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.     

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.     

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.     

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.     

Polybutadiene/polystyrene interpenetrating polymer networks

Interpenetrating polymer networks (IPN's) of polybutadiene (PB) and polystyrene (PS) were prepared using both random (containing 36% cis, 55% trans, and 9% 1,2 vinyl) PB and high-cis PB. For both series, a wide range of PB/PS compositions were synthesized. Using samples stained with osmium tetroxide, electron microscope studies revealed an irregular cellular structure of a few hundred Ångstrom diameter with the first component, PB, making up the cell walls. The size of the cells was found to depend on the PB crosslink density for the random materials. Modulus-temperature data revealed two distinct glass transitions, confirming the microscopy finding of two phases. However, the transition temperature and transition slope varied with composition, and with the microstructure of the polybutadiene, giving evidence of significant molecular mixing. Stress-strain data on the IPN's showed that materials rich in PB behave like self-reinforced elastomers. Charpy impact resistance experiments on materials rich in PS indicated values of 5 ft-lb/in. of notch, which compares well with graft-type polyblends of similar PB/PS composition. The results were interpreted in the light of the recent theoretical work of Bragaw, who considered the importance of the distances between domain boundaries with respect to crack acceleration mechanics. Although the IPN's considered herein exhibited somewhat less than the predicted optimum phase dimensions, the arrangement of the domains is different from ordinary impact resistant plastics.     

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.     

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。     

Polyurethane—polystyrene interpenetrating polymer networks

Two component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester-polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass-transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress-strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.     

Two and three component interpenetrating polymer networks

Two and three component interpenetrating polymer networks (IPNs) have been prepared from polyurethanes, epoxy resins, and acrylic copolymers using the simultaneous technique (SIN). These materials exhibited a variety of morphologies and properties dependent on the types of polymer, molecular weight of precursors, presence of charge groups, and presence of intentional grafts between the component polymer networks. In general, decreasing molecular weight of prepolymers, presence of intentional grafts, and presence of charge groups of opposite charge resulted in increased homogeneity (interpenetration). In addition, increased homogeneity resulted in enhanced mechanical properties.     

Structure-Property-Processing relationships of polyurethane-polyester interpenetrating polymer networks

Interpenetrating polymer networks of polyurethane and unsaturated polyester were prepared by reaction injection molding (RIM) and transfer molding. The structures of the molded samples were analyzed by electron microscopy and dynamic mechanical analysis. It was found that polymer morphology and dynamic mechanical properties depend strongly on the molding temperature, reaction rate and reaction sequence. Simplified structure models based on Takayanagi's model and sample morphology can predict the storage modulus reasonably well but not the tanδ.     

Thermodynamic state of reinforced interpenetrating polymer networks

The free energies of mixing of two networks in the interpenetrating polymer network based on crosslinked polyurethane and poly(ester acrylate) have been determined by the vapour sorption method. It was established that the constituent networks in the IPN are not miscible. The introduction of fillers of different chemical nature increases the compatibility. The thermodynamic affinity of the fillers to the individual networks and IPN was estimated. It was established that when the free energy of interaction of one or both components of the IPN with the filler is negative, reinforcement leads to the formation of a compatible and equilibrium system. For fillers having no affinity to the polymers, compatibilization is observed, which is connected with slowing down of phase separation in the system in the presence of filler.     

Polyisobutene/polycyclohexyl methacrylate interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) combining polyisobutene (PIB) and poly(cyclohexyl methacrylate) (PCHMA) networks were prepared using an in situ strategy. PIB networks were formed by alcohol-isocyanate addition between the hydroxyl end groups of telechelic dihydroxypolyisobutene and an isocyanate cross-linker, catalyzed by dibutyltindilaurate (DBTDL). PCHMA networks were obtained from free-radical copolymerization of cyclohexyl methacrylate (CHMA) with ethylene glycol bismethacrylate (EGDM) in the presence of dicyclohexyl peroxydicarbonate (DCPD) as the initiator. The network formations into the IPN architecture were followed by FTIR spectroscopy. In a large composition range, transparent IPNs exhibit two mechanical relaxation temperatures as determined by dynamic mechanical thermal analysis (DMTA), corresponding to those of a PIB enriched phase and of one interpenetrating phase containing the PCHMA network. This morphology was confirmed by IPN surface analysis by AFM. As expected, mechanical properties of PIB networks are improved by the presence of PCHMA network in such IPN architectures.     

