Domain Structure, Thermal and Mechanical Properties of Polycaprolactone-Based Multiblock Polyurethane-Ureas under Control of Hard and Soft Segment Lengths

Abstract

A series of multiblock polyurethane-ureas (PUU) based on polycaprolactone diol (PCL) with a molecular mass of 530 or 2000 g/mol, as well as hard segments of different lengths and structures, were synthesized by the step-growth polymerization method. The chemical structure of the synthesized multiblock copolymers was confirmed by IR- and NMR-spectroscopy. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to determine the relaxation and phase transition temperatures for the entire series of the obtained PUU. The X-ray diffraction (XRD) method made it possible to identify PUU compositions in which the crystallizability of soft segments (SS) is manifested due to their sufficient length for self-organization and structuring. Visualization of the crystal structure and disordering of the stacking of SS with an increase in their molecular mobility during heating are shown using optical microscopy. The change in the size of the hard phase domains and the value of the interdomain distance depending on the PCL molecular mass, as well as the length and structure of the hard block in the synthesized PUU, were analyzed using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The evolution of the domain structure upon passing through the melting and crystallization temperatures of PUU soft blocks was studied using SANS. The studies carried out made it possible to reveal the main correlations between the chemical structure of the synthesized PUU and their supramolecular organization as well as thermal and mechanical properties.

A Comprehensive Study of Polyurethane Potting Compounds Doped with Magnesium Oxide Nanoparticles

“…The assumption of molecular scale contiguity between polyurethane hard segments and MgO results in a reduction in the mobility of the chain segments and increases the cooperative nature of the corresponding relaxation process. This subsequently leads to a reduction in the number of interactions between the hard and soft segments in the polyurethane matrix and changes in the mechanical properties, which have already been confirmed by other studies [ 8 , 101 , 102 ].…”

“…Focusing on the positive properties mentioned above, these are mainly due to the two-phase microstructure composed of hard and soft segments [ 5 , 7 ]. It can thus be argued that a PUR is a block copolymer with alternating soft and hard segment components along the macromolecular chain [ 8 ]. The soft segments (polyol) contribute to the elasticity, toughness, and resiliency of the material, and the hard segments (diisocyanate and chain extender) provide physical cross-linking points, with the ratio of these segments affecting the final properties of the synthesized material [ 7 , 9 , 10 , 11 ].…”

Synthesis, characterization, and potential application of polyurethane foam as an effective alternative for dental aspiration substrate in liquid absorption/retention and mechanical properties

“…The soft segment, also known as the flexible segment, has low polarity and is mainly composed of polyols containing ester or ether groups on the chain. Its hard section, also known as the rigid segment, has extraordinarily high polarity and is mostly composed of diisocyanate and chain extender with low molecular weight 13 . However, the structure of PU molecules is regular, firmly ordered, and includes hydrogen bonds with strong polar groups, resulting in poor liquid absorption and retention performance, which cannot meet the requirements of modern dental absorbent hemostatic materials.…”

“…Its hard section, also known as the rigid segment, has extraordinarily high polarity and is mostly composed of diisocyanate and chain extender with low molecular weight. 13 However, the structure of PU molecules is regular, firmly ordered, and includes hydrogen bonds with strong polar groups, resulting in poor liquid absorption and retention performance, which cannot meet the requirements of modern dental absorbent hemostatic materials. It is necessary to synthesize and design PU with high liquid absorption and retention that can meet performance standards.…”