## 3 Experimental Section  
Carbon dioxide with a purity of 99.99% was provided from a commercial source. 1-Vinylimidazole (Vlm, 98%), 1,6-dibromohexane, 1,8-dibromooctane, 1,12-dibromododecane, ethylene glycol dimethacrylate (EGDMA, 98%), and divinyl benzene (DVB, 98%) were brought from Aladdin Reagent Co. (Shanghai, China). The inhibitor in VIm, EGDMA, and DVB were removed through distillation on vacuum. Azobisisobutyronitrile (AlBN) was purchased from Tianjing Chemical Reagent Company (Tianjing, China), and recrystallized from methanol before use. Other reagents, such as 2,6-Ditertbutyl-4-methylphenol, methanol, diethyl ether, and acetone were A.R. grade and used without further purification. Fourier transform infrared (FT-IR) spectra were recorded on a DIGIL FTS3000 spectrophotometer (DIGILAB, Randolph, MA, USA) using KBr tablets. \({}^{1}\)H- and \({}^{13}\)C-NMR spectra were recorded on a Brucker AM 400 MHz spectrometer (Bruker, Faellanden, Switzerland) at 25 \({}^{\circ}\)C. Thermogravimetric analyses (TGA) were measured on a Perkin Elmer TG/TGA 6300 (Perkin E Itachi instruments, Norwalk, USA) at a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\). Differential scanning calorimetry (DSC) measurements were recorded on a DSC 822e thermal analysis system (Mettler Toledo Instruments Inc., Greifensee, Switzerland) at a heating rate of \(\pm\)1 \({}^{\circ}\)C/min with nitrogen protected (80 mL min\({}^{-1}\)). The morphology of nanogels was observed by scanning electron microscopy (SEM, JSM 67001F JEOL, Tokyo, Japan), and the samples were prepared by dispersing the dried nanogels in methanol under sonication at room temperature. The X-ray diffraction analysis was recorded on a Philips X'Pert using Cu K\(\alpha\) radiation at 40 kV (Rigaku, Tokyo, Japan). Dynamic light scattering (DLS) measurements were performed at 25 \({}^{\circ}\)C and a scattering angle of 90\({}^{\circ}\) on a commercial laser light scattering (ALV/SP-125) equipped with an ALV-5000 multi-\(\uptau\) digital time correlator and ADLAS DPY425 solid-state laser (output power = 22 mW at \(\uplambda\) = 632.8 nm) (ALV-GmbH, Langen, Germany). Zeta potential values were calculated according to \begin{table}
\begin{tabular}{c c c c c c} \hline
**Entry** & **Catalyst b** & **Temperature (\({}^{\circ}\)C)** & **CO2 (MPa)** & **Yield (\%)** & **Selectivity (\%)** \\ \hline
1 & 3:1 & 160 & 3 & 99.7 & 89.0 \\
2 & 5:1 & 160 & 3 & 99.8 & 93.0 \\
3 & 10:1 & 160 & 3 & 100 & 100 \\
4 & 15:1 & 160 & 3 & 100 & 96.4 \\
5 & 5:1 & 120 & 3 & 87.7 & 99.3 \\
6 & 5:1 & 140 & 3 & 96.1 & 96.1 \\
7 & 5:1 & 150 & 3 & 99.5 & 99.2 \\
8 & 5:1 & 160 & 2 & 95.7 & 97.3 \\
9 & 5:1 & 160 & 5 & 99.7 & 100 \\ \hline \end{tabular}  
*: Reaction condition: ECH 3 mL, nanogel 0.1 g, time 6 h; b: feed ratio of [C\({}_{6}\)Vlm]Br to EGDMA.  
\end{table} 
Table 2: Performance of BIm-based nanogel catalyst for the cycloaddition reaction of CO2 with ECH in different temperature a.  
Smolochowski equation and each sample was analyzed in triplicate (Malvern instruments Ltd., Worcestershire, UK). The upper critical solution temperature (UCST) of thermo-sensitive nanogels was measured by turbidimetry at 500 nm using a spectrophotometer (UV-VIS Spectrometer, Lambda 20, Perkin-Elmer, Waltham, MA, USA). The elemental analyses are measured directly without any additives using a Vario EL Cube (Elementar, Hanau, Germany), and mass spectroscopy were performed using water as the solvent without additives on a micrOTOF-QII mass spectrometer (Bruker Daltonics, Billerica, MA, USA). _1,6-Hexanediyl-3,3'-bis-1-vinyl imidazolium bromide ([CsVIm]Br)_ 1-vinyl imidazole (5.18 g, 55 mmol) and 1,6-dibromohexane(2.79 g, 22 mmol) were dissolved in methanol (50 mL) in a round-bottom flask fitted with a condenser and N2 bubbler. Subsequently, the mixture was stirred at 80 \({}^{\circ}\)C for 48 h under a nitrogen atmosphere. After then, the reaction mixture was precipitated from diethyl ether (150 mL), and recrystallized twice from diethyl ether.