Acoustical,damping and thermal properties of polyurethane/poly(methyl methacrylate)-based semi-interpenetrating polymer network foams

In the present study, the interpenetrated polymer networks (IPN) foams of polyurethane (PU) and poly(methyl methacrylate) (PMMA) with different ratio of PU/PMMA (i.e. 85/15, 75/25 and 65/35) were prepared using the polymerisation process. The acoustical, damping and thermal properties of synthesised IPN foams with regard to different compositions were studied. As indicators of effective damping capability, viscoelastic parameters including loss factor (tan δ), glass transition temperature (T_g) and effective damping interval (tan δ?>?0.3) were also determined. The results show that the T_g shifted to higher temperature ranges, and the damping temperature range (tan δ?>?0.3) increased when the IPN was formed. The sound absorption coefficient results show that because of the formation of IPN, the sound-absorbing capacity of prepared samples increased at a certain frequency, and the resonance frequency shifted to lower frequencies by increasing the PMMA content in IPN foams.     

GEORDNETE EPOXIDNETZWERKE AUS 4-GLYCIDYLPHENYL-4-GLYCIDYL-BENZOAT und 3- BZW. 4-AMINOPHENYL-4-AMINOBENZOAT

The introduction of mesogenic groups in main- and sidechains of epoxy thermosets results in an ordered multiphase network with cellular structure, if gelation occurs below the maximal cure temperature T_max. T_max is individual for a given combination of monomers. The multiphase network consists of relatively soft anisotropic cell nuclei and hard isotropic cell walls. If gelation occurs above T_max single phase networks are obtained. The size of the cell nuclei strongly depends on the used monomers and varies up to two orders of magnitude. The multiphase structure was found to have no impact on the tensile elastic modulus.     

Simultaneous interpenetrating networks of a polyurethane and poly(methyl methacrylate). II. Partitioning of MMA monomer in the last stages of polymerization

In a model polyurethane/poly(methyl methacrylate) (PU/PMMA) system, the partitioning of unreacted methyl methacrylate monomer (MMA) is studied in the late stages of its polymerization, simulated by incorporating controlled amounts of MMA in otherwise fully cured simultaneous interpenetrating networks (SIN) samples. Glass transitions temperatures (T_g) were determined using dynamic mechanical spectroscopy and differential scanning calorimetry as a function of MMA content of the SINs. The lowering of T_g in each phase due to the plasticization effect of MMA is used to calculate a plasticization coefficient for each phase, finally allowing calculation of the partition coefficient of MMA between the two phases. It is found that the MMA monomer distributes itself almost uniformly across the two phases of the current SIN system, leading to speculation as to the locus of late SIN polymerization. © 1995 John Wiley & Sons, Inc.     

Comparison of viscoelastic properties of polydimethylsiloxane/poly(2‐hydroxyethyl methacrylate) IPNs with their physical blends

Interpenetrating polymer networks (IPNs) of polydimethylsiloxane (PDMS) and poly(2‐hydroxyethyl methacrylate) (PHEMA) were prepared by sequential method. The dynamic mechanical parameters of obtained IPNs and their variations with the structural composition were evaluated. The results for the IPNs were compared with corresponding physically blended systems. The tensile properties and damping factor (tan δ) were assessed by stress–strain measurement and dynamic mechanical thermal analysis (DMTA), respectively. The glass–rubber transition temperature (T_g) was assessed by DMTA and differential scanning calorimetry (DSC). The results showed higher tensile strength and elongation at break for IPNs than those for physical blends. The shifts of T_g for that two components that make up the IPNs were greater than those for corresponding blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3480–3485, 2002     

Effect of Hindered Phenol AO‐80 on the Damping Properties for Nitrile‐Butadiene Rubber/Phenolic Resin: Molecular Simulation and Experimental Study

