title: The beneficial influence of ultrasound in the polymerization of epsilon-caprolactam to polyamide-6 (Nylon 6). Part II: additional experiment to understand the "pre-sonication effect".
abstract: Ultrasound (US) "pre-sonication effect" is the beneficial effect of US in the hydrolytic polymerization of epsilon-caprolactam (CL) mixtures with very low water concentrations (about 0.1-1 wt%). It appears after a mild initial treatment of the mixtures with US [17.5-20 kHz, short times (5-15 min), low temperatures (70-110 degrees C)] followed by heating at 220-260 degrees C. An explanation is proposed on the basis of the formation in mild conditions (100 degrees C) of low concentrations of cyclic oligomers never detected in the literature at those conditions. These, under US irradiation, produce linear amino acid oligomers, which are strong activators of polymerization when the mixture of CL and water, after US irradiation, is heated at the suitable polymerization temperature indicated above.
authors.affiliation: Department of Physical Chemistry and Electrochemistry, University of Milan via Golgi no. 19, I-20133 Milano, Italy. bittorio.ragaini@unimi.it
authors.forename: Vittorio
authors.initials: V
authors.lastname: Ragaini
authors.forename: Carlo
authors.initials: C
authors.lastname: Pirola
authors.forename: Giulio
authors.initials: G
authors.lastname: Rocco
authors.forename: Cesare
authors.initials: C
authors.lastname: Guaita
mesh_terms: D002209:Caprolactam / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000528:radiation effects; D011091:Polyesters / Q000737:chemistry* / Q000528:radiation effects*; D011108:Polymers / Q000138:chemical synthesis* / Q000528:radiation effects*; D011829:Radiation Dosage; D012996:Solutions; D013010:Sonication; D014867:Water / Q000737:chemistry
chemical_list: D011091:Polyesters; D011108:Polymers; D012996:Solutions; D014867:Water; C016240:polycaprolactone; C009916:nylon 6; D002209:Caprolactam