Crystalline Hard Segments Research Articles

Partial crystalline organosilicon-based polysiloxane-polyurethane copolymers

Partial crystalline polysiloxane-based polyurethane copolymers were prepared by using hydroxyethoxypropyl capped polydimethylsiloxane (PDMS) as soft segment and α,ω-(bis (hydroxyethylthioether) ethyl)-disiloxane as chain extender. Due to this partial crystalline structure, the copolymer shows fairly good tensile properties and multiple shape deformation property. Repeated tensile tests revealed that stretch led to crystal destruction, and the microstructure of samples became stable after twice stretches. The lost crystallinity got 85.1% recovered upon treated at 60 °C for 1 h. It was proved that partial crystallization properties of the polysiloxane-polyurethane copolymer were from combined effects of polysiloxane soft segment and disiloxane chain extender. This unique crystallization kinetics of -(Si-O-Si)x- structure coexisting in soft and hard segments is regarded as one main reason to form crystalline hard segment domains in a common two-step synthesis.

Aromatic thermoplastic polyurethanes synthesized from different potential sustainable resources

Thermoplastic polyurethanes (TPUs) are known for their versatility due to the wide range of macromolecular architectures available. This study focuses on the synthesis and the architecture-properties relationships of new sustainable aromatic TPUs, derived from different potential sustainable resources, such as biomass and plastic waste. Thus, new sustainable aromatic short diols were synthesized from 4–hydroxybenzoic acid and syringic acid, and named HB.diol and Syr.diol, respectively. Subsequently, TPUs were prepared with these original diols as chain extenders, alongside conventional aromatic and aliphatic sustainable chain extenders, like 1,4–benzenedimethanol (BDM) and 1,4-butanediol. The investigation explored the effect of these chain extender structures on the properties of the resulting TPUs, using both aromatic and aliphatic diisocyanates in the synthesis. The thermal and mechanical characteristics of the TPUs were evaluated to identify key structural parameters that influence the properties of the macromolecular architectures. Notably, the presence of aromatic rings enhanced the incompatibility between soft and hard segments (HS), resulting in greater phase segregation. Ether bonds in HB.diol and symmetric structures in BDM enhanced hydrogen bonding, promoting the development of organized and crystalline HS, enhancing phase segregation, thus improving thermo–mechanical and mechanical properties. On opposite, methoxy groups in Syr.diol and the asymmetry of the aromatic diisocyanate hindered the organization of HS, leading to reduced TPUs structuration and lower mechanical properties. Overall, these findings highlight the potential for creating sustainable TPU macromolecular architectures with desirable properties by selecting appropriate raw materials.

Enhanced foaming ability of thermoplastic polyurethane by crystallization during mold-opening foam injection molding with supercritical N2 as blowing agents

This study provides an insight into the foaming of thermoplastic polyurethane (TPU), which was improved by the crystallization of hard segment domains. This study investigated the effects of packing time in the mold-opening foam injection molding (MOFIM) technology on the crystallization behavior of hard segments in TPU and the cell morphology of TPU foams. It was observed that the prolongation of the packing time, corresponding to a longer crystallization time before foaming, induced an increased crystallinity in the injection-molded TPU solids and foams due to the crystals becoming more close-packed. The enhancement of the foamability of TPU was attributed not only to the increased crystallinity of hard segments, but also to the broader distribution of crystals at the same crystallinity. Furthermore, TPU foams with greater hardness have smaller cell size, higher cell density, and narrower distribution in cell size owing to their higher viscosity and storage modulus than those with lower hardness prepared under the same conditions.

