Thermoplastic Polyurethane Elastomer Melt Polymerization Study

Abstract

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.

Investigation of Ageing Mechanisms in Thermoplastic Polyurethanes by Means of IR and Raman Spectroscopy

“…photooxidative degradation mechanisms result in the formation of chromophoric groups. [19,39,21] In Figure 3 ATR spectra of TPU exposed to UV for various times are compared. At the top ATR spectra of the directly exposed surface are shown.…”

Thermo gravimetric analysis and morphological behavior of castor oil based polyurethane–polyester nonwoven fabric composites

“…Yang et al16 showed that the degradation of urethanes based on 4,4′‐diphenylmethane diisocyanate and 1,4‐butane diol gives isocyanates and alcohol at elevated temperatures. Schollenberger et al17 have also reported that the urethane linkages may be broken because of the high shear and stress at the elevated processing temperature. Kinetic parameters of the degradation reaction of short fiber polyester fiber reinforced thermoplastic PU were studied by Ronald et al18 Agi et al19 estimated the kinetic parameters for thermal degradation of PU elastomers based on poly (ether polyol) soft segment and aromatic‐type diisocyanates.…”

Effect of the crosslink density on the morphology and properties of reaction‐injection‐molding poly(urethane urea) elastomers

“…Therefore, only the network, in the absence of dangling chains and loops, is a perfect network; in other words, the crosslink network of PUU with the highest T g s value is perfect. The degree of phase separation (DPS) can be cross-estimated from the specific heat change at the glass transition (⌬C p ) as follows: Table 2 also shows that the magnitude of the specific heat at T g s for the linear PUU elastomer (1) is a bit smaller than that of the other crosslinked PUU elastomers (2)(3)(4). These data imply that there is a better phase segregation system in the linear PUU polymer.…”

“…The relationship between the properties and structure of polyurethane, poly(urethane urea) (PUU), and polyurea has been widely studied. [1][2][3][4][5][6][7][8][9] The physical and thermal properties depend not only on the phase separation but also on the crosslink network. In contrast to previous works on the properties and structure, attempts have been made to determine the PUU properties in terms of the crosslink density (CD); however, literature that describes in detail the relationship between the properties and crosslink network is rare.…”