Polypropylene glycol

Salmeterol xinafoate (SX) and fluticasone propionate (FP) were obtained from Vamsi Labs, India (BN. SX-0081010) and LGM Pharma, USA (BN. 5501-B-11030), respectively. Cyclohexane was purchased from VWR International Ltd, UK. Sorbitan monooleate 80 (Span 80) and Polypropylene glycol 400 (PEG400) were from Sigma Aldrich Ltd, UK. Methanol (Fisher Scientific Ltd, UK) and ammonium acetate (Chromanorn Hipersolv for HPLC, BDH Prolabo, VWR International Ltd, UK) were high performance liquid chromatography (HPLC) grade. Whatman^TM nylon filters (pore size 0.2 μm and 0.45 μm, diameter 47 mm) and hexane were purchased from Fisher Scientific Ltd, UK. Polypropylene glycol (average Mn approx. 1000) was from Sigma Aldrich Ltd, UK, and size 3 gelatin capsules were from Capsugel, France.

Polypropylene glycol with a molecular weight of 400 g mol⁻¹ (PPG 400), polyethylene glycol with a molecular weight of 400 g mol⁻¹ (PEG 400), ABTS (≥ 98 wt% purity) and dopamine hydrochloride (98 wt% purity) were acquired from Sigma-Aldrich. The ILs, cholinium dihydrogen phosphate ([Ch][DHP], >98 wt% purity) and cholinium acetate ([Ch][Acet], 98 wt% purity) were both purchased from IoLiTec, and cholinium dihydrogen citrate ([Ch][DHC], ≥98% wt% purity) from Sigma-Aldrich. Dipotassium hydrogen phosphate trihydrate (K₂HPO₄.3H₂O, 98 wt% purity) was purchased from Scharlau.
Commercial laccase from Trametes versicolor (10 U mg⁻¹) was acquired from Sigma-Aldrich. Sodium acetate (CH₃COONa) pure from AnalaR Normapur and acetic acid (CH₃COOH, 99 wt% purity) from Fisher Chemical was used to prepare sodium acetate buffer; disodium phosphate (Na₂HPO₄, 99 wt% purity) and citric acid (C₆H₈O₇, 99.5 wt% purity), both acquired from Panreac were used to prepare citrate-phosphate buffer; Tris-HCl buffer was prepared by using tris (hydroxymethyl) aminomethane [NH₂C(CH₂OH)₃, >99 wt% purity] from PRONALAB and a hydrochloric acid solution (HCl, 1 M).

Two types of silica powder, differing in production method and particle morphology, were used as the solid phase of the shear thickening fluids. KE-P10 is an amorphous silica made by the sol-gel Stöber process [78 (link)]. According to the manufacturer’s specification (Nippon Shokubai, Tokyo, Japan), the powder particles have a spherical shape, and their size is in the range of 100–200 nm. The purity of silica is ≈90%, and the main impurities are the methyl and butyl alcohols remaining after the production process.
The second ceramic powder was fumed silica (SF), supplied by Sigma-Aldrich, St. Louis, MO, USA. According to the information provided by the manufacturer, the nanometric (7–14 nm) powder particles have an irregular shape and form agglomerates with a size of 200 to 300 nm.
Poly(propylene glycol) with an average molar mass of 425 g/mol, provided by Sigma-Aldrich, St. Louis, MO, USA, was utilized as a carrier fluid in all STFs obtained.
MM 922 molding silicone (ACC Silicones, Bridgwater, Somerset, UK) was used to produce composite samples of STF–silicone for the first kinetic energy dissipation tests. MM922 silicone has a density of 1.26 g/cm³, a hardness of 22 °ShA, a tensile strength of 3.64 MPa, and an elongation at a break of 497%. The cross-linking time initiated with the MM CAT B5 catalyst (ACC Silicones, Italy) was 8–12 h.

Isophorone diisocyanate (IPDI) (>99%), isopropylthioxanthone (ITX) (>98%), Sudan-1 (>93%), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (>98%) were purchased from Tokyo Chemical Industry (TCI) (https://www.tcichemicals.com/ES/en/). Hexamethylene diisocyanate (HDI) (≥98.0%), polyethylene glycol (PEG) (M_n: 400 g/mol), polypropylene glycol (PPG) (M_n: 2000 g/mol) and, (M_n: 1000 g/mol) 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD), trimethylpropane tris(3-mercaptopropionate) (triSH) (≥95.0%), and 1,1,3,3-tetramethylguanidine (TMG) (99.0%), were obtained from Sigma-Aldrich (https://www.sigmaaldrich.com/ES/es). Sodium tetraphenylborate (NaBPh₄) (99%) was purchased from ABCR (https://abcr.com/de_en/). PPG-di-IPDI 2000 was kindly supplied by Cidetec (https://www.cidetec.es). TBD·HBPh₄ salt preparation: 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (1 eq.) was dissolved in 10% HCl aqueous solution and dropwise added to a sodium tetraphenylborate (1.1 eq.) aqueous solution. The subsequent mixture was filtered and washed thoroughly with water and chilled MeOH. The photocatalyst was obtained as a white powder in quantitative amounts, and characterized by ¹H NMR. Isocyanate-terminated prepolymers were prepared by the addition of 2.1 eq. of isocyanate into 1 eq. of polyol previously dried under reduced pressure. The conversion of the reaction monitored by FTIR spectroscopy.