Fatigue Characteristics of Poly(ether-b-amide) Elastomers during Cyclic Dynamic Tests and the Underlying Microstructural Evolution

The dynamic fatigue behavior of the poly(ether-b-amide) (PEBA) elastomers was characterized by a combination of step increase load test (SILT), step increase strain test (SIST), and single load dynamic creep (SLDC). PEBA had crystalline hard segments of polyamide 12 (PA12) and soft segments of poly(tetramethylene oxide) (PTMO). The crystalline morphologies before and after the tests were studied by ex situ wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). Fast stress relaxation can be seen under the applied strain well below than the elongation at break. Remarkable dynamic creep can be observed under the applied load triggering yielding of the specimen, which is substantially less than the ultimate tensile strength. Although the presence of high content of amorphous PTMO renders high entropic elasticity, the disintegration of the crystalline hard domains of PA12 is expected to determine the relaxation rate, creep rate, and modulus, as strain-induced crystallization in soft domains did not occur and no trace was found by WAXD. SAXS patterns showed that the orientation of the PA12 lamellae at lower stresses or strains can largely be restored. However, the fractured and highly aligned PA12 lamellae resulted in classic four-point or two-lobe SAXS patterns, which implied the underlying microstructural changes after the cyclic dynamic tests.

High-Strength Heat-Elongated Thermoplastic Polyurethane Elastomer Consisting of a Stacked Domain Structure.

We found that a high-strength elastomer was obtained by the heat elongation of a thermoplastic polyurethane (TPU) film consisting of a high content of crystalline hard segments (HS). The stress upturn continuously increased with the elongation ratio without a decrease in the strain recovery by heat elongation, i.e., the stress at break of a quenched TPU film was increased from 55 to 136 MPa by heat elongation at an elongation ratio of 300%. The results of small-angle X-ray scattering, DSC, and AFM observations revealed that: (1) anisotropically shaped HS domains were stacked at a nanometer scale and the longer direction of the HS domains was arranged perpendicular to the elongated direction due to the heat elongation, (2) the densification of the HS domains increased with increases in the elongation ratio without a significant increase in the crystallinity, and (3) the stacked domain structure remained during the stretching at 23 °C. Thus, the strengthening of the elongated TPU might be attributed to the densification of the HS domains in the stacked structure, which prevents the fracture of the HS domains during the stretching.

Biodegradable and Biocompatible Thermoplastic Poly(Ester-Urethane)s Based on Poly(ε-Caprolactone) and Novel 1,3-Propanediol Bis(4-Isocyanatobenzoate) Diisocyanate: Synthesis and Characterization.

A series of non-toxic biodegradable and biocompatible polyurethanes bearing p-aminobenzoate moieties are presented. The introduction of this attractive motif was carried out by the synthesis of a novel isocyanate. These biodegradable polymers were chemically and physically characterized by several techniques and methods including bioassay and water uptake measurements. The molecular weight of the soft segment (poly-ε-caprolactone, PCL) and hard segment crystallinity dictated the mechanical behavior and water uptake. The behavior of short PCL-based polyurethanes was elastomeric, whilst increasing the molecular weight of the soft segment led to plastic polyurethanes. Water uptake was hindered for long PCL due to the crystallization of the soft segment within the polyurethane matrix. Furthermore, two different types of chain extender, hydrolyzable and non-hydrolyzable, were also evaluated: polyurethanes based on hydrolyzable chain extenders reached higher molecular weights, thus leading to a better performance than their unhydrolyzable counterparts. The good cell adhesion and cytotoxicity results demonstrated the cell viability of human osteoblasts on the surfaces of these non-toxic biodegradable polyurethanes.

End-Terminated Poly(urethane-urea) Hybrid Approach toward Nanoporous/Microfilament Morphology.

In the present work, the effect of heteroatomic hydrogen bonding on the properties of −OH/–NH-terminated soft-segment-free polymers, viz, polyurethane (P-UT), polyurea (P-UR), and their hybrid (P-UT–UR), is explored. P-UT was synthesized from phloroglucinol and P-UR was synthesized from 1,3,5-triazine-2,4,6-triamine by employing hexamethylene diisocyanate as a counterpart. P-UT exhibited a spherulitic structure with varying sizes, whereas P-UR displayed a fibrillar structure characteristic as that of crystalline hard segments. The P-UT–UR hybrid exhibited a fine nanospherulitic structure with a high order of interconnectivity. Negative surface skewness values of −0.47 and −0.18 were measured (by AFM) for P-UT and P-UT–UR, respectively, which revealed that the surface is not smooth and is covered with features. Due to the increased H-bonding (−N–H···O–H) in P-UT–UR, its transparency decreased. A block copolymer hybrid of urethane–urea was synthesized, which preferred homoatomic H-bonding, whereas random urethane/urea bridges favored hetreoheteroatom H-bonding. A pentafluorophenyl end-functional hybrid (PFI–P-UT–UR) was synthesized, which displayed filaments of ∼2–3 μm length in contrast to the interconnected nanospherulitic structure observed for P-UT–UR. The self-aggregation and end folding led to the formation of a filament structure. By altering the chemical structure slightly, nano-ordered polyurethanes or their hybrids can be achieved.

