Soft Segment Length Research Articles

Single-Step Synthesis and Characterization of Non-Linear Tough and Strong Segmented Polyurethane Elastomer Consisting of Very Short Hard and Soft Segments and Hierarchical Side-Reacted Networks and Single-Step Synthesis of Hierarchical Hyper-Branched Polyurethane.

Polyurethane elastomers are among the most versatile classes of industrial polymers-typically achieved through a two-step synthesis of segmented block copolymers, comprising very long and soft segments that provide elasticity and significantly long and hard segments that provide strength. The present research focused on the design of a single-step synthesis of a new segmented polyurethane consisting of very short soft and hard segments, crosslinked by preferentially side-reacted hierarchical tertiary oligo-uret network structures, thus exhibiting significant strength, elasticity, and toughness. Despite the theoretically linear structure, both FTIR and solid-state 13C NMR spectroscopy analyses indicated the quasi-equal presence of urethane groups and tertiary oligo-uret structures in the resulting polymer, indicating a preferential consecutive side reaction mechanism. Thermal analysis indicated the significant crystallization of soft segments consisting of only four ethylene oxide units, which was, hereby, demonstrated to occur via an extended chain mechanism. Tensile mechanical properties included significant strength, elasticity, and toughness. Increasing the soft segment length led to a decreased tertiary oligo-uret secondary crosslinking efficacy. The preferential hierarchical side reaction mechanism was, hereby, further confirmed through the synthesis of a completely new type of hyper-branched polymer via diisocyanate and a mono-hydroxy-terminated reagent. The structure-property relations and reaction mechanisms demonstrated in the present research can facilitate the design of new polyurethanes of enhanced performance and processing efficacy for a variety of novel applications.

Study on the effect of soft segment length on the performance of polyether-based polyurethane modified asphalt

The molecular structure of the polyurethane soft segment has significant influence on the performance of polyurethane modified asphalt (PUMA). To investigate the effect of soft segment length on the performance of PUMA, three kinds of polytetramethylene ether glycol (PTMEG) with different molar masses were selected to synthesize three polyurethane prepolymers (PUP) with various soft segment lengths. As a result, modifying asphalt with these PUPs lead to three PUMAs. Research showed that the initial decomposition temperature of the PUP rised with the increment of soft segment length and eventually above the base asphalt. The high and low temperature properties of PUMA were enhanced with increasing the soft segment length. However, the dispersion of modifier in the asphalt became worse with higher soft segment length. It should be attributed to the interaction between PUP and asphalt molecules and the crystallization of soft segments. This study provides a good reference for the selection of materials for PUMA.

Rational design for the development of thermoplastic poly(ether-ester) elastomers from bio-based 2,5-furandicarboxylic acid with high elasticity

Development of bio-based thermoplastic poly(ether-ester) elastomer (TPEE) with high performance similar to commercial and petroleum-based TPEE is of great interesting nowadays. Herein, by considering both the hard and soft segments, a rational design strategy is proposed for the synthesis of bio-based TPEE with high elasticity based on a bio-based aromatic monomer 2,5-furandicarboxylic acid (FDCA). The hard segment is poly(neopentyl glycol 2,5-furandicarboxylate) (PNF), a FDCA-based polyester with both high melting temperature and crystallization ability. While the soft segment is poly(tetramethylene glycol) (PTMG), which is widely used for the synthesis of TPEE. By adjusting the molecular weight (Mn) of PTMG soft segment from 650 to 2900 g/mol and its content from 50 to 70 wt%, a series of bio-based TPEEs with excellent performance were synthesized. Our preliminary study of PNF-PTMG multiblock copolymers has shown that the elastic recovery rate is outstanding. The initial elastic recovery ratio at 200 % strain can approach 80 % when the Mn of PTMG is 2000 g/mol and the wt.% of PTMG was 70 %, which is significantly higher than those of the commercial TPEEs. PNF-PTMG displays increasing thermal resistance with Tm up to 194 °C with the increasing of soft segment length. This study suggests a feasible solution for the preparation of bio-based TPEE with ideal performance.

Effect of hard segment chemistry and structure on the self‐healing properties of UV‐curable coatings based on the urethane acrylates with built‐in Diels–Alder adduct

AbstractThe development of new photoreactive resins to obtain smart coatings and enhance the self‐healing (SH) properties of photoreactive resins has attracted great interest in the past few years, and the investigation of the relationship between phase structure and smart properties is necessary. Herein, four types of urethane acrylate resins with built‐in DA structures with different hard segment structures, and a slight change in the length of the polyol soft segment were prepared. The hard segments were made of hexamethylene diisocyanate (HDI) with a linear structure and isophorone diisocyanate (IPDI) with an alicyclic structure, and the soft segments consisted of polyethylene glycols (PEG 400 and PEG 1000, respectively). The obtained resins were used to prepare polymer films that were cured using UV radiation. The coatings obtained in this way were tested for the influence of the polymer chain architecture on the kinetics of photopolymerization, the properties of the cured coatings, as well as the thermal characteristics and thermoreversibility performance of the cured coatings and their SH ability.

