Polyurethanes having shape memory effects

A series of polyether-based thermoplastic polyure thanes, varying in soft segment molecular weight and hard seg ment content was prepared and studied. Poly(oxypropylene- oxyethylene) diols of Mn of 1000, 2000, 3000, and 4000 were the soft segment polyols. The hard segment, 4,4'-diphenyl methane diisocyanate (MDI) extended with 1,4-butanediol (BDO), and also the soft segment content were varied from 20 to 80 weight percent. Physical-mechanical, thermal (DSC) and dynamic-mechanical property data are used to elucidate the mechanical and morphological behavior of these polymers. Two distinct phases are detected in most of the polymers. The Tg of the amorphous soft phase decreases with increasing polyether molecular weight and is relatively unaffected by soft segment content except at very low levels (≤ 30%). Hard segments appar ently separate into ordered structures which melt between 150 and 220°C. The melting points and the heats of fusion generally increase with hard segment content and soft segment Mn. Soft segment molecular weight also has a significant influence on the mechanical properties of the polymers. In general, the ambient flexural moduli and the dynamic moduli (E') increase with in creasing soft segment Mn and the modulus/temperature curve is flattened.

Three series of segmented polyurethanes, based on polytetramethylene oxide (PTMO) soft segments, having molecular weights of 650, 1000, and 2000 and MDI/butane diol hard segments, were synthesized and their dielectric properties examined. The effect of the soft segment length, soft segment concentration (ssc) as structural variables, and frequency and temperature as experimental variables, on relative permittivity and tan δ, were examined. The results were discussed in terms of the structural parameters such as the degree of phase separation and soft segment phase state. It was found that both soft segment length and ssc strongly affect dielectric behavior.

Effect of the degree of soft and hard segment ordering on the morphology and mechanical behavior of semicrystalline segmented polyurethanes

Thermal and dynamic mechanical behaviour of calcium containing co-polyurethanes

The phase separation and morphology in poly(urethane urea)s were investigated as soft segment length and chain extender structure were varied. Increases in soft segment length led to increased phase separation that resulted in greater mobility of the soft segment. This was shown by lower soft segment glass transition temperatures in differential scanning calorimetry (DSC) as well as a shift of Emax″ and tan δmax to lower temperatures. Also the structure of the chain extender affected the degree of phase separation and mixing of the soft and the hard blocks in an interphase. Atomic force microscopy (AFM) was used to visualize the structure of the phase‐separated domains. The hard domains were in the form of spheres 5–10 nm, or long needles 5 nm thick and 50–300 nm long. As the soft segment length increased, there were more pure soft segment phase areas between the hard domains. At high hard segment content, a larger scale structure was found, consisting of both hard and soft segments.DSC thermograms of poly(urethane urea)s containing different soft segment lengths.magnified imageDSC thermograms of poly(urethane urea)s containing different soft segment lengths.

This article examines the effects of the soft-segment composition on the structure and physical properties of waterborne polyurethane (WBPU) based on polycaprolactone–poly(ethylene glycol)–polycaprolactone (PCL–PEG–PCL) triblock copolydiol as the soft segment. The molecular weight of PEG in the soft-segment composition and soft-segment content (SSC) are varied in this study. The water-vapor permeability (WVP) for the WBPU-coated nylon fabric is also studied. The results showed that the glass transition temperatures (Tg's) of the soft segment decreased and its temperature range (ΔTg's) narrowed with increase of SSC up to 63 wt % and decrease of the PEG molecular weight. The dynamic mechanical analysis results showed that the α-peak height of the soft segment increased with SSC when the SSC was less than 63 wt %. However, when SSC was more than 63 wt %, the α-peak height became smaller with increasing SSC due to the crystallization of the soft segment. At the same SSC, the number of spherulites was reduced and the spherulites become larger with decrease of the PEG molecular weight. As for the mechanical properties of the WBPU cast film, the breaking stress decreased and the breaking elongation increased with increasing SSC or decreasing PEG molecular weight. For the WBPU-coated nylon fabrics, either higher SSC or higher PEG molecular weight improves the WVP. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:883–892, 1997

Effect of soft segment length on the thermal behaviors of fluorinated polyurethanes

Effect of intersegmental interactions on the morphology of segmented polyurethanes with mixed soft segments: A coarse-grained simulation study

