Activated molecular sieves

The commercially available triblock co-polymer Poloxamer^® 407 (P407, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO, $\overline{M_n}$ = 12,600 Da) was purchased from Sigma Aldrich (Milan, Italy) and used as macrodiol for PEU synthesis after drying at 100 °C for 8 h and cooling at 40 °C under a vacuum (approx. 200 mbar). Furthermore, 1,6-hexamethylene diisocyanate (HDI) and N-Boc serinol were also purchased from Sigma Aldrich (Milan, Italy) and used as a diisocyanate and chain extender during PEU synthesis, respectively. Before use, HDI was distilled under reduced pressure to remove moisture and stabilizers, while N-Boc serinol was stored in a desiccator under a vacuum. The organotin compound dibutyltin dilaurate (DBTDL) was purchased from Sigma Aldrich (Milan, Italy) and added in a catalytic amount to catalyze the PEU synthesis reaction. The synthesis was performed using 1,2-dichloroethane (DCE, Carlo Erba Reagents, Milan, Italy) as a solvent. Before the synthesis procedure, DCE was anhydrified over activated molecular sieves (4 Å, Sigma Aldrich, Milan, Italy, activation at 120 °C overnight) under nitrogen atmosphere overnight. All other solvents required for PEU synthesis were purchased from Carlo Erba Reagents (Milan, Italy) in analytical grade and used as received.

Before the synthesis, reagents (i.e., macrodiol, diisocyanate, and chain extender) were treated to remove residual water content and stabilizers according to the methods proposed by Pontremoli, Boffito et al. [18 (link)]. Briefly, Poloxamer^® 407 (P407, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) PEO-PPO-PEO triblock copolymer, M_n 12,600 Da, 70% w/w PEO) was dried at 100 °C for 8 h while keeping low pressure (i.e., 200 mbar) and then cooled down at room temperature (RT) under vacuum. 1,6-hexamethylene diisocyanate (HDI) was distilled under reduced pressure, meanwhile 1,4-cyclohexanedimethanol (CDM) was kept at RT under vacuum in a dessicator. Anhydrous 1,2-dichloroethane (DCE) was prepared by pouring the solvent over activated molecular sieves (3 Å, Sigma Aldrich, Milan, Italy) under constant nitrogen flow until use. P407, HDI, CDM, and dibutyltin dilaurate (DBTDL) as catalyst were purchased from Sigma Aldrich, Milan, Italy, while solvents were purchased from CarloErba reagents (Cornaredo, Italy) in their analytical grade.

β-cyclodextrin hydrate (β-CD) (99 %, Acros Organics), tetraethyl orthosilicate (TEOS) (≥99 %, Merck), (3-aminopropyl)triethoxysilane (APTES) (≥99 %, Merck), N,N′-carbonyldiimidazole (CDI) (≥98 %, Merck), and cetyltrimethylammonium bromide (CTMABr) (≥97 %, Merck) were used as purchased, and no further purification was performed. Aqueous ammonia (25 %), ethanol (96 %), and hydrochloric acid (37 %) were purchased from Reakhim and used without additional purification. Acetone (extra pure, Merck) and N,N′-dimethylformamide (DMF) (pure analytical, Reakhim) were dried for 48 h before utilization with activated molecular sieves (0.3 nm, Merck). Benzene (pure analytical, Reakhim) was used to prepare benzene solutions in water. Distilled water was used in all experiments.