Higashimura, has extensively studied the HI/I2 and HI/Lewis acid initiated cationic polymerisations of acyclic vinyl ethers.
We have conducted similar polymerisations using isobutyl vinyl ether, 2,3-dihyrofuran and 3,4-dihydropyran, which provide suitable models for our glycal substrates.
Isobutyl vinyl ether
For comparison with our polymerisation studies of dihydrofuran these reactions were run over a longer period of time than reported by Higashimura.1 This is reflected in the slightly larger polydispersities than those achieved previously, representing the onset of chain transfer processes.
Polymerisations in hexane give low conversion of monomer which may be a consequence of poor polymer solubility.
The number average molecular mass increases in direct proportion to monomer conversion in dichloromethane at -78 °C, however, polydispersity does not indicate a living polymerisation. This may be an effect of the long reaction times necessary to achieve full conversion allowing competing chain transfer processes.
In dichloromethane at -15 °C polymerisation is complete within 30 min and not indicative of living polymerisation.
High molecular mass polymers are obtained when ZnI2 is used as co-catalyst, indicating cross-linked material.
The polymerisation of dihydrofuran using acetyl perchlorate as initiator has been extensively studied and sets a precident for future investigations.2
The cationic polymerisation of dihydropyran has long been known.3 However, materials with low Mpk values4 and wide polydispersities have been obtained when HI/I2 is used as initiator.