Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. I. The polyurethane networks

The polyurethane networks based on commerical prepolymer, Adiprene L-100, and trimethylol propane (system 1) and on toluene diisocyanate, polypropylene gylcol, and trimethylol propane (system 2) were prepared and characterized in a number of ways. The materials constitute the first formed networks in a series of interpenetrating polymer networks and semi-interpenetrating polymer networks to be reported in subsequent papers in this series. System 1 networks were characterized by swelling tests which showed the M _c values to be sensitive to the amount of polyurethane present in the polymerization solvent. Stress–strain, stress–relaxation, and dynamic mechanical analyses wer also conducted. For system 2, M _c was measured, by both the swelling and the Mooney–Rivlin techniques, for materials in which the diol-to-triol ratios had been altered. the latter showed C₁ increasing as M _c decreased while C₂ was small and changed onlyy slightly indicating approximately ideal behavior. These M _c values were about 13 % larger than predicted by swelling.     

Semi- and fully-interpenetrating polymer networks based on polyurethane–polyacrylate systems. XII. The influence of polymerization pressure on morphology and properties

Polyurethane–poly(methyl acrylate) interpenetrating polymer networks (IPNs) of fixed composition (50/50) were prepared at 60°C and a range of pressures. Increased synthesis pressures generally resulted in improved mixing of the two networks. The physical properties of the IPNs initially improved as a result of the enhanced mixing, reaching a maximum for specimens synthesized at 250 MPa. The poorer properties for the IPNs, prepared at higher synthesis pressures, have been ascribed to decreased uniformity in the network.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. VII. Polyurethane–poly(methyl acrylate) interpenetrating polymer networks

A series of polyurethane–poly(methyl acrylate) sequential interpenetrating polymer networks containing 40 wt % polyurethane were prepared. The triol/diol ratio used in the preparation of the first formed polyurethane network was changed so that the average molecular weight between crosslinks ranged from 9500 to 500 g/mol. In addition to decreasing this average molecular weight, changing the triol/diol ratio alters the hard segment content of the polyurethane. The extent of mixing of the components in these IPNs was investigated using electron microscopy, dynamic mechanical analysis, tensile testing, and sonic velocity measurements. The polyurethane networks were also characterized by swelling studies. It was concluded that, as the triol/diol ratio increased, the extent of mixing increased and there was evidence of phase separation of the hard segments of the polyurethane component at high triol/diol ratios.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. III. Polyurethane–poly(methyl acrylate) semi-2-interpenetrating polymer networks

Two series of semi-2-IPNs based on a polyurethane and a poly(methyl acrylate) crosslinked with divinyl benzene were prepared and investigated using dynamic mechanical analysis, sonic velocity measurements, and electron microscopy. In the one series, the level of crosslinking was varied to give ultratight networks. In the other, the composition was altered, but the amount of the crosslinking agent used was kept constant. For the first series, it was concluded that the degree of crosslinking had a significant influence on the morphology and properties by controlling the amount of enforced mixing. The dynamic mechanical data for the second series fitted the Davies modulus–composition equation, indicating that both phases are continuous.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. V. An isomerically related semi-1-interpenetrating polymer network system

A series of polyurethane–poly(vinyl acetate) semi-1-IPNs were synthesized, and certain physical properties investigated. Electron microscopy showed all the materials to be substantially phase-separated, but evidence from dynamic mechanical analysis indicated that some mixing occurred, because the polyurethane glass transition was shifted in both the tan σ? and the E″–temperature curves. The variation of modulus with composition was found to be reasonably close to the predictions of the Davies equation. When the exponent in that relation was changed to ?, a good fit was obtained. Synergism with respect to tensile strength was observed for two of the semi-1-IPNs. Stress–relaxation measurements, over a fairly narrow temperature range, were made on the semi-1-IPN containing 40% by weight of the polyurethane network. A master curve was constructed. It was noted that the WLF equation was not obeyed by this semi-1-IPN at temperatures above about 50°C.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. II. Polyurethane–poly(methyl acrylate) semi-1-interpenetrating polymer networks

A series of semi-1-IPNs based on polyurethane networks and poly(methyl acrylate) were prepared, and their properties and morphologies investigated. All the materials showed substantial phase separation, but the phase sizes were orders of magnitude smaller than those observed for blends of the same linear polymers. The effects of the isocyanate/hydroxyl ratio used in the preparation of the polyurethane, of the molecular weight of the linear polymethyl acrylate component, of the overall composition, and of the molecular weight between crosslinks in the polyurethane networks were investigated. Stress-relaxation experiments were conducted over a range of temperatures and master curves were produced for both components of the semi-1-IPNs and for a semi-1-IPN containing 40 wt% polyurethane. It was found that both the components obeyed a WLF type of equation, but that the semi-1-IPN only showed this type of behavior over a limited temperature range. Several reinforcement theories were applied to experimental dynamic storage modulus data. The closest fit was given by the Davies equation and by the logarithmic rule of mixing. By changing the exponent in the Davies equation to 1/10, a close fit was found. Application of a modified Takayanagi model indicated that these semi-1-IPNs showed some dual phase continuity when the poly(methyl acrylate) composition was relatively high.     

