Phenylphosphonic dichloride

9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from Chemos GmbH, Germany, and it was freshly dehydrated before use. Phenylphosphonic dichloride, 4-hydroxybenzaldehyde, 4-aminophenol, N,N-dimethylformamide (DMF), triethylamine (Et₃N), BaTiO₃ nanoparticles (cubic crystalline phase, <100 nm particle size (BET)), and 4,4′-diphenylsulfone (DDS) were provided by Sigma-Aldrich and used as received. Epoxy resin based on bisphenol A diglycidyl ether, with an epoxy equivalent weight (EEW) of 0.53 equiv. per 100 g (Mn~377 g/mol), was purchased from Sigma Aldrich. A hyperbranched Cu phthalocyanine polymer (HPc) was synthesized starting from 4,4′-bis(3,4-dicyanophenoxy)biphenyl and CuCl, following a method adapted from a previously reported procedure [32 (link)]. The chemical structure of HPc is shown in Figure 1.
Aromatic dialdehyde, bis(4-formylphenyl) phenylphosphonate, was prepared by the reaction of phenyl phosphonic dichloride and 4-hydroxybenzaldehyde according to a method previously described [27 (link)].

Partially hydrolyzed PVA (Mowiol 26–88 (KURARAY POVAL 26–88)) with a molecular weight of 160,000 g/mol and an 87.7 percent degree of hydrolysis was supplied by ZAUBA (Munchen, Germany) and used as received. Chitosan hydrochloride (Mw = 302.11 kDa, DAC degree = 82%), titanium (IV) oxide nanopowder (21 nm primary particle size), and glacial acetic acid were purchased from Sigma-Aldrich (St. Louis, MO, USA). 3,3′-Diaminodiphenyl sulfone, 4-hydroxybenzaldehyde, tetrahydrofuran anhydrous (THF), N,N-dimethylformamide (DMF), and phenylphosphonic dichloride were purchased from Sigma-Aldrich (Taufkirchen, Germany).
9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from Chemos GmbH, Germany and dehydrated before use. Polyphosphonate additive (PFR-3) has been prepared in our laboratory according to an adopted procedure from a previous work [47 (link)], starting from 3,3′-diaminodiphenyl sulfone and 4-hydroxybenzaldehyde. All other reagents were used as received from commercial sources.

Partially hydrolyzed PVA–Mowiol 26–88 (M_w = 160,000 g/mol, degree of hydrolysis = 87.7%) was purchased from Zauba (Munchen, Germany). 4,4′-Sulfonyldianiline (DDS), vanillin, LiClO₄, BaTiO_3, graphene-oxide (GO), oxalic acid (OA), tetrahydrofuran (THF), N,N′-dimethylformamide (DMF), and phenylphosphonic dichloride were provided from Sigma-Aldrich and used as received. 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was purchased from Chemos GmbH, Altdorf, Lower Bavaria, Germany and dehydrated before use.