Non-Isocyanate Polyurethane Thermoplastic Elastomer: Amide-Based Chain Extender Yields Enhanced Nanophase Separation and Properties in Polyhydroxyurethane

Non-isocyanate polyurethane (NIPU) was synthesized via cyclic carbonate aminolysis using poly­(ethylene oxide) (PEO)- and poly­(tetramethylene oxide) (PTMO)-based soft segments, divinylbenzene dicyclocarbonate as hard segment, and diamine–diamide (DDA) chain extender. Characterization of the resulting segmented polyhydroxyurethanes (PHUs) reveals that the use of amide-based DDA chain extender leads to unprecedented improvements in nanophase separation and thermal and mechanical properties over segmented PHUs without DDA chain extender. With PEO-based soft segments, previously known to yield only phase-mixed PHUs, use of DDA chain extender yields nanophase-separated PHUs above a certain hard-segment content, as characterized by small-angle X-ray scattering. With PTMO-based soft segments, previously known to yield nanophase-separated PHUs with broad interphase, use of DDA chain extender produces nanophase-separated PHUs with sharp domain interphase, leading to wide, relatively temperature-independent rubbery plateau regions and much improved thermal properties with flow temperature as high as 200 °C. The PTMO-based PHUs with 19–34 wt % hard-segment content exhibit tunable mechanical properties with Young’s modulus ranging from 6.6 to 43.2 MPa and tensile strength from 2.4 to 6.7 MPa, with ∼300% elongation at break. Cyclic tensile testing shows that these PHUs exhibit elastomeric recovery with attributes very similar to conventional, isocyanate-based thermoplastic polyurethane elastomers

Nonisocyanate Thermoplastic Polyhydroxyurethane Elastomers via Cyclic Carbonate Aminolysis: Critical Role of Hydroxyl Groups in Controlling Nanophase Separation

Thermoplastic polyhydroxyurethanes (PHUs) were synthesized from cyclic carbonate aminolysis. Because of the hydroxyl groups in PHU, the choice of soft segment has a dramatic influence on nanophase separation in polyether-based PHUs. Use of a polyethylene glycol-based soft segment, which results in nanophase-separated thermoplastic polyurethane elastomers (TPUs), leads to single-phase PHUs that flow under the force of gravity. This PHU behavior is due to major phase mixing caused by hydrogen bonding of hard-segment hydroxyl groups to the soft-segment ether oxygen atoms. This hydrogen bonding can be suppressed by using polypropylene glycol-based or polytetramethylene oxide (PTMO)-based soft segments, which reduce hydrogen bonding by steric hindrance and dilution of oxygen atom content and result in nanophase-separated PHUs with robust, tunable mechanical properties. The PTMO-based PHUs exhibit reversible elastomeric response with hysteresis, like that of conventional TPUs. Because of nanophase separation with broad interphase regions possessing a wide range of local composition, the PTMO-based PHUs also demonstrate potential as novel broad-temperature-range acoustic and vibration damping materials, a function not observed with TPUs

Behavior of Spherical Poly(2-acrylamido-2-methylpropanesulfonate) Polyelectrolyte Brushes on Silica Nanoparticles up to Extreme Salinity with Weak Divalent Cation Binding at Ambient and High Temperature

The colloidal stability of nanoparticles (NPs) stabilized by grafted polyelectrolyte (PE) brushes in concentrated divalent ion solutions, at either ambient or high temperature, is of interest in a wide variety of applications including medicine, personal care products, oil and gas recovery, reservoir imaging, and environmental remediation. Previous attempts to determine the length of PE brushes at these conditions have been limited by lack of colloidal stability particularly when divalent ions form complexes with the charges on the brushes. We find that brushes of highly acidic strong PE poly­(2-acrylamido-2-methyl­propane­sulfonate, AMPS) end-grafted to silica NPs provide colloidal stability at salinities up to 4.5 M CaCl₂ or NaCl. Thus, the brush behavior could be studied with dynamic light scattering (DLS) and the electrophoretic mobility by phase analysis light scattering (PALS) from the salt-free condition to the extreme salinities of 4.5 M. In monovalent NaCl solutions, the highly extended poly­(AMPS) brushes at low salt concentration (<i>C</i>_s) collapse monotonically with increasing <i>C</i>_s. On the other hand, in divalent CaCl₂ solutions the brushes underwent four distinct regimes of (i) a low <i>C</i>_s collapse regime, (ii) a relatively broad plateau regime (0.1 M ≤ <i>C</i>_s < 1 M), (iii) a weak reswelling regime, and (iv) a high <i>C</i>_s collapse regime. The novel behavior in regimes ii–iv may be attributed to weak interactions of the poly­(AMPS) brushes with Ca²⁺. We also find that the brushes are more extended at 90 °C as thermal energy weakens interchain bridging, which is consistent with the behavior of free polymer chains dissolved in CaCl₂ solutions at extreme salinities