We have investigated ultrasonic degradations of poly(ethylene oxide) (PEG) and poly(methyl methacrylate) (PMMA) in aqueous media by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The ultrasonic degradation of polymers was monitored as a function of ultrasonication duration to examine the structural details of ultrasonic degradation polymers. PEG solution ultrasonication produced five types of oligomers (M approximately 1000 Da) with different end groups, irrespective of the initial average molecular masses (M=2, 6, 20, and 2000 kDa). Several degradation pathways with free radical reactions have been suggested to explain these degradation products: the ultrasonic degradation of PEG is initiated by breaking of the C-O bond in the PEG chain, generating polymeric radicals with two terminal groups, i.e., X*( approximately CH2CH2*) and Y*( approximately CH2CH2O*), followed by termination with extraction or release of a hydrogen atom. However, PMMA (M=1630 Da) ultrasonication generated only one type of degradation oligomer, which has a hydrogen group at both ends, the same as that of the original oligomer. It has been suggested that the presence of the radical terminal groups X*( approximately CH2*) and Y*( approximately (CH3)CCOO(CH3)C*) is due to selective C-C bond breaking in the chain during the ultrasonic degradation of PMMA. The MALDI-TOFMS combined with the ultrasonic degradation technique (UD/MALDI-TOFMS) developed in this study could be extended to the analysis of synthetic polymer structures with high molecular weights.

Butyl vinyl ether (BVE) was polymerized radically, and the resultant oligomeric poly(BVE)s were characterized mainly using MALDI-TOF-MS spectrometry. For a further structural identification, the poly(BVE) obtained in bulk was subsequently subjected to 1 H NMR measurement. Notably, an intensive peak assignable to -CH 2 C(dO)CH 2protons was observed unexpectedly although a peak assignable to -CHO proton as the terminal end-group generated via β-scission of growing polymer radical as a presumed chain-end forming reaction appeared only weakly. Thus, a plausible chain-end forming reaction would be the intramolecular (backbiting) hydrogen abstraction to form mid-chain radical which subsequently undergoes β-scission resulting in oligomeric poly(BVE) with carbonyl group in the polymer backbone. Then, the specific polymerization mechanism involving β-scission of mid-chain radical yielding oligomers is discussed. The hydrogen abstraction ability of growing poly(BVE) radical was checked by using toluene as a solvent having labile hydrogen. The dependence of the degree of polymerization on initiator concentration was examined because the occurrence of primary radical termination was remarkable, probably leading to reduced chain length. Finally, the reinitiation reaction by butyl group generated via β-scission of mid-chain radical was pursued.

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When patients received H2RA or PPI, the laxative effect of MgO is decreased possibly due to the low solubility of MgO at the higher gastric pH and less generation of MgCl2 and Mg(HCO3)2. Higher dosing level of MgO or another laxative should be used in patients taking H2RA or PPI, as well as the case of patients with total gastric resection.

Determination of Stability Constants (in SupramolecularChemistry) -(212 refs.). -(TSUKUBE, H.; FURUTA, H.; ODANI, A.; TAKEDA, Y.; KUDO, Y.; INOUE, Y.; LIU, Y.; SAKAMOTO, H.; KIMURA, K.; Compr. Supramol. Chem. 8 (1996) 425-482; Edited by Davies, J. E. D.; Ripmeester, J. A.; Elsevier, Oxford, UK; EN)