A combined study of molecular dynamics (MD) simulation, experimental, and linear regression analysis method is presented for hindered phenol of 3,9‐bis[1,1‐dimethyl‐2‐{b‐(3‐tertbutyl‐4‐hydroxy‐5‐methylphenyl)propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro‐[5,5]‐undecane (AO‐80)/nitrile‐butadiene rubber/linear phenolic resin (AO‐80/NBR/PR) composites with different AO‐80 contents to quantitatively establish the relations between microstructure and damping performance. The number of hydrogen bonds (N_HBs), the fractional free volume (FFV), and the binding energy (E_binding) of AO‐80/NBR/PR composites with different AO‐80 content are calculated by MD simulation from the microscopic scale. Damping parameters, including the loss factor peak (tan δ_max) and the loss peak area (TA) (tan δ > 0.3), are obtained by dynamic mechanical analysis from macroscopic scale. The quantitative relationships between microstructure parameters (N_HBs, E_binding, and FFV) and macroscopic damping properties (tan δ_max and TA) are obtained by linear regression analysis. This research is expected to provide a theoretical guidance for improving the damping performance of rubber‐based organic hybrid composites.     

Pultruded fiber reinforced blocked polyurethane (PU) composites. II. Processing variables and dynamic mechanical properties

Unidirectional fiber reinforced blocked polyurethane (PU) composites have been prepared by the pultrusion process. The effects of processing variables on the mechanical properties and dynamic mechanical properties of fiber reinforced PU composites by pultrusion have been studied. The processing variables investigated included pulling rate (in-line speed), die temperature, postcure time and temperature, and filler type and content. The dynamic mechanical properties of the composites produced by the process were studied utilizing dynamic mechanical spectrometer. Results show that the composites possessed various optimum pulling rates at different die temperatures. From the DSC data analysis, swelling ratio, and mechanical properties, the optimum die temperature was determined. It was found that the mechanical properties increase with filler content for various types of filler. The increasing of mechanical properties depends on the optimum postcure temperature and time. However, the properties decreased for longer postcure times since the composite materials were degraded. The glass-transition temperature (T_g) increased slightly and the damping peak (tan δ) was broadened due to fiber reinforcement. The dynamic mechanical moduli (G′, G″) of pultruded PU composites are apparently higher than those of the matrices. The moduli (G′, G″) increase with increasing fiber and filler content, and the damping peak becomes broad. Effect of postcuring on the degree of crosslinking, T_g, and dynamic modulus will be discussed.     

Chemorheological characterization of thermosetting polyurethane formulations containing different chain extender contents

Chemorheological analyses of thermosetting polyurethane (PU) formulations containing various amounts of chain extender were carried out. In the first part of the present research, effect of chain extender content on the gel time and its dependency with temperature were investigated for PU formulations. Gelation temperature (T_gel) and gel time (t_gel) of reactive systems were determined using temperature sweep and time test measurements under dynamic linear viscoelastic deformations. The results of temperature sweep experiments for the samples containing various chain extender weight percents showed that the gelation temperature declined by increasing the chain extender content of PU formulations. The analysis made on gel times determined in a wide temperature range indicated that the activation energy for the gelation process declined and 1/t_gel, as a measure of the rate of gelation process, dramatically increased with increasing chain extender concentration. In the second part of this study, calculation of viscoelastic characteristics at the gel point was performed. The results showed that the relaxation exponent (n) declined with increasing chain extender, while the fractal dimension increased. These results confirmed that the gel structures became more elastic and with a tighter structure by increasing the chain extender concentration in PU formulations. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Curing studies on the epoxides of carbono- and thiocarbonohydrazones

The curing behavior of a new class of N? N bonded epoxy resins has been analyzed using the simultaneous DTA-TG, dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA) techniques. The resin systems, viz, diglycidyl ether of furfuraldehydecarbonohydrazone (DGFCH), diglycidyl ether of furfuraldehydethiocarbonohydrazone (DGFTCH), and tetraglycidyl ether of vanillinthiocarbonohydrazone (TGVTCH) with the curative, diaminodiphenylmethane (DDM), taken in stoichiometric amounts have been examined. The curing exotherm could be resolved from the decomposition exotherm qualitatively using DTA-TG analysis. The DMA has been carried out in both the dynamic and isothermal mode to follow the curing process of the systems DGFCH/DDM and TGVTCH/DDM. The storage modulus (G′), loss modulus (G″), complex viscosity (η) and creep factor (tan δ) were measured simultaneously. The crossover point of G′ and G″, taken as the gelation point in isothermal runs, was determined to obtain time to gelation at that temperature. The isothermal runs at different temperatures have been used to calculate activation energy of the curing process up to gelation. For the difunctional resin DGFTCH, the activation energy value was found to be 18.7 kcal/mol. The thermomechanical analysis (TMA) has been used to find the glass transition (T_g0, and melt transition (T_m) temperatures. The cured tetrafunctional TGVTCH/DDM system as expected, has higher T_g than those of the two difunctional resin systems. © 1994 John Wiley & Sons, Inc.     

