Quick Molecular Weight Determination of Polyester-Polyurethane Soft Blocks with Phenylisocyanate Using High-Frequency Heating Technique

Abstract

The chemical degradation method of polyester-polyurethanes using a high-frequency heating technique was investigated. Model polyester-polyurethanes were prepared from 4,4'-dicyclohexylmethane diisocyanate (H12MDI), poly(butylene adipate) or poly(ethylene adipate)-polyols and isophoronediamine as a chain extender. The number-average molecular weights of their polyesterpolyols were 3500 Da. Phenylisocyanate was an effective reagent to decompose the urethane bond selectively without cleaving the ester bond. After 30 mg of a polyurethane sample was heated at 255°C in a mixture of phenylisocyanate in a sealed glass tube, the urethane bond was decomposed after 30 minutes under this condition. After the reaction, the molecular weight and the composition of the polyesterpolyols were determined by MALDI TOF-MS and SEC. The separation between the peaks of the main series consisted with repeated polyesterpolyols units. The ions consisted of a polyester chain with N -phenylurethane terminal groups from MALDI spectra. SEC chromatograms of degraded samples were consistent with the model N -phenylurethane-terminated polyester. The combination of selective degradation with SEC, MALDI and a high-frequency heating technique, using phenylisocyanate, is a viable method for easy and quick polyurethane polyol characterization.