Phase Separation Of Hard Segments Research Articles

Thermal analysis of polyurethane elastomers matrix with different chain extender contents for thermal conductive application

Polyurethane elastomers (PUR) based on polypropylene glycol and 4,4′-diphenylmethane diisocyanate were prepared with various monoethylene glycol (mEG) contents. The aim of this study is to find a reliable polymer matrix for composites of improved thermal conductivity and testing fully in order to collect knowledge about its structure. Thermal conductivity was improved from 0.255 to 0.329 W m−1 K−1 when increasing chain extender content. This attributed to a high appearance crystalline ordering level when adding high mEG content. Differential scanning calorimetry revealed a low transition temperature of soft segment at the same temperature around − 64 °C, due to constant polyol content. The enthalpy of melting increases with increasing mEG content. This is due to the increasing crystalline phase and hard segment phase separation within the PUR structure. Dynamic mechanical analysis results show the glass transition temperature of soft segment in the same temperature range between − 57 and − 52 °C and intensity peak of tanδ tends to decrease when mEG content was increased. On the other hand, the glass transition temperature of hard segment tends to increase from 10 to 93 °C and has high intensity peak of tanδ with increasing mEG content. Increasing the chain extender content can be enhancing the hard segment length in PUR structure and affecting both soft segment motion and hard segment motion. Increasing hard segment length might be obstructing soft segment motion and influence hard segment motion which is hard to move at low temperatures. Phase separation of soft and hard segment clearly observed using the DMA technique.

Novel bio-based thermoplastic poly(ether-urethane)s. Correlations between the structure, processing and properties

The main purpose of this work was to analyze the effect of the number of unreacted isocyanate groups and the [NCO]/[OH] molar ratio during the chain extension of a prepolymer during the polymerization process on the structure, processing and selected properties of thermoplastic poly(ether-urethane)s. Three series of novel thermoplastic polyurethanes were obtained via a prepolymer route. Three prepolymers were synthesized from diisocyanate and bio-based polyol, which contained 6, 7 and 8% of unreacted isocyanate groups. The prepolymer chains were extended by using bio-based 1,4-butanediol with four different [NCO]/[OH] molar ratios. It was confirmed that the concentration of unreacted isocyanate groups in the prepolymer has an effect on the degree of the hard segment phase separation of poly(ether-urethane)s. It was also found that the melt flow index has a significant impact on the processing of polyurethanes which can be correlated to the chemical structure and dynamic mechanical properties of the polyurethanes.

Reactively dispersed olefins in polyurethanes: A new class of polymer/polymer composite

Maleic anhydride grafted polyethylenes (MAH-g-PE) can be reacted with polyols to create fine phase dispersions in polyurethanes. Desirable blends can only be realized when the anhydrides are in the dehydrated state prior to reaction. The reaction of anhydride with hydroxyls can occur with the polyol prior to addition of isocyanate and chain extender to make the polyurethane, or with an already formed polyurethane heated up above its reversion temperature when hydroxyl functionality becomes available. Phase dispersion kinetics are a function of MAH-g-PE molecular weight and percentage grafted maleic anhydride along the chain, but also on viscosity matching of the forming polyurethane and the MAH-g-PE during the blending operation which maximizes shear stress between the phases. The final result is not strongly dependent on the preparation path. Thermoplastic polyurethane elastomers (TPUs) based on polypropylene oxide and polyethylenoxide/polypropylene oxide triblock copolymer soft segments are compared to industry standard TPUs prepared from polytetramethylene ether glycol (PTMEG) and polycaprolactone (PCL) soft segments. The control TPUs prepared from polypropylene oxide and the polyether triblock are inferior to those of PTMEG and PCL. However; when the polypropylene oxide and the triblock soft segments are prepared with 20% substitution of MAH-g-PE, the creep, thermal and solvent resistance of these elastomers exceeds those of the industry standards, and the tensile properties are comparable. Additionally, TPUs from PTMEG and PCL with added MAH-g-PE can also have their properties improved. The property improvements are a function of improved hard segment phase separation from the soft segment, and the creation of polyester crosslinks between the MAH-g-PE and the polyurethane.

Waterborne polyurethane elastomer using renewable polyols

A series of waterborne polyurethane (WPU) elastomers were synthesized from isophorone diisocyanate, polycaprolactone diol (PCL), 1,3-propanediol produced from a glucose fermentation process (Bio-PDO), 1,4-butanediol, and dimethylolbutanoic acid as a function of Bio-PDO/PCL composition. With the addition and increasing amount of Bio-PDO, particle size of dispersion, hardness, water swelling, initial modulus, and stress at break decreased, while contact angle with the water drop of the dispersion cast film increased. The PCL WPU showed a single-step thermal degradation at about 370°C, while those of Bio-PDO-containing WPUs showed two step degradations at about 350 and 400°C suggesting the soft segment–hard segment phase separation.

