Reaction Monitoring of Toluenediisocyanate (TDI) Polymerization on a Non-Mixable Aqueous Surface by MALDI Mass Spectrometry

Abstract

The polymerization reaction of toluene diisocyanate (TDI) and hydroxyl compounds has been widely used for the production of polyurea resins. Since the composition and molecular-weight distribution of polymer adducts greatly influence the final properties of the resuting polymer, the development of analytical tools capable of monitoring the polyaddition reactions is important to control them as well as the properties of the resuting polymer. Here we report that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) is useful to precisely monitor time-dependent dynamic events occurring in the polymerization reaction of TDI with water. For this purpose, the polymerization reactions were conducted in two different reaction systems, continuously supplying sufficient water and depleting water after an initial exposure of water to provide an anhydrous storage condition of prepolymer adducts. Samples prepared in a time course from the two different reaction systems were analyzed by a MALDI TOF mass spectrometer. The polymerization adducts of TDI and water were monitored and showed to consist of three structural types of polymer adduct series, including diisocyanate, monoamino, and diamino series. These MALDI mass data efficiently reflected changes in the reaction conditions of each TDI polymerization reaction, thereby providing precise information at the molecular level for time-dependent events occurring during the polymerization reaction. These events included changes between the polymer adduct series and in the molecular-weight distribution of each polymer adduct series. The results obtained in this study suggest that high-throughput MALDI MS-based dynamic monitoring of polymerization can be used to precisely control the polymerization reaction as well as to rapidly monitor the state of prepolymers in storage.

Absorption, distribution, metabolism, and excretion of methylene diphenyl diisocyanate and toluene diisocyanate: Many similarities and few differences

“…This is expected to result in an increased formation of TDA compared to less acidic environments, and to a yield of TDA that decreases with increasing dosing. These results are consistent with the general formation of polyurea as the main product and of TDA as a side product (Ahn et al, 2013;Yakabe et al, 1999).…”

“…With mono-isocyanate model compounds like PhI, typically investigated at 0.1–1 mM level combined with higher solvent concentrations, the formation of substituted ureas (reaction with the amine) was invariably observed (Castro et al, 1985; Ekberg and Nilsson, 1976; Naegeli et al, 1938a, 1938b). Under heterogeneous conditions and in the absence of nucleophiles more potent than water (see sections on reaction with N- and S-centered nucleophiles), substituted ureas were the main hydrolysis products of TDI and MDI and the corresponding diamines, TDA and MDA, respectively, are formed in minor yield only (<1%) (Ahn et al, 2013; Yakabe et al, 1999).…”

“…When diisocyanates are dispersed in water (two-phase system), any diamine initially formed by hydrolysis very rapidly lead to the formation of oligo- and poly-ureas by reaction with other diisocyanate molecules (Ahn et al, 2013; Yakabe et al, 1999). Up to a temperature of at least 333 K, the di-aryl substituted urea bond was shown to be stable to hydrolysis over a very broad pH-range and can be regarded as permanent in the mammalian organism (Audu and Heyn, 1988; Sendijarevic et al, 2004).…”

Exploring structure/property relationships to health and environmental hazards of polymeric polyisocyanate prepolymer substances-1. Design of experiments, aquatic exposure, and acute aquatic toxicity

“…When stirred into water, the major part of the test substances resulted in a non-soluble residue in which NCO groups could no longer be detected (Figure 3). This was an expected observation, since in the organic phase, initially, NCO-terminated ureas are formed, of which the terminal groups hydrolyze to form aminoterminated ureas (Ahn et al, 2013;Herbold et al, 1998;Yakabe et al, 1999). At ambient conditions, the substituted ureas of TDI and MDI are stable under a broad range of pH values (Sendijarevič et al, 2004).…”