Forward and reverse reactions of N-methylaniline-blocked polyisocyanates: a clear step into double Arrhenius plots and equilibrium temperature of thermally reversible reactions

Nasar, A. Sultan; Libni, G.

doi:10.1039/c7ra03734a

Cited by 7 publications

(6 citation statements)

References 42 publications

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“…For this, 0.72 mmol of the catalyst was used in all cases. Online FTIR was employed to monitor on the one hand the disappearance of the stretching isocyanate peak (NCO) at 2273 cm –1 and on the other hand the formation of the stretching peak of the secondary amide (CO) ranging between 1470 and 1570 cm –1 . , Based on this catalyst screening (Table S1), DBU was shown to be the most efficient catalyst for AFA bond formation, as the full reaction of the isocyanate with the acetoacetate is achieved in only 3 h in the presence of this catalyst (Figure S6). DBU was therefore used in the upcoming material synthesis.…”

Section: Resultsmentioning

confidence: 99%

Reprocessable Polyurethane Foams Using Acetoacetyl-Formed Amides

Kassem,

Imbernon,

Stricker

et al. 2023

ACS Appl. Mater. Interfaces

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Like any other thermosetting material, polyurethane foams (PUFs) contain permanent cross-links that hinder their reprocessability and make their recyclability a tedious and environmentally unfriendly process. Herein, we introduce acetoacetyl-formed amides, formed by the reaction of isocyanates with acetoacetate groups, as dynamic units in the backbone of PUFs. By extensive variation of the foam composition, optimum parameters have been found to produce malleable foams above temperatures of 130 °C, without the requirement of any solvent during the foaming process. The PU cross-linked material can be compressionmolded at least three times, giving rise to PU elastomers and thus maintaining a cross-linked network structure. Characterization of the original foams shows comparable properties to standard PUFs, for example, having a density of 32 kg/m 3 , while they show similar chemical and thermal properties upon reprocessing to strong PU elastomers, exhibiting T g ranging from −42 to −48 °C. This research provides a straightforward method to produce thermally reprocessable PUFs as a promising pathway to address the recycling issues of end-of-life foams.

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Section: Resultsmentioning

confidence: 99%

Reprocessable Polyurethane Foams Using Acetoacetyl-Formed Amides

Kassem,

Imbernon,

Stricker

et al. 2023

ACS Appl. Mater. Interfaces

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“…In addition, a peak attributed to NH stretching appeared in the region at approximately 3300 cm −1 when –N=C=O groups were bonded [ 32 , 46 ], and the intensity of the peak at approximately 2300 cm −1 (corresponding to the HDI isocyanate group) was very weak (i.e., 0.1). Furthermore, the spectrum for the HDI 0.3 blend specimen clearly showed peaks attributed to the HDI isocyanate group [ 47 ], suggesting that the HDI had reacted appropriately with the PBSeT and PLA.…”

Section: Resultsmentioning

confidence: 99%

Characterization of PLA/PBSeT Blends Prepared with Various Hexamethylene Diisocyanate Contents

et al. 2021

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Poly (lactic acid) (PLA) is the most widely available commercial bioplastic that is used in various medical and packaging applications and three-dimensional filaments. However, because neat PLA is brittle, it conventionally has been blended with ductile polymers and plasticizers. In this study, PLA was blended with the high-ductility biopolymer poly (butylene-sebacate–co–terephthalate) (PBSeT), and hexamethylene diisocyanate (HDI) was applied as a crosslinking compatibilizer to increase the miscibility between the two polymers. PLA (80%) and PBSeT (20%) were combined with various HDI contents in the range 0.1–1.0 parts-per-hundred rubber (phr) to prepare blends, and the resulting physical, thermal, and hydrolysis properties were analyzed. Fourier-transform infrared analysis confirmed that –NH–C=OO− bonds had formed between the HDI and the other polymers and that the chemical bonding had influenced the thermal behavior. All the HDI-treated specimens showed tensile strengths and elongations higher than those of the control. In particular, the 0.3-phr-HDI specimen showed the highest elongation (exceeding 150%) and tensile strength. In addition, all the specimens were hydrolyzed under alkaline conditions, and all the HDI-treated specimens degraded faster than the neat PLA one.

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“…Blocked isocyanate is an ultimate choice of organic candidates as its formation and its dissociation could be conveniently studied from room temperature to 125 °C. Very recently we reported double Arrhenius plots and a method for the determination of equilibrium temperature from such plots for the first time for a variety of phenol and amine‐blocked polyisocyanates ,,. Such method of treating the kinetic data paved the way to look the blocked isocyanate at its equilibrium.…”

Section: Resultsmentioning

confidence: 99%

“…Very recently we reported double Arrhenius plots and a method for the determination of equilibrium temperature from such plots for the first time for a variety of phenol and amine-blocked polyisocyanates. [27,28,31] Such method of treating the kinetic data paved the way to look the blocked isocyanate at its equilibrium. For the present work, the double Arrhenius plots were constructed for uncatalysed and catalysed reactions and are shown in Figure 8.…”

Section: Deblocking Kinetics (A Comparison With the Blocking Reaction)mentioning

confidence: 99%

Catalysis of Forward and Reverse Reactions of ϵ-Caprolactam-Blocked Polyisocyanate: Double Arrhenius Plots and Equilibrium Temperatures of a Thermally Reversible Reaction

Libni

Nasar

2017

ChemistrySelect

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ϵ‐Caprolactam blocked‐polyisocyanate is a commercially valuable raw material used mainly in the single‐package polyurethane coatings. In this study, kinetics of forward (blocking) and the reverse (deblocking) reactions of ϵ‐caprolactam‐blocked polyisocyanate catalysed by DABCO ‐ a tertiary amine, bismuth neodecanoate, calcium(II) 2‐ethylhexanoate – both non‐tin organometallics and a tin catalyst were studied using a hot stage FT‐IR spectrophotometer. It was found that calcium(II) 2‐ethylhexanoate showed highest catalytic activity in the forward reaction whereas this catalyst showed lowest activity in the reverse reaction. DABCO and bismuth neodecanoate showed same catalytic activity and that activity was high compared to that of tin(II) 2‐ethylhexanoate in the forward reaction whereas only DABCO showed high activity in the reverse reaction. As these reactions were carried out adapting neat condition, the rate constants obtained were used to construct the double Arrhenius plots for this thermally reversible reaction. All the double Arrhenius plots showed intersection, from the intersection point, equilibrium temperature and equilibrium rate constants of these reactions were determined. Compared to uncatalysed reaction, DABCO reduced the deblocking temperature 25 °C and shifted the equilibrium temperature 6 °C. The data such as time required for 60% conversion into product, deblocking temperature and equilibrium temperature reported in this paper are vital in the manufacturing and in the application of ϵ‐caprolactam‐blocked polyisocyanate.

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Forward and reverse reactions of N-methylaniline-blocked polyisocyanates: a clear step into double Arrhenius plots and equilibrium temperature of thermally reversible reactions

Abstract: In this paper we report, the reaction parameters playing a vital role in the preparation and applications of industrially important N-methylaniline blocked polyisocyanates.

Cited by 7 publications

References 42 publications

Reprocessable Polyurethane Foams Using Acetoacetyl-Formed Amides

Reprocessable Polyurethane Foams Using Acetoacetyl-Formed Amides

Characterization of PLA/PBSeT Blends Prepared with Various Hexamethylene Diisocyanate Contents

Catalysis of Forward and Reverse Reactions of ϵ-Caprolactam-Blocked Polyisocyanate: Double Arrhenius Plots and Equilibrium Temperatures of a Thermally Reversible Reaction

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