Triazolinedione-“clicked” poly(phosphoester)s: systematic adjustment of thermal properties

Abstract

The thermal properties of halogen-free flame retardant poly(phosphoester)s from acyclic diene metathesis polycondensation have been optimized by a systematic post-modification using 1,2,4-triazoline-3,5-dione derivatives. The straightforward modification not only increased their glass transition temperatures significantly but also improved the thermal stability with respect to their char yields.Poly( phosphoester)s (PPEs) can be prepared via both ringopening polymerization and polycondensation.1,2 We recently applied ADMET polycondensation to prepare a variety of PPEs. [3][4][5][6] Currently, PPEs are studied in biomedical applications for their biocompatibility, 7 biodegradability and adjus- show higher resistance to leaching and migration, compared to low molecular weight additives. 9 Indeed, phosphorus is an efficient char promoter forming an accumulated protective layer on the materials surface, which limits the release of fuel to the flame. 10,11 Additionally, PPEs typically show low toxicity or almost smoke-free burning. 12,13 Recently, the combination of phosphorus-containing flame retardants with nitrogen compounds has attracted much attention. The combination of both elements physically and chemically can dramatically improve the action of the phosphorus species in the condensed phase upon combustion. 14,15 Nitrogen compounds are believed to act by the release of inert gases or by the promotion of char formation as a result of a condensation reaction.Besides phosphorus and nitrogen, the introduction of aromatic structures is also often mentioned to promote the charring. 16As a systematic study on the thermal properties and char yield, with structural variation of the main-and side chains of PPEs, is missing in the current literature, the main goal of this research was the preparation of modified PPEs via ADMET polycondensation, as a result of the variation of both the backbone and side chains. Furthermore, we used the efficient, recently revisited "click chemistry" of 1,2,4-triazoline-3,5-diones (TAD) 17,18 to modify the double bonds along the PPE backbone to further adjust the material properties. This TADene chemistry can not only be applied as a reliable and convenient post-modification reaction of unsaturated polymers but will also introduce additional nitrogen atoms into the PPEs, which is expected to have a positive influence on their flame retardant performance. TADs are one of the most reactive (di)enophiles and show quantitative conversions at room temperature with isolated alkenes or conjugated dienes, respectively in an Alder-ene or Diels-Alder reaction. TAD has recently been applied in a wide range of applications, such as self-healing, 19 surface chemistry, 20-22 and post-modification of unsaturated ADMET polymers. 23This is the first report on the post-modification of PPEs via their internal double bonds for tuning their thermal properties. Supposing that TAD-modification can increase the glass transition temperature (T g ), this would undoubtedly broaden the range of applications for PPEs...

Expanding the Material Space of Biosustainable Poly(sophorolipids) by Modular Functionalization

“…Obviously, the TAD functionalization introduces an additional structural element to the parent polymer. Decomposition of this starts rather independent of functionalization degree or type of TAD functionality at a rather similar temperature range, which is consistent with the literature as at 300 °C the TAD compound degrades via scission of the carbon–nitrogen bond …”

Synthesis and characterization of modular polyphosphonate homopolymers and copolymers

“…Polymers containing nonmetals from the third row or below of the Periodic Table (phosphorus, sulfur, selenium) in their backbones are particularly interesting due to their potentially wider range of chemical, physical, and optical properties compared to those of their organic counterparts. Specifically, phosphorus‐based polymers are interesting due to the number of different types of phosphorus groups that can be incorporated into the polymer backbone, the ability of some of these groups to bind to metals and other Lewis acids and the unique physical properties that they impart such as enhancing flame retardancy or electrical resistivity 1–11 …”

Polyphosphonates as ionic conducting polymers

“…Polyethylene oxides have been widely studied as SPEs, and polyphosphonates derived from tetraethylene glycol, which have similar cation binding groups, may exhibit similar cation binding abilities. In addition, it may be possible to tune the cation binding abilities of the polyphosphonates derived from tetraethylene glycol by the appropriate choice of R and X groups 14–17 . Further, similar phosphorus‐containing polymers are typically flame‐resistant.…”

“…In addition, it may be possible to tune the cation binding abilities of the polyphosphonates derived from tetraethylene glycol by the appropriate choice of R and X groups. [14][15][16][17] Further, similar phosphorus-containing polymers are typically flame-resistant. Finally, the presence of 31 P nuclei in the polymer backbone should allow 31 P{ 1 H} NMR spectroscopy to be used to probe the cation binding and its effect on the polymer microstructure.…”