Influence of cross-link density on the properties of ROMP thermosets

A norbornene-based cross-linker was synthesized and mixed at different loadings with two separate monomers for self-healing polymer applications: 5-ethylidene-2-norbornene (ENB) and endo-dicyclopentadiene (endo-DCPD). The monomer/cross-linker systems were polymerized by ring-opening metathesis polymerization (ROMP) with Grubbs' catalyst. The thermal-mechanical properties of the polymerized networks were evaluated by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) and the curing process was monitored by parallel plate oscillatory rheometry. The viscosities of the pre-polymer blends are shown to be adequately low for self-healing, and exhibit a high ROMP reactivity to form cross-linked networks with enhanced thermal-mechanical properties. The addition of cross-linker increases the glass transition temperature (T_g) and the storage modulus both above and below T_g. The storage modulus increase above T_g is used to estimate the molecular weight (M_c) between entanglements or cross-link sites for both ENB and endo-DCPD-based networks. The cross-linker also greatly accelerates network formation as defined by the gelation time.     

Solute and solvent effects on the thermorheological properties of poly(oxyethylene)–poly(oxypropylene) block copolymers: Implications for pharmaceutical dosage form design

Despite their widespread use as platforms for topical drug delivery systems, there is a relative lack of information concerning the thermorheological and viscoelastic properties of poloxamer systems and the effects of formulation components on these properties. To address this deficit, we examined the effects of the poloxamer concentration (25 and 35% w/w), molecular weight blend (poloxamer 407 and poloxamer 188), cosolvents (ethanol, propylene glycol, and glycerol), and presence of inorganic and organic electrolytes (sodium chloride and tetracaine hydrochloride, respectively) on these properties. The rheological properties were examined with a rheometer (4‐cm‐diameter, stainless steel, parallel‐plate geometry) in either thermal sweep (0.5 Hz) or frequency sweep (0.01–1.0 Hz and 37°C) modes. Increasing the poloxamer concentration increased the elasticity [i.e., increased the storage modulus (G′) and reduced the loss tangent (tan δ)] and reduced the sol–gel transition temperature (T_m) of all the formulations. Decreasing the ratio (407:188) increased T_m and reduced the elasticity of all the formulations. Increasing the concentration of ethanol, propylene glycol, or glycerol in the solvent reduced T_m. The presence of ethanol reduced G′ and increased tan δ in a concentration‐dependent fashion, whereas the viscoelastic properties of the poloxamers were more tolerant of glycerol (in particular) and propylene glycol. The elasticity of the formulations containing up to 10% glycerol and 5% propylene glycol was increased with respect to their aqueous counterparts. The presence of sodium chloride reduced T_m and, at lower concentrations (1 and 3%), increased G′ and reduced tan δ for aqueous poloxamer systems. Conversely, the addition of a model therapeutic agent, tetracaine hydrochloride (5 and 7% w/w), significantly increased T_m and altered the viscoelastic character of the poloxamer system, notably reducing G′ and increasing the loss modulus and tan δ. Alterations in the viscoelastic and thermorheological properties of aqueous poloxamer systems will have implications for their clinical performance. This study, therefore, has highlighted the need for the rational selection of components in the formulation of poloxamer systems as platforms for topical drug delivery. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1016–1026, 2003     

Comparison of thermal techniques for glass transition measurements of polystyrene and cross-linked acrylic polyurethane films