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

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.

Segmented shape memory polyurethane: Influence of soft segment types and length

Shape-memory polyurethanes (SMPUs) with heat induced characteristic can be altered to a programmed shape and return to its original shape upon thermal stimuli. SMPU has prompted a lot of interest for various applications such as biomedical appliances, fabrics, coatings, and sensors. In this study, a series of polyols (polycaprolactone (PCL), polyethylene glycol (PEG), polypropylene glycol (PPG)) with different molecular weight were used to synthesize SMPU together with 4,4-methylenebis(cyclohexyl isocyanate) (HMDI) as diisocyanate, and 1,4-butanediol (BD) as chain-extender via two-step bulk polymerization technique. Palm kernel oil-based polyol (PKO-p) was introduced as part of the soft segment. The SMPUs were analyzed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), shape memory and tensile tests. The results showed that SMPU with lower molecular weight (PU-PCL2) achieved higher tensile strength (7.58 MPa) compared to higher molecular weight of PCL (1.55 MPa) apparently due to the low crystallinity. Moreover, PEG based SMPU (PU-PEG3) exhibited good shape memory property with 82% of shape fixity and shape recovery of more than 80%. It was revealed that the variation in molecular weight of the soft segments provides significant effects on the tensile and shape memory properties of SMPU.

Microstructural evolution of polyurea under hydrostatic pressure

Polyurea (PU) is a versatile high strain rate elastomeric polymer that has attracted significant interest due to its utility as a blast and ballistic resistant coating. Predictive design of PU materials, particularly with a focus on structure, is complicated by the occurrence of both high pressure and high strain rate effects in response to blast and ballistic impact. To help elucidate the behavior of PU under such conditions, we sought to characterize the microstructural evolution of PU under hydrostatic compression. To this end, we utilized a diamond anvil cell with in-situ X-ray scattering to monitor the compression-induced microstructural changes of two PU materials differing in their soft segment length. We found that regardless of soft segment length, the initially phase separated structure becomes increasingly mixed during hydrostatic compression up to ~1 GPa. Despite this increase in phase mixing, the interchain network between urea linkages formed through hydrogen bonds remains apparent at pressures well above 1 GPa. The mean spacing associated with the interchain hydrogen-bonded network within the hard segment domains contracts under hydrostatic compression and in some cases recovers upon load removal. Furthermore, the extent of both deformation and recovery depends upon the degree of microphase separation as dictated by the length of the soft segment, wherein PU with a longer soft segment deforms less and recovers more.

Influence of hard segment content and soft segment length on the microphase structure and mechanical performance of polyurethane-based polymer concrete

Understanding the structure–property relationship of polyurethane (PU) binders is of critical importance in the construction engineering applications. A series of rapid room temperature-curable PU binders were prepared using polyoxypropylene glycol as the soft segments, along with polymethylene polyphenylene isocyanate and 4,4′-methylene-bis(2-chlorobenzenamine) as the hard segments. This work investigated the influence of the hard segment content (40 wt%, 45 wt%, and 50 wt%) and the soft segment molecular weight (1000 g/mol, 2000 g/mol, 3000 g/mol, and 4000 g/mol) on the microphase structure of the PU binders. Their influence on the compressive behaviors, flexural behaviors, impact strengths, and slant shear strengths of the PU-based polymer concretes was also investigated. Structural characterization revealed that increasing either the hard segment content or the larger soft segment molecular weight effectively enhanced hydrogen bonding as well as microphase separation. Our results also demonstrated that a higher hard segment content resulted in better mechanical performance and shorter pot life. In addition, the PU-based polymer concrete using 2000 g/mol polyoxypropylene glycol reached optimal mechanical performance when the hard segment was held constant. Hence, varying the hard segment content and soft segment length can be an effective method to adjust the engineering performance of PU-based polymer concrete.