Semi- and fully interpentrating polymer networks based on polyurethane–polyacrylate systems. IV. Grafted semi-1-interpenetrating polymer networks

A series of semi-1-IPNs containing 40% polyurethane and 60% polymethyl acrylate was synthesized using Adiprene L-100, trimethylol propane, and polybutadiene diol. This diol was chosen to yield polyurethanes with a large number of potential graft sites for the methyl acrylate which was polymerized after the polyurethane network had been formed. A series of linear polyurethane–polymethyl acrylate blends, covering a range of compositions, was also prepared. The polyurethane for these polyblends was synthesized from Adiprene L-100 and butane-1,4-diol. Both sets of materials were investigated by dynamic mechanical analysis. On the basis of a comparison of solubility parameters, the polyurethanes and polymethyl acrylate would be expected to be incompatible. In the dynamic loss modulus-temperature plots of the polyblends there was a significant shift of the polyurethane T_g to higher temperature, but the polymethyl acrylate transition did not shift. The polyurethane transitions of the semi-1-IPNs were also shifted, but considerably more than in the case of the polyblends. For both systems, it was postulated that grafting had occured to a significant extent. With the semi-1-IPNs, it was found that as M?_c decreased the extent of grafting apparently increased. This was rationalized on the grounds that as the network chain lengths decrease, a higher proportion of the methyl acrylate monomer, prior to polymerization, was close to polyurethane segments and that this is a situation likely to lead to more grafting.     

Semi- and fully interpenetrating polymer networks based on polyurethane–polyacrylate systems. VI. Polyurethane–poly(methyl acrylate-co-ethyl acrylate) semi-1-interpenetrating polymer networks

Dynamic mechanical and longitudinal sonic velocity measurements have been made on a series of semi-1-IPNs in which the network component is a polyurethane and the linear constituent a copolymer of methyl acrylate and ethyl acrylate. Dynamic mechanical analysis reveals phase separation. The shifting of the polyurethane glass transition in both the tan δ? and the E″–temperature plots indicates that some mixing occurs. The longitudinal sonic velocity results indicate that the polyurethane is present as a continuous phase in all the materials investigated.     

Stress–strain properties of polyurethane–polyacrylate interpenetrating polymer networks

Two-component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks) were prepared from two different polyurethanes (a polyester type and a polyether type) and a polyacrylate of two different crosslink densities. The linear polymers and prepolymers were combined in solution, together with crosslinking agents and catalysts, films cast, and subsequently chain extended and crosslinked in situ. In all cases, maxima in tensile strengths significantly higher than the tensile strengths of component networks occurred. This was explained by an increase in crosslink density due to interpenetration.     

Semi- and fully interpenetrating polymer networks based on polyurethane-polyacrylate systems. X. Polyurethane-poly(ethyl acrylate) interpenetrating polymer networks

A series of polyurethane-poly(ethyl acrylate) interpenetrating networks (IPNs) containing 40 wt% polyurethane were prepared, in which the cross-link density of the polyurethane component was varied by altering the ratio of diol/triol. Decreasing the molecular weight between crosslinks from 9500 to 1200 g/mol brought about an increase in the tensile strength accompanied by a decrease in elongation at break. The tensile properties of the IPNs are, however, poorer than those of the equivalent polyurethane homopolymers. Electron microscopy showed that the polyurethane was present as distinct phases, connected by a cellular fine structure, in the poly(ethyl acrylate) matrix. Dynamic mechanical analysis as well as sonic velocity studies gave results which were consistent with this morphological picture.     

Semi- and fully interpenetrating polymer networks based on polyurethane-polyacrylate systems. VIII. The influence of the degree of crosslinking of the second formed network on the morphology and properties of polyurethane polymethylacrylate interpenetrating polymer networks

A series of polyurethane–polymethylacrylate sequential interpenetrating polymer networks containing 40% by weight of polyurethane were prepared in which the levels of crosslinking in the second formed network—polymethylacrylate—was systematically altered over a wide range. The polymethylacrylate networks and the interpenetrating polymer networks were investigated using dynamic mechanical analysis, sonic velocity measurements, and tensile testing. In addition, the interpenetrating polymer networkds were studied using transmission electron microscopy. The interpenetrating polymer networks showed high values of the Oberst damping factor. It was concluded that tightening the second formed network does not produce the dramatic effects associated with decreasing the average molecular weight between crosslinks of the first formed network.     

