Mechanical and surface properties of membranes prepared from waterborne cationic hydroxyl‐terminated polydimethylsiloxane/polyurethane surfactant‐free micro‐emulsion

With the action of catalyst and cosolvent, a series of hydroxyl‐terminated polydimethylsiloxane (HPMS) based polyurethane (PU) micro‐emulsion were gotten by surfactant‐free copolymerization. They were successfully prepared by reacting isophorone isocyanate, poly(tetramethylene glycol), and HPMS with N‐methyldiethanolamine (MDEA) as chain extender and trimethylolpropane (TMP) as crosslinker. After neutralizing with dimethyl sulfate and inversing the emulsion polymerization with deionized water, a series of microemulsions were obtained. The emulsions were then cast into membranes named as PU–HPMS. The mechanical properties and water absorption of the PU–HPMS were determined and simultaneously the effects of the content of hard segment, solvent, TMP, MDEA, HPMS, and the molecular weight of soft segment were studied. It is noticed that the tensile strength decreased and elongation at break increased in the HPMS/PU when compared with pure PU, which confirm that PU was end‐capped with PDMS. It is also noticed that water absorption increased in the HPMS/PU when compared with pure PU. As HPMS content increased from 0.0 to 25.0 wt %, the surface free energies decreased from 0.3446 to 0.2317 mN/cm and water absorption decreased from 11.2% to 0.14%. The surface free energies of the membranes were decreased by more than 32.76%, which demonstrate that the membrane surfaces have excellent water and oil repellency. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 40–46, 2006     

Influence of hydroxyl‐terminated polybutadiene additives on the poly(ether sulfone) ultra‐filtration membranes

Hydroxyl‐terminated polybutadiene (HTPB) was blended into a poly(ether sulfone) (PES) casting solution used to prepare ultra‐filtration (UF) membranes via the phase inversion technique. The membranes were then characterized by contact angle (CA) measurements and UF experiments. The CA was increased with the addition of HTPB in the PES membrane and also by lowering the gelation bath temperature. It was observed that the CA was lower for membranes prepared with N‐methyl‐2‐pyrrolidinone (NMP) as the solvent than those using N,N‐dimethylacetamide (DMAc) as solvent. The flux values were higher for membranes made using a 4°C gelation bath when compared with the ambient temperature ((25 ± 1)°C) irrespective of the cast solvents, NMP or DMAc. The flux values were much higher and the solute separations were lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast with DMAc as a solvent. On the other hand, both flux and separation values were much lower for the HTPB‐based PES membranes than for the pure PES membrane, when the membranes were cast using NMP. Atomic force microscopy and scanning electron microscopy were used for morphological characterization and the correlation of topography/photography with the performance data was also examined. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2292–2303, 2006     

Fine‐tuning the mechanical properties of hydroxyl‐terminated polybutadiene/ammonium perchlorate‐based composite solid propellants by varying the NCO/OH and triol/diol ratios

Changes in the mechanical properties of hydroxyl‐terminated polybutadiene/ammonium perchlorate‐based composite solid propellants were studied during the curing period with respect to variations in the crosslink density, which was predominantly determined by the equivalent ratio of diisocyanate to total hydroxyl (NCO/OH ratio) and the equivalent ratio of triol to diol (triol/diol ratio). For this purpose, 16 propellants were prepared in different compositions through changes in the NCO/OH ratios (0.81, 0.82, 0.83, and 0.85) for each triol/diol ratio (0.07, 0.09, 0.11, and 0.13) and were tested for their mechanical properties immediately after curing. The propellants with an NCO/OH ratio of 0.82 had minimum stress, modulus, and hardness with maximum strain capability, whereas the propellants with an NCO/OH ratio of 0.85 showed just the opposite behavior. Variations in the isocyanate level seemed to have more effect on the mechanical properties at higher triol/diol ratios. It was also concluded that the propellants with triol/diol–NCO/OH combinations of 0.11–0.83, 0.11–0.85, 0.13–0.81, 0.13–0.83, and 0.13–0.85 were not acceptable for upper stage case‐bonded rocket applications because of either high tensile strength or high modulus. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2072–2079, 2002; DOI 10.1002/app.10605     

Rheo‐kinetic evaluation on the formation of urethane networks based on hydroxyl‐terminated polybutadiene