Molecular engineering and morphology of polyurethane elastomers containing various molecular weight of macrodiol

A series of polyurethane elastomers (PUEs) based on 4,4′-cyclohexamethylene diisocyanate (H12MDI)/1,2-ethanediol as hard segment with the soft segments having different molecular weights of polycaprolactone diols, were effectively polymerized by two step technique. The structural characterization was performed by FT-IR spectroscopy. The X-ray diffraction (XRD) technique was used to study the crystallinity and hydrophilicity of the prepared polymer films. It was found that crystallinity and hydrophilicity increased with increasing the chain length of soft segments. The effect of molecular weight of polyols on the contact angle, water absorption (%) and swelling behavior of the synthesized polyurethanes were also studied. Moreover, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques revealed that the degree of micro-phase separation increases with increasing molecular weight of polyol which confirmed the results pattern shown by XRD diffractogram.

Polyurethane as smart biocoatings: Effects of hard segments on phase structures and properties

Development of smart polyurethane (PU) coatings for enhancing the biocompatibility of the metal scaffold has attracted great interest in the past few years, and the investigation of the relationship between phase structure and smart properties is necessary. Herein, two series of PU biocoatings with different hard segment structures and soft segment length were prepared, and the soft segments consist of the polycaprolactone diols (PCL) with different molecular weights, and the hard segments were made of 1, 4-butanediol (BDO) and hexamethylene diisocyanate (HDI) with linear structure, or BDO and isophorone diisocyanate (IPDI) with alicyclic structure, respectively. To understand the phase structures, the chemical structure, surface micromorphology, and segmental incompatibility of the PU films were characterized, which reveals that IPDI-based PU possesses a phase compatible structure with a single-phase transition above 0 °C. Besides, the IPDI-based PU shows the thermal-responsive deformation at the temperature of 45 °C, slightly higher than the human body temperature. In contrast, the HDI-based PU possesses the excellent shape memory property caused by the microphase separation structure, because of the crystallization of soft and hard segments from the melt. Further, based on the characteristics of phase structure, the potential application of the IPDI-based PU and HDI-based PU is explored, offering a useful approach to effectively design the structures and properties of PU coatings.

Coarse-Grained Molecular Dynamics Modeling of Segmented Block Copolymers: Impact of the Chain Architecture on Crystallization and Morphology

We extend our recent coarse-grained model describing semicrystalline homopolymers to simulate the morphology and phase transitions of thermoplastic elastomers made of segmented (hard/soft) block copolymers. The generic model is adapted to match the physical characteristics of the two chemical units involved in the copolymer chains by using classic scaling rules. We investigate the crystallization kinetics of the hard segments as well as their phase separation from the soft units in either triblock or pentablock copolymers. We identify the soft segment molecular weight as a key parameter resulting in the following observations when decreasing the temperature from a homogeneous state. On the one hand, the phase separation preceding the crystallization process in triblock copolymers results in a constant temperature of crystallization when varying the soft segment length. On the other hand, the limited phase separation achieved in pentablock copolymers constrains them to crystallize at progressively lower temperatures while increasing the soft segment length. Finally, increasing the soft segment molecular weight was found to lead to a higher relative crystallinity which can be interestingly related to a rise of the loop segment’s content.

An investigation on structural and gas transport properties of modified cross-linked PEG-PU membranes for CO2 separation

In this paper, modified poly(ethylene glycol)-polyurethane (PEG-PU) membranes were synthesized applying thiol-epoxy click polymerization to separate CO2 (the most important greenhouse gas) form light gases. PEG was initially reacted with isophorone diisocyanate (IPDI) and the NCO-terminated prepolymer was end-capped with glycidol to form epoxy-terminated prepolymer (EPU). The cross-linked membranes were eventually obtained through thiol-epoxy click polymerization reaction using a tetrathiol cross-linker (PETMP) in presence of poly(ethylene glycol) diglycidyl ether (PEGDE). The prepared membranes were characterized by ATR-FTIR, DSC, TGA and tensile analyses. The best fabricated membrane was chosen and named EMT2 which exhibited promising structural, thermal and mechanical properties. It was then employed for further gas transport properties studies. Permeability, solubility, and diffusion coefficients of CO2, N2, CH4, and O2 gases over wide ranges of temperature (308–348 K) and pressure (2–16 bar) were investigated. It was found that EMT2 membrane offers higher CO2 permeability coefficients, compared to some other PEG-PU membranes in the literature fabricated with a same length of soft segment.

Polyurea Elastomers: Astute Choice of Building Blocks for Obtaining Predictable Material Properties

Polyurea is a reaction product of an isocyanate with an amine and protective coatings based on polyurea are finding extensive application in diverse fields, especially towards protection of underlying structures for any particular isocyanate, the properties of the final product can be tailored by tweaking the constituents of the amine resin blend, especially chain extenders, chain length and crosslinker. In this review, we explicate the effect of various factors viz. soft segment length, type and concentration of chain extender and crosslinker on the material properties of polyurea.