Rapid Carbon Dioxide Foaming of 3D Printed Thermoplastic Polyurethane Elastomers

Polymeric foam preparation using the carbon dioxide (CO2) foaming technique is fascinating. Until now, the CO2-based foaming process has been carried out for a long saturation time. Once it is possible to produce a polymeric foam in a low saturation time, it can enhance foam production. This study investigates the foaming behavior of 3D printed TPU samples with three different hardness values. The variation of infill density in 3D printed samples provides a macroporous range in the sample and creates a path for the gas molecules to reach the polymer. Such a gas flow path expands the foam processing technique to be carried out at low saturation time and pressure. The foaming process carried out here follows two steps: first, CO2 gas saturation in a high-pressure stainless-steel vessel; second, then hierarchical microporous generation by devising a thermodynamically unstable condition by placing the gas saturated sample in a hot water bath set up. The results showed that the increase in saturation time and pressure increases the expansion behavior of the foam samples, whereas an increase in infill density restricts the foam expansion behavior. The crystalline hard segment (HS) enhances the heterogeneous cell nucleation and reduces the shrinkage of the foam samples. The foam sample with low infill density showed low compression strength. It could be improved by filling the macroporous gap with hydrogel during printing. This hydrogel-packed low infill density foam showed an increased compression strength of 0.8 MPa at 80% strain than the neat foam sample (without hydrogel) 0.12 MPa at 80% strain, confirmed through the cyclic compression test. Hence, this 3D printing integrated subcritical solid-state foaming system offers unparalleled freedom to design and create foam and increase its production. The one-pot preparation of low-density higher compression strength foam using hydrogel makes this technique more feasible for high-end applications.

Structure and morphology of thermoplastic polyamide 6 elastomers with different soft segment content and their foaming behavior using supercriticalCO2

AbstractThermoplastic polyamide elastomers (TPAEs) were synthesized using polyamide 6 (PA6) as hard segments and polyethylene glycol (PEG) as soft segments. The prepared TPAEs showed a superior mechanical property and thermal property, which the strength and elongation‐at‐break reached 35.50 ± 3.54 MPa and (316.05 ± 20.58)%, respectively, when the molecular weight of soft segment was 600. Furthermore, crystallization property and microphase separation of TPAEs were also investigated in detail, having a significant influence on the foaming behavior of the obtain elastomers. Owing to the restriction of crystalline hard segments, only a few cells formed in the amorphous soft segment regions at foaming temperature of 140°C, while it transformed to larger cells with a thin cell wall at foaming temperature of 160°C and above. When the molecular weight of soft segment increased from 300 to 1000, the average cell size of the foamed TPAEs at 160°C enlarged from 28.73 to 42.17 μm, while the cell density decreased from 5.26 × 108#/cm3to 4.25 × 108#/cm3, both expansion ratio and shrinkage ratio increased gradually.

Study of thermoplastic elastomer synthesis, characterization, crystallization based on crystallizable amide segment contains conducting moiety

Thermoplastic elastomers (TPE'S) with a conducting moiety are made from Poly (tetramethylene oxide), hard segments TΦT, and sodium salt of Dimethyl-5-isothalate (DM5SIS). In the synthesis procedure, different mole percentages of the conducting moiety DM5SIS are used to see if the presence of salt affects the polymerization process and, as a result, the crystallinity of the hard segment. The synthesis of the polymer is confirmed using the 1H NMR method. The produced polymer had an inherent viscosity of 2.4–3.6 dl/g, indicating that the polymer had a high molecular weight. FT-IR techniques were used to determine the crystallinity of the hard segment in the copolymers, which revealed that the hard segment is entirely crystallised (>90%). The crystallinity is extremely reversible, according to a temperature-dependent IR investigation. The synthesised segmented copolymers DSC heating curve revealed two transitions: Tm of soft segment (SS) and melting of hard segment (HS). These materials have a very low undercooling value (about 20 °C), implying that the hard segment will crystallise quickly. The segmented copolymer that was created was clear, had a high molecular weight, and contained crystalline HS. Because the addition of a conducting moiety to the polymer chain has no effect on the polymerization process or the crystallinity of the hard segment, the polymer could be a good option for proton exchange membranes in fuel cells.

