Pentaerythritol

SPc was synthesized following a previously described method [12 (link)]. Briefly, the star initiator Pt-Br is constructed by adding 2-bromo-2-methylpropionyl bromide (HEOWNS) dropwise into the pentaerythritol (Alfa Aesar) solution in dry tetrahydrofuran and triethylamine (Beijing Chemical Works). The initiator Pt-Br was further polymerized with DMAEMA (Energy Chemical) under a nitrogen atmosphere with the help of tetrahydrofuran, PMDETA (Sigma-Aldrich) and CuBr (Sigma-Aldrich). Dialysis was carried out to purify the crude product and SPc was obtained as white powder after being freeze-dried. A 60 g/L stock of SPc was prepared with double distilled water (ddH₂O). To synthesize fluorescent SPc, TPE-pentaerythritol was used instead of pentaerythritol to prepare the TPE-4Br star initiator and the subsequent steps were the same.

All simulants described in this paper were cylindrical with a diameter of 60 ± 1 mm. The length of simulants depended on their composition and mass. The main components used for the construction of simulants were boron carbide powder (B₄C) (Alfa Aesar, Kandel, Germany), aluminium oxide powder (Al₂O₃) (VWR, Leuven, Belgium), lithium carbonate powder (Li₂CO₃) (VWR, Leuven, Belgium) and liquid polyurethane rubber, VytaFlex^® 30 series (Smooth-On, Macungie, PA, USA), with a shore hardness of 30A according to ASTM D-2240. For the production of negative silicone moulds, OOMOO 30 (Smooth-On, Macungie, USA) liquid silicone rubber with shore hardness of 30A was used.
For long-term stability studies and calibration purposes, pure polyoxymethylene (Delrin), polytetrafluoroethylene (PTFE), graphite, silicon and aluminium rods with the diameter of 60 mm and length of 200 mm, from American Elements (Los Angeles, CA, USA) were used.
Chemicals used for synthesis of explosives for doping of simulants were: concentrated nitric and sulphuric acids, hexamethylenetetramine and ethylene glycol (all Merck, Darmstadt, Germany), pentaerythritol (Alfa Aesar, Kandel, Germany) and deionized water.

Oleic acid 90+ % was purchased from Croda Int. as Priolene 6936. This product is a mixture of distilled fatty acids and contains <3 wt% of 18 acids, 2 wt% of 18:0 acid, 92 wt% of C_18:1n9 acid, 3 wt% of C_18:2n6 acid, 0.3 wt% of C_18:3n3 acid and <1 wt% of >C₁₈ acids (GC). Isostearic acid was purchased from Unichema (UK) as Prisorine 3603. This product contains ca. 83 %wt of branched and saturated acids C₁₆–C₂₂. Pentaerythritol was purchased from Alfa Aesar. Trimethylolpropane dimer was purchased from Perstorp (Sweden).
As catalysts we used selected commercially available homogeneous metallic Sn, Ti and Zr catalysts. All of the catalysts used are listed in Table 2.Table 2

List of organometallic catalysts used in study

Catalyst	Trade name	Abbreviation	Supplier
Di(n-butyl)tin oxide	–	Bu2SnO	Alfa Aesar
n-Butyltin hydroxide oxide	–	BuSn(O)OH	Alfa Aesar
Tin bis-(2-ethylhexanoate)	Fascat 2003	F 2003	PMC
Butyl tin tris-(2-ethylhexanoate)	Fascat 4102	F 4102	PMC
Tetra-(n-butyl) titanate	Tyzor TBT	T TBT	DuPont
Tetra-(isopropyl) titanate	Tyzor TPT	T TPT	DuPont
Tetra-(n-butyl) zirconate	Tyzor NBZ	T NBZ	DuPont