Alan K. Schrock’s research while affiliated with Dow Chemical Company and other places

The relationship between polymer network parameters and speed of viscoelastic (VE) recovery was studied for viscoelastic polyurethane foams. Reactive network simulation method was developed which use relative reactivity parameters derived from literature and from experiment. Relative reactivity of butylene-oxide (BO) based secondary hydroxyl groups were estimated by comparing simulation results with experimentally derived sol fraction. From the analysis, it is found that BO and propylene oxide (PO) hydroxyl end groups have relative reactivity to isocyanates that are not very different. We also find that the isocyanate conversion is lower only about 91–96%, even though the isocyanates are the limiting factor (i.e. molar ratio NCO:OH = 0.9). It is also found that a foam with faster VE recovery is predicted to have smaller elastically effective chain (EEC) mass fraction (i.e. more imperfect polymer network) and higher sol fraction. Surprisingly, the same foam after solvent extraction was found to have slower VE recovery. It is concluded for foam systems with Tg near ambient temperature, that while lower EEC fraction can lead to slower VE recovery, a large amount of sol fraction in the foam system can cause faster VE recovery via plasticization of the polyurethane matrix.

Thermoset elastomer compositions are disclosed. Such elastomers are the reaction product of (a) an ambient temperature liquid epoxy-terminated prepolymer formed by reacting a polyoxyalkyleneamine having a molecular weight of from 3000 to 20,000 with an excess of epoxide, wherein the polyoxyalkyleneamine has at least 3 active hydrogen atoms and (b) a curing agent comprising at least one amine or polyamine having an equivalent weight of less than 200 and having 2 to 5 active hydrogen atoms. Such elastomers can be used in applications such as for sealants, adhesives, coatings, gaskets, jointing and cast elastomers.

Embodiments of the present invention disclose viscoelastic foams having a renewable natural resource contents of between about 1 and about 25 wt % of the foam. The foams may have a ratio of elastic modulus (E′) at 20° C. to 25% compression force deflection (CFD) of 25 to 125.

In this study, the distributions of hard segment lengths in flexible and viscoelastic polyurethane foams are investigated. To that extent, MALDI spectra of hard segment chains from polyurethane ("PU") viscoelastic ("Visco") and conventional flexible ("Flex") foam series were obtained and analyzed. Results indicate that within each foam series, there was no significant difference at different water levels. However, comparing Visco and Flex shows that the distribution is shifted to lower urea count for the case of Visco. The experimentally determined peak in the distribution was 1-2 urea repeats, in contrast with what is reported in literature. To understand the fine impacts of formulation, Monte Carlo simulations were performed on the Visco and Flex foam formulations, with urethane-urea catalysis ratio and water levels being varied within each foam series. Experimentally obtained distributions agree very well with the simulation results. Values for number-average degree of polymerization from simulations agree with those predicted from the Schulz-Flory distribution. Furthermore, one finds that the while the calculated shape of the hard segment length distributions is predicted to be sensitive to the catalytic enhancement factor, the average hard segment length values are predicted to be essentially independent of catalysis. The fraction of diurethane linkages was calculated and is found to be sensitive to catalysis (more urethane catalysis = more diurethane linkages). Furthermore, the fraction of diurethane linkages as simulated from foam formulation is correlated well with the T-g of the Flex foam series as obtained from DMA. The same relationship for the Visco foam series is also discussed.

Correlations between polyurethane foam formulation and foam aging are shown to simplify when sufficient data are available to eliminate casual relationships. The numerous factors that are purported to result in faster or slower foam aging are shown to primarily reflect how those factors influence polyurethane hard segment structure. Specifically, changes in formulation that results in better phase separated (but co-continuous) structures exhibit less humid and heat aging than foams with poorer phase separation (broader interfacial phase mixing). This is demonstrated for aging tests that probe the polymer phase structure at higher stress or strain levels than that sometimes used. Tests that do not adequately stress the foam do not truly probe differences in foam structure that result in property decrements. Humid aged compression set and heat aged load loss data for a large number of foams are related to their formulation, catalysis, foaming rheology, and their hard segment structure determined by AFM and X-ray analyses.

We describe a new modeling approach to prediction of Young's modulus of segmented polyurethanes. This approach combines micromechanical models with thermodynamic considerations based on the theory of block copolymers. The resulting model predicts both the equilibrium morphology and the “ideal” Young's modulus of a segmented polyurethane polymer as a function of its formulation (hard segment chemical structure, hard segment weight fraction, soft segment equivalent weight) and temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2123–2135, 2007

A model is presented in which compression set of TDI foams is a result of thermal and stress-induced relative flow of the hard and soft phase following hydrogen bond disruption. The majority of the soft segment consists of a mobile phase that exhibits liquid-like dynamics. However, a significant fraction of the soft segment is immobilized due to hydrogen bond interactions with the phase-separated polyurea hard segment. As temperature is increased, the hydrogen bonding between the soft and hard segment progressively weakens until there is little or no interaction and the phases are free under stress to flow past each other. FTIR data do not indicate that changes in the hard–soft phase interactions are accompanied by changes in intra-hard segment hydrogen bonding. Upon cooling, the hard–soft segment hydrogen bond interactions can re-establish themselves in a new compressed geometry if the phase separated, co-continuous hard segment does not provide sufficient restorative force to regain the initial dimensions. This model is based on data obtained by DSC, SEM, temperature-dependent FTIR, solid state NMR, SAXS and compression set measurements.

We develop new theoretical framework to study the relationship between composition and mechanical properties in segmented polyurethanes (PU) and poly(urethane-ureas) (PUU). In particular, we analyze polymer mechanical properties (quasi-static Young's modulus, E, and temperature-dependent storage shear modulus, G') as function of the hard and soft segment chemistry, hard segment weight fraction, soft segment molecular weight, and temperature. It has been known for some time [1] that in many segmented PU and PUU polymers, the hard-soft microphase separation causes the formation of a ``percolated hard phase''. We propose a new formalism that enables one to predict the onset of the hard phase percolation as function of temperature, soft segment molecular weight, and chemical structures of hard and soft segments. Based on this formalism, we can build micromechanical models to estimate mechanical properties of segmented polyurethanes as function of temperature. We used this theoretical framework to simulate storage moduli of several model compounds, and found very reasonable qualitative agreement with experimental data. [1] See, e.g., A. J. Ryan et al., Macromolecules, 24, 2883 (1991); Polymer 32, 1426 (1991).