Design and Performance of Polyurethane Elastomers Composed with Different Soft Segments.

Thermoplastic polyurethane elastomers (TPUs) are widely used in a variety of applications as a result of flexible and superior performance. However, few scholars pay close attention on the design and synthesis of TPUs through the self-determined laboratory process, especially on definite of chemical structures and upon the influence on properties. To investigate the properties of synthesized modifier based on chemical structure, firstly each kind of unknown structure and composition ratio of TPUs was determined by using a new method. Furthermore, the thermal characteristics and mechanical properties of modifiers were exposed by thermal characteristics and mechanics performance tests. The experimental results indicate that TPUs for use as an asphalt modifier can successfully be synthesized with the aid of semi-prepolymer method. The linear backbone structure of TPUs with different hard segment contents were determined by micro test methods. The polyester-based TPUs had thermal behavior better than the polyether-based TPUs; conversely, the low temperature performance of polyether-based TPUs was superior. Most importantly, it was found that the relative molecular mass of TPUs exhibited a weak effect on the mechanical properties, whereas the crystallinity of hard segment showed a significant influence on the properties of TPUs.

Biodegradable poly(urethane-urea-amide): Synthesis, characterization and mechanical studies

Biodegradable polyurethane with excellent mechanical property finds a lot of applications in the biomedical field. In this study, multi block copolymer poly(urethane-urea-amide) (PUUA) is prepared using polyethylene oxide, 1,6-hexamethylene diisocyanate and diamide (N1, N4-bis(6-aminohexyl)benzene-1,4-dicarboxamide (6T6) or N1, N6-bis(6-aminohexyl)hexanediamide (6A6)) by a method of solution/melt polymerization techniques. The polymer formation is confirmed by the 1H NMR spectroscopic method. Other techniques such as viscosity measurements, FT-IR, DSC, TGA, and biodegradability are used to characterize the synthesized copolymers. The hard segment crystallinity is an analyzed by FT-IR spectroscopy, it revealed that the 6T6 based polymer showed 70% of crystallinity. The synthesized copolymer shows three transitions in the DSC curve. The melting enthalpy of the hard segment depends on the amide unit employed in the polymerization process. These materials are fast crystallizing due to low under cooling value. This material has a very high thermal stability and stable up to 400°C. Tensile test confirms the strain induced crystallization of hard segment occurred in the PUUA. The biodegradability of the polymer depends on the pH and chain extenders. This type of materials can be a good candidate for tissue engineering application.

Morphology evolution and thermodynamic behavior of the “soft core hard shell” structure formed by reactive amino triblock in epoxy resin

In this study, a novel triblock copolymer poly(e-caprolactam)-block-poly(dimethylsiloxane)-block-poly(e-caprolactam) (PLC-b-PDMS-b-PLC) was synthesized by ring-opening polymerization. The approach of improving thermal and mechanical properties of thermosetting epoxy resin (ER) used methyl hexahydrophthalic anhydride as hardener and PLC-b-PDMS-b-PLC as modifier. The test results showed the chemical structure and molecular weight of PLC-b-PDMS-b-PLC can be controlled, and PLC-b-PDMS-b-PLC was self-assembled in the epoxy hybrid system to form nanophase separation structure. From the test of thermal and mechanical properties, it can be known that the amount of block in ER will affect the morphology and density of nanophase, thus affecting the toughness of the material. In the “soft-core hard-shell” nanodomain, the interaction of crystalline hard segments and non-crystalline PDMS soft segments overlapped adjacent stress fields, which helped the material absorb energy when subjected to external impact. The fracture toughness and impact strength of the modified resin were increased by up to 1.52 and 2.19 times compared to neat ER, respectively.

