SUMMARY:This paper reviews several types of thermoplastic polyurethane elastomers, and the unique properties these polymers have. I n discussing the hydrolysis stability of thermoplastic polyurethane elastomers the suitability of these polymers for such study was pointed out. A relationship between poly(ester-urethane) composition in terms of methylene group concentration, hardness and chain stiffness, and hydrolysis stability was shown. The dominant role of polyurethane acid number in thermoplastic poly(est,er-urethane) hydrolysis stability was demonstrated and the origin of this unexpected acid number was discussed. The pronounced stabilizing action of added poly(carbodiimide) in thermoplastic poly(ester-urethane) hydrolysis was shown, as well as the severe destabilizing act.ion of a carboxylic acid, stearic acid. The hydrolysis st,abilities of thermoplastic poly(ester-urethane) elastomers based on poly(s-caprolactone) glycol and on poly(hexamethy1ene carbonate) glycol were also described. ZUSAMMENFASSUNG :Die Hydrolysestabilitat einiger thermoplastischer Poly(ester-urethan)-Elastomerer in Abhangigkeit vom molekularen Aufbau wird untersucht. Entscheidend fur den hydrolytischen Abbau dieser Polymeren ist das Auftreten von Carboxylgruppen. Es werden Moglichkeiten aufgezeigt, diesen Abbau zu verringern, $3 z . B. durch Zusatz von Poly(carbodiimiden). AbschlieBend werden die Hydrolyaestabilitat von thermoplastischen Poly(ester-urethan)-Elastomeren untersucht, die Poly-( E Caprolacton) und Poly(hexamethy1encarbonat) als Glykolkomponente enthalten.

Front dynamics in the frontal polymerization of two multifunctional acrylate monomers, 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane ethoxylate triacrylate (TMPTA), with Lupersol 231 [1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane] as the initiator, are studied. In most frontal polymerization systems, the dynamics are associated with a planar front propagating through the sample. However, in some cases, front behavior can be altered: the front becomes nonplanar characterized by complex patterns like spin modes and pulsations. To determine how these periodic and aperiodic modes arise, reactant solutions consisting of HDDA diluted with diethyl phthalate (DEP) and TMPTA diluted with dimethyl sulfoxide (DMSO) were used in the study. In the study we reveal frontal behavior characteristic of period-doubling behavior, a doubling of spin heads that degenerate into an apparently chaotic mode. Also, a pulsating symmetric mode has been observed. These observations have a striking similarity to observations made in studies of self-propagating high-temperature synthesis (SHS) in which the addition of an inert diluent afforded a rich variety of dynamical behavior. The degree of cross-linking has also been found to be a bifurcation parameter. The energy of activation of multifunctional acrylate polymerization is a strong function of the degree of polymerization. By adding a monoacrylate (benzyl acrylate: BzAc), such that the front temperature was invariant, we observed a period-doubling bifurcation sequence through changes in the energy of activation, which has not been previously reported. (c) 1999 American Institute of Physics.

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This paper reviews several types of thermoplastic polyurethane elastomers, and the unique properties these polymers have. In discussing the hydrolysis stability of thermoplastic polyurethane elastomers the suitability of these polymers for such study was pointed out. A relationship between poly(ester‐urethane) composition in terms of methylene group concentration, hardness and chain stiffness, and hydrolysis stability was shown. The dominant role of polyurethane acid number in thermoplastic poly(ester‐urethane) hydrolysis stability was demonstrated and the origin of this unexpected acid number was discussed. The pronounced stabilizing action of added poly(carbodiimide) in thermoplastic poly(ester‐urethane) hydrolysis was shown, as well as the severe destabilizing action of a carboxylic acid, stearic acid. The hydrolysis stabilities of thermoplastic poly(ester‐urethane) elastomers based on poly(ϵ‐caprolactone) glycol and on poly(hexamethylene carbonate) glycol were also described.

It is concluded from the present study that the slightly modified Brabender PlastiCorder torque rheometer is well suited to the study of thermoplastic polyurethane elastomer melt polymerization. The instrument is sensitive and responsive enough over a broad range to sense and record continuously even small changes in polymerizate temperature and viscosity as a function of time. This capability has enabled us to follow the full course of such polymerizations, with the exception of the final polymer maturation process which customarily is effected in the quiescent state. In our study, the effects of several polymerization variables were clearly and quantitatively apparent, including the effects on the course of polymerization and its degree of: macroglycol acidity; antioxidant (stabilizer); temperature; catalyst; polymer composition; presence of shortstop; and reactant balance. The results demonstrate the known acid catalysis of the hydroxyl-isocyanate reaction as well as polyurethane molecular weight modification by polyester glycol acidity. The inclusion of a commercial phenolic antioxidant in the polymerization charge did not have any obvious effect on the course of polymerization but may have limited degree of polymerization somewhat. Increased urethane content greatly speeds the viscosity increase, demonstrating urethane autocatalysis as well as its viscosity contribution, and even low stannous octoate catalyst levels appreciably speeded the inherently rapid polymerization. The shortstopping action of fugitive and persistent primary alcohols is prompt and effective, but excessive amounts produce some irreversible polymer reversion as they readjust the polymer chain molecular weight distribution present in maintaining the urethane equilibrium. This equilbrium also showed clear response to polymerization temperature, reversible urethane dissociation reducing viscosity with increasing temperature. The effect of polymerization reactant imbalance was readily apparent in the appreciably reduced rate and degree of polymerization attending minor isocyanate deficiency. Mastication experiments in the PlastiCorder show dried preformed polyurethane elastomer to drop quickly to viscosity levels much below that reached by the same compositions during polymer formation. The viscosity loss of the former is attributed to polyurethane chain rupture promoted by virtual network restrictions to chain slippage, while the virtual network has not yet developed in the forming polymer.

Germany m the Main Scientific Laboratories first, of I. G. Farbenindustrie and then Farbenfabriken Bayer has spawned a giant industry which continues to proliferate today. In the course of this development the chemical industry has built great capacity to produce various di-and poly-isocyanates and polyols as well as added capacity to produce certain diamines, glycols, and urethane polymerization catalysts.Everything considered, polyurethane elastomer formation by the poly-addition process must be termed unique among commercial polymerization reactions. It is perhaps the most obviously dependent on the broad precepts of stoichiometric organic chemistry, responding predictably to steric, electronic, functional group, and catalyst effects through a variety of known chemical reactions. This rich chemistry promises to provide important opportunities to the polyurethane chemist for years to come. It produces segmented (block structured) polymer chains which result in heterophase solid polymers having morphology-dependent properties. This morphology is both composition and process-dependent and is capable of regulation by the polymer scientist.It proceeds at moderately rapid rates in bulk or in solution without excessive heat evolution or monomer explosion hazard.It is not an unduly sensitive polymerization and proceeds reasonably well even in the presence of minor reactive impurities and in the absence of ideal stoichiometry. Of course, gross deviations from optimum polymerization conditions are not tolerated. This relative insensitivity enables the production of reasonably stable, terminally reactive, low molecular weight liquid &dquo;prepolymers&dquo; which can be handled by practical methods in air without the absolute exclusion of moisture, to provide cast vulcanizates. Sensitivity to catalysis although high is still reasonable and concentration dependent.The foregoing polymerization characteristics mark the polyurethanes as materials of versatile processability and enable their utilization by casting, thermo-J.

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