Chemical synthesis and physical blending methods were used to prepare thermal sensitive polyurethanes (TSPU) with single or double thermal switches. In the design of the formula, polycaprolactone diol (PCL) with a molecular weight 10,000 and 4,000 and polytetramethylene glycol (PTMG) with a molecular weight 3,000 and 2,000 were used as the soft segments. The effects of the crystallinity and compatibility of the soft segments on the phase transition temperatures of the soft segments of TSPU (defined as switch temperature, Ts) were investigated in detail. To examine the thermal sensitivity of the thermal switch, water vapor permeability (WVP) experiments were performed to investigate the mass transport as a function of temperature. Differential scanning calorimetry (DSC) indicated that all the original TSPUs had a phase separated structure that was independent of the phase transition temperature of the soft and hard segments. The Ts values are determined mostly by the melting temperatures of the soft segments. On the other hand, for their blends, the Ts values are determined by the compatibility of the soft segments and the blending weight ratio. The blends of the PCL-based TSPUs showed good compatibility and single Ts due to the similar structure of the soft segments (just a difference in molecular weight), whereas for the PCL-based and PTMG-based TSPUs (the molecular structure is very different) blends, the Ts two independent values and blending weight ratio-dependent features due to the difference in the structure of the soft segments. Water vapor permeability analysis revealed the mass transport showed switching features to thermal stimuli, i.e. when the temperature reached the Ts, the WVPs of membranes showed rapid changes. On the other hand, the sensitivity of the thermal switch characterized by WVP improvement showed a dependence on the degree of crystallinity of the soft segments, i.e. well-organized soft segment structure is beneficial for improving the thermal sensitivity. Overall, TSPU membranes with a single Ts and different thermal sensitivity can be prepared using different crystalline poly-diols as the soft segments and blending two types of TSPUs with similar soft segments in the molecule structure, whereas TSPU with a double Ts can be achieved easily by blending two types of TSPUs with different soft segments.

Water-soluble and ultraviolet (UV)-curable urethane acrylate anionomers containing dimethylolpropionic acid (DMPA) were synthesized with varying molecular weight of soft segment and degree of neutralization. The ion group incorporated was confirmed by 1 H-NMR and 13 C-NMR spectra. In viscosity measurements, the enhancement of viscosity was achieved with increasing of ionic strength or pH of the solution. However, when the molecular weight of soft segment was high, the viscosity little changed for given parameters. This indicates that the strong hydrophobic interaction caused by the long soft segment made the anionomer chain aggregate. The UV coating properties of urethane acrylate anionomer films were depended on the molecular weight of soft segment and the degree of neutralization. For the films of high ion content and low molecular weight of soft segment, the tensile strength had a tendency toward increasing, on the contrary, for the films of low ion content and high molecular weight of soft segment, the tensile strength displayed reverse tendency. However, compared with general urethane acrylate films, overall coating properties were significantly improved. This was believed that the ionic groups acted as reinforcing filler by means of the phase separation from the crosslinked urethane acrylate network.

Morphology and properties of thermoplastic polyurethanes with dangling chains in ricinoleate-based soft segments

