Polyurethanes with monodisperse rigid segments based on a diamine–diamide chain extender

Abstract

Polyether(bisurethane-bisurea-bisamide)s (PEUUA) based on poly(tetramethylene oxide) (PTMO) were synthesized by chain extension of PTMO endcapped with a diisocyanate (DI), and a diamine-diamide extender. The prepolymers were PTMOs with molecular weights between 1270 and 2200 g mol 21, either endcapped with 4,4 0 -diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (2,4-TDI), or 1,6-hexane diisocyante (HDI) and with a low content of free diisocyanate (<0.1 wt %). The diaminediamide (6A6) extender was based on hexamethylene diamine (6) and adipic acid (A). In this way, segmented polyurethanes with monodisperse rigid segments (DI-6A6-DI) were obtained. The PEUUAs were characterized by DSC as well as temperature-dependent FTIR and DMTA. The mechanical properties of the polymers were evaluated by compression set and tensile test measurements. The polyurethanes with monodisperse rigid segments displayed low glass transition temperatures, almost temperature-independent rubbery plateaus and sharp melting temperatures. The crystallinities of the hard segments were 70-80% upon heating and 40-60% upon cooling. The rate of crystallization was moderately fast as the supercooling (T m 2 T c ) was in the order 36-548C. The polyurethanes based on HDI had a much higher rubber modulus as compared to the MDI and 2,4-TDI-based polymers, because of a higher degree of crystallinity and/or a higher aspect ratio of the crystallites. The HDI residues are flexible and not sterically hindered and could therefore be more easily packed than MDI or 2,4-TDI residues. Polyurethanes with monodisperse DI-6A6-DI hard segments have interesting properties.

Polyurethanes with Narrow‐ and Polydisperse Hard Segment Distributions

“…[4] Mono-disperse HS shows an enhanced thermal stability when constituted of diurethanediurea-diamide since trans-reactions do not change the distribution of these HSs. [9,10] Nowadays polyurethanes are often synthesized in a two-step process. First, a soft segment (SS) prepolymer, end-capped with diisocyanate is prepared with excess diisocyanate.…”

Well‐defined Biobased Segmented Polyureas Synthesis via a TBD‐catalyzed Isocyanate‐free Route

“…TPUs with monodisperse HSs generally show a higher elastic modulus, a less temperature-dependent plateau modulus between the T g of the SS and the T m of the HS, and a more predictable processing temperature. [3][4][5][6] Conventionally, TPUs are prepared from polymeric diols (which act as SS), diisocyanates and low molecular diol or diamine chain extenders (the low molecular compounds, together forming the HS). However, the toxicity of diisocyanates [7] should not be ignored, especially for TPUs which are applied in biomedical applications.…”

Thermal Conductivity and Interconnectivity of Hexamethylene Diisocyanate Contained Polyurethane Grafted Multiwall Carbon Nanotube/Polyurethane Nanocomposite Film

“…The characteristics of incompatibility of alternating segments and microphase separation in PU are well known. 8) Therefore, the steric hindrance of the diisocyanate in a hard segment may affect the crystallization of the urethane segment. A previous study conducted by Gaymans et al 8) explained the different crystalline behavior of PU with hard segments.…”

“…8) Therefore, the steric hindrance of the diisocyanate in a hard segment may affect the crystallization of the urethane segment. A previous study conducted by Gaymans et al 8) explained the different crystalline behavior of PU with hard segments. According to this study, steric hindrance arising from the hard segments is related to the phenyl ring.…”