Filled interpenetrating networks: their formation and viscoelastic properties

The kinetics of curing, the microphase separation process (MPS) and the viscoelastic properties of interpenetrating polymer networks (IPNs) based on crosslinked polyurethane and linear poly(butyl methacrylate) were studied in the presence of two fillers—talc and polymeric fine-disperse triethylene glycol dimethacrylate. It was found that introducing filler into the reaction mixture changes the reaction kinetics and degree of microphase separation, which in turn affects the viscoelastic properties of the IPNs. The data obtained by dynamic mechanical spectroscopy and differential scanning calorimetry for filled semi-IPNs and calculations of the degree of segregation of the components show that filler introduction results in MPS inhibition on account of a local increase in viscosity near the solid interface, i.e. compatibility is increased.     

Mechanical properties of polyurethane-unsaturated polyester interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) based on a polyurethane (PU) and two unsaturated polyester (UPE) resins (a commercially available UPE and a partially endcapped UPE) were prepared. The mechanical properties, such as tensile strength, elongation at break, impact strength, and dynamic mechnical properties of IPNs, were studied by changing reaction temperature, PU reaction rate, and UPE reaction rate. Owing to the unique microgel formaton of UPE, the first formed network tends t be the dispersed phase in the PU-UPE IPN system. The reaction sequence was found to be an important factor in determining the phase mixing and phase morphology of the IPNs. When the PU reaction was faster, extensive phase mixing due to strong grafting or chain interpenetration was obtained. When the UPE reacted first, grafting was retarded by the microgel formation of the UPE network. It was found that simultaneous reaction of the two reacting system resulted in a co-continuous structure that provided enhanced tensile properties and impact strength.     

Mechanical and swelling properties of PDMS interpenetrating polymer networks

Poly(dimethylsiloxane) (PDMS) interpenetrating networks (IPNs) of two different molecular weight PDMS were prepared. Six series of IPNs were obtained by first tetra-functionally end-linking long vinyl-terminated PDMS (molar mass 23 × 10³ or 21 × 10³ g mol⁻¹) neat or in a 50% solution with unreactive PDMS chains. These networks were then dried and swollen with short reactive telechelic PDMSs (molar mass 800, 2.3 × 10³ or 5.7 × 10³ g mol⁻¹) that were subsequently end-linked. The mechanical, toughness and swelling properties of these IPNs were investigated. We found that the correlation between modulus (E) and equilibrium swelling (Q) in toluene of the PDMS IPNs obeys a scaling relation identical to that of a normal unimodal PDMS network. This result strongly suggests effective load transfer between the networks. The results of the elastic modulus and of the toughness of the networks represented by the energy required to rupture them were analyzed in terms of a recent model by Okumura [Europhys Lett 2004;67:470.]. Although the modulus results are in reasonable agreement with the equal-stress model of Okumura, the toughness results are not. In addition, our measured toughness decreases instead of increases with composition in an opposite trend to that predicted by the equal-strain model. An empirical model based on fracture mechanics gives a good representation of the toughness data.     

Recent studies on interpenetrating polymer networks

Recent investigations on interpenetrating polymer networks (IPNs) have included two component IPNs from polyurethanes and poly(methacrylates) and two component IPNs from polyurethanes and epoxies. All the IPNs were prepared by the simultaneous polymerization technique (SIN-IPNs). Two types of IPNs, polyurethane-poly(methyl methacrylate) (PU/PMMA) and polyurethane-poly(methyl methacrylate-methacrylic acid) (PU/PMMA-MAA) were prepared. Improved phase miscibility and decreasing extent of phase separation was observed in both types of IPNs with increasing the NCO/OH ratio, decreasing molecular weight of the polyol in the PU and introduction of charge groups. A comparison was made between full-IPNs, pseudo-IPNs, graft copolymers and related homopolymers from polyurethanes and epoxies. Increased compatibility in full-IPNs and graft copolymers was observed by means of DSC, SEM and was also further substantiated by a shift toward single T_gs as determined by dynamic mechanical spectroscopy. The introduction of opposite charge groups in two-component IPNs from polyurethanes and epoxies led to improved compatibility (no phase separation) and enhanced mechanical properties.     

