ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
The study of the structure of the end-groups of poly(β-propiolactone) and poly(ε-caprolactone) by 1H, 31P{1H} NMR, and IR spectroscopy revealed that the mode of ring scission in the monomer in the first propagation step depends on the initiator used. In the initiation of the β-propiolactone and ε-caprolactone polymerization with halonium salts ((CH3)2Br⊕SbF6⊖ or (CH3)2I⊕SbF6F6⊖) the exocyclic oxygen atoms in the monomer molecules are attacked and oxonium ions are formed. The propagation steps proceed with alkyl-oxygen bond scission in the active center and with attack at the exocyclic oxygen atom in the subsequent monomer molecule. Thus, the tertiary oxonium ions are the exclusive active species from the very beginning of the polymerization. Acylium cations (CH3CO⊕ SbF6⊖ or CH3CH2CO⊕SbF6⊖) as initiators attack both exo-and endocyclic oxygen atoms in the monomers and the initiation proceeds with almost equal proportions of alkyl-oxygen and acyl-oxygen bond scission. Thus, in the polymerization of β-propiolactone the concentration of the acylium growing species decreases with increasing number of propagation steps and finally the tertiary oxonium ions are becoming the exclusive growing species. In the polymerization of ε-caprolactone the active acylium centers apart from propagation participate also in side reactions leading to the cleavage of a proton.
Zusätzliches Material:
9 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1984.021850405
