Uncatalyzed reactions of 4,4′-diphenylmethane-diisocyanate with polymer polyols as revealed by matrix-assisted laser desorption/ionization mass spectrometry

Abstract

The uncatalyzed reactions of polyols including polypropylene glycol (PPG, M n ¼ 2000 g mol À1 ), polytetrahydrofuran (PTHF, M n ¼ 1000 g mol À1 ), poly(3-caprolactone)-diol (PCLD, M n ¼ 2000 g mol À1 ) and polypropylene glycol glycerol triether (PPG_GL, M n ¼ 1000 g mol À1 ) with 4,4 0 -diphenylmethanediisocyanate (MDI) were studied using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The reactions between these polyols and MDI were monitored in time and first-order consecutive reaction kinetics for the formations of polyols end-capped with MDI units were established. The fractional MALDI-TOF MS intensities obtained for the different polymer series at various reaction times were converted into molar fractions versus time data by means of the estimated relative MALDI-TOF MS response factors from which the corresponding rate constants and the relative reactivities of the hydroxyl groups of polyols were determined. It was found that the pseudo first-order rate constants for the polyol-MDI reaction decreased in the order of PCLD > PTHF > PPG z PPG_GL. It was also ascertained that the reactivity of the unreacted hydroxyl groups of the diols does not change significantly after the first one has reacted. On the contrary, in the case of PPG_GL it was found that the reactions of the hydroxyl groups with MDI proceed faster after any of the three hydroxyl groups has reacted, suggesting a positive substitution effect for this system. Reaction of polymer diols with MDIPolymer diols including polypropylene glycol (PPG, M n ¼ 2000 g mol À1 ), polytetrahydrofuran (M n ¼ 1000 g mol À1 ) andScheme 2 The reaction of polypropylene glycol glycerol triether (PPG_GL) with MDI (a) and the products obtained after quenching the reaction mixture by methanol (b).47026 | RSC Adv., 2016, 6, 47023-47032This journal is

Kinetics of Uncatalyzed Reactions of 2,4′- and 4,4′-Diphenylmethane-Diisocyanate with Primary and Secondary Alcohols

“…A similar negative substitution effect was published for TDI . This become more evident and can be effectively visualized when the X MDI4,4R values are plotted as a function of X MDI4,4 (Fig. ).…”

“…As it was shown in [18] in the case of k 1,44 = k 2,44 , i.e., in the absence of any substitution effect both the value of α and the maximum of X MDI4,4R should be 0.5 , but the experimental X MDI4,4R versus X MDI4,4 data are significantly above the curve calculated by Eq. with a value of α = 0.5.…”

“…One of the crucial parameters in these syntheses is the reactivity of the isocyanate groups toward the polyols. Thus, large efforts have been devoted so far to study the reaction kinetics of industrially important isocyanates including, e.g., 4,4′‐diphenylmethane‐diisocyanate (4,4′‐MDI) , toluene‐diisocyanete (TDI) , and hexamethylene diisocyanates with various alcohols using different reaction conditions and monitoring methods such as titration , UV–vis photometry combined with high‐performance liquid chromatography (HPLC) , fluorescence spectroscopy , and mass spectrometry . It is now generally accepted that aromatic isocyanates have higher reactivity than that of the aliphatic ones, and they are used in many polyurethane formulations.…”

Reactions of 2,6‐Toluene Diisocyanate with Alcohols: Kinetic Studies in the Absence and Presence of Catalysts

“…Hence, the corresponding molar fraction for the products can easily be calculated as shown in the Experimental section. To obtain information about the value …”

“…To obtain information about the value of the ratio of k 1 /k 2 , eq. 1 can be used as a first approximation, [18]…”