Copolymerization of oxetane with 3,3-dimethyloxetane : I. Reactivity parameters and microstructure of the copolymers

The copolymerization of 3,3-dimethyloxetane and oxetane has been studied in methylene chloride at 20°, with triethyloxonium tetrafluoroborate as initiator. The copolymerization reactivity parameters are rDMOx = 0.95 and rOx = 1.19. By means of 300 MHz 1H-NMR spectroscopy, the microstructure of the copolymers could be analyzed in terms of triad abundances. The observed values are in good agreement with the values calculated from the reactivity parameters thus showing the absence of penultimate effects and of re-distribution of the structural units in the copolymers. The results demonstrate that Ox is more reactive than DMOx to either of the two growing species in the copolymerization

Cyclic oligomers in cationic polymerization of 3,3-dimethyloxetane

The formation of cyclic oligomers in the cationic polymerization of 3,3-dimethyloxetane (1) was investigated. By means of gas chromatography coupled with mass spectroscopy, cyclic oligomers from tetramer up to nonamer (2a–f) were detected in decreasing concentration. The oligomer/polymer ratio at complete monomer consumption changes with the initiating system used. This ratio is not influenced by the initiator concentration but it increases with decreasing monomer concentration. It is proposed that the cyclic oligomers are formed by reaction of the monomer with macrocyclic oxonium ions of type 5 which in turn are formed by an intramolecular (temporary) termination reaction. The high preference to form cyclic tetramer is discussed in terms of the preferred polymer backbone conformation. In the polymerization of oxetane, cyclic tetramer is the most important oligomer, but, contrarily with previous reports, higher oligomers were also found to be present

Copolymerization of oxetanes : 2. Co-oligomers in the copolymerization of oxetane with 3,3-dimethyloxetane

The cyclic oligomers which are formed during the cationic copolymerization of oxetane (1) with 3,3-dimethyloxetane (2) were analyzed qualitatively and quantitatively by means of gas chromatography and mass spectroscopy. Cyclic oligomers from trimer up to octamer were detected but, as with the homopolymerizations, the cyclic tetramers were the most abundant. The relative abundances of the different tetramer co-oligomers were compared with the theoretical abundances, calculated from the reactivity parameters of the copolymerization and the monomer feed ratio, using the method of Ito and Yamashita. There was no agreement between the calculated and experimental values. This was attributed to a lower tendency to cyclize for polymer chains having a 2-oxonium chain end compared with polymer chains having a 1-oxonium chain end

Chemical ionization mass spectroscopy of some crown ethers

Methane and isobutane chemical ionization mass spectrometry is superior to the classical electron impact technique for the analysis of aliphatic macrocyclic polyethers of the 4n-crown-n type. The latter reagent gas is particularly suited for molecular weight determinations