There are few quantitative comparisons in the literature between glass transitions (T_g) measured by differential scanning calorimetry (DSC) and by dynamic mechanical analysis (DMA). Also, in the case of DMA, two different operational definitions have been used to obtain the glass transition, namely, the loss modulus (E″) and damping (tan δ) peak temperatures. We propose a new DMA definition of T_g and demonstrate that it agrees with DSC T_g measurements within ±2°C for both thermoplastic polystyrene and thermoset cross-linked acrylic polyurethane films with measurable tan δ peaks. The glass transitions for a single polystyrene standard and several cross-linked acrylic polyurethane films were measured by DSC. Additionally, E″ and tan δ peak temperatures were measured by DMA as a function of frequency and temperature. Empirically, it was determined that the average of the E″ and tan δ peak temperatures measured at 1 rad/s oscillation frequency corresponds to the glass transition measured by the ASTM E1356 DSC test method. © 1994 John Wiley & Sons, Inc.     

Kinetic and rheological relationships of dicyanate ester polycondensation for the resin transfer molding process

Kinetic and rheological behavior of a liquid dicyanate ester catalyzed by a copper salt was studied with a view to controlling the RTM process. The kinetics are satisfactorily modeled with a simple second order model until vitrification occurs. Independent of the catalyst concentration, the relationship between glass transition temperature T_g and conversion x was well validated, indicating that vitrification occurs well before T_g(x) reaches the curing temperature. The rheological study allowed gelation (tanδ crossover) and vitrification times at different curing temperatures to be determined. The values of tanδ at gel point were found to be slightly higher than those usually found. In order to carry out a simulation of the RTM process, viscosity and conversion were also linked with an empirical model.     

Semi‐interpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. II. Dielectric relaxation and thermal behaviour

Semi‐interpenetrating polymer networks (semi‐IPNs) based on crosslinked polyurethane (PU) and linear polyvinylpyrrolidone (PVP) were synthezised, and their thermal and dynamic mechanical properties and dielectric relaxation behavior were studied to provide insight into their structure, especially according to their composition. The differential scanning calorimetry results showed the glass transitions of the pure components: one glass‐transition temperature (T_g) for PU and two transitions for PVP. Such glass transitions were also present in the semi‐IPNs, whatever their composition. The viscoelastic properties of the semi‐IPNs reflected their thermal behavior; it was shown that the semi‐IPNs presented three distinct dynamic mechanical relaxations related to these three T_g values. Although the temperature position of the PU maximum tan δ of the α‐relaxation was invariable, on the contrary the situation for the two maxima observed for PVP was more complex. Only the maximum of the highest temperature relaxation was shifted to lower temperatures with decreasing PVP content in the semi‐IPNs. In this study, we investigated the molecular mobility of the IPNs by means of dielectric relaxation spectroscopy; six relaxation processes were observed and indexed according the increase in the temperature range: the secondary β‐relaxations related to PU and PVP chains, an α‐relaxation due to the glass–rubber transition of the PU component, two α‐relaxations associated to the glass–rubber transitions of the PVP material, and an ionic conductivity relaxation due to the space charge polarization of PU. The temperature position of the α‐relaxation of PU was invariable in semi‐IPNs, as observed dynamic mechanical analysis measurements. However, the upper α‐relaxation process of PVP shifted to higher temperatures with increasing PVP content in the semi‐IPNs. We concluded that the investigated semi‐IPNs were two‐phase systems with incomplete phase separation and that the content of PVP in the IPNs governed the structure and corresponding properties of such systems through physical interactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1191–1201, 2003     

Glass transitions of topologically interpenetrating polymer networks

Two component topologically-interpenetrating polymer networks were made of the SIN type (simultaneous interpenetrating network) composed of two polyurethanes (a polyether-based and a polyester-based) in combination with an epoxy resin, a polyacrylate and two unsaturated polyesters. The linear polymers and/or prepolymers were combined in solution and in bulk together with the necessary crosslinking agents and catalysts. Films were cast and chains extended and crosslinked in situ. All of the IPN's exhibited one glass transition (T_g) intermediate in temperature to the T_g's of the component networks, and as sharp as the T_g's of the components. This suggests that phase separation may not occur and thus some chain entanglement (interpenetration) of the two networks is involved. The observed T_g's are always several degrees lower than the arithmetic means of the component T_g's. A theory based on interpenetration is developed to account for this.     

Semiinterpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. I. Thermodynamic state and dynamic mechanical analysis

Semiinterpenetrating polymer networks (semi‐IPNs) based on polyurethane (PU) and polyvinylpyrrolidone (PVP) have been synthesized, and their thermodynamic characteristics, thermal properties, and dynamical mechanical properties have been studied to have an insight in their structure as a function of their composition. First, the free energies of mixing of the two polymers in semi‐IPNs based on crosslinked PU and PVP have been determined by the vapor sorption method. It was established that these constituent polymers are not miscible in the semi‐IPNs. The differential scanning calorimetry results evidence the T_g of polyurethane and two T_g for PVP. The dynamic mechanical behavior of the semi‐IPNs has been investigated and is in accordance with their thermal behavior. It was shown that the semi‐IPNs present three distinct relaxations. If the temperature position of PU maximum tan δ is invariable, on the contrary, the situation for the two maxima observed for PVP is more complex. Only the maximum of the highest temperature relaxation is shifted to lower temperature with changing of the semi‐IPNs composition. It was concluded that investigated semi‐IPNs are two‐phase systems with incomplete phase separation. The phase composition was calculated using viscoelastic properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 852–862, 2001     

Properties and interfacial bonding for regenerated cellulose–polyurethane/amylose acetate sipn composite films

Composite films were obtained by placing a polyurethane/amylose acetate semi‐interpenetrating polymer network (SIPN) coating onto the surfaces of regenerated cellulose (RC) film. The properties of the composite film, such as tensile strength, 79.9 MPa (in dry state), 49.5 MPa (in wet state), water resistance (R), 0.62, dimensional stability (S_c), 3.0%, and water vapor permeability (P), 5.96 × 10⁻⁵ Kgm⁻²h⁻¹, are better than those of the uncoated RC film or RC film with PU coating. The interfacial strength was characterized with infrared spectroscopy (IR), ultraviolet spectroscopy (UV), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA). The results showed the existence of covalent and hydrogen bonds between the SIPN coat layer and the RC layer. It was also found that the PU prepolymer in the coating layer penetrated into the cellulose bulk, and reacted with the cellulose molecules, which formed another SIPN.     

Quantitative relationships between intermolecular interaction and damping parameters of irganox‐1035/NBR hybrids: A combination of experiments,molecular dynamics simulations,and linear regression analyses

The damping mechanism of phenol(3,5‐bis(1,1‐dimethylethyl)‐4‐hydroxybenzenepropanoic acid thiodi‐2,1‐ethanediyl ester, abbreviated as Irganox‐1035)/nitrile‐butadiene rubber hybrids was studied by combining experiments, computer simulations, and linear regression analyses. Four important damping parameters [loss peak (tan δ_max), effective loss area (TA), glass transition temperature (T_g), and effective temperature region (ΔT)], were obtained by dynamic mechanical thermal analyses. Three intermolecular interaction parameters [the number of intermolecular hydrogen bonds (N_HBs), binding energy (E_binding), and fractional free volume (FFV)], were calculated by molecular dynamics simulations. Using linear regression analyses, the quantitative relationships between the intermolecular interaction and damping parameters were investigated. Linear and significant relationships between intermolecular interactions (N_HBs and E_binding) and damping parameters (tan δ_max and TA) (R² > 0.9; P < 0.001) were noted; FFV showed moderate linear correlations with damping parameters (R² < 0.9; P < 0.05); only E_binding showed strong correlations with T_g and ΔT (R² > 0.9; P < 0.001). Besides, after nondimensionalization, multivariate linear fitting equations based on intermolecular interaction parameters were developed to accurately predict damping parameters (R² > 0.98, P < 0.001). These studies were expected to provide the useful information in understanding the damping mechanism and to attempt a quantitative tool for designing high damping materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46202.     

