Structurally Ordered NIPUs via Catalyst-Free Synthesis with Hard Segments Based on Erythritol and a Long-Chain Diamine

A series of linear isocyanate-free polyurethanes (NIPUs) were obtained by aminolysis of erythritol dicarbonate (EDC) with polyethers (diamino-PEG, diamino-PPO and diamino-PEG/PPO) and 1,12-diaminododecane (DADD), which acts as a chain extender to form hard segments. The obtained NIPUs contained different concentrations of DADD relative to the polyether (72.5–80 wt%). Detailed chemical structure analysis of synthesized NIPU was performed using a combination of FTIR and 1H NMR. FTIR spectra confirmed that the EDC-DADD segments formed a network of hydrogen bonds. This is reflected in WAXD diffractograms showing ordered crystalline domains originating in DADD. The reflections assigned to the DADD segments exhibited changes in their position and intensity with decreasing concentration, indicating an increase in interplanar spacing and a loss of higher-order order. WAXD also showed that the soft segments of PEG and PEG/PPO retain their ordered crystal structure regardless of the DADD content. At a larger length scale, SAXS revealed similar micromorphology for the different polyethers, with a broad peak indicating long-range order in the DADD-rich segments and a weak separation of the soft and hard phases. DSC analyses confirmed the complex phase behavior, where the PEG-based materials showed melting of crystalline fragments and the amorphous PPO showed a glass transition. DMA indicated the stability of the glass transition temperature in the PPO samples and the presence of an unusual structural transition. The results emphasize the influence of the type of poly(ether) on the thermal and microphase properties of the studied non-isocyanate polyurethanes.