone)s, a recently reported class of pyrrolidone-based polymers prepared from pyroglutamic acid, a bio-derived resource.