Rheo‐kinetic studies on bulk polymerization reaction between hydroxyl‐terminated polybutadiene (HTPB) and di‐isocyanates such as toluene‐di‐isocyanate (TDI), hexamethylene‐di‐isocyanate (HMDI), and isophorone‐di‐isocyanate (IPDI) were undertaken by following the buildup of viscosity of the reaction mixture during the cure reaction. Rheo‐kinetic plots were obtained by plotting ln (viscosity) vs. time. The cure reaction was found to proceed in two stages with TDI and IPDI, and in a single stage with HMDI. The rate constants for the two stages k₁ and k₂ were determined from the rheo‐kinetic plots. The rate constants in both the stages were found to increase with catalyst concentration and decrease with NCO/OH equivalent ratio (r‐value). The ratio between the rate constants, k₁/k₂ also increased with catalyst concentration and r‐value. The extent of cure reaction at the point of stage separation (x_i) increased with catalyst concentration and r‐value. Increase in temperature caused merger of stages. Arrhenus parameters for the uncatalyzed HTPB‐isocyanate reactions were evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1869–1876, 2001     

Semi‐interpenetrating networks based on poly(N‐isopropyl acrylamide) and poly(N‐vinylpyrrolidone)

Three series of novel semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropylacrylamide), PNIPA, and different amounts of the linear poly(N‐vinylpyrrolidone), PVP, were synthesized to improve the mechanical properties and thermal response of PNIPA gels. The effect of the incorporation of the linear PVP into the temperature responsive networks on the temperature‐induced transition, swelling/deswelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with varying molar ratios (25/1 to 100/1) of the monomer (N‐isopropylacrylamide) to the crosslinker (N,N′‐methylenebisacrylamide). The hydrogels were characterized by determination of the equilibrium degree of swelling, the dynamic shear modulus and the effective crosslinking density, as well as tensile strength and elongation at break. Furthermore, the deswelling kinetics of the hydrogels was studied by measuring their water retention capacity. The inclusion of the linear hydrophilic PVP in the PNIPA networks increased the equilibrium degree of swelling. The tensile strength of the semi‐interpenetrating networks (SIPNs) reinforced with linear PVP was higher than that of the PNIPA networks. The elongation at break of these SIPNs varied between 22% and 55%, which are 22 – 41% larger than those for pure PNIPA networks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Natural rubber/poly(acrylic acid) semi‐interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures

Pervaporation membranes for the dehydration of water–ethanol mixtures were prepared from a semi‐interpenetrating polymer network (semi‐IPN) of natural rubber (NR) and crosslinked poly(acrylic acid) (PAA). The swelling studies revealed that hydrophilic PAA present in the semi‐IPN membranes caused the membranes to swell greatly in water. The swelling degree of the membranes in water was significantly affected by the amount ratio between the hydrophobic NR and the hydrophilic PAA. The sorption experiments of the NR/PAA membranes in various concentrations of water–ethanol mixtures suggested the preferential sorption to water. However, for the membrane with high PAA content, the water sorption selectivity decreased considerably at high water concentration of water–ethanol mixtures because the membrane was in the highly swollen state. Pervaporation separations of water–ethanol mixtures using NR/PAA membranes were performed and it was found that at low water concentrations of feed mixtures, increasing the PAA content of the membrane can enhance both water permeation flux and selectivity. Additionally, under low feed water concentration, increasing the feed temperature would increase the water flux with the decreasing of the ethanol flux. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Toughening of epoxy resin using hydroxyl‐terminated polyesters

Epoxy resins are increasingly finding applications in the field of structural engineering. A wide variety of epoxy resins are available, and some of them are characterized by relatively low toughness. Several approaches to improve epoxy resin toughness include the addition of fillers, rubber particles, thermoplastics, or their hybrids, as well as interpenetrating networks and flexibilizers, such as polyols. It seems that this last approach did not receive much attention. So in an attempt to fill this gap, the present work deals with the use of hydroxyl‐terminated polyester resins as toughening agents for epoxy resin. For this purpose, the modifier, that is, a hydroxyl‐terminated polyester resin (commercially referred to as Desmophen), which is a polyol, has been used at different concentrations. The prepared modified structure has been characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) prior to mechanical testing in terms of impact strength and toughness. Two types of Desmophen (800 and 1200) have been used as modifiers. The obtained results showed that hydroxyl‐terminated polyester improves the epoxy toughness. In fact, the impact strength increases with Desmophen content and reaches a maximum value of 7.65 J/m at 10 phr for Desmophen 800 and 9.36 J/m at 7.5 phr for Desmophen 1200, respectively. At a critical concentration (7.5 phr), Desmophen 1200 (with higher molecular weight, longer chains, and lower branching) leads to better results. Concerning K_c, the effect of Desmophen 800 is almost negligible; whereas a drastic effect is observed with Desmophen 1200 as K_c reaches a maximum of 2.41 MPa m^1/2, compared to 0.9 MPa m^1/2 of the unmodified epoxy prior to decreasing. This is attributed to the intensive hydrogen bonding between epoxy and Desmophen 1200, as revealed by FTIR spectroscopy. Finally, the SEM analysis results suggested that the possible toughening mechanism for the epoxy resin being considered, which might prevail, is through localized plastic shear yielding induced by the presence of the Desmophen particles. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 29–38, 1999     