Chemical Modification of β-Cyclodextrins: Balancing Soft and Rigid Domains in Complex Structures.

Crystalline polymers such as β-cyclodextrin (βCD) can be modified with polyethylene glycol (PEG) diglycidyl ether cross-linkers (262, 394, 500 Da). In this work, the authors show that the quantity and length of the PEG soft segments influence the solubility and malleability of the products, which are water soluble and easily converted to nitrated analogues under standard reaction conditions. Inert and nitrated derivatives containing longer PEG segments showed the ability to self-heal. The degree of cross-linking and decomposition temperatures and energies depended on the quantity and length of the soft segment. Nitrated cross-linked βCD containing longer PEG segments did not ignite following an electrostatic discharge of 4.5 J. The chemical stability of βCD/PEG binders was tested by heat flow calorimetry at 80 °C. The balanced incorporation of soft PEG and rigid βCD segments was found to improve the processability of cross-linked βCDs and desensitised their nitrated derivatives, offering new solutions for inert and energetic binders.

Study of waterborne polyurethane materials under aging treatments. Effect of the soft segment length

Coatings made of waterborne polyurethane dispersions are a promising alternative to solvent-borne ones but their mechanical and thermal properties under harsh outdoor conditions such as high temperature and humidity are somewhat limited. In this work saturated polyesters (PBA) with different molecular weights (800–2600 g/mol) were synthesized by reacting adipic acid with 1,4 butanediol. These polyols, an internal emulsifier, and an aliphatic diisocyanate were used as raw materials to synthesize polyurethane (PU) aqueous dispersions with solids contents of 29–38 wt%. The increase of the molecular weight of the polyol decreased the mean particle size of the PU dispersions from 308 to 78 nm.Polyurethane (PU) films were obtained by water evaporation of the PU dispersions and they were annealed at 80 °C for 2 h. Accelerated aging studies were performed by submerging the PU films in the water at 80 °C for 2 h. The PU films synthesized with the polyols with lower molecular weight exhibited enhanced phase miscibility, giving place to storage and loss moduli of similar magnitudes in a wide temperature range and they were less susceptible to hydrolytic degradation. Microphase miscibility was favored when shorter polyols are used. Contact angle measurement and cross-hatch adhesion test on PU coatings placed on stainless steel plate, before and after annealing and water aging were carried out. All PU coatings retained the adhesion to the substrate after aging, the PU coatings synthesized with shorter polyols exhibited enhanced adhesion.

Flexible and coatable insulating silica aerogel/polyurethane composites via soft segment control

We herein propose a facile approach to fabricate foldable and coatable silica aerogel polyurethane composites (APCs). For the flexibility control, the soft segment of polyurethane (PU) is manipulated. The change in soft segment length induces a difference in overall glass transition temperature of PU. When the silica aerogel content is increased, the PU with a shorter soft segment length shows brittle fracture behavior, while the PU with a longer soft segment length shows no breakage after bending. The thermal insulation properties of APCs were enhanced by 72% reduction in thermal conductivity upon 30 wt% aerogel loading and theoretically verified by a micromechanics-based thermal conductivity model considering the effects of interface and agglomeration. In addition, for the combustion behavior measurements, heat release rate and heat release capacity are substantially reduced for the APCs compared to neat PUs. Those enhanced thermal insulation properties may have a commercial impact on thermal insulation applications.

Effect of Domain Structure of Segmented Poly(urethane-imide) Membranes with Polycaprolactone Soft Blocks on Dehydration of n-Propanol via Pervaporation.

Segmented poly(urethane-imide)s (PUIs) were synthesized by polyaddition reaction and applied for preparation of membranes. Tolylene-2,4-diisocyanate, pyromellitic dianhydride, and m-phenylenediamine for chain extension were used to form hard aromatic blocks. Polycaprolactone diols with molecular weights equal to 530 and 2000 g mol−1 were chosen as soft segments. The effect of the length of soft segments on the structure, morphology, and transport properties of segmented poly(urethane-imide) membranes were studied using atomic force microscopy, small-angle and wide-angle X-ray scattering, and pervaporation experiments. It was found that a copolymer with a shorter soft segment (530 g mol−1) consists of soft domains in a hard matrix, while the introduction of polycaprolactone blocks with higher molecular weight (2000 g mol−1) leads to the formation of hard domains in a soft matrix. Additionally, the introduction of hard segments prevents crystallization of polycaprolactone. Transport properties of membranes based on segmented PUIs containing soft segments of different length were tested for pervaporation of a model mixture of propanol/water with 20 wt % H2O content. It was found that a membrane based on segmented PUIs containing longer soft segments demonstrates higher flux (8.8 kg μm m−2 h−1) and selectivity (179) toward water in comparison with results for pure polycaprolactone reported in literature. The membrane based on segmented PUIs with 530 g mol−1 soft segment has a lower flux (5.1 kg μm m−2 h−1) and higher selectivity (437).

