Epichlorohydrin ech

The cellulose used was Sigmacell Cellulose powder, Type 20 (average particle length 20 µm), purchased from Sigma-Aldrich (Sigma-Aldrich, St. Louis, MO, USA). Sodium Hydroxide (purity 97%) was purchased in pellet form from Thermo Fisher Scientific (Waltham, MA, USA). Urea (ACS grade), and Epichlorohydrin (ECH) (purity 98%) were also purchased from Sigma-Aldrich. All chemicals were used as-received.

All chemical reagents and solvents were obtained from Sigma-Aldrich (Munich, Germany), Scharlab (Barcelona, Spain) and Eurisotop (Saint-Aubin, France). Tetrahydrofuran (THF, ≥99.9% (GC), Scharlab, Barcelona, Spain) was dried using a drying agent (calcium hydride, CaH₂, 95%, Aldrich, Munich, Germany), degassed by three freeze-degas-thaw cycles and distillated under reduced pressure at 323 K. (±)-Epichlorohydrin (ECH, ≥99% (GC), Sigma Aldrich) was purified by distillation following the same procedure explained before for the purification of THF. The purification of tris(pentafluorophenyl)borane (B(C₆F₅)₃, 95%, Sigma Aldrich) was performed by sublimation under reduced pressure at 333 K using a cold finger condenser. Dichloromethane (CH₂Cl₂, anhydrous, Sigma Aldrich) was degassed by bubbling Argon for 30 min prior to use. (+)-Sodium l-ascorbate (BioXtra, ≥99% (NT), Sigma Aldrich), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA, 99%, Sigma Aldrich), Propargyl ether (98%, Sigma Aldrich), N,N-dimethylformamide (DMF, anhydrous, ≥99.8%, Scharlab), sodium azide (NaN₃, ≥99.5%, Sigma Aldrich), and methanol (MeOH, ≥99.9%, Scharlab) were used as received. Copper (I) bromide (CuBr, 98%, extra pure, Acros Organics, Fair Lawn, NJ, USA) was purified following the Keller and Wycoff method [16 (link)].

tert-Butyl glycidyl ether
(tBGE, 99%, Sigma-Aldrich) and epichlorohydrin (ECH,
99%, Sigma-Aldrich) were dried over CaH₂ (93%, Thermofisher)
for 24 h under a N₂ atmosphere and distilled before use.
2,2-Dipyrazol-1-yl-ethanamine (pz-NH₂) was synthesized
following the procedure of Reger et al.^{62 (link)} All other chemicals were obtained from commercial sources and were
used without further purification.

To synthesize azido TPU, epichlorohydrin (ECH) (≥99%), boron trifluoride THF complex (>99.5%), dibutyltin dilaurate (95%), and MDI (98%) were obtained from Sigma-Aldrich chemical Co. Methylene chloride (MC) (99.5%), THF (99.5%), N, Nʹ-dimethylformamide (DMF) (99%), and sodium azide (99%) were purchased from SAMCHUN Chemical Co. To fabricate spiropyran (SP) including alkyne group, 1-(2-Hydroxyethyl)-3,3-dimethylindolino-6′-nitrobenzopyrylospiran (>93.0%) was purchased from TCI (Tokyo Chemical Industry Co.). propionic acid (95%), DCC (99%) and 4-(Dimethylamino)pyridine (DMAP) (≥99%) were obtained from Sigma-Aldrich Chemical Co. For the click reaction between azido-TPU and spiropyran, copper (II) sulfate pentahydrate (99.0%) and sodium ascorbate (98%), which act as catalysts, were obtained from Sigma-Aldrich chemical Co.