Adhesion Mechanisms of Polyurethanes to Glass Surfaces. III. Investigation of Possible Physico-Chemical Interactions at the Interphase

Surface free energies of polyurethanes made from toluene diisocyanate and 1, 4 butanediol-based hard segments and caprolactone polyol-based soft segments were calculated using additive functions. Good agreement was found between the calculated values based on additive functions and the calculated values based on contact angle measurements. The phase-separated polyurethanes were found to have a higher polar surface free energy component (γ^P). This was linked to the preferential segregation of butanediol/butanediol-derived moieties to the polyurethane surfaces due to phase separation. The adhesion values of these polyurethanes to soda-lime glass were correlated with their respective γ^P values and a linear relationship was found. It was also shown that the adhesion values of the low γ^P polyurethanes improved substantially when the glass surfaces were coated with a thin layer of butanediol prior to the bonding. The modulus of the interphase region rich in butanediol was evaluated. Although a modulus increase was found at the interface, this increase was found to play a secondary role in the adhesion. The chemical interactions at the polyurethane/glass interphase were investigated by pre-treating the glass surfaces with methyl-trimethoxysilane and trimethylchlorosilane prior to adhesion testing. The adhesion data showed no significant difference between the uncoated and the silane-treated glass substrates. Based on this experimental evidence, the possibility of any covalent or ionic bonding at the polyurethane/glass interphase was assumed negligible. It was determined that the mechanism of adhesion between the polyurethanes and the glass surface could be through the formation of an interphase region in which hydrogen bonding between the butanediol-rich interphase region and the hydroxylated glass surface plays a key role.     

Polyurethanes with long fluorinated side chains

Copolymer triols were prepared from propylene oxide and glycidyl (α,α,ω-trihydrododecafluoroheptyl) ether or pentadecafluoroheptylepoxyethane. Cationic polymerization was used and block copolymers were obtained in the molecular weight range of 1,000 to 3,000. These copolymer triols were reacted with an 80/20 mixture of 2,4-/2,6-tolylene diisocyanate, giving polyurethanes with the same polymer backbone as the conventional polyurethanes based on polyoxypropylene triols and tolylene diisocyanate. It was found that these polyurethanes, containing between 0% and 45% fluorine, showed increasing adhesion to anodized aluminum with increasing urea bond content of the polymer. However, the fluorine content did not show the expected effect on adhesion. Isothermal gravimetric analysis showed that the heat stability of the fluorourethanes was lower than for conventional urethanes on a weight basis, only because the segments split off in heat degradation were heavier for the fluorourethane. This phenomenon might possibly also apply to urethanes with a fluorinated backbone. On a mole basis fluorourethanes might be as stable as nonfluorourethanes. It was also found that the thermostability, as measured by weight loss, increased with an increasing degree of crosslink density in the polymers.     

Adhesion Mechanisms of Polyurethanes to Glass Surfaces. III. Investigation of Possible Physico-Chemical Interactions at the Interphase

Surface free energies of polyurethanes made from toluene diisocyanate and 1, 4 butanediol-based hard segments and caprolactone polyol-based soft segments were calculated using additive functions. Good agreement was found between the calculated values based on additive functions and the calculated values based on contact angle measurements. The phase-separated polyurethanes were found to have a higher polar surface free energy component (γ^P). This was linked to the preferential segregation of butanediol/butanediol-derived moieties to the polyurethane surfaces due to phase separation. The adhesion values of these polyurethanes to soda-lime glass were correlated with their respective γ^P values and a linear relationship was found. It was also shown that the adhesion values of the low γ^P polyurethanes improved substantially when the glass surfaces were coated with a thin layer of butanediol prior to the bonding. The modulus of the interphase region rich in butanediol was evaluated. Although a modulus increase was found at the interface, this increase was found to play a secondary role in the adhesion. The chemical interactions at the polyurethane/glass interphase were investigated by pre-treating the glass surfaces with methyl-trimethoxysilane and trimethylchlorosilane prior to adhesion testing. The adhesion data showed no significant difference between the uncoated and the silane-treated glass substrates. Based on this experimental evidence, the possibility of any covalent or ionic bonding at the polyurethane/glass interphase was assumed negligible. It was determined that the mechanism of adhesion between the polyurethanes and the glass surface could be through the formation of an interphase region in which hydrogen bonding between the butanediol-rich interphase region and the hydroxylated glass surface plays a key role.     

