Poly(phosphonate)s via Olefin Metathesis: Adjusting Hydrophobicity and Morphology

Abstract

Olefin metathesis step-growth (acyclic diene metathesis (ADMET)) and chain-growth (ring-opening metathesis) polymerization was used to prepare linear poly-(phosphonate)s with variable hydrophilicity. The first phosphonate monomer, i.e., di(undec-10-en-1-yl) methylphosphonate, for ADMET polymerization was developed, and potentially degradable and biocompatible, unsaturated poly(phosphonate)s were prepared with molecular weights up to 23 000 g mol −1 with molecular weight dispersities Đ < 2. These polymers were studied with respect to their interaction with a calcium phosphate bone substitute material from an aqueous nanoparticle dispersion that was prepared by a solvent evaporation miniemulsion protocol. Ring-opening metathesis polymerization (ROMP) was employed to synthesize more hydrophilic amorphous polyphosphonates from a novel seven-membered cyclic phosphonate monomer, i.e., 2-methyl-4,7dihydro-1,3,2-dioxaphosphepine 2-oxide, as well as hydrophobic crystalline copolymers with cis-cyclooctene. ROMP yielded polymers with molecular weights up to 6000 g mol −1 (homopolymer) and 47 000 g mol −1 (copolymers). Poly(phosphonate)s are potentially hydrolytically degradable materials and therefore promising materials for biomedical applications.

Poly(phosphonate)-mediated Horner–Wadsworth–Emmons reactions

“…After complete addition the solution was stirred for 2 hours and stored over night at −28°C to facilitate the precipitation of the pyridinium hydrochloride. 27 Monomer 2 (4.792 g, 12 mmol) was placed in an oven-dried Schlenk tube and Grubbs' first generation catalyst (118 mg, 144 µmol, 1.2 mol%) dissolved in 1 mL chlorobenzene was added under an argon atmosphere with stirring. Column chromatography (ethyl acetate-petrol ether 1 : 2 R f = 0.35) yielded the desired product (23.96 g, yield: 60%).…”

“…[16][17][18][19][20] Several reaction conditions have been reported to prepare polymers for applications in lubricants, optics, medicine and, most importantly, as flame-retardant additives. 27,28 Nevertheless, the alkyl side-chain in these systems remain untouched and unreactive, which is beneficial for biomedical applications and a controlled degradation behavior. ADMET of acyclic unsaturated phosphonates yields hydrophobic materials that show similar bone-targeting properties as their phosphate counterparts.…”

“…Therefore only a few examples of functional poly( phosphonate)s have been reported so far, carrying a vinyl or a sulfonic acid group. 27 We have realised two approaches to functionalize poly( phosphonate)s for the HWE reaction: postpolymerization modification of a poly(alkylene methylphosphonate)s and polymerization of a prefunctionalized monomers. Furthermore, metathesis polymerization is known to tolerate a range of different functionalities, including carbonyl and phosphonate compounds.…”

“…27,28,[35][36][37][38] Tailoring these properties allowed us to enhance the HWE reaction and its workup procedure in several model reactions. 27,28,[35][36][37][38] Tailoring these properties allowed us to enhance the HWE reaction and its workup procedure in several model reactions.…”

“…27,28,35,36,38 With this report we introduce this material into the organic-chemical science and give chemists and researchers an adjustable and versatile tool to improve their synthesis in the lab and industry. In addition, this is the first report on the synthesis of linear poly (hydroxyalkylene phosphate)s from poly(alkylalkylene phosphonate)s. In our current and past work on this versatile class of materials we have demonstrated the usability of poly( phosphonate)s in materials science and the biomedical field.…”