Methacrylate Polymer Monoliths for Separation Applications

Abstract

This review summarizes the development of methacrylate-based polymer monoliths for separation science applications. An introduction to monoliths is presented, followed by the preparation methods and characteristics specific to methacrylate monoliths. Both traditional chemical based syntheses and emerging additive manufacturing methods are presented along with an analysis of the different types of functional groups, which have been utilized with methacrylate monoliths. The role of methacrylate based porous materials in separation science in industrially important chemical and biological separations are discussed, with particular attention given to the most recent developments and challenges associated with these materials. While these monoliths have been shown to be useful for a wide variety of applications, there is still scope for exerting better control over the porous architectures and chemistries obtained from the different fabrication routes. Conclusions regarding this previous work are drawn and an outlook towards future challenges and potential developments in this vibrant research area are presented. Discussed in particular are the potential of additive manufacturing for the preparation of monolithic structures with pre-defined multi-scale porous morphologies and for the optimization of surface reactive chemistries.

Keywords: additive manufacturing; chromatography; methacrylate; microfluidics; monoliths; porous materials; stationary phase.

Figure 1

Chemical structures of (1) methacrylic acid; (2) glycidyl methacrylate; (3) methyl methacrylate; and (4) PMMA.

Figure 2

SEM images of (a) poly(ethyleneglycol) diacrylate (PEGDA) monolith formed via directional freezing, reproduced from [52] with permission of The Royal Society of Chemistry; and (b) a glycidyl methacrylate co- Ethylene DiMethacrylate (EDMA) monolith, reproduced (adapted) with permission from [9], Copyright 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany.

Figure 3

Chemical structures of commonly used porogenic solvents, (5) cyclohexanol; (6) dodecanol; (7) 1,4 butane-diol; (8) toluene; (9) poly ethylene glycol; (10) dimethyl sulfoxide; (11) Tetrahydrofuran.

Figure 4

Chemical structures of commonly used cross-linking agents for polymerization reactions. Agents are: (12) ethylene glycol dimethacrylate; (13) 2-methyl-1, 8-octanediol dimethacrylate; (14) methylene bis acrylamide; (15) tri methylol propane trimethacrylate.

Figure 5

Examples of chemical routes to functional groups on polymer monolith surface using the epoxy group as the starting point, (a) functionalization with diethyl amine ethyl; (b) Alkyl addition via Grignard reaction; (c) alkylation; (d) hydrolysis; (e) sulfonation; (f) biofuctionalization, adapted and redrawn from [9].

Figure 6

Chemical structure of cysteamine (16) crosslinked with glycidyl methacrylate and Au nanoparticle.

Figure 7

Formation of methacrylate monolith with alkyne functional group, and reaction scheme of the CuAAC reaction for the modification of polymer surface with C₈ and C₁₈ ligands. Redrawn from [111].

Figure 8

(A,B) Computer Aided Design (CAD) drawings of the (A) pre-concentrator and (B) a layer of ordered cuboids in the extraction channel; (C) Photograph of the printed device; two flat-bottom female connectors with a piece of Poly Tetra Fluoro-Ethylene (PTFE) tubing were fitted to allow connection to an Flow Injection Analysis (FIA) interface; (D,E) Photographs of the configuration of the ordered cuboids printed without the surrounding of the extraction channel. Reproduced with permission from [54], Copyright (2015) American Chemical Society.

Figure 9

Chemical structures of herbicides ((17) fluometuron; (18) chlortoluron; (19) buturon and (20) chloroxuron), used by Lin et al. [124].

Figure 10

Chromatogram showing separation of a mixture of PAH compounds, on low density methacrylate monolith. Key: (1) thiourea; (2) naphthalene; (3) fluorine; (4) anthracene; (5) pyrene; (6) benz(a)anthracene; and (7) benzo(a)pyrene. Reprinted with permission from [35], Copyright (2005) American Chemical Society.

Figure 11

Reverse Phase separation of protein mixture on two different Lauryl methacrylate monoliths, (a) fabricated using photo-initiated polymerization and (b) fabricated via thermally initiated polymerization. Peaks are: (1) impurity; (2) ribonuclease A; (3) Cytochrome C; and (4) Myglobin. Reproduced from [85] with permission from The Royal Society of Chemistry.

Figure 12

SEC separation on methyl ether acrylate monolith using different column lengths (A) and diameter (B). Mobile phase was 20 mM phosphate with NaCl. Key: TG: Thyroglobulin; BSA: Albumin; STR: Trypsin Inhibitor; ANG1: Angiotensin 1; LE; Leucine encephalin. Reprinted with permission from [155], Copyright (2009), American Chemical Society.

Figure 13

(a) PDMS Chip with Butyl Acrylate Monolith in a Silica Capillary; (b) Separation of Arginine-NDA (1) and Dopamine-NDA (2) on Acrylate Monolith on PDMS Reproduced with permission from [158], Copyright 2007 WILEY-VCH VerlagGmbH & Co. KGaA, Weinheim, Germany.

Figure 14

Chemical structures of Arginine (21) and Dopamine (22).

Figure 15

(a) Separation of peptide mixture on acrylate monolith. Peptides are (1) papain inhibitor; (2) proctolin; (3) Opioid peptide (R-casein fragment 90–95); (4) Ileangiotensin III; (5) angiotensin III; and (6) GGG; (b) Separation of amino acid mixture on same monolith. Image adapted with permission from [159]. Copyright (2002), American Chemical Society.