Radical Ring-Opening Polymerization of Phosphorus Heterocycles: Computational Design of Suitable Phosphetane Monomers

Abstract

High-level ab initio calculations have been used to determine the propensities of various phosphetanes towards radical ring-opening polymerization. At the G3(MP2)-RAD level of theory, the propagation rate constants of 1-methylphosphetane (7.5 × 10 4 L mol −1 s −1 ), 1-phenylphosphetane (4.6 × 10 5 L mol −1 s −1 ), cis,cis-2,4-dichloro-1-phenylphosphetane (3.8 × 10 7 L mol −1 s −1 ), cis,cis-2,4-difluoro-1-phenylphosphetane (3.0 × 10 7 L mol −1 s −1 ), and 1-phenyl-3-oxaphosphetane (4.0 × 10 6 L mol −1 s −1 ) are very high, rendering them unsuitable for copolymerization with common alkenes. In contrast, the propagation rate constants of 1-tert-butylphosphetane (1.7 × 10 3 L mol −1 s −1 ) and cis,cis-2,4-dimethyl-1-phenylphosphetane (9.2 × 10 2 L mol −1 s −1 ) indicate that either incorporation of a t-butyl substituent at phosphorus or alkylation at the 2-and/or 4-positions will produce monomers with more compatible reactivities for copolymerization with alkenes. In the case of 1-tert-butylphosphetane, however, homolytic substitution of the propagating radical with the t-butyl substituent at P will be competitive with the propagation step and could affect the microstructure of the polymer. The borane adduct and the oxide of 1-phenylphosphetane were both found to be unreactive towards radical ring-opening. The calculations suggest that, for chiral phosphetanes, the ring-opening reaction is enantioselective at phosphorus and the resulting polymer will be isotactic.

P-Heterocycles as Ligands in Homogeneous Catalytic Reactions

“…It was found that, in the case of 1- tert -butylphosphetane, homolytic substitution of the propagating radical with tert -butyl substituents at phosphorus will be competitive with the propagation. The calculations also suggest that, for chiral phosphetanes, the ring-opening reaction is enantioselective at P and the polymer is expected to be isotactic …”

“…The calculations also suggest that, for chiral phosphetanes, the ring-opening reaction is enantioselective at P and the polymer is expected to be isotactic. 172…”

Inorganic and organometallic polymers

“…Several ab initio studies have been reported that evaluate the feasibility of the radical ring-opening polymerization of several phosphorus-containing heterocycles. 82,83 Novel copper halide coordination polymers were prepared using a P 4 S 3 ligand. 84 Phosphonate-capped dendrimers have been prepared and were shown to promote the multiplication of human natural killer cells.…”

From Fundamentals to Applications: Living Polymer Science at the 29th Australasian Polymer Symposium

“…They show that ab initio quantum chemical calculations can be efficiently employed to predict a novel route to the radical ring-opening polymerization of phosphetanes to polyphosphines, with the aim of incorporating phosphorus atoms into polymer backbones to improve their polarity and metal-binding characteristics. [12] In an example of fundamental polymer physics in action, John Torkelson and his team investigate the effects of nanoscale confinement and interfaces on the glass transition temperature of poly(n-methacrylates). [13] The 29th APS and this special issue of Australian Journal of Chemistry thus demonstrate the importance of maintaining a balance as well as an efficient feedback loop between fundamental approaches and applications-(and sometimes commercially) driven research, focussing on fields such as polymer-based drug delivery, optoelectronics, or tissue engineering.…”