Polyether Based Thermoplastic Polyurethanes Effect of the Soft Segment Molecular Weight

Abstract

A series of polyether-based thermoplastic polyurethanes, varying in soft segment molecular weight and hard segment content was prepared and studied. Poly(oxypropyleneoxyethylene) diols of M n of 1000, 2000, 3000, and 4000 were the soft segment polyols. The hard segment, 4,4'-diphenylmethane diisocyanate (MDI) extended with 1,4-butanediol (BDO), and also the soft segment content were varied from 20 to 80 weight percent. Physical-mechanical, thermal (DSC) and dynamic-mechanical property data are used to elucidate the mechanical and morphological behavior of these polymers. Two distinct phases are detected in most of the polymers. The Tg of the amorphous soft phase decreases with increasing polyether molecular weight and is relatively unaffected by soft segment content except at very low levels (≼ 30%). Hard segments apparently separate into ordered structures which melt between 150 and 220°C. The melting points and the heats of fusion generally increase with hard segment content and soft segment M n . Soft segment molecular weight also has a significant influence on the mechanical properties of the polymers. In general, the ambient flexural moduli and the dynamic moduli (E') increase with increasing soft segment M n and the modulus/temperature curve is flattened.

Effects of ion group content and polyol molecular weight on physical properties of HTPB‐based waterborne poly(urethane‐urea)s

“…The glass transition temperature ( T g s ) and heat capacity (Δ C ) of the soft segments of WPUUs are respectively, higher and much smaller than those of HTPB polyols. Similar results have been reported in many PU articles 21–23. Since the chain ends of the soft segments were locked at the rigid surfaces of the hard phases (chain‐end restriction), resulting in the decrease in the mobility of the soft segment and the increase of T g s .…”

“…Since the chain ends of the soft segments were locked at the rigid surfaces of the hard phases (chain‐end restriction), resulting in the decrease in the mobility of the soft segment and the increase of T g s . The dispersed hard domains reduced the free volume of the soft segments (free‐volume restriction), leading to the decrease of Δ C 21–23…”

“…When Mn s decreases or the COOH group content increases, the increase of T g s and the decrease of Δ C indicate that the degree of phase mixing and free‐volume restriction increase, respectively 21–24. It shall be mentioned that the nonpolar HTPB‐based WPUUs have a much higher degree of phase separation.…”

Properties of segmented polyurethanes derived from different diisocyanates

“…However, the T g (S) of the segmented polyurethane materials with aromatic HS is about −42°C and significantly higher than that of the corresponding polyurethanes without HS. The significant shift in T g (S) indicates that SS is partially miscible with the HS in these segmented polyurethane materials with aromatic HS 17.…”

The Cross‐Linking of Polyurethane Incorporated with Starch Granules and their Rheological Properties: Influences of Starch Content and Reaction Conditions

“…[1][2][3][4][5][6][7][8] Differential scanning calorimetry (DSC) measurements indicate several endothermic peaks related to the glass transition of soft segments, the morphological transitions of hard segment, dissociation of ordering in the hard micro-phase, and the melting transition of the hard segment crystal structure. [1,9] The polyurethane synthesized at a high temperature(> 150 8C) could also form a crosslinked network polymer system through allophanate/biuret bonding, which is more complicated.…”