Semi- and fully interpenetrating polymer networks based on polyurethane-polyacrylate systems. IX. Properties of an isomerically related interpenetrating network

Two polyurethane–poly(vinyl acetate) interpenetrating polymer networks of differing composition were synthesized and certain physical properties investigated. The results are compared with semi-1-interpenetrating polymer networks of the same system as well as with, where appropriate, polyurethane-poly(methyl acrylate) interpenetrating polymer networks. Dynamic mechanical analysis clearly indicated phase separation for both compositions. The poly(vinyl acetate) glass transition showed a shift to lower temperatures accompanied by a shift to higher temperatures of the polyurethane transition. Such shifts indicate a certain extent of mixing. Electron microscopy confirmed phase separation and for a material with 20% by weight of polyurethane indicated that both components are continuous. This latter material also had a higher tensile strength and elongation at break than the corresponding poly(vinyl acetate) homopolymer. At 60% by weight of polyurethane the stress-strain characteristics are those of a reinforced rubber. Certain modulus–composition theories, and, also, sonic velocity measurements were consistent with these morphological conclusions.     

Polyurethane–polyacrylate interpenetrating polymer networks. II

Two component topologically interpenetrating polymer networks of the SIN type (simultaneous interpenetrating networks) composed of a melamine-cured polyacrylate and three different polyether-based polyurethanes were prepared. The linear polymers and prepolymers were combined in solution, together with the necessary crosslinking agents and catalysts, films were cast and subsequently chain extended and crosslinked in situ. In all cases, maxima in tensile strength significantly higher than the tensile strengths of the component networks occurred at 50% polyurethane : 50% polyacrylate. This was explained by an increase in crosslink density resulting from interpenetration. One of the interpenetrating polymer networks showed only one glass transition temperature (T_g) (measured calorimetrically) intermediate in temperature to the T_g's of the components and as sharp as the component T_g's. This is indicative of phase mixing and indicates at least partial chain entanglement (interpenetration). Some enhancement of other physical properties was also noted.     

Thermomechanical properties and morphology of interpenetrating polymer networks of polyurethane–poly(methyl methacrylate)

Interpenetrating networks (IPNs) of polybutadiene‐based polyurethane (PU) and poly(methyl methacrylate) (PMMA) were synthesized. The effect of the incorporation of 2% glycidyl methacrylate (GMA) and 2‐hydroxyethyl methacrylate (2‐HEMA) on the thermal, mechanical, and morphological properties of IPNs was investigated. Both 2‐HEMA and GMA led to improvements in these properties. However, 2‐HEMA‐containing IPNs showed somewhat better tensile strength, elongation, and damping characteristics. The morphology of IPNs containing 2‐HEMA showed better mixing of the components. The improvement in the properties was observed for up to 40% PMMA in the IPNs. Differential scanning calorimetry thermograms showed the presence of three glass transitions. The third glass‐transition temperature was explained by possible grafting of methyl methacrylate onto PU. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1576–1585, 2002     

Stress–strain properties and thermal resistance of polyurethane–polyepoxide interpenetrating polymer networks

Two-component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks) were prepared from three different polyurethanes and two epoxies. The linear prepolymers were combined in solution, together with crosslinking agents and catalysts, films cast, and subsequently chain extended and crosslinked in situ. Two of the IPN's showed significant improvement in thermal resistance, as measured by thermogravimetric analysis (TGA). All of the IPN's showed maxima in tensile strength significantly higher than the tensile strengths of the component networks at 25% polyurethane and minima at 75% polyurethane. The minima were explained by an initial dilution of the strong polyurethane hydrogen bonds by the epoxies, and the maxima, by an increase in crosslink density due to interpenetration.     