Properties of ultraviolet cured polydimethylsiloxane–urea acrylates

A series of polydimethylsiloxane–urea acrylate prepolymers was synthesized by reacting aminopropyl-terminated polydimethylsiloxane (ATPS) with isocyanatoethyl methacrylate (IEM). The oligomers were cured using ultraviolet radiation in the presence of different reactive diluents. Three systems were prepared with varying ATPS soft segment molecular weight. All of the samples were transparent. However, microphase separation was indicated by the observation of two glass transition temperatures attributed to separate ATPS and IEM/reactive diluent phases. Increasing ATPS molecular weight led to a lower rubbery phase transition temperature and a smaller rigid phase volume fraction. These effects were reflected in lower modulus and tensile strength at room temperature, and higher elongation at break. An increase in the reactive diluent content resulted in an increase in Young's modulus and the ultimate tensile strength of these materials. Increasing reactive diluent content caused the rubbery phase transition peak to decrease in magnitude without changing its position and shifted the hard segment transition to higher temperature. The tensile strengths and moduli of these materials were higher than those reported in the literature for other polydimethylsiloxane and urethane acrylate materials.     

Morphology of polyurethane–isocyanurate elastomers

The dynamic viscoelastic properties and thermal transition behavior of reaction injection molding (RIM) and cast polyurethane—isocyanurate elastomers have been studied as a function of various segments (soft and hard urethane, and hard isocyanurate) content. RIM and cast elastomers were prepared at different concentrations of soft and hard urethane, and hard isocyanurate segments. RIM elastomers with the higher isocyanate index (lower hard urethane and greater isocyanurate segment content) displayed an unchanged T_g (glass transition temperature of soft segment) and increasing T_gh (glass transition temperature of hard segment) related to the hard urethane and isocyanurate segments. This is due to the phase separation between the soft and the hard segments. Cast elastomers synthesized from the higher amount of 1,4-butanediol (greater hard urethane and less hard isocyanurate segment content) showed an increasing T_gs, decreasing T_gh of hard urethane segments, and an unchanged T_gh of isocyanurate segments. This is related to the phase mixing between the soft and the hard urethane segments and the phase separation of hard isocyanurate and hard urethane segments.     

Properties of polyisobutylene-polyurethane block copolymers: I. Macroglycols from ozonolysis of isobutylene-isoprene copolymer

The properties of a series of polyisobutylene (PIB) based polyurethanes were studied and compared to those reported in the literature for polyether, polyester, and polybutadiene-based polyurethanes. Good phase separation was reflected in the invariance of the soft segment T_n with increasing hard segment content. Increasing hard segment content resulted in larger domains, higher modulus and lower ultimate elongation. The modulus above the soft segment T_n was higher than that previously reported for polyurethanes of similar hard segment contant; improved phase separation and short contour lengths of the PIB chains were cited as possible causes of this behavior. Stress-strain data indicated a change from isolated to interconnected domain morphology with incerasing hard segment contant. Generally similar trends were seen for all types of urethanes. The overall properties of polybutadiene polyurethanes were closest to those of the polyisobutylene polyurethanes studied. The properties of both of these systems were suggested to suffer from significant synthesis problems in urethane formation due to the incompatibility of the nonpolar hydrocarbon soft segment and the polar diol chain extender. Preliminary environmental tests indicated that polyisobutylene based materials exhibit improved hydrolytic stability and reduced moisture permeability compared to polyether and polyester polyurethanes and greater oxidative stability compared to polybutadiene based materials.     

Polyurethanes having shape memory effects

Segmented polyurethanes (PUs) were prepared from polycaprolactone diols (PCLs), 4,4′-diphenylmethane diisocyanate, and 1,4-butanediol, and tested for shape memory effects. Effects of soft segment molecular weight (M_n = 2000, 4000 and 8000), soft segment content (50–90%), and maximum strain (_m = 100, 200, and 600%) on the cyclic tensile properties as well as the dynamic mechanical, and mechanical properties below (25°C) and above (65°C) the shape recovery temperatures were studied. With increasing soft segment contents: i) glassy state modulus increased and rubbery state modulus decreased; ii) hardness increased at room temperature, and decreased at 65°C; iii) recovery strain decreased with PCL 2000, and increased with PCL 8000 based PUs. On the other hand, the increase in soft segment length resulted in: i) increased rubbery state modulus as well as glass state modulus; ii) increased hardness at room and high temperatures; iii) increased recovery strain at high soft segment content. Tensile yielding became clear with increasing soft segment length and content. Strain upon cooling and unloading (_u) and residual strain (_p) increased, and recovery strain (_r) decreased with cycling. Among these, residual strain was most sensitive to the cycling. Most of the cycling effects were confined during the first one or two cycles. These results were interpreted in terms of soft segment-hard segment phase separation and soft segment crystallization.     