Novel AB crosslinked polymer networks based on 1‐vinylimidazole‐ terminated polyurethane and poly(methyl methacrylate)

1‐Vinylimidazole‐terminated telechelic polyurethanes were prepared from 1‐vinylimidazole and bromine‐terminated polyurethane. This vinyl‐terminated telechelic polyurethane (VTPU) and methyl methacrylate were polymerized in the presence of benzoyl peroxide to prepare novel AB crosslinked polymer networks (ABCPs). These were characterized by spectral, thermal and mechanical studies. The absence of the characteristic peak of vinyl group in infrared spectra of ABCP films confirms the occurrence of crosslinking. Static mechanical testing showed that the tensile strength of ABCP increases with increasing poly(methyl methacrylate) content. Dynamic mechanical studies revealed that ABCPs, at equal compositions of VTPU and methyl methacrylate, show good damping properties. Copyright © 2006 Society of Chemical Industry     

Semi‐ and full‐interpenetrating polymer networks based on polyurethane produced from canola oil and poly(methyl methacrylate)

Semi‐ and full‐interpenetrating polymer networks (IPNs) were prepared using polyurethane (PUR) produced from a canola oil‐based polyol with primary terminal functional groups and poly(methyl methacrylate) (PMMA). The properties of the material were studied and compared using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and tensile measurements. The morphology of the IPNs was investigated using atomic force microscopy (AFM). Semi‐IPNs demonstrated different thermal mechanical properties, mechanical properties, phase behavior, and morphology from full IPNs. Both types of IPNs studied are two‐phase systems with incomplete phase separation. However, the extent of phase separation is significantly more advanced in the semi‐IPNs compared with the full IPNs. All the semi‐IPNs exhibited higher values of elongation at break for all proportions of acrylate to polyurethane compared with the corresponding full IPNs. These differences are mainly due to the fact that in the case of semi‐IPNs, one of the constituting polymers remains linear, so that it exhibits a loosely packed network and relatively high mobility, whereas in the case of full IPNs, there is a higher degree of crosslinking, which restricts the mobility of the chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of polyurethane/poly(vinylidene chloride) interpenetrating polymer networks

A series of polyurethane (PU)/poly(vinylidene chloride) (PVDC) interpenetrating polymer networks (IPNs) were synthesized through variations in the amounts of the prepolyurethane and vinylidene chloride monomer via sequential polymerization (80/20, 60/40, 50/50, 40/60, 30/70, and 20/80 PU/PVDC). The physicomechanical and optical properties of the IPNs were investigated. Thermogravimetric analysis (TGA) studies of the IPNs were performed to establish their thermal stability. TGA thermograms showed that the thermal degradation of the IPNs proceeded in three steps. Microcrystalline parameters, such as the crystal size and lattice disorder, of the PU/PVDC IPNs were estimated with wide‐angle X‐ray scattering. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1375–1381, 2007     

Structure and properties of polyurethane acrylate prepolymers based on hydroxy‐terminated polybutadiene

Precursors of polyurethane acrylate based on hydroxy‐terminated polybutadiene (HTPB) soft segments, different diisocyanate and hydroxy ethyl acrylate (HEA) as hard units, were synthesized in bulk or in solution in methyl methacrylate. During precursor synthesis (in bulk), microphase separation was observed by small‐angle X‐ray scattering (SAXS). Diffusing particles are around 50 Å in size and are assumed to be assembling of hard segments. From these morphologies, it can be deduced that some isocyanate groups were trapped/or buried in hard domains. At a larger scale, around millimeters, hard segment crystallites were observed. Properties such as molar masses, melting and glass‐transition temperatures, and viscosities were correlated with precursor structure and morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 225–233, 2002     

Characterization of poly(dimethylsiloxane)‐poly(methyl hydrogen siloxane) composite membranes for organic water pervaporation separation