Effect of microstructural arrangement of MDI‐based polyurethanes on their photoproperties

ABSTRACTAmong the vast variety of polyurethane applications, several applications use the fluorescing nature of some of the polyurethanes. Even though 4,4′‐methylenebis(phenylisocyanate) (MDI)‐based polyurethanes fluoresce, their applications are rare because of the lack of knowledge about the fluorescence behavior of these polymers. In this study, the fluorophores responsible for the emission spectra of MDI‐based polyurethanes were identified, and their emission behavior was investigated. When excited, these polymers produce two prominent emission peaks located at 356 nm and 423 nm, which are assigned to the radiative relaxation of excited isolated hard segments and excited crystalline hard segment bundles of the MDI‐based polyurethanes, respectively. It was found that both chromophores can be excited by 293 nm UV radiation. The observed intensity variations of the two peaks with exposure time were attributed to the localized UV melting‐assisted migration of isolated hard segments. This migration facilitates the formation of crystalline hard segments. As the two chromophore populations are inversely propositional to each other, the relative intensity of the two emission peaks varies with UV exposure in a similar manner. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47431.

Effect of graphene loading on mechanical properties of polyurethane elastomer

Abstract The elastomeric polyurethane (PU) nanocomposites prepared by in- situ polymerization of diisocyanate with graphene nanoplatelets (GNPs) dispersion in polyol. Mechanical properties of polyurethane exhibited a significant improvement through incorporation of GNPs is observed. Morphologies study showed that there is a strong interaction between GNPs and hard segments of PU that allows effective load transfer. Two – dimensional structure of GNPs can help to prevent formation of crystalline hard segments. The tensile strength and tearing strength was improved by ∼1.9 times by with the incorporation of 1.0 vol. % of GNP.

Effect of soft/hard segments in poly (tetramethylene glycol)-Polyurethane for water barrier film

A series of thermoplastic polyurethanes (TPUs) with the same molecular weight but different soft/hard ratios were synthesized by in-situ condensation polymerization using poly (tetramethylene glycol) (PTMG) as the polyol and methylene diphenyl diisocyanate (MDI) as the isocyanate. The weight fractions of the hard segments were varied from 0.0 to 0.4. The structures of the TPU series were analyzed by Fourier transform infrared spectroscopy and gel permeation chromatography. The changes in the thermal and optical properties due to the hard segment crystallinity were also measured by differential scanning calorimetry and UV–vis spectroscopy. Increasing the hard content promoted phase separation and served as absorption blocks in the TPU. The water vapor permeability of the TPU films with different soft/hard ratios ranged from 223.63 to 116.26 g/m2 day.

Microstructural evolution underlying the ternary stages of the elastic behaviors for poly(ether‐b‐amide) copolymer elastomers

ABSTRACTThree stages of elastic behavior were observed during cyclic deformations for poly(ether‐b‐amide) (PEBA) segmented copolymers based on crystalline hard segments of polyamide 12 (PA12) and amorphous soft segments of poly(tetramethylene oxide) (PTMO). The underlying microstructural evolution was characterized by a combination of in situ Fourier transform infrared spectroscopy (FTIR), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS) technologies. The γ–α″ phase transition of crystalline PA12 occurred upon stretching, and the orientation of the α″ phase was less reversible under larger strains. PTMO chain orientation cannot be restored to the initial state, contributing to plastic deformation. Driven by the entropy effect, the strain‐induced crystallization of PTMO can fuse during sample retarding, exerting little influence on the residual strain. For PEBA with a shore D hardness of 35 D, the long period (L) can be restored to the initial L after the sample was unloaded until system fibrillation. The tie molecules between adjacent oriented lamellae can be by drawn out high stress in a PEBA material with a shore D hardness of 40 D, and the relaxation led to a second long period. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 855–864

Biocompatible Polyurethane Scaffolds Prepared from Glycerol Monostearate-Derived Polyester Polyol