Thermal and mechanical properties of fiber‐forming poly(urethane semicarbazide)s

Fiber‐forming poly(urethane semicarbazide)s were prepared with poly(butylene adipate)glycol as soft‐segment domains and hexamethylene diisocyanate/terephthalic dihydrazide as hard‐segment domains. The hard‐segment content was varied via variations in the polyol/isocyanate molar ratio, and the films were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The effect of the hard‐segment‐content variation on the properties was studied by differential scanning calorimetry, stress–strain analysis, and dynamic mechanical testing. Differential scanning calorimetry showed that the samples exhibited a very low level of hard/soft‐segment phase mixing. The stress–strain analyses revealed that the elongation at break decreased with an increase in the hard‐segment content and that the mechanical property depended on the overall crystallinity of the samples. Dynamic mechanical tests revealed a high glassy‐to‐rubbery state modulus and a high degree of phase separation between the hard and soft segments. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 86–93, 2002     

Polyurethanes containing a crystalline polyol and semiflexible urethane segments

Ultradrawing semicrystalline polymers is an intriguing approach to develop stiff, strong, and tough polymeric fibers. In the research field of polyurethane copolymer elastomers the term “soft segment” usually refers to the medium molecular weight glycol while the term “hard segment” stands for the urethane rich or isocyanate‐short glycol segments. Here we investigate the influence of semiflexible segment content in the urethane rich phase on the mechanical properties and morphology of polyurethanes synthesized with a crystalline polyol as a “soft” segment. Materials with lower semiflexible urethane segment content developed stiffer and stronger materials upon drawing. This was related to greater soft segment crystallization along the draw direction. Materials with a higher fraction of semiflexible urethane segments were more elastic (higher yield strains and strengths) but exhibited more brittle‐like fracture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41281.     

Thermal and mechanical properties of linear segmented polyurethanes with butadiene soft segments

A series of segmented polyurethanes based on a hydroxyl terminated polybutadiene soft segment (HTPBD) have been prepared with varying hard segment content between 20 and 60 weight percent. These materials are linear and amorphous and have no potential for hydrogen bonding between the “hard” and “soft” segments. The existence of two-phase morphology was deduced from dynamic mechanical behavior and thermal analysis. Both techniques showed a soft segment glass transition temperature, T_gs, at ?56°C and hard segment transitions between 20 and 100°C, depending on the urethane content. The low value of T_g, only 8° higher than the T_g of free HTPBD and independent of hard segment concentration indicated nearly complete phase segregation. Depending on the nature of the continuous and dispersed phases, the urethanes behaved as elastomers below 40 weight percent hard segment or as glasslike materials at higher hard segment contents. The effect of thermal history on transitions of the HTPBDurethanes was also investigated and the results suggest that the absence of hydrogen bonding to the soft segment must account for the extraordinary insensitivity to thermal history in dynamic mechanical, thermal and stress-strain behavior. Comparisons are made to the more common polyurethanes containing polyether and polyester soft segments.     

Diffusion of gases through polyurethane block polymers

The diffusivities of simple gases through a series of polyurethane block copolymers of differing aromatic urethane content and type of soft segment were measured using a quadrapole mass spectrometer as a detecting device. Although an Arrhenius expression generally described the temperature dependence of diffusion in this system, a discontinuity was observed in the Arrhenius plots for some materials, and the discontinuity was found to be related to the onset of the glass transition in the hard domains. Increasing the hard segment content of the materials decreased the diffusivity due to the increase in the activation energy of diffusion. Increasing the soft segment length brought about a decrease in the activation energy with an increase in diffusivity. Polyster urethanes had lower activation energies for diffusion than polyether urethanes of similar hard segment composition. Finally, as the penetrant diameter was increased, a decrease in the diffusivity and an increase in the activation energy was noted.     