Synthesis and characterization of polyurethane–chitosan interpenetrating polymer networks

A polyurethane–chitosan (PU–CH) coating was synthesized from castor-oil-based PU prepolymer and highly deacetylated and depolymerized chitosan. The films cast with the coating were used for the characterization. X-ray photoelectron spectroscopy, a surface-sensitive technique, indicated the chemical bonding between the chitosan and PU prepolymer as well as the enrichment of chitosan on the surface of the film PU–CH. Electron spin resonance (ESR) spectroscopy using the nitroxyl radical 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (4-hydroxy-TEMPO) as a reporter group was used to study the chain mobility in the film PU–CH. It was observed that T_50G of the probe and the first glass transition temperature (T_g1) of the film PU–CH were 10 and 18°C higher than those in the PU film, respectively, and the activation energy (27.0 kJ mol⁻¹) of tumbling for the probe covalently bonded with PU–CH was 12.8 kJ mol⁻¹ higher than that of the probe with the film PU. It suggests that the molecular motion in the PU–CH was restricted by grafted and crosslinked interpenetrating polymer networks (IPNs). The results of the differential thermal analysis and thermogravimetric analysis proved that the thermostability of the film PU–CH was significantly higher than that of the film PU, and the T_g1 value is in good agreement with that calculated from ESR. It could be concluded that the IPNs resulted from the chitosan grafting and crosslinking with PU exist in the film PU–CH. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1321–1329, 1998     

Permeation of oxygen through polyurethane–polyepoxide interpenetrating polymer networks

Oxygen permeation studies on polyurethane (PU)/polyepoxide (EP) interpenetrating polymer networks show that the increased crosslinking density owing to additional permanent chain entanglement (resulting from interpenetration) can decrease the coefficients of permeation, diffusion, and oxygen solubility. At 20% PU, at which the crosslinking density is maximum, these coefficients retain minimum values, while the tensile strength retains a maximum value.     

Polyurethane interpenetrating polymer networks. V. Engineering properties of polyurethane–poly(methyl methacrylate) IPN's

The engineering properties of polyurethane–poly(methyl methacrylate) simultaneous interpenetrating networks (SIN's) were evaluated. The hardness behavior reflected the observed phase inversion in the electron-microscopic studies. The maximum ultimate tensile strength was observed at 85% polyurethane–15% poly(methyl methacrylate) IPN and was due to the filler-reinforcing effect of the rigid poly(methyl methacrylate) phase. The ultimate tensile strenght of the 75/25 polyurethane–poly(methyl methacrylate) IPN was higher than that of the corresponding pseudo-IPN's (only one network crosslinked) and the linear blend. The leathery and glassy compositions did not show any reinforcement in the ultimate tensile strength. This indicated that the reinforcement in the ultimate tensile strength was not directly related to interpenetration (by increased physical entanglement crosslinks), but indirectly related by reducing the rigid phase domain sizes and increasing the adhesion between the two phases, thus enhancing the filler-reinforcing effect similar to that observed in a carbon black-filled rubber. The tear strengths of the polyurethane-rich IPN's pseudo-IPN's, and linear blends were found to be higher than that of the pure polyurethane as a combined result of increased modulus and tensile strength. The weight retentions in the thermal decomposition of the IPN's, pseudo-IPN's, and linear blends were higher than the proportional average of the component networks. The results seemed to indicate that this enhancement was related to the presence of the unzipped methyl methacrylate monomer. It was suggested that the monomers acted as radical scavengers in the polyurethane degradation, thus delaying the further reaction of the polyurethane radicals into volatile amines, isocyanates, alcohols, olefins, and carbon dioxide.     

丙烯酸酯系胶乳互穿聚合物网络的合成及阻尼性能

以种子乳液聚合法合成了聚苯乙烯／聚丙烯酸乙酯、聚甲基丙烯酸乙酯／聚丙烯酸丁酯的核-壳胶乳互穿聚合物网络(LIPN),分别测试了不同配比LIPN及其共混物的阻尼性能、物理机械性能和吸水性能。结果表明,LIPN共混物是具有阻尼温域宽、阻尼性能优、物理机械性能良好和吸水率较低的阻尼材料,其阻尼性能主要取决于共混组分的性能、配比和内耗能的贡献,并且与共混物的织态结构也密切相关。     

Damping properties of interpenetrating polymer networks of polyurethane‐modified epoxy and polyurethanes

Interpenetrating polymer networks (IPNs) were prepared from polyurethane (PU)‐modified epoxy with different molecular weight of polyol and polyurethanes based on the mixture of polydiol and polytriol by a one‐shot method. Two types of PU‐modified epoxy: PU‐crosslinked epoxy and PU‐dangled epoxy were synthesized, and the effects of the different molecular weights of polyol in the PU‐modified epoxy/PU IPNs on the dynamic mechanical properties, morphology, and damping behavior were investigated. The results show that the damping ability is enhanced through the introduction of PU‐modified epoxy into the PU matrix to form the IPN structure. As the molecular weight of polyol in PU‐modified epoxy increases, the loss area (LA) of the two types of the IPNs increases. PU‐dangled epoxy/PU IPNs exhibit much higher damping property than that of the PU‐crosslinked epoxy/PU IPNs with 20 wt % of PU‐crosslinked epoxy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 328–335, 1999