## 2 Materials and Methods
### Synthesis of the Catalyst  
The solid acid catalyst, poly (styrenesulfonic acid)-graft-silica (SBA-15-PSSA), was synthesized following a four-step protocol (Figure 1).  
Step (i)--preparation of SBA-15. Pore-expanded mesoporous silica (SBA-15) was prepared implementing a modification of the method described in several reports [10, 16, 19]. In a 250-mL round-bottom flask, a solution of P123 (3.6 g)/NH\({}_{4}\)F (0.041 g)/1.3 M HCl (126 mL) was stirred at 17 \({}^{\circ}\)C for 1 h, in a water bath whose temperature was controlled by a chiller device (Recirculating Chiller F-105, Buchi, Flawil, Switzerland). To this solution, was added dropwise a mixture of TEOS (8.25 mL) and TIPB (1.8 mL); the obtained mixture was stirred at 17 \({}^{\circ}\)C for 24 h and, subsequently, refluxed at 130 \({}^{\circ}\)C overnight. The white precipitate produced was washed several times, sequentially, with distilled water and EtOH (5 \(\times\) 15 mL) employing a repeated suspension-centrifugation process; it was then dried in a vacuum oven at 40 \({}^{\circ}\)C until a constant weight was achieved. Finally, the obtained silica was calcined at 550 \({}^{\circ}\)C, reached at a ramp rate of 2 \({}^{\circ}\)C/min, for 5 h in a nitrogen gas environment.  
Step (ii)--synthesis of amino-functionalized silica (SBA-15-NH\({}_{2}\)). Attachment of amine functionalities onto the surface of SBA-15 was performed following a standard method described in the literature [10, 20, 21]. Here, 1.5 g of SBA-15 was suspended in 50 mL of APTS/toluene (1:100 by volume), and the resulting mixture was refluxed with stirring in an oil bath at 110 \({}^{\circ}\)C for 24 h. The resultant SBA-15-NH\({}_{2}\) was collected by centrifugation, washed with EtOH (3 \(\times\) 15 mL), and dried as in step (i).  
Step (iii)--synthesis of the initiator-modified intermediate (SBA-15-Br). The synthesis of the SBA-15-supported ATRP initiator was carried out through the Yamamoto method [19]. To a stirred mixture of SBA-15-NH\({}_{2}\) (0.5 g)/TMA (0.75 mL, 9.5 mmol)/DCM (25 mL) was added dropwise a solution of BMPB (1.2 mL) in DCM (5 mL) over 10 min. After 48 h of stirring, about 20 mL DCM was added to the mixture, which was then sonicated for 5 min; the solvent was subsequently evaporated with a rotary evaporator ([PERSON], R-210, Boston LabCo, Boston, MA, USA) at 40 \({}^{\circ}\)C. The final solid product was washed with EtOH (3 \(\times\) 15 mL) and dried as described above.  
Step (iv)--polymerization of SBA-15-Br with sodium 4-styrensoflunate to produce SBA-15-PSSNa. The surface-initiated ATRP reaction of SBA-15-Br with SSNa was carried out under a nitrogen gas inert atmosphere in a 100-mL three-necked flask equipped with a magnetic stir bar and a reflux condenser. Initially, a solution containing SBA-15-Br (100 mg) and SSNa (412 mg, 2 mmol) in 6 mL of MeOH was bubbled with nitrogen gas at 40 \({}^{\circ}\)C while stirring. After 15 min, a mixture of BiPy (31.23 mg, 0.2 mmol) and CuCl (0.197 mg, 0.002 mmol) was added to the solution, and the polymerization was allowed to proceed overnight at room temperature under nitrogen atmosphere. The product was filtered off, washed with water and EtOH, and dried under vacuum. Finally, the obtained SBA-15-PSSNa was acidified with an excess of 0.2 M HCl for 1 h; it was then naturalized with water and dried as above.