Waterborne polyurethane dispersions obtained with polycarbonate of hexanediol intended for use as coatings

Three waterborne polyurethane dispersions derived from polycarbonate of hexanediol (PCD) with molecular weight of 1000 Da were synthesized by the acetone method and used as coatings for stainless steel plates. Different hard segments content in the polyurethanes were obtained by varying the isocyanate/macroglycol (NCO/OH) molar ratio. A decrease in the NCO/OH ratio produced an increase in the mean particle size as well as a decrease in the Brookfield viscosity of the dispersions. Furthermore, the greater the NCO/OH ratio the higher the urea and urethane hard segment content, the higher the glass transition temperature value and the higher the elastic modulus of the polyurethane was. On the other hand, the NCO/OH ratio affected the adhesion of the polyurethanes. The adhesion was evaluated by using three different procedures: T-peel strength tests of flexible PVC/waterborne polyurethane dispersion/flexible PVC joints; single lap-shear tests of aluminium/waterborne polyurethane dispersion/aluminium joints and cross-cutter adhesion test of polyurethane coatings on stainless steel pieces. Finally, several properties of the polyurethane coatings on stainless steel pieces were tested including Persoz hardness, gloss, chemical resistance and yellowness index.     

Thermoplastic urethane elastomers. II. Effects of variations in hard-segment concentration

The dynamic mechanical properties of thermoplastic urethane elastomers have been charac-terized for polymers composed of varying hard-segment concentrations and for two different molecular weight polyester diols as soft segments. The urethane polymers based on an 830 M?_n polycaprolactone diol exhibited a progressive increase in glass transition temperature at increased levels of hard segments. In contrast, a similar series of polymers prepared with a 2100 M?_n polycaprolactone diol as the soft segment maintained a relatively constant glass transition temperature. These differences are attributed to the relative degree of phase separation between the constitutive blocks of the copolymer. The polymers of both series possessed two lower-temperature, secondary relaxations, which are ascribed to methylene sequence mobility within the polycaprolactone units and to possible disruption of interfacial associations between the hard- and soft-segment structures.     

Block copolymer of trans‐polyisoprene and urethane segment: Crystallization behavior and morphology

A new type of urethane segmented copolymer was prepared from hydroxyl‐terminated trans‐polyisoprene (HTTPI) and toluene diisocyanate (TDI). The structures of the copolymer were characterized by FTIR and GPC. Crystalline properties of trans‐polyisoprene (TPI) segments were investigated using WAXD and DSC techniques. The crystals of TPI segments are inclined to exist in low‐melting form (LM). The melting temperature of TPI shifts to a lower temperature as the urethane segment was introduced. DMA studies show that, when TPI crystals were at the melting state, the storage modulus of the copolymer depended on the content of urethane segment. The hard segment here serves as physical crosslinkage. Nonisothermal crystallization kinetics of TPI segment was studied on the basis of the Ozawa equation. It was found that the hard segment suppresses the crystallization of the TPI segment. Morphology of two‐phase separation was observed in the copolymer by SEM. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2286–2294, 2004     

Synthesis and characterization of biodegradable poly(ester‐urethanes) based on bacterial poly(R‐3‐hydroxybutyrate)

A series of poly(R‐3‐hydroxybutyrate)/poly(ε‐caprolactone)/1,6‐hexamethylene diisocyanate‐segmented poly(ester‐urethanes), having different compositions and different block lengths, were synthesized by one‐step solution polymerization. The molecular weight of poly(R‐3‐hydroxybutyrate)‐diol, PHB‐diol, hard segments was in the range of 2100–4400 and poly(ε‐caprolactone)‐diol, PCL‐diol, soft segments in the range of 1080–5800. The materials obtained were investigated by using differential scanning calorimetry, wide angle X‐ray diffraction and mechanical measurements. All poly(ester‐urethanes) investigated were semicrystalline with T_m varying within 126–148°C. DSC results showed that T_g are shifted to higher temperature with increasing content of PHB hard segments and decreasing molecular weight of PCL soft segments. This indicates partial compatibility of the two phases. In poly(ester‐urethanes) made from PCL soft segments of molecular weight (M_n ≥ 2200), a PCL crystalline phase, in addition to the PHB crystalline phase, was observed. As for the mechanical tensile properties of poly(ester‐urethane) cast films, it was found that the ultimate strength and the elongation at the breakpoint decrease with increasing PHB hard segment content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 703–718, 2002     

Thermal and dynamic mechanical properties of polyurethaneureas

Measurements were made of the thermal and dynamic mechanical properties of 22 polyurethaneureas of varying diol molecular weight, type of aromatic chain extender, diol molecular weight distribution, and chain extender stoichiometry. The dynamic mechanical data, obtained as a function of temperature and frequency (in the kHz region), were used to construct master curves of shear modulus and loss factor over a wide range of reduced frequencies. Based on these master curves, interpreted in conjunction with the thermal analysis results, it was found that: Soft segment crystallization occurs at the higher diol molecular weights, dynamic mechanical properties are well correlated with the soft segment glass transition, diol molecular weight influences dynamic mechanical properties by affecting the degree of phase separation and hence glass transition temperature, and neither diol molecular weight distribution nor chain extender stoichiometry have a significant effect, in the ranges studied, on transition temperatures or dynamic mechanical properties.     

