Synthesis, Mechanisms and Kinetics of Formation of Bi-Component Polyurethanes

Abstract

In order to understand the single-step molten state reactivities of a diaromatic isocyanate (4,4’ dPDhenylmethane diisocyanate MDI), the mechanisms and reaction kinetics were modelled using a monofunctional aromatic isocyanate (para-tolyisocyanate p-TI) and hydroxytelechelic polyols (polyethylene glycol PEG) (polypropylene glycol PPG) with variable macromolecular chains and structure (from 200 to 2000 g.mol-1). The molar ratio of reactive functions NCO/OH was set at 1.1. We were able to characterise the bi-component polyurethanes synthesised and identify side products formed (urea, trimer, allophanate…). The results were obtained by the use of a panoply of classical analytical techniques (NMR, FTIR, HPLC/UV/MS, ESI/MS, DSC) or those more recent in the field of synthetic polymers (MALDI-TOF). This work shows the necessity of using several efficient and complementary techniques in order to understand the molten state reaction mechanisms and kinetics of these complex PU systems.

Preparation and chemical reactions of rigid cross‐linked poly(vinyl chloride) foams modified by epoxy compounds

“…A very evident carbon signal of methylene attached to epoxy ring at 68.80 ppm (Scheme a) in the spectrum of the mixture of TDI and E51 (T/E‐b) indicated that there was almost no reaction between TDI and E51. However, the signals of 154.91 and 151.06 ppm appeared clearly in the spectrum of the mixture of TDI and EOH (T/EOH‐b), which corresponded to the two CO carbons from allophanate (Scheme b), according to the literature . The peak at 72.11 ppm was attributed to the tertiary carbon connected with oxygen in allophanate.…”

Kinetic Investigation of Polyurethane Rubber Formation from CO2‐Containing Polyols

“…Allophanate is formed by the reaction of isocyanates with urethanes with sufficient acidity of urethane nitrogen at elevated temperatures (> 100 °C) .…”

“…For the OH group, no relevant side reactions in this reaction medium can be imagined. The NCO group can particularly react in the following ways (see also ): Formation of urea from isocyanate and water is avoided with sample preparation. Allophanate is formed by the reaction of isocyanates with urethanes with sufficient acidity of urethane nitrogen at elevated temperatures (> 100 °C) . Trimerization of isocyanates producing isocyanurates by trend occurs at high concentrations and temperatures in absence of suitable urethanization catalysts or with alkaline catalysts , e.g., tertiary amines. Radical cross‐linking between a polyol double bond and an isocyanate group are promoted by radical forming conditions, e.g., oxygen being activated by light. Carbamate amidation, i.e., reaction of isocyanates with urethanes, carboxylate esters, or terminal carboxylic acids, is unlikely due to low nucleophilicity and unfavorable steric configuration but cannot be excluded. …”

Synthesis and evaluation of mechanical and thermal properties of segmented condensation polyurethanes

“…[1][2][3] However, their high price combined with the toxicity of isocyanates' integral components constitute another disadvantage of PURs. Polyurethanes are synthesised by different methods including conventional polyaddition and polycondensation.…”