# Methacrylate Polymer Monoliths for Separation Applications
## 2 Methacrylate Polymer Monoliths
### Morphology of Monoliths  
The morphology of methacrylate monoliths have been extensively studied using Scanning Electron Microscopy (SEM) as a means of correlating preparation conditions with observed performance of the monolith in its separation and/or pre-concentration capability. Two examples of SEM images of acrylate-based monoliths are poly-ethylene glycol diacrylate and glycolidyl methacrylate, as shown in Figure 2. It should be noted that while the structure in Figure 2a appears to be ordered and unidirectional, the separation achieved using these monoliths for proteins and lysosomes was actually quite poor, indicating the complex relationship between structure and performance for these materials. The monolith material in Figure 2b appears to be more isotropic in structure. Other monoliths fabricated using similar synthesis methods showed similar structural patterns and varying levels of porosity, which were dependent on the choice of porogenic solvent used in their manufacture. These previous works highlight the practical challenges, as well as importance of using characterization methods, such as SEM and Transmission Electron Microscopy (TEM) [51], to analyze monolithic structures. Layer-by-layer analysis methods using automated serial Focused Ion Beam (FIB) etching, coupled with SEM, as well as serial-block face SEM and X-ray micro-tomography, provide the means to better relate monolith fabrication parameters to resulting fabricated architecture characteristics, including pore volume and surface area. Details on 3D reconstruction analysis of polymer monolith architectures are discussed further in Section 2.3.  
Figure 1: Chemical structures of (**1**) methacrylate acid; (**2**) glycolidyl 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 glycolidyl methacrylate co- Ethylene DiMethacrylate (EDMA) monolith, reproduced (adapted) with permission from [9], Copyright 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany.  
Methacrylate monoliths have also been fabricated within microfluidic devices or channels; for example, in polymer High Internal Phase Emulsion (polyHIPE) separation columns [53] and in monolithic pre-concentration devices [54; 55]. The integration of methacrylate and other monolithic materials into microfluidic devices has benefited both analyte separation and pre-concentration in modular microfluidics as the quest for the miniaturization of chromatographic devices continues [56; 57; 58; 59; 41; 55; 56; 57; 58; 59; 60; 61; 62; 63; 64; 65; 66; 67; 68; 69; 70].  
One other important preparation method involves the co-polymerization of the functional monomer and cross-linker in the presence of a templating agent yielding a Molecular Imprinted Monolith (MIM). This templating agent is chosen based on the intended application (_i.e._, what the intended analytes will be) as it will need to be a similar size and shape and possess similar chemical functionality. Acrylate based monoliths which are fabricated using this method have received much attention, including several reviews, [71; 72]. They are particularly useful for chiral protein separations, facilitated by a chiral templating agent [73]. The area itself is fascinating and quite extensive and, while it will not be discussed further in this contribution, it really merits a review of its own; however, it remains a very interesting research theme and the interested reader is directed to the above-cited reviews for a more detailed treatment.