A kinetic investigation of polyurethane polymerization for reactive extrusion purposes

Abstract

ABSTRACT:The effects of the reaction conditions on the kinetics of two different polyurethane systems were investigated. To do so, three different kinetic methods were compared: adiabatic temperature rise (ATR), measurement kneader, and high-temperature measurements. For the first polyurethane system, consisting of 4,4-diphenylmethane diisocyanate (4,4-MDI), butane diol, and a polyester polyol, the reaction conditions did not seem to matter; a kinetically controlled reaction was implicated for all reaction conditions. The reaction was second order in isocyanate concentration and 0.5th order in catalyst concentration and had an activation energy of 52 kJ/mol. The second polyurethane system consisted of a mixture of 2,4-diphenylmethane diisocyanate and 4,4-MDI, methyl propane diol, and a polyester polyol. For this system, each of the three measurement methods showed different behavior. Only at a low catalyst concentration did the ATR experiments show catalyst dependence; at higher catalyst levels and for the other two measurement methods, no catalyst dependence was present. Furthermore, the ATR experiments proceeded much faster. Presumably, for this system, the rapid diffusion interfacial of the species present was hindered by the presence of bulky oligomer molecules. The result was a diffusion limitation reaction at low conversions and an inhomogeneous distribution of species at higher conversions.

Scalable processing of thermoplastic polyurethane nanocomposites toughened with nanocellulose

“…Although the urethane formation reaction is fast at temperatures above 60 °C, an external catalyst was also used to facilitate the polymerisation. The kinetic and mechanistic details of polyurethane polymerisation in reactive extrusion can be found elsewhere [30]. The polymerisation was observed as a changing in torque (viscosity) just a few minutes after injecting the precursors into the hopper (in zone 1), and the change in the colour and physical appearance of composites from clear liquid (in zone 1) to white turbid liquid (in zone 7) and subsequently to transparent molten semi-solid material (die).…”

Kinetic Investigation of Polyurethane Rubber Formation from CO2‐Containing Polyols

“…A further increase in isocyanate excess could not be examined as it would entail a substantial alteration of the reaction mixture's properties, e.g., viscosity and polarity, and consequently distort the reaction system. 6) The obtained catalyst order of 0.582 when employing DBTL as catalyst is in accordance with literature . Reaction heat, order, and activation energy remain unaffected; thus, this set of experiments supports the initial findings as listed in Sect.…”

“…2) In addition, long(er) chains are increasingly intertwined. A general slowdown of polyurethane formation due to physical effects is reported by several authors , , more specifically, a deviation from second order kinetics at higher conversion or with an onset of diffusion influence (described as transition from liquid to solid) , , , with an example of about 1 (and low autocatalytic effect) reported by Lucio et al. for a reaction of long‐chain hydroxyl‐terminated polybutadiene with isophorone diisocyanate.…”

“…It is suspected that the vigorous mixing leads to substantial intertwining of the polyols and, thus, the reaction already starts in a state of very low chain mobility. For lengthy molecules, in the case of thermoplastic polyurethanes (TPUs), and fast urethane reactions, especially at higher temperatures, the general assumption of functional group reactivity being independent of molecule size was reported to be questionable ; the experimental results shown above suggest a diffusion influence for the whole of the performed reaction.…”

In Situ synthesis of multiblock copolymers of poly(ϵ‐caprolactone) with different poly(ether diols) based polyurethane by reactive extrusion

“…Thus, the rest is the common urethane reaction between the PTMG-PCL copolymer diol and diisocyanate, and the formed PCLU is linear when the molar ratio of hydroxyl groups to isocyanate is kept at 1 : 1. The reaction of isocyanate and hydroxyl group should be catalyzed and accelerated by proper metallic compounds, such as bismuth octoate 21 or titanate 22 (alkoxy titanium), to meet the requirement of an extremely short residence time for reactions proceeding in an extruder to obtain a high-molecularweight polyurethane.…”