Phase behavior and hydrogen bonding in biomembrane mimicing polyurethanes with long side chain fluorinated alkyl phosphatidylcholine polar head groups attached to hard block

To achieve a good biocompatibility, two sets of novel segmented polyurethanes, namely, poly(ether urethane)s and poly(carbonate urethane)s, with long side chain fluorinated alkyl phosphatidylcholine polar head groups attached to hard block have been synthesized recently in our laboratory by using a new diol with a long side chain fluorinated alkyl phosphatidylcholine polar head group 2-[2-[2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-10-ethoxy-decyloxy]-N-(2-hydroxy-1-hydroxymethyl-1-methyl-ethyl)-acetamide] phosphatidylcholine, HFDAPC as an extender. These novel polyurethanes have shown a potential to be used as bio-membrane mimicry. In this article we investigated the phase behavior of these materials by Instron, DSC, DMA, and AFM because the phase behavior has a great effect on the surface properties thus the biological-related perspective. T_g decreases first then increases for the poly(carbonate urethane)s, but increases first then decreases for the poly(ether urethane)s with an increasing in fluorinate phosphatidylcholine content. On the other hand, the tensile modulus was found decrease for the poly(carbonate urethane)s but increase for the poly(ether urethane)s with an increasing in fluorinate phosphatidylcholine content. It was found via AFM that the phase separation increases in poly(ether urethane)s but phase mixing increases in poly(carbonate urethane)s, with increasing content of fluorinated phosphatidylcholine side chain. The interaction between hard and soft segment, particularly, the hydrogen bonding was investigated by FTIR. The effect of fluorinated phosphatidylcholine side group on the phase separation of polyurethane was discussed and compared with that of fluorinated polyurethanes containing only fluorinated side chains. Our result demonstrated how the phase behavior of polyurethanes could be controlled by tailoring the interaction between hard and soft segment.     

Structure-property behavior of elastomeric segmented PTMO–ionene polymers. II

A series of segmented ionene polymers based on the reaction of α,ω-bis(dimethyl amino)polytetramethylene oxide with various dihalide compounds were investigated with respect to their structure–property behavior. The placement of quaternary ammonium ions and halide counterions along the polymer chains was varied by changing the molecular weight of the PTMO soft segment and the structure of the dihalide linking agent. The techniques of dynamic mechanical spectroscopy, thermal analysis, small angle X-ray scattering, and stress–strain behavior analysis were applied. For the case when the PTMO soft segment was amorphous, the ambient temperature properties of these materials displayed low modulus, high strength, and high elongation elastomeric behavior with tensile strength enhanced by the strain-induced crystallization of the PTMO. A high level of phase separation existed between the dihalide component relative to the PTMO soft segment. Due to the Coulombic association of the ionene species, these materials displayed many similarities to the segmented urethane ionomers. In particular, distinct domain structure was noted by SAXS, whose dimensional scale was similar to the segmented urethanes. It was also shown, however, that the driving forces for the microphase separation was caused by favorable electrostatic or Coulombic interactions in contrast to segment–segment incompatibility features as in the segmented urethanes.     

Thermoplastic urethane elastomers. I. Effects of soft-segment variations

A series of thermoplastic urethane elastomers with soft segments of varying sequence length was prepared and their dynamic mechanical properties were characterized over a wide temperature range. The polymers were prepared using various molecular weight polycaprolactone diols as the soft segment and 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment. The urethane elastomer exhibited soft-segment crystallization when a polycaprolactone diol greater than 3000 M?_n was used. The glass transition temperature of these materials progressively shifted to lower temperatures as the chain length of the soft segment was increased. This dependence was interpreted in terms of a molecular weight relationship similar to that associated with amorphous homopolymers. The dynamic mechanical properties of these polyurethanes appear to be consistent with responses observed for compatible copolymers.     

Polyurethanes and polyurethane cationomers bearing nitroaromatic groups and their photobehavior

Elastomer-type polyether urethanes and polyether urethane cationomers with nitroaromatic groups were prepared and the effect of UV irradiation on their characteristics was evaluated comparatively with a model compound. The photobehavior by UV irradiation with a high-pressure Hg lamp was studied in solution, following the change of absorption bands characteristic for nitro structures as a function of irradiation time. UV irradiation causes diminution of the intensity of characteristic UV absorption bands and a decrease of molecular weight.