Mechanical properties of blocked polyurethane/epoxy interpenetrating polymer networks

The mechanical properties of blocked polyurethane(PU)/epoxy interpenetrating polymer networks (IPNs) were studied by means of their static and damping properties. The studies of static mechanical properties of IPNs are based on tensile properties, flexural properties, hardness, and impact method. Results show that the tensile strength, flexural strength, tensile modulus, flexural modulus, and hardness of IPNs decreased with increase in blocked PU content. The impact strength of IPNs increased with increase in blocked PU content. It shows that the tensile strength, flexural strength, tensile modulus, and flexural modulus of IPNs increased with filler (CaCO₃) content to a maximum value at 5, 10, 20, and 25 phr, respectively, and then decreased. The higher the filler content, the greater the hardness of IPNs and the lower the notched Izod impact strength of IPNs. The glass transition temperatures (T_g) of IPNs were shifted inwardly compared with those of blocked PU and epoxy, which indicated that the blocked PU/epoxy IPNs showed excellent compatibility. Meanwhile, the T_g was shifted to a higher temperature with increasing filler (CaCO₃) content. The dynamic storage modulus (E′) of IPNs increased with increase in epoxy and filler content. The higher the blocked PU content, the greater the swelling ratio of IPNs and the lower the density of IPNs. The higher the filler (CaCO₃) content, the greater the density of IPNs, and the lower the swelling ratio of IPNs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1826–1832, 2006     

Recent advances in interpenetrating polymer networks

Interpenetrating polymer networks (IPN's) can be defined as a combination of two polymers in network form, at least one of which was synthesized and/or crosslinked in the immediate presence of the other. Historically, the science of IPN's began with the papers of J. R. Millar in 1960 on homo-IPN's made from polystyrene, but the first recorded publication is a patent by J. W. Aylsworth in 1914. This latter system was based on phenol-formaldehyde for one network, and sulfur cured natural rubber for the other network. Early academic laboratories interested in IPN's include the Frisch team at Detroit and SUNY, who soon added their former student, Danny Klempner, and Yuri Lipatov's team at the Ukranian SSR Academy of Sciences in the USSR, as well as the author's laboratory. More recent academic teams interested in IPN's include Douglas Hourston at the University of Lancaster, England; Robert Cohen at MIT; S. C. Kim at the Korea Advanced Institute of Science and Technology, Seoul, Korea; G. Meyer and J. M. Widmaier in Strasbourg, France; and many others. Numerous industrial laboratories are interested, noting that about 90 U.S. patients have been granted, most of them in the past ten years. Systems of special interest include the new thermoplastic IPN's, which are really hybrid materials between polymer blends and IPN's, and the IPN-based RIM (reaction injection molding) materials. Other materials include the sequential IPN's and the SIN's, which have both polymers simultaneously polymerized, and the latex IPN's, which often exhibit core-shell characteristics.     

Recent advances in interpenetrating polymer networks

We review the synthesis, morphology, and physical and mechanical properties of IFNs as well as the related pseudo-IPNs, in which only one of the polymers is crossliriked. Recent studies have shown that the degree of phase separation achieved in these materials is strongly dependent on the compatibility of blends of the linear polymer constituents of the IPN components as well as the kinetics of chain extension and the presence of grafting between component polymers. We illustrate this by a series of IPNs consisting of a polyurethane and an acrylic copolymer. The acrylic is a typical automotive enamel. An enhancement in properties results, which is dependent on the amount of grafting and the kinetics of polymerization. Also discussed are IPNs of a polyurethane and an epoxy, which exhibit a synergism in adhesive properties, and IPNs of a RIM polyurethane with several epoxies and unsaturated polyesters. In addition, also reported are the preliminary studies on the first successful preparation of a three-component IPN, consisting of a polyurethane, an epoxy, and an acrylic.     