Design and formulation of soybean oil derived flexible polyurethane foams and their underlying polymer structure/property relationships

A series of water blown polyurethane foams was produced in which polyether polyol content was progressively reduced by the addition of a designed soybean oil derived polyol (SBOP). A sample from each foam was tested for a variety of standard properties and a sample from the same foam was also compression molded into plaques which were tested for elastomer properties. The morphology of the foams and their underlying elastomers was probed by SEM, AFM, DMA, X-ray, FTIR, tensile properties and cyclic stress/strain (hysteresis) experiments. The properties of the polyether control and SBOP containing foams are representative of their underlying polymers. However, foams containing SBOP do not have well developed hard segment organization relative to that of polyether soft segment control foams. Similarly, the SBOP foams do not have as good hard segment organization as the elastomers derived by compression molding the same foams. This suggests that hard segments of SBOP containing foams do not reach thermodynamic equilibrium prior to vitrification during the foaming process. It is possible that this is an artifact of the low equivalent weight (ca. 670 gr/eq) of SBOP which promotes gelation ahead of phase separation. The fact that the elevated temperature modulus is independent of the amount of added SBOP suggests that tensile properties of the foam are not a function of the soft segment crosslink density, but rather the hard segment phase separation. Other foam properties such as airflow and tear strength are shown to be related to the same factors. Improvements in foam properties are achieved by designing the foam formulation to increase phase separation.

Composites of carbon nanofibers and thermoplastic polyurethanes with shape‐memory properties prepared by chaotic mixing

AbstractComposites of carbon nanofibers (CNFs), oxidized carbon nanofibers (ox‐CNFs), and shape‐memory thermoplastic polyurethane (TPU) were prepared in a chaotic mixer and their shape‐memory properties evaluated. The polymer was synthesized from 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol chain extender, and semicrystalline poly(ε‐caprolactone) diol soft segments. The shape‐memory action was triggered by both conductive and resistive heating. It was found that soft segment crystallinity and mechanical reinforcement by nanofibers produced competing effects on shape‐memory properties. A large reduction in soft segment crystallinity in the presence of CNF and stronger mechanical reinforcement by well‐dispersed ox‐CNF determined the shape‐memory properties of the respective composites. It was found that the maximum shape recovery force, respectively, 3 and 4 MPa, was obtained in the cases of 5 and 1 wt% CNF and ox‐CNF, respectively, compared with ∼1.8 MPa for unfilled TPU. The degree of soft segment and hard segment phase separation and thermal stability of the composites were analyzed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.

Investigation of kinetics and morphology development for polyurethane-urea extended by DMTDA

The relationship between the reactions kinetics and morphology development during the polyurethaneurea (PUU) curing process has been investigated simultaneously by in situ Fourier transform infrared spectroscopy (FTIR). The data of the FTIR spectra showed that with the increase of conversion, the absorbance of NH bands increases and its band sites shifts to lower wavenumbers; the absorbance of free urethane carbonyl kept nearly constant at low conversion, and then decreased much because of the interaction of the formed urea links, and then changed little at high conversion owing to the diffuse control. The band sites of hydrogen bonded urea carbonyl similarly shifted to lower wavenumbers and the absorbance of the hydrogen bonded urea carbonyl, associated with the phase separation of hard segments, became stronger with buildup of hydrogen bond between urea links. The carbonyl bands available during curing process were further assigned. Both interactions, such as hydrogenised effect and phase separation, played a major role in the matrix formation of the PUU polymer.

FTIR investigation of the influence of diisocyanate symmetry on the morphology development in model segmented polyurethanes

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol ( M n=1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans-1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (C O) peaks. Depending on the structure of the diisocyanate used, while the intensity of free C O peaks around 1720–1730 cm −1 decreased, the intensity of H-bonded C O peaks around 1670–1690 cm −1, which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of C O region and analysis of the relative absorbances in C O region.

Reaction kinetics of thermoplastic polyurethane polymerization in situ with poly(vinyl chloride)

In this study, the reaction kinetics of thermoplastic polyurethane (TPU) polymerization in situ with poly(vinyl chloride) (PVC) was characterized with differential scanning calorimetry. The presence of PVC appeared to enhance the thermodynamic drive for TPU hard segment phase separation and domain ordering from the PVC/TPU reactant mixture. Prior to hard segment phase separation, and thus some critical conversion, TPU polymerization in situ with PVC obeyed the same nth order, phenomenological kinetic rate law followed by neat TPU polymerization. In addition, the overall rate constant employed in the rate law increased in the presence of PVC. After hard segment phase separation, and the resulting physical cross-linking of the PVC/TPU reactant mixture, the reaction kinetics of TPU polymerization in situ with PVC became diffusion controlled.