Biodegradable polyester polyol was synthesized from oleochemical glycerol monostearate (GMS) and glutaric acid under a non-catalyzed and solvent-free polycondensation method. The chemical structure of GMS-derived polyester polyol (GPP) was elucidated by FTIR, 1H and 13C NMR, and molecular weight of GPP was characterized by GPC. The synthesized GPP with acid value of 3.03 mg KOH/g sample, hydroxyl value of 115.72 mg KOH/g sample and Mn of 1345 g/mol was incorporated with polyethylene glycol (PEG) and polycaprolactone diol (PCL diol) to produce a water-blown porous polyurethane system via one-shot foaming method. The polyurethanes were optimized by evaluating glycerol as a crosslinker, silicone surfactant and water blowing agent on tensile properties of polyurethanes. All polyurethanes underwent structural change, and crystalline hard segments of polyurethanes were shifted to higher temperature suggested that hard segments undergone re-ordering process during enzymatic treatment. In terms of biocompatibility, polyurethane scaffold produced by reacting 100% w/w of GPP with isophorone diisocyanate and additives showed the highest cells viability of 3T3 mouse fibroblast (94%, day 1), and MG63 human osteosarcoma (107%, day 1) and better cell adhesion as compared to reference polyurethane produced by only PEG and PCL diol (3T3 cell viability: 8%; MG63 cell viability: 2%). The current work demonstrated GPP synthesized from renewable and environmental friendly resources produced polyurethanes that allows improvement in physico-chemical, mechanical and biocompatibility properties. By blending with increasing content of GPP, the water-blown porous polyurethane scaffold has shown great potential as biomaterial for soft and hard tissue engineering.

Structure-properties relationships of novel poly(carbonate-co-amide) segmented copolymers with polyamide-6 as hard segments and polycarbonate as soft segments

Novel poly(carbonate-co-amide) (PCA) block copolymers are prepared with polycarbonate diol (PCD) as soft segments, polyamide-6 (PA6) as hard segments and 4,4’-diphenylmethane diisocyanate (MDI) as coupling agent through reactive processing. The reactive processing strategy is eco-friendly and resolve the incompatibility between polyamide segments and PCD segments in preparation processing. The chemical structure, crystalline properties, thermal properties, mechanical properties and water resistance were extensively studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Differential scanning calorimetry (DSC), Thermal gravity analysis (TGA), Dynamic mechanical analysis (DMA), tensile testing, water contact angle and water absorption, respectively. The as-prepared PCAs exhibit obvious microphase separation between the crystalline hard PA6 phase and amorphous PCD soft segments. Meanwhile, PCAs showed outstanding mechanical with the maximum tensile strength of 46.3 MPa and elongation at break of 909%. The contact angle and water absorption results indicate that PCAs demonstrate outstanding water resistance even though possess the hydrophilic surfaces. The TGA measurements prove that the thermal stability of PCA can satisfy the requirement of multiple-processing without decomposition.

Surface and mechanical properties of waterborne polyurethane films reinforced by hydroxyl-terminated poly(fluoroalkyl methacrylates)

Novel waterborne fluorinated polyurethane (WFPU) based on hydroxyl-terminated poly(fluoroalkyl methacrylates) (HTPFMA) was prepared successfully. The microstructures and micro-phase separation of WFPU were evaluated through infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic mechanical analysis (DMA), and scanning electron microscope (SEM). FT-IR revealed that the H-bonded carbonyl in hard domains increased with the increasing of fluorine content, resulting in enhancing the extent of micro-phase separation between hard and soft segments. XRD results indicated that the crystallinity of hard segment was enhanced with the increasing of fluorine content. The direct visual microstructures by SEM showed that the micro-phase separation was more significant when the fluorine content increased. DMA also revealed strengthened micro-phase separation with increasing fluorine content. The studies of mechanical properties confirmed that WFPU based on HTPFMA had outstanding mechanical properties. The effects of fluorine content on the static contact angles, surface free energy, and surface composition were also studied. The static contact angles of the WFPU films against water and methylene iodide reached around 108° and 84°, respectively. X-ray photoelectron spectroscopy (XPS) confirmed that the fluorine surface enrichment factor in the outermost 10 nm depth was about 10–18 fold higher than its bulk level.