Acronal-polymethyl acrylate interpenetrating polymer networks

Four interpenetrating polymer networks were prepared by swelling crosslinked Acronal (a copolymer of styrene and butyl acrylate) with methyl acrylate plus crosslinking agent and then polymerizing the methyl acrylate in situ. Certain properties of the constituent network materials, plus the interpenetrating polymer networks which contained 70, 50, 35 and 25% by weight of polymethyl acrylate, were investigated. Electron microscopy showed the interpenetrating polymer networks to be two-phase materials with the polymethyl acrylate domain size increasing with increasing polymethyl acrylate content. Longitudinal sonic velocity measurements indicate that at around 50% by weight of polymethyl acrylate both phases become continuous while dynamic mechanical spectroscopy leads to the view that the constituent networks were not extensively mixed.     

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。     

Dynamic mechanical properties of some polyurethane-acrylic copolymer interpenetrating polymer networks

Dynamic mechanical properties have been investigated for interpenetrating-network systems based on polyol-cured polyurethanes (PU) and 2 to 1 n-butyl acrylate-n-butyl methacrylate (Ac) networks. The systems were formed simultaneously (SIN) from all of the precursors and reactants for both networks in the same vessel, and sequentially (SIPN) by swelling a precured PU with the reactants that will form the Ac network. If the Ac network is formed after gelation of the PU, the IPNs are transparent and appear to have single T (tan δ_max) between those of the homonetworks; visible-phase separation occurs if the Ac is intentionally polymerized prior to PU gelation. Damping curves were lower and broader and the T (tan δ_max) and rubber moduli were higher for the SIN than for the SIPN systems. Up to 65 percent Ac, the T (tan δ_max) data for both SIN and SIPN fit the Gordon-Taylor equation if a T (tan δ_max) for the Ac homonetwork 7°C higher than observed is used, suggesting a higher crosslink density for the Ac network under these conditions. The differences in properties of the SIN and SIPN are assumed to be dependent on sample homogeneity and upon the presence of a tin catalyst in the SIN preparation. This can result in limited Ac-network formation and consequent phase separation before PU gelation has occurred, and the catalyst may also increase the extent of interaction, such as grafting or hydrogen-bond formation between the networks.     

Elastomeric domain-type interpenetrating polymer networks

Elastomeric latex interpenetrating polymer networks (IPNs) can result from a two-stage emulsion polymerization procedure in which styrene is polymerized and cross-linked on a lightly cross-linked polyacrylate (PA) seed latex in a ratio of 75 : 25 PA-PS. The multiphase nature of these IPNs is indicated by two distinct T_gs and is confirmed by cold-stage transmission electron microscopy and by the unique mechanical and rheological properties that are intimately related to the material's structure. PS microdomains reinforce the elastomeric PA, yielding a significant modulus, and interparticle PS physical ties yield a significant ultimate tensile strength. The elastomeric latex IPN's dual thermoset-thermoplastic nature is revealed in a stick, slip, roll flow mechanism of the cross-linked submicrometer particles, which can be injection molded as a thermoplastic. The relationships among the polymerization procedure, the structure, and the physical properties are characterized by the examination of several different materials using a variety of analytic techniques.     

Homogeneous epoxy-acrylic interpenetrating polymer networks: preparation and thermal properties

Summary The simultaneous interpenetration of two networks, one based on diglycidyl ether of bisphenol A crosslinked by an aliphatic diamine and the other one based on diglycidyl ether of bisphenol A dimethacrylate, leads to systems transparent to visible light. The measurement of glass transition temperature of these IPNs as a function of the composition and of the crosslinks density, gives relatively low and single values. This behavior is interpreted by the homogeneous structure of these systems.Presented at the 7th Discussion Conference IUPAC Polymer Networks, Karlovy Vary, CSSR, September 15–19, 1980     

Thermodynamic characterization of interpenetrating polymer networks

Crosslinked poly(methyl methacrylate) (PMMA-c), poly(carbonate-urethane) (PCU-c), poly(vinyl pyridine) (PVP-c), and full, simultaneous interpenetrating polymer networks (IPNs) based on the above polymers were characterized by precise heat capacity (C_p) measurements in the temperature interval 4.2–450 K. The raw values of C_p scaled with temperature (T) as C_p ∼ T^d with d = 2 and 5/3, as expected for a fracton-like vibration regime, in the temperature intervals 8–10 and 10–30 K, respectively. A single glass transition temperature (T_g) and two T_g's were observed for apparently homogeneous and microphase-separated IPNs, respectively. Judged by the positive sign of the excess Gibbs free energy, the apparently single-phase state of homogeneous IPNs is thermodynamically unstable; however, its kinetic stability is ensured by permanent topological constraints (network junctions) prohibiting the incipient phase separation.     

