The effect of mixed soft segment on the microstructure of thermoplastic polyurethane

Abstract

In this work, we fixed the hard segment content (Ch%) and synthesized thermoplastic polyurethane (TPU) elastomers with one‐soft segment (HTPB‐PU, PTMG‐PU, and PCL‐PU) and bi‐soft segment (PTMG‐HPU and PCL‐HPU), using 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol, and different oligomer diols as raw materials. This work was used to explore the impact of two polar diols (polytetrahydrofuran diol [PTMG]; polycaprolactone diol [PCL]) of the hydroxy‐terminated polybutadiene (HTPB)‐based TPU on the microstructure and macroscopic properties. Using Fourier transform infrared spectroscopy, X‐ray diffraction, and differential scanning calorimetry to characterize TPU, the results showed that the introduction of PCL was better than PTMG in promoting microphase mixing and crystallization, and reducing microphase separation. This result was closely related because the carbonyl group in PCL was stronger than the ether bond in PTMG in forming hydrogen bonds with ─NH bond. Through mechanical test and isopropyl alcohol (IPA) resistance test, the results showed that HTPB‐based TPU with PCL (PCL‐HPU) significantly improved tensile strength and elongation at break, and only a small reduction of Young's modulus was observed. PCL‐HPU had the best retention of the IPA resistance of HTPB‐based TPU.

Structural and Viscoelastic Properties of Thermoplastic Polyurethanes Containing Mixed Soft Segments with Potential Application as Pressure Sensitive Adhesives

“…In this study, ATR-IR spectroscopy and DSC were mainly used for assessing the degree of micro-phase separation and miscibility of the TPUs synthesized with PPG+PAd mixed SS. Several previous studies [19][20][21][22][23][24][25] have demonstrated that the degree of microphase separation of the TPUs can be assessed by using these experimental techniques. The…”

“…In this study, ATR-IR spectroscopy and DSC were mainly used for assessing the degree of micro-phase separation and miscibility of the TPUs synthesized with PPG+PAd mixed SS. Several previous studies [19][20][21][22][23][24][25] have demonstrated that the degree of microphase separation of the TPUs can be assessed by using these experimental techniques. The ATR-IR spectrum of 1.30/PPG in Figure 3 shows the bands of the urethane HS at 3303 cm −1 (N-H stretching), 1728 cm −1 (C=O stretching), 1598 cm −1 (benzene ring of MDI) and 1535 cm −1 (N-H bending), and the ones of the PPG SS appear at 2941 and 2867 cm −1 (asymmetric and symmetric C-H stretching respectively) and 1091 cm −1 (C-O stretching of ether).…”

“…The derivative of the weight loss curves show the existence of two thermal deg- The evidence obtained from the DSC traces of the TPUs synthesized with PPG+PAd agrees well with their X-ray diffractograms (Figure 6). The X-ray difractogram of 1.30/PPG (75)PAd (25) shows a broad peak with a small crystalline peak at 2θ value of 21 • indicating a dominant amorphous structure typical of the MDI+BD hard segments [50]. However, 1.30/PPG(50)PAd(50) and 1.30/PPG(25)PAd(75) show sharp peaks at 2θ values of 21, 22 and 24 • , and these diffraction peaks correspond to the PAd soft segments (Figure A2).…”

“…Mirhosseini et al [24] have shown that the use of mixed soft segments accelerated the micro-phase separation process as compared with TPUs containing one type of polyol, and the TPUs made with mixed soft segments showed enhanced elongation-at-break and toughness. In the same direction, Cui et al [25] have shown that the introduction of polycaprolactone (PCL) polyol promoted micro-phase mixing and crystallization, and reduced micro-phase separation in the polyurethanes better than polytetramethyleneglycol polyol did; this was ascribed to the stronger carbonyl group in PCL in forming hydrogen bonds with -NH bond. On the other hand, the polyurethanes synthetized with MDI, 1,4-butanediol chain extender and polyester polyols of different nature and molecular weights showed different degrees of crystallinity and mobility of the HS depending on the length of the carbon atoms in the polyols [19].…”

“…The miscibility of the SS provided different degrees of micro-phase separation and distinct hydrogen bonds interactions among the HS [1,2,[12][13][14][15][16][17][18]. However, the structure-property relationship of the TPUs synthesized with two polyols of a different nature, i.e., TPUs with two kinds of SS, have been less studied [19][20][21][22][23][24][25].…”