Hydrophobic composite membranes with a crosslinked poly(dimethylsiloxane)‐poly(methyl hydrogen siloxane) selective layer were prepared by using a new laboratory made catalyst agent. The pervaporation separation of five organic solvent–water mixtures was carried out with these composite membranes, together with swelling experiments in the same feed mixtures. The volatile organic compounds employed were ethanol, methanol, 1‐butanol, acetone, and ethyl acetate. The pervaporation and swelling experiments revealed that both the 1‐butanol and the ethyl acetate solutions showed the highest affinity for the composite membrane. When these components were employed as feed solutions, the membranes showed both high selectivity and high permeation. Mechanical–dynamical experiments of swollen and nonswollen composite membranes were also performed. The relaxation spectra were analyzed in terms of the interaction of the components of the different mixtures with the composite membrane, and the free volume corresponding to the each sample was obtained. Once the membranes had reached an equilibrium swelling, a decrease in the free volume was observed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 546–556, 2001     

Effect of solvent exposure on the properties of hydroxy‐terminated polybutadiene‐based polyurethanes

Hydroxy‐terminated polybutadiene‐based prepolyurethanes and diamine chain extended polyurethane‐ureas were prepared and treated with various organic solvents in the moisture‐cured state in order to modify their ultimate strength. FTIR studies with solvent‐treated polyurethanes and polyurethane‐ureas confirmed that organic solvents penetrated inside the polyurethane hard segments and affected hydrogen bonding. The polar and non‐polar solvents showed different abilities to penetrate into polyurethane hard segments. Solvent treatment after moisture curing increased the tensile strength of these polyurethanes and polyurethane‐ureas with respect to control samples. The stress–strain behaviour of solvent‐treated polyurethane follows the constrained junction model. The change in hard segment crystallinity on solvent treatment has been explained by wide‐angle X‐ray diffraction study. The better orientation in polybutadiene soft segments evidenced from SEM (scanning electron microscopy) pictures is believed to be the main reason behind the improved tensile properties of solvent‐treated polyurethane samples. The effect of solvent treatment, as well as stretching, on the diffusion coefficient of hexane in polyurethanes was investigated. Copyright © 2003 Society of Chemical Industry     

Polymethylsilsesquioxane and hydroxyl‐terminated polydimethylsiloxane composite: Vapor incubation before thermal curing

A composite film of polymethylsilsesquioxane (PMSQ) and hydroxyl‐terminated polydimethylsiloxane (PDMS) was prepared by incubating PMSQ prepolymer and PDMS solution in a vapor environment before thermal curing. Vapor incubation has a significant influence on the morphology and properties of the cured composite, and the vapor incubation was conducted under three different conditions, i.e., acidic, neutral, and basic. In the acidic vapor of a pH rather lower than the isoelectric point (IEP) of the silanol, the reaction between PMSQ and PDMS through silanol condensation was promoted by the protonation of silanol. PDMS rubber particles with a domain size of about 100 nm were formed in PMSQ matrix, and the flexible modulus of the film was improved. While, the morphology of the resultant film was smooth and uniform after incubation in a neutral water vapor. The basic vapor facilitated the gelation of composite due to high pH inducing more rapid silanol condensation in PMSQ than phase separation. Moreover, excellent optical transparency, insulation, and thermal stability of the composite were also retained after the PDMS incorporation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dynamic mechanical study on the thermal aging of a hydroxyl‐terminated polybutadiene‐based energetic composite

In an attempt to determine the aging behavior of hydroxyl‐terminated polybutadiene‐based composite solid propellants, viscoelastic measurements were used to study the effect of thermal aging on this kind of energetic material. Accelerated‐aging tests at 40, 60, and 80°C were performed for 5000 h. The changes in the dynamic mechanical properties, including the storage modulus (E′) and loss factor or damping efficiency (tan δ), with time and temperature were measured to determine the aging rate and likely mechanisms occurring during this process. An Arrhenius analysis based on the determination of relative rate constants showed a linear tendency from tan δ values, whereas a significant curvature was found from E′ values. In addition, the effects of external (surface) and internal (core) sampling in the intensification of the aging process were analyzed. The results confirmed dynamic mechanical analysis as a powerful tool for determining the aging characteristics of composite propellants. This technique allows the evaluation of the actual state of a propellant grain with a small sample and a straightforward measurement. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2397–2405, 2003     

Pervaporation separation of methanol/methyl tert‐butyl ether with poly(lactic acid) membranes

