Abstract
Polymers with a phosphorus-boron main chain have attracted interest as novel inorganic materials with potentially useful properties since the 1950s. Although examples have recently been shown to be accessible via several routes, the materials reported so far have been limited to P-mono(organosubstituted) materials, [RHPBH2] n , containing P-H groups. Here we report a general route for the post-polymerisation modification of such polyphosphinoboranes giving access to a large range of previously unknown examples featuring P-disubstituted units. Insertion of alkenes, R'CH[double bond, length as m-dash]CH2 into the P-H bonds of poly(phenylphosphinoborane), [PhHPBH2] n was facilitated by irradiation under UV light in the presence of the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPAP) and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) under benchtop conditions giving high molar mass, air-stable polymers [PhR'PBH2] n with controlled functionalisation and tunable material properties. The mechanistic explanation for the favourable effect of the addition of TEMPO was also investigated and was proposed to be a consequence of reversible binding to radical species formed from the photolysis of DMPAP. This new methodology was also extended to the formation of crosslinked gels and to water-soluble bottlebrush copolymers showcasing applicability to form a wide range of polyphosphinoborane-based soft materials with tunable properties.
Highlights
Polymers featuring elements other than carbon in the main chain are attracting widespread interest as functional so materials with an expanding range of applications
When the reaction mixture was irradiated under UV light for 20 h at 20 C (Table 1, entry 1), a single peak emerged in its 31P NMR spectrum at d 1⁄4 À23.5 ppm with no apparent 1JPH coupling
The 1H NMR spectrum of the reaction mixture showed a signi cant reduction in the intensity of the P–H resonances and emergence of a number of broad peaks in the 0.8–1.3 ppm region corresponding to new aliphatic protons
Summary
Polymers featuring elements other than carbon in the main chain are attracting widespread interest as functional so materials with an expanding range of applications. Unlike for the aforementioned phosphine-borane adducts studied by Gaumont, heating 1 (0.2 mmol) with 1-octene (0.2 mmol) in THF (0.5 ml) at 60 C for 24 h did not result in detectable insertion of the alkene into the P–H bonds of the polymer based on 31P NMR analysis.
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