## 4 Conclusions  
The synthesis and optimization of new polymers is an important branch of research that has been intensively pursued for years. This has allowed SPE to be continuously improved and advanced, making it by far the most important method in analytical sample preparation. Nowadays, there is a wide range of different polymers available and every year new, even more efficient sorbents are developed and manufactured. The preparation of novel SPE materials is feasible in particular due to the huge variety of existing monomers and crosslinkers. In this study we focused on the effect of the type of crosslinker and the ratio between the monomer and crosslinker on the extraction efficiency toward phenolic acids. We synthesized and used [C\({}_{6}\)-bis-VIM] [Br] as a crosslinker for the preparation of porous polymers. Subsequently, sorbents with the commonly used crosslinkers EGDMA and DVB were prepared and compared with the poly(n-VIM/C\({}_{6}\)-bis-VIM) polymer. It was found that the type of crosslinker had a significant influence on the adsorption properties of the polymer. This finding strongly emphasizes the importance of selecting suitable crosslinkers for the preparation of efficient SPE materials. It was observed that polymers prepared with the commonly used crosslinkers EGDMA, or DVB exhibited lower extraction recoveries for the majority of phenolic acids. The developed DSPE procedure for the extraction of phenolic acids represents an efficient analytical sample preparation method. It is simple and fast with maximum recoveries ranging between 84.1 and 92.5%. It was also shown that the DSPE procedure gave reproducible results, as the RSD values were very low. In addition, the developed extraction procedure was adapted to cartridges. No residual phenolic acids could be found in the supernatant and the extraction recoveries were ranging between 97.2 and 98.5%. It was demonstrated that the poly(n-VIM/C\({}_{6}\)-bis-VIM) polymer could also compete with the commercially available sorbent Oasis(r) MAX from Waters(tm). Significantly, higher extraction recoveries for all analyzed phenolic acids were obtained, which were on average 5% higher than with Oasis(r) MAX. Furthermore, it was demonstrated that the poly(n-VIM/C\({}_{6}\)-bis-VIM) polymer could be regenerated and reused for the majority of analytes. Therefore, the novel sorbent is a good contender for its use in sustainable analytical sample preparation. This aspect is of great significance, as the minimization of resources is becoming more and more important in the development of new sample preparation methods. Due to the ionic properties of [C\({}_{6}\)-bis-VIM] [Br], it is well suited for the preparation of anion exchange sorbents. Due to its physicochemical properties, [C\({}_{6}\)-bis-VIM] [Br] is not only an excellent constituent for the preparation of polymers but also because its synthesis is facile and inexpensive with high yields. Therefore, [C\({}_{6}\)-bis-VIM] [Br] could present a good alternative to conventional crosslinkers such as EGDMA and DVB, which exhibited different properties when incorporated into vinylimidazole polymers. In conclusion, this study clearly highlights the yet untapped potential of the crosslinker [C\({}_{6}\)-bis-VIM] [Br] with respect to the synthesis of new anion exchange polymers for their application in the field of SPE. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/separations9030072/s1](https://www.mdpi.com/article/10.3390/separations9030072/s1)]([https://www.mdpi.com/article/10.3390/separations9030072/s1](https://www.mdpi.com/article/10.3390/separations9030072/s1)), Figure S1. BET adsorption and desorption isotherm; Figure S2. Pore size distribution; Figure S3. SEM image; Figure S4. ATR-FTIR spectra; Table S1. Optimization of the [C\({}_{6}\)-bis-VIM] [Br] crosslinked polymer; Table S2. Conditioning solution; Table S3. Eluting solution; Table S4. Calibration results 25-250 mg L\({}^{-1}\); Table S5. Calibration results 250-500 mg L\({}^{-1}\); Table S6.