Ultrasonic Modification of Polymers. I. Degradations of Polystyrene in the Presence of Various Poly(alkyl Methacrylates)

Ultrasonic (70 W, 20 kHz) degradations of polystyrene (PS) have been carried out with various poly(alkyl methacrylates) (PRMA) for periods of 3 h at 27°C in toluene (2.0 to 5.0% solutions). The isolation of sequence copolymers thus prepared from their associated homopolymers was achieved by employing selective solvents (solvent for one homopolymer but a precipitant for the second homopolymer in the mixture). The recovered products were analyzed by gel permeation chromatography (GPC), infrared spectroscopy (IR), and viscometry. These analyses showed that when the substituents in PRMA were methyl, ethyl, isopropyl, n-butyl, isobutyl, or phenyl, sequence copolymers with segments from PS as well as from poly(alkyl methacrylate) were obtained. However, when the substituents on PRMA were hexyl, isodecyl, lauryl, hexadecyl, octadecyl or isobornyl there were no sequence copolymers formed. The decrease in the intrinsic viscosity of the recovered homopolymers and shifts of their GPC chromatograms toward the low molecular weight end suggest that on sonification PRMA samples having bulkier substituents do degrade and yield radicals which, however, do not recombine with those from polystyrene. Furthermore, ultrasonic degradation of polystyrene is found to be dependent on the chain stiffness of the poly(alkyl methacrylates).