Factors Influencing Curing Behavior in Phase-Separated Structures

Abstract

Using time-resolved Fourier transform infrared spectroscopy, the reaction kinetics of ternary blends consisting of crystallizable polyester [poly(hexamethylene adipate) (PHMA)], polyether [poly(propylene glycol) (PPG)], and poly(methyl methacrylate-co-n-butyl methacrylate) [P(MMA-co-nBMA)] has been characterized. As the polyester and polyether have reactive isocyanate (NCO) units, they are able to react with water vapor in the environment. A specially designed cell was constructed to obtain reaction kinetics for samples of varying thickness at different relative humidity and temperature. Without catalysts, the reaction kinetics obtained is significantly slower than expected for the diffusion-limited mechanism of a homogeneous medium, indicating that the reaction-limited mechanism controls primarily curing in these thin films. As shown previously, the miscibility behavior of these blends at various temperatures is complex. The morphological features, which have been characterized by vibrational spectroscopy, optical microscopy, and atomic force microscopy, depend on thermal history and initial phase behavior. Reaction rates were shown to be highly dependent on sample morphology, being faster with smaller phase-separated domains and lower degrees of crystallinity.

The phase mixing studies on moisture cured polyurethane-ureas during cure

“…An overtone of deformation vibration of NH group increased by Fermi resonance at 3185 cm K1 was also observed [29]. The conversion, r NCO of NCO groups was derived from the equation [23] …”

“…For comparison purpose thick film (0.3 mm) of PTMG/TMP/TDI (NCO:OH ratio of 1.6:1) was also casted. The morphology of such PU-urea films significantly depends upon the film thickness [23], because the film Scheme 2. Two hydrogen bonded structure responsible for phase separation and phase mixing characteristics in the MCPU.…”

“…Comyn and co-workers [22] measured the depth of moisture cure (z) of two reactive hot melt adhesives. Jeong et al [23] studied the curing kinetics of NCO terminated prepolymer as a function of sample thickness. However, in case of a particular humidity level other than saturated one, the film during the cure has to be evaluated a number of times to obtain any information about the changes in structure on molecular level.…”

Structure–property relationships in acrylate/epoxy interpenetrating polymer networks: Effects of the reaction sequence and composition

“…17,18 The morphology of IPNs has been characterized by optical microscopy, 19 scanning electron microscopy (SEM), 13,20 transmission electron microscopy, 21 and atomic force microscopy. 13,15,17,22 These studies have also shown that reaction conditions and sequence impact the final microstructure of IPNs.…”

Off‐line and in‐line analysis of phase morphology and evolution during solidification process of PP/PEOc blend in an internal mixer

“…On the other hand, it must be taken into account that the final morphology also depends on the quenching processing conditions. Up to now, the research fields of solidification process mainly focused on metal materials and thermosetting resin composites [8, 9]. As for the latter, it mainly paid attention to the studies of curing reaction and its kinetic.…”