Poly(lactic acid), as a natural source polymer, was used to prepare pervaporation dense membranes. The performance of these membranes for the separation of the methanol (MeOH)/methyl tert‐butyl ether (MTBE) mixtures was investigated. The effects of different operating conditions, including the feed concentration of MeOH, temperature, and flow rate, were examined. Several characterization tests were performed as well. The swelling results, scanning electron microscopy images, contact angles, and mechanical strength measurements are presented. These membranes were found to be selective to MeOH, particularly for traces of MeOH in MTBE with a separation factor of more than 30. There was a small decrease in the separation factor when the feed temperature was increased; meanwhile, the total flux increased to some extent. This could be explained with respect to the thermal motions of the polymer chains and the permeating molecules. With an increase in the feed flow rate, both the selectivity and total flux increased because the concentration and temperature polarizations decreased. At higher flow rates, the feed components were homogeneously distributed over the membrane surface, whereas there may have been a concentration or temperature gradient at lower flow rates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Viscoelastic behavior in a hydroxyl‐terminated polybutadiene gum and its highly filled composites: Effect of the type of filler on the relaxation processes

Investigations have been ongoing to learn the rheological and/or mechanical behavior of composite solid propellants based on hydroxyl‐terminated polybutadiene (HTPB). The mechanical properties of these materials are related to the macromolecular structure of the binder as well as to the content and nature of the fillers. The viscoelastic behavior of an HTPB binder and its composites with different types of fillers was surveyed by dynamic mechanical analysis over a wide range of temperatures. This technique has clearly demonstrated a two‐phase morphology developed in these systems. The temperature location, intensity, and apparent activation energy of the distinct relaxations are discussed. The dependency of the relaxation processes on filler content in a series of composites has elucidated the interactions between the filler particles and the existing hard‐ and soft‐segment domains within the polyurethane matrix. It was observed that the nature of the filler significantly affects the relaxation process associated with the hard‐segment domains of the polymeric structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1705–1712, 2003     

Effect of hydroxyl‐terminated poly(fluoroalkyl methacrylate) main‐chain length on the microphase separation of waterborne fluorinated polyurethane

Waterborne fluorinated polyurethanes (WFPUs) based on hydroxyl‐terminated poly(fluoroalkyl methacrylate)s (HTPFMAs) with different main‐chain lengths were synthesized. The structure of HTPFMA was characterized using ¹H NMR spectroscopy, measurements of hydroxyl values and gel permeation chromatography. The microstructures of WFPUs were investigated using Fourier transform infrared spectroscopy, which indicated that hydrogen bonding interactions in hard segments of WFPUs were enhanced by the introduction of HTPFMA and increased with increasing main‐chain length of HTPFMA. The results of X‐ray diffraction demonstrated that increasing the main‐chain length of HTPFMA resulted in an increase of crystallinity in hard segments. Differential scanning calorimetry revealed that the melting temperature of micro‐crystallites in hard segments and the microphase separation increased with an increase of HTPFMA main‐chain length. Dynamic mechanical analysis and scanning electron microscopy also confirmed that HTPFMA with longer main‐chain length can promote the extent of microphase separation of WFPUs between soft and hard domains. The mechanical properties of WFPUs were improved due to the increase of microphase separation with increasing HTPFMA main‐chain length. © 2018 Society of Chemical Industry     

Effects of the polybutadiene/poly(styrene‐co‐acrylonitrile) ratio in a polybutadiene‐g‐poly(styrene‐co‐acrylonitrile) impact modifier on the morphology and mechanical behavior of acrylonitrile–butadiene–styrene blends

Polybutadiene‐g‐poly(styrene‐co‐acrylonitrile) (PB‐g‐SAN) impact modifiers with different polybutadiene (PB)/poly(styrene‐co‐acrylonitrile) (SAN) ratios ranging from 20.5/79.5 to 82.7/17.3 were synthesized by seeded emulsion polymerization. Acrylonitrile–butadiene–styrene (ABS) blends with a constant rubber concentration of 15 wt % were prepared by the blending of these PB‐g‐SAN copolymers and SAN resin. The influence of the PB/SAN ratio in the PB‐g‐SAN impact modifier on the mechanical behavior and phase morphology of ABS blends was investigated. The mechanical tests showed that the impact strength and yield strength of the ABS blends had their maximum values as the PB/SAN ratio in the PB‐g‐SAN copolymer increased. A dynamic mechanical analysis of the ABS blends showed that the glass‐transition temperature of the rubbery phase shifted to a lower temperature, the maximum loss peak height of the rubbery phase increased and then decreased, and the storage modulus of the ABS blends increased with an increase in the PB/SAN ratio in the PB‐g‐SAN impact modifier. The morphological results of the ABS blends showed that the dispersion of rubber particle in the matrix and its internal structure were influenced by the PB/SAN ratio in the PB‐g‐SAN impact modifiers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2165–2171, 2005