MALDI-MS analysis of pyrolysis products from a segmented polyurethane

Abstract

A segmented polyurethane consisting of 4,4′-methylenebis-(phenylisocyanate), (MDI), poly(butylene adipate) (PBA) and 1,4-butanediol (BDO) was subjected to low temperature pyrolysis. Polymer samples were pyrolyzed in open-ended Pyrex tubes placed at the end of the carrier gas inlet line in a gas chromatograph. Pyrolysis was carried out under argon flow in the temperature range 250–325°C. After pyrolysis, the residue in the pyrolysis tube was analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Several different series of oligomeric pyrolysis products were observed over the mass range ~800–10000 Da. Linear polyester oligomers were detected having hydroxyl and/or vinyl end groups. Cyclic polyester oligomers were also observed. At lower pyrolysis temperatures, some of the pyrolysis products contained the MDI and BDO moieties. The pyrolysis products can be explained by two principal mechanisms. The first is dissociation of the urethane linkage (or `depolymerization'), which yields products with isocyanato and hydroxyl end groups. The second is ester exchange, which produces the cyclic oligomers. At the higher pyrolysis temperatures, dehydration occurs to yield products with unsaturated end groups. The use of MALDI-MS to examine higher mass pyrolysis products of a polyurethane and a polyester has been demonstrated. We expect that this approach will have numerous applications in studying the pyrolysis products and degradation mechanisms of various synthetic polymers.