Castor oil and PEG-based shape memory polyurethane films: effect of chain extender amount on some polymer properties and performance

A series of polyurethane (PU) films were synthesized via one-shot bulk polymerization with polyethylene glycol, castor oil, hexamethylene diisocyanate, and 1,4-butanediol (BD) at three different chain extender ratios. Since it was found in our previous study that hard segment content is more effective on shape memory property than soft segment length (Bonfil, M., Sirkecioglu, A., Bingol-Ozakpinar, O., Uras, F., Guner, F. S. J. Appl. Polym. Sci. 2014 , 131 , 1-12), in this study the effects of BD amount on some physical properties, thermal properties, and shape memory performance of the films were investigated. Shape fixity and shape recovery were achieved under two different cooling/heating regimes. The amount of BD is an important parameter affecting the physical properties, chemical structure, and thus shape memory performance. Decreasing the BD amount increased the crystallinity and the films, being of relatively high crystallinity, showed the highest shape recovery ratio. Increasing BD amount in PU films increases the hydrogen-bonded structure and the films having a relatively high degree of hydrogen-bonded structure showed the highest shape fixity ratio. The samples showed higher shape memory performance at high cooling and heating rates.

Theoretical predictions on microphase separation in polyurethane: Combinatorial design, synthesis and demonstration of shape memory property

Hydrogen bonding interactions among hard segments and crystallization of soft segments being critical factors for microphase-segregated morphology in shape memory polyurethane, tuning these parameters would lead to enhancement of the shape memory behavior. We investigated this morphological importance and contribution of each segment by combinatorial design of polyurethane using polyethylene glycol, toluene diisocyanate, 4,4′-methylenebis(phenyl isocyanate), butane-1,4-diol and ethylene diamine as building blocks. In a dual approach, a combined theoretical and experimental approach was adopted for optimization of shape memory property. The hard segments were modeled using density functional theory (DFT) using B3LYP method and 6–31G** basis set. Extent of phase separation and mixing were predicted from bond distances of H-bonded carbonyls (NH⋯OC) and that between NH group and ether oxygen (NH⋯O). The frequency shifts were computed and stability was determined from binding energies using localized pseudospectral methods (PS-LMP2). MDI_EDA system with shorter predicted bond length imparted better phase separation. PU samples were synthesized and characterized by spectroscopy (IR, NMR), polarized optical microscopy, XRD, DSC, DMA and AFM analyses. Tuning of phase segregation was achieved by varying both soft segment length and hard segment content. PEG6000_MDI_EDA showed improved properties with 340% elongation at break and tensile strength of 11 MPa. Thermomechanical cyclic tensile testing revealed shape recovery ratio of the sample to be 96.4% while fixity ratio was 51.4%. The shape memory behavior was successfully demonstrated in an electric circuit where polyurethane actuator acted as circuit breaker at time of overload thus ensuring circuit safety. Furthermore, an intrinsic fluorescence from samples in film and fiber form was observed which widens the scope of research in area of light emitting shape memory polyurethanes.

Tuning the properties of segmented polyurea by regulating soft‐segment length

ABSTRACTPolyurea is being widely advocated as a “retrofit” coating on structures, which mandate protection against blast. The physical properties of polyurea can be tuned by judicious choice of reactants, and the processing methodology employed for its preparation. The purpose of this study is to establish the dependence of material properties on the soft segment length in polyurea. Polyurea formulations were prepared by reaction of commercially available isocyanate prepolymer with poly(propylene oxide) based amines of varying molecular weights (230–2000 g/mol). The effect of increasing the soft segment length on the mechanical properties of polyurea under both quasi‐static as well as dynamic conditions was determined. Ductility was found to increase proportionally with increasing soft segment length, with a concomitant decrease in the tensile strength. All the compositions exhibited sub‐ambient glass transition temperature, which was found to reduce with increasing soft‐segment length. Time–temperature superposition principle was used to arrive at master curves for all compositions. The frequency essential to initiate the process of dynamic “rubber to glass” transition was found to be directly proportional to the soft segment length. All the formulations were found to be capable of exhibiting an elastomeric response even under high frequencies typical of blast loadings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46284.