Spectroscopic and Rheological Cross-Analysis of Polyester Polyol Cure Behavior: Role of Polyester Secondary Hydroxyl Content

Abstract

The sol–gel transition of a series of polyester polyol resins possessing varied secondary hydroxyl content and reacted with a polymerized aliphatic isocyanate cross-linking agent is studied to elucidate the effect of molecular architecture on cure behavior. Dynamic rheology is utilized in conjunction with time-resolved variable-temperature Fourier-transform infrared spectroscopy to examine the relationship between chemical conversion and microstructural evolution as functions of both time and temperature. The onset of a percolated microstructure is identified for all resins, and apparent activation energies extracted from Arrhenius analyses of gelation and average reaction kinetics are found to depend on the secondary hydroxyl content in the polyester polyols. The similarity between these two activation energies is explored. Gel point suppression is observed in all the resin systems examined, resulting in significant deviations from the classical gelation theory of Flory and Stockmayer. The magnitude of these deviations depends on secondary hydroxyl content, and a qualitative model is proposed to explain the observed phenomena, which are consistent with results previously reported in the literature.

The Influence of Neem Oil and Its Glyceride on the Structure and Characterization of Castor Oil-Based Polyurethane Foam

“…This is because neem oil has no reactive hydroxyl group, which reduces the structure of urethane, urea, amide II and, amide III ( Table 3 ). The previous study also indicated polyol with secondary hydroxyl groups can increase the crosslinking density of PU resin [ 34 ]. The results demonstrate that NOG can enhance the solvent resistance of bio-based PU foam.…”

“…The densities of O1-2, O2-2 and, O3-2 are 116.2, 81.4 and 70.8 kg/m 3 , respectively. This result is due to NOG polyol with secondary hydroxyl groups which helps the PU resin to cure rapidly and maintain the foam’s structural integrity during the foaming process [ 34 ]. Figure 4 displays the PU foam micrographs.…”

“…This can be attributed to a high NCO/OH ratio resulting in an increase of hard segment content, which led to increased absorption intensity [ 35 ]. Furthermore, secondary hydroxyl groups of NOG polyol reacted with isocyanate which increased stiffness of chain reduces chain mobility and increasing hard segment content [ 34 ]. Although NCO/OH ratios of O1-2, O2-2 and O3-2 are higher than that of N1-2, N2-2 and N3-2, the result indicated that adding neem oil reduces the relative absorption intensities of urea, amide II, amide III and urethane because of the dilution of PU resin.…”

“…This is because a high NCO/OH ratio increases the crosslinking and hard segment domain [ 41 ]. On the other hand, NOG can help react with isocyanate to increase the stiffness of the chain and improve the specific compressive strength in a low NCO/OH ratio [ 34 ]. The specific compressive strength at 25% strain of O2-2 is higher than that of N3-2 at NCO/OH ratio of ca.…”

Green alternative cosolvents to N-methyl-2-pyrrolidone in water polyurethane dispersions

“…Reaction rate was evaluated by monitoring the conversion of NCO groups ($2260 cm À1 ) using Fourier-transform infrared spectroscopy (FTIR), 39 which is a technique widely used in the synthesis of polyurethane. [40][41][42][43] The polyurethanes synthesized in green solvents achieved similar NCO conversion with time to the polyurethane synthesized in NMP (see ESI †). However, at intermedium reaction times NMP and GVL achieved higher conversion grades than CY.…”