Aqueous polyurethane dispersions derived from various polycarbonatediols, carboxylic diols, and m‐di(2‐isocyantopropyl)benzene (TMXDI) were prepared by a solvent‐free process. The dispersing procedure was investigated by Fourier transform infrared spectroscopy and it was found that the use of TMXDI could avoid the over hydrolysis of the isocyanate groups during dispersing in water. The molecular weight tends to reach a maximum around an NH2/NCO ratio during chain extension of 0.8 : 1.0. The particle size, tensile properties, thermal properties, and dynamic mechanical properties of the polyurethane dispersions were investigated. The properties were significantly influenced by the molecular weight of the polycarbonatediols and the chemical structure of the carboxylic diols, and described by the effects of the ionic content, miscibility between the polycarbonate soft segment and the polyurethane segment, and the soft segment content. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A series of novel tetrad high aspect ratio mesogenic diol monomers 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐benzoic acid 4‐{[4‐(n‐hydroxyalkoxy)‐phenylimino]‐methyl}‐phenyl ester were prepared with varying alkoxy spacer length (n=2,4,6,8,10) by reacting 4‐formylbenzoic acid 4‐formylphenyl ester and 4‐(n‐hydroxyalkoxy) anilines. Two series of thermotropic main chain liquid crystalline unsegmented polyurethanes (PUs) were obtained by the polyaddition of the mesogenic diols with hexamethylene diisocyanate (HMDI) and methylene bis(cyclohexylisocyanate) (H12MDI) in dimethylformamide respectively. The effect of the incorporation of a third component namely polyol on the liquid crystalline properties of the polyurethanes was also studied. Linear segmented PUs were synthesised by a two‐step block copolymerisation method. The PUs synthesised were based on six spacer mesogenic diol chain extender, soft segments poly(tetramethylene oxide)glycol (PTMG) (Mn= 650,1000,2000) and polycaprolactone diol (PCL) (Mn=530,1250,2000) of varying molecular weights and different diisocyanates including HMDI, H12MDI and methylene bis(phenylene isocyanate) (MDI). Structural elucidation was carried out by elemental analysis, fourier transform infra red (FT‐IR), nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopy. Inherent viscosity of the unsegmented polymers measured in methanesulphonic acid at 26°C was in the range of 0.13 ‐ 0.65 dL/g while the molecular weights and molecular weight distribution of the segmented polyruethanes was determined using gel permeation chromatography (GPC). Mesomorphic properties were studied by differential scanning calorimetry (DSC) and hot stage polarising optical microscopy and the thermal stability was determined by thermogravimetric(TG)analysis. The monomeric diols and the polyurethanes exhibited nematic texture and good mesophase stability. It was observed that the partial replacement of the mesogenic diol by the polyol of varying molecular weights influenced the phase transitions and the occurrence of mesophase textures. The phase transition temperatures of the investigated polyurethanes showed dependence on the chain length of the soft segment and on the content of the mesogen moiety. A higher content of mesogenic moiety was needed to obtain liquid crystalline property when the soft segment length was increased as observed in the case of PTMG. Grained and threaded textures were observed depending on the molecular weight of the soft segment, the mesogen content and the diisocyanate. The stress‐strain analyses showed that the polymers bused on high molecular weight PTMG soft segment have elastomeric property while the PCL based PUs displayed no elastomeric property.

Alternating polyols of oxymethylene and oxyalkylene were synthesized and used as precursors for thermoplastic poly(ether-ester) elastomers (TPEs). The polyols were synthesized by reacting diols having different methylene units with dichloromethane in the presence of a phase transfer catalyst. The number of methylene units in the alkylene oxides was varied from 3 to 6. TPEs were prepared using the polyols as soft segments and poly(butylene terephthalate) units as hard segments. The polyols and TPEs synthesized were characterized using FTIR, NMR, GPC, DSC, and polarized optical microscopy. The polyols showed a profound odd-even effect on the melting(Tm) and glass transition temperatures(Tg). Polyols with odd numbers of methylene groups in the alkylene units have higher transition temperatures than polyols with odd number of methylene groups. The tendency is still kept in TPEs, even though theTg of soft segment in TPEs are slightly higher than those of corresponding neat polyols. TheTm andTg of soft segments are almost constant in the range of 20 to 60 wt % contents of soft segments. On the other hand, the normalized heat of fusion of hard segment decreased with increasing the content of soft segment.

Various segmented polyurethanes of different soft segment structure with hard segment content of about 50 wt% were prepared from 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol and different polyols with a M n of 2000 by a one‐shot, hand‐cast bulk polymerization method. The polyols used were a poly(tetramethylene ether)glycol, a poly(tetramethylene adipate)glycol, a polycaprolactonediol and two polycarbonatediols. The segmented polyurethanes were characterized by gel permeation chromatography (GPC), UV‐visible spectrometry, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X‐ray diffraction, and their tensile properties and Shore A hardness were determined. The DSC and DMA data indicate that the miscibility between the soft segments and the hard segments of the segmented polyurethanes is dependent on the type of the soft segment, and follows the order: polycarbonate segments > polyester segments > polyether segments. The miscibility between the soft segments and the hard segments plays an important role in determining the transparency of the segmented polyurethanes. As the miscibility increases, the transparency of the segmented polyurethanes increases accordingly. The segmented polyurethanes exhibit high elongation and show ductile behavior. The tensile properties are also affected by the type of the soft segment to some extent. POLYM. ENG. SCI., 47:695–701, 2007. © 2007 Society of Plastics Engineers.