Time-temperature–transformation (TTT) diagrams of high Tg epoxy systems: Competition between cure and thermal degradation

The cure behavior and thermal degradation of high T_g epoxy systems have been investigated by comparing their isothermal time-temperature-transformation (TTT) diagrams. The formulations were prepared from di- and trifunctional epoxy resins, and their mixtures, with stoichiometric amounts of a tetrafunctional aromatic diamine. The maximum glass transition temperatures (T_g∞) were 229°C and > 324°C for the fully cured di- and trifunctional epoxy materials, respectively. Increasing functionality of the reactants decreases the times to gelation and to vitrification, and increases the difference between T_g after prolonged isothermal cure and the temperature of cure. At high temperatures, there is competition between cure and thermal degradation. The latter was characterized by two main processes which involved devitrification (decrease of modulus and T_g) and revitrification (char formation). The experimentally inaccessible T_g∞ (352°C) for the trifunctional epoxy material was obtained by extrapolation from the values of T_g∞ of the less highly crosslinked systems using a relationship between the glass transition temperature, crosslink density, and chemical structure.     

Simultaneous interpenetrating networks of a polyurethane and poly(methyl methacrylate). I. Metastable phase diagrams

Any simultaneous interpenetrating network (SIN) synthesis contains three key events. These are gelation of polymer I, gelation of polymer II, and phase separation of polymer I from polymer II. Metastable phase diagrams of SINs are developed, in which the time occurrence of these three events is represented. A polyurethane/poly(methyl methacrylate) (PU/PMMA) system was chosen as a model. Polymerization kinetics were followed in situ for both PU and PMMA using Fourier Transform Infrared Spectroscopy (FTIR) with the aid of a heated demountable cell. Glass transitions of fully cured samples were determined by dynamic mechanical spectroscopy (DMS) and differential scanning calorimetry (DSC). Phase separation was determined by the onset of turbidity, and gelation of the first gelling polymer was determined by the sudden resistance of the system to flow. As a result, a metastable phase diagram was constructed for the four-component SIN system (the two monomers and their respective polymers) as a tetrahedron in three dimensions with the two monomers and two polymers at the four apexes. Phase separation and gelations of the two polymers are indicated by various surfaces. These surfaces intersect at lines and curves, representing unique conditions of an SIN synthesis, e.g., simultaneous gelation of both polymers, or simultaneous phase separation and gelation of polymer I, etc. These conditions are critical in terms of the development of the SIN morphology, dividing the reaction space into specific regions. Finally, it is shown how the tetrahedron diagram helps visualize the course of the three key events during SIN synthesis, and provides direction for controlling them. © 1995 John Wiley & Sons, Inc.     

Chemorheology on simultaneous IPN formation of epoxy resin and unsaturated polyester

Study of the simultaneous interpenetrating polymer network (IPN) between diglycidyl ether of bisphenol-A (DGEBA) and unsaturated polyester (UP) was carried out at ambient temperature. Fourier transform infrared (FTIR) spectroscopy was employed to investigate the intermolecular H-bonding and functional group changes. Viscosity changes due to H-bonding and crosslinking were examined with a Brookfield viscometer. Gelation time was measured by a Techne gelation timer. Complexation between Co(II) (the promoter for UP cure) and diamine (the curing agent for DGEBA) was detected with UV-visible spectrometer. Experimental evidence revealed that intermolecular interactions were observed in systems such as DGEBA/UP, DGEBA/diamine, Co(II)/diamine, DGEBA/uncured UP, and UP/uncured DGEBA. All such interactions had measurable effects on the curing behaviors for both networks, as were indicated by the viscosity changes and gelation time. The IPNs thus obtained were further characterized with rheometric dynamic spectroscopy (RDS) and differential scanning calorimetry (DSC). Partial compatibility between UP and DGEBA networks was evidenced from a main damping peak with a shoulder near glass transition temperature (T_g) for lower UP content; while at higher UP content, only a main damping peak near T_g was observed. DSC revealed a broad glass transition for all IPNs. The resultant IPN materials were all transparent. © 1992 John Wiley & Sons, Inc.