互穿聚合物网络研究进展

综述了互穿聚合物网络（ＩＰＮ）研究的进展，介绍了ＩＰＮ在体系，表征，应用等方面的新动向。     

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.     

Mechanical and viscoelastic properties of semi‐interpenetrating polymer networks of poly(vinyl chloride)/thermosetting resin blends

Semi‐interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepared by premixing porous, 150 μm diameter particles of PVC and a small quantity (from 5 to 15% by weight) of a single thermosetting liquid preresin from one of five types (e.g. methylene bis‐phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, and vinyl ester resins, respectively). Two roll milling of these mixtures was followed by hot‐press curing. Mechanical testing indicated that most of these blends exhibited increased tensile, impact, and flexural strengths. The strength increments were greater when going from 0 to 5% thermoset content than when going from 5 to 10% or 10 to 15% thermoset. In many cases, increasing thermoset content from 10 to 15% gave slightly decreased or unchanged tensile, impact, and flexural strengths. This behavior is in accord with a “thermoset dilution effect” in PVC. Most of these SIPN blends exhibited a tan δ peak temperature lower than that for pure PVC in the glass transition region. The tan δ peak temperatures were progressively lowered as the amounts of thermoset increased. Also, a single distinct peak existed in the E″ curves for most of the blends. Only the PVC/epoxy (90/10) blend showed two peak maxima in E″ vs. temperature curves. All blends exhibited peak E″ values at a lower temperature than those of PVC which had been exposed to the same processing temperatures. These observations seem to rule out the presence of large domains of PVC, which are phase‐separated from PVC/thermoset SIPN, and pure thermoset domains. A substantial amount of the added thermoset appears to exist in SIPN type phases in these five blend types.     

Barrier and surface properties of polyurethane-epoxy interpenetrating polymer networks. II

We have measured the advancing contact angles of drops of methanol-ethylene glycol mixtures on films of previously studied polyurethane-epoxy interpenetrating polymer networks. The extrapolated critical surface tensions were in excellent agreement with those obtained from advancing contact angles of drops of water-methanol mixtures. A sharp minimum is observed in the critical surface tension at network compositions where we have previously found maxima in ultimate mechanical properties. We advance a physical explanation based on unrelieved surface strains. We have also measured the toluene vapor transmission (permeability, diffusion and sorption coefficients) in these films. These results, together with the previously obtained water vapor permeabilities, are in complete accord with the expected morphologies of these networks.     

PU/BA-HEMA互穿网络型聚合物的合成及性能

以异佛尔酮二异氰酸酯（IPDI）、二羟甲基丙酸（DMPA）为硬段,聚醚多元醇（N220）为软段,以丙烯酸丁酯（BA）和甲基丙烯酸羟乙酯（HEMA）改性,制备了水性聚氨酯（PU）分散液,测定了水分散液及其膜的物理性能和力学性能。结果表明,与未改性的PU水分散液相比,改性聚氨酯水分散液的粒径均有所增大,表面张力减小,力学性能和硬度提高。HEMA 的引入,形成了具有化学交联的核-壳互穿网络结构的聚合物,说明改性材料中分子链硬段与PA分子链具有较高的相容性。     

EA/St-AN互穿聚合物网络的加工和力学性能

以丙烯酸乙酯为软单体 ,苯乙烯和丙烯腈为硬单体 ,二乙烯基苯或三乙二醇双丙烯酸酯为交联剂 ,采用多步种子乳液聚合技术制备了半互穿和全互穿聚合物网络 ,研究了软、硬单体配比 ,交联剂用量 ,加工次数对共聚物流变行为、力学性能和结构形态的影响。结果表明 ,制备的半互穿和全互穿聚合物网络均可在适宜的条件下流动成型。如果配方选择适当 ,反复加工后力学性能基本不变