Phosphorus pentafluoride, initiation

Polymerization of 4-bromo-6,8-dioxabicyclo[3.2.1 ]octane 2 7 in dichloromethane solution at —78 °C with phosphorus pentafluoride as initiator gave a 60% yield of polymer having an inherent viscosity of 0.10 dl/g1. Although it is not described explicitly, the monomer used seems to be a mixture of the stereoisomers, 7 7a and 17b, in which the bromine atom is oriented trans and cis, respectively, to the five-membered ring of the bicyclic structure. Recently, the present authors found that pure 17b was very reluctant to polymerize under similar conditions. This is understandable in terms of a smaller enthalpy change from 17b to its polymer compared with that for 17a. In the monomeric states, 17b is less strained than 17a on account of the equatorial orientation of the bromine atom in the former, whereas in the polymeric states, the polymer from 17b is energetically less stable than that from 17a, because the former takes a conformation in which the bromine atom occupies the axial positioa Its flipped conformation would be even more unstable, because the stabilization by the anomeric effect is lost, in addition to the axial orientation of the methylene group. 

Attempted polymerization of ds-7,9 dioxabicyclo[4.3.0]nonane 43 with phosphorus pentafluoride as initiator at temperatures ranging from -25 to 0 °C provided only a cyclic dimer 44 in high yield35. Under similar conditions trans-7,9-dioxabicyclo-[4.3.0]nonane 45 polymerized almost instantly to polymer 46 with number average molecular weight of several thousands, along with a small amount of a cyclic dimer 47. 

As far as the polymerisations of DCA other than DXL by non-protonic initiators are concerned, Kops and Spanggaard [11] favour the ring expansion mechanism for the dimerisation and polymerisation of the cis- and tnms-7,9-dioxabicyclo[4.3.0] nonanes by phosphorus pentafluoride or triethyloxonium hexachloroantimonate, although they have not obtained any definitive evidence for it. 

No triester of levoglucosan was found92 that polymerized at temperatures much below 0°. At —78°, the triacetate complexed with phosphorus pentafluoride, and, at high concentration, precipitated from solution.91 The tris(monofluoroacetate) failed to polymerize under a variety of conditions.91 The trinitrate polymerized at 0°, but the product was not fully characterized.92 Polymerization of the triacetate proceeded to reasonable conversions with a number of catalysts at 0°, but the viscosity and the stereoregularity of these polymers were low.92 In a simple, copolymerization experiment, it was demonstrated that the low polymerizability of levoglucosan triacetate was due not only to a failure to initiate but also to sluggish propagation.92... 

Several catalysts and initiator systems have been tested for the polymerization of GlcAnBzl3, including the following Lewis acids boron trifluoride and its etherate, phosphorus pentafluoride, titanium tetrachloride, and antimony pentachloride and pentafluoride. Several cationic initiators have also been used, including (triphenylmethyl) antimony hexachloride, 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl hexa-fluorophosphate, acetyl hexafluorophosphate, pentamethylbenzyl hexa-fluorophosphate (most of which were generated in situ), and triethyl-... 

Compared with 49, 2,5-dioxabicyclo[2.2.2]octan-3-one (54) prepared from sodium 3,4-dihydro-2//-pyran-2-carboxylate has a much low polymerization reactivity [54] Lewis acids such as antimony pentachloride, phosphorus pentafluoride, and boron trifluoride etherate were not effective at all to initiate the polymerization of 54. Trifluoromethanesulfonic acid induced the polymerization of 54, but the yield and molecular weight of the polymer were low. Bicyclic lactone 54 was allowed to polymerize with anionic and coordination initiators such as butyl-lithium, lithiumbenzophenone ketyl, and tetraisopropyl titanate. However, the... 

Monomer [9] was polymerized with 20 mol% phosphorus pentafluoride as initiator in dichloromethane at -78°C for 6 min and the corresponding polymer was obtained in 67% yield. Its conventional debenzylation yielded a comb-shaped polysaccharide [P9] of DPn = 40. 

Therefore, PFe has been supposed to react with oxonium ions of the diepoxide to form hexafluorophosphoric acid, which in turn decomposes into hydrofluoric acid and phosphorus pentafluoride. HPFg, HF and PF5 are considered to be potential initiators for cationic polymerizations [23]. 

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