Tuning interaction parameters of thermoplastic polyurethanes in a binary solvent to achieve precise control over microphase separation

Thermoplastic polyurethanes (TPUs) are designed using a large variety of basic building blocks but are only synthesized in a limited number of solvent systems. Understanding the behavior of the copolymers in a selected solvent system is of particular interest to tune the intricate balance of microphase separation/mixing, which is the key mechanism behind the structure formation in TPUs. Here, we present a computationally efficient approach for selecting TPU building blocks and solvents based on their Flory–Huggins interaction parameters for a precise control over the microphase separation/mixing. We first cluster eight soft segments (PEO, PPO, PTMO, PBA, PCL, PDMS, PIB, or PEB) used frequently in TPUs into three categories according to the strength of their interactions with the binary solvent THF/DMF. We then perform a comprehensive set of dissipative particle dynamics simulations of the TPUs in a range of solvent ratios. This enables us to demonstrate the emergence of the unusual channel-like structures in a narrow range of parameters and to determine the critical interactions operative for obtaining either microphase separated or mixed structures. The findings are supported by thermodynamic arguments. The approach developed here is useful for designing novel TPUs with well-defined conformational characteristics, controlled morphologies, and advanced functional properties

A sustainable approach to produce stiff, super-tough, and heat-resistant poly(lactic acid)-based green materials

Circumventing inherent embrittlement, poor heat resistance, and melt elasticity of poly(lactic acid) (PLA) without compromising its remarkable stiffness and strength has become a particular challenge in polymer science due to increasing demand for green materials in emerging applications of sustainable chemistry and engineering. Achieving this without using any high-cost reagent/additive and/or complex processing technique is another critical aspect for developing industrially viable alternatives to petroleum-based commodity plastics. Here we demonstrate that high-shear mixing of PLA with waste cross-linked polyurethanes and waste cellulose fibers allows for overcoming its inherent embrittlement, poor heat resistance, and melt elasticity without compromising its superior stiffness and strength while suggesting a sustainable way of recycling/reusing industrial wastes as high added-value additives. We therefore achieve to produce stiff, strong, super-tough, and heat-resistant PLA-based green materials, for instance, with an elastic modulus of 4 GPa at 25 °C (∼30% higher than that of pure PLA), a storage modulus of 312 MPa at 90 °C (∼44 times higher than that of pure PLA), a tensile strength of 65 MPa (comparable to that of PLA), and an impact strength (toughness) of 52 kJ/m2 (∼2.3 times higher than that of pure PLA)

Blends of highly branched and linear poly(arylene ether sulfone)s: multiscale effect of the degree of branching on the morphology and mechanical properties

This study reports the synthesis of highly branched poly(arylene ether sulfone)s (HBPAES) and their incorporation into linear poly(arylene ether sulfone) (LPAES) to investigate the effect of branched topology on the morphological and mechanical properties of final polymer blends. The A2 + B3 polymerization was utilized to synthesize HBPAESs with varying distance between branch points by reacting monomeric 4,4′-dichlorodiphenyl sulfone (DCDPS) or pre-synthesized chlorine terminated linear oligomers with various degrees of polymerization as the A₂ species with 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) as the B₃ monomer. The chemical structure and the degree of branching of synthesized HBPAESs were characterized by 1H Nuclear Magnetic Resonance (NMR) spectroscopy, while Size Exclusion Chromatography (SEC) and Differential Scanning Calorimetry (DSC) were used for the determination of their molecular weight and glass transition temperatures. Polymer blends of HBPAES and LPAES (10/90 w/w) were solution cast into free-standing, dry films and characterized by tensile tests, Dynamic Mechanical Analysis (DMA), Atomic Force (AFM) and Scanning Electron (SEM) Microscopies. Complementary to experimental studies, these blends were modeled with dissipative particle dynamics (DPD) simulations to explain their microphase behavior, miscibility, and morphology. The experimental and computational studies together revealed that understanding the effect of the degree of branching on the intermolecular interactions of highly branched polymers with their linear analogues is critical to obtain final polymer blends with tunable mechanical properties and enhanced fracture behavior