## 1 Introduction
In this regard, polymer-based sorbents still count as one of the most important SPE materials with progressive research being conducted over the last decades [27; 28; 29; 30]. The structure of polymerizable compounds and the polymerization process are primarily responsible for the physical and chemical properties of the obtained polymer [31]. There are several mechanisms for polymer synthesis with free-radical polymerization (FRP) being one of the most significant. Its robustness against impurities of the raw materials and the possibility to customize polymer properties by the choice of initiator and polymerization conditions are the main advantages over other processes. FRP is of enormous industrial importance, due to the large-scale production of vinyl polymers [32; 33]. Furthermore, this method is also highly significant for the synthesis of efficient sorbents for SPE applications regarding scientific research. It is one of the most widely used techniques for the preparation of crosslinked polymers, both by academics and industrialists [34]. Incorporating compounds that have at least two free-radically polymerizable double bonds, so-called crosslinking agents or crosslinkers, enables the synthesis of polymers with three-dimensional networks. By changing the monovinyl to divinyl molar ratios, the degree of cross-linking can be altered to form weakly to highly crosslinked materials, which directly affects the properties of the obtained polymer. Many commercially available polymers owe their value to their specific three-dimensional structures, which makescrosslinking an important tool for polymer tuning [35]. Commonly used free-radically polymerizable crosslinking agents are divinylbenzene (DVB) or ethylene glycol dimethacrylate (EGDMA) [33]. DVB, for example, is an important crosslinker for commercial SPE sorbents, with Oasis(r) from Waters(tm) and Strata(tm)-X from Phenomenex(r) being two of the most significant product lines regarding analytical sample preparation. EGDMA has become increasingly important in scientific research due to its higher polarity compared with DVB and the possibility to form hydrogen bonds with certain types of analytes [36; 37; 38; 39]. A newly developed crosslinker that has been utilized for the synthesis of polymers is 3,3\({}^{\prime}\)-(hexane-1,6-diyl)bis(1-vinylimidazolium) bromide [C\({}_{6}\)-bis-VIM] [Br]. Recent studies have shown that it can be used for the preparation of thermally and mechanically robust hydrogels [40], inverse opal microspheres [41], monolithic stationary phases [42] as well as anion-exchange membranes [43]; however, after a thorough search of the literature, it became apparent that [C\({}_{6}\)-bis-VIM] [Br] has not yet been applied as a crosslinking agent for the preparation of SPE materials. Due to its structural properties, [C\({}_{6}\)-bis-VIM] [Br] appeared to be well suited for the preparation of anion exchange sorbents and according to [PERSON] et al., its synthesis is simple and feasible with high yields [40]. Phenolic acids can be isolated by different SPE materials, such as mixed-mode, ion-exchange, or reversed-phase sorbents. [PERSON] et al. reported the extraction of phenolic acids using different commercially available sorbents including Chromabond(r) C18, SAX and Oasis(r) HLB [44]. Furthermore, phenolic acids and flavonoids could be isolated and determined in honey by applying Bond Elut C18, Oasis(r) HLB, Strata-X and Amberlite XAD-2 [45]. Recent studies have shown that, in addition to commercially available sorbents, there is still great potential for the preparation of novel SPE materials to further improve the extraction of phenolic acids [46; 47]. The aim of the presented study was to synthesize a novel [C\({}_{6}\)-bis-VIM] [Br] crosslinked anion exchange polymer and subsequently develop an efficient extraction procedure for phenolic acids. Therefore, differently crosslinked polymers were prepared and compared with respect to their sorption capacity and analyte recoveries.