Naturally functionalized triglyceride oils in interpenetrating polymer networks

The use of naturally functionalized triglyceride oils in interpenetrating polymer networks (IPNs) is reviewed. An oil bearing either hydroxyl or epoxide functionality may be crosslinked to form a soft elastomer in the presence of another monomer or network to form an IPN, or in the presence of a linear polymer, to form a semi-IPN. Polymerization and characterization of naturally functionalized triglyceride oils are mentioned, with emphasis on the distribution and effect of nontrifunctional triglycerides on elastomer properties. The simultaneous synthesis of polystyrene/functional triglyceride oil IPNs is reviewed, and several factors influencing IPN morphology and mechanical properties are discussed. The synthesis and properties of poly(ethylene terephthalate)/functional triglyceride oil semi-IPNs are emphasized, with the importance of ester interchange in the synthetic procedure, and factors influencing crystallinity and morphology are introduced.     

Castor-oil-based interpenetrating polymer networks: Synthesis and characterization

Castor oil was polymerized and crosslinked with sulfur or diisocyanates to form the vulcanized and urethane derivatives, respectively. Both types were swollen with a plastic-forming monomer plus crosslinker, and a second polymerization was carried out in situ. Polyblends were also made by emulsion polymerization of styrene and methyl methacrylate employing hydrolyzed castor oil as the soap. In all three polymerizations, a wide range of compositions was obtained. The resulting interpenetrating polymer networks were characterized using electron microscopy, modulus–temperature measurements, and stress–strain analysis. The polystyrene phase size of the castor oil–urethane/polystyrene IPN was shown to decrease with increased crosslinking of the castor oil component and with increased polystyrene contents. The modulus–temperature study showed two distinct glass transitions in all cases, with evidence of significant mixing of the two components in many cases. The stress–strain results show that some of the IPN's behave as reinforced, highly extensible elastomers at low polystyrene levels, and a rubber-toughened plastics at high levels of polystyrene or crosslinking.     

互穿聚合物网络的研究与应用进展

简要介绍了互穿聚合物网络(IPN)的基本结构、制备以及在树脂改性、胶粘剂、阻尼材料、多孔材料和医药等领域中的应用情况。由于IPN可以兼具多种聚合物的优点,并且其制备简单、设备要求较低,故其应用范围越来越广泛,应用前景也越来越好。     

Epoxy/castor oil graft interpenetrating polymer networks

Full-interpenetrating polymer networks (IPNs) were prepared from epoxy and castor oil-based polyurethane (PU), by the sequential mode of synthesis and were characterized by different techniques: swelling test, scanning electron microscopy (SEM), thermomechanical analysis (TMA), thermogravimetric analysis (TGA), tensile test, and instrumented impact test. 2,4-Toluene diisocyanate (TDI) was used as a curing agent for castor oil, at a NO/OH ratio = 1.50. Diglycidyl ether of bisphenol A (DGEBA) was cured and crosslinked using 2,4,6-tris(dimethylaminomethyl)phenol (TDMP) at 1.5%, by weight, of epoxy resin. The homogeneous morphology of IPN samples of PU compositions up to 40%, by weight, revealed by SEM may be attributed to some extent to grafting of the PU phase onto the epoxy matrix, which results from the reaction between NCO groups in the PU phase with OH groups in the epoxy matrix. This has some synergistic effect on the thermal resistance and tensile properties of IPNs compared to those of the pure components, such as illustrated by the data from TGA and tensile tests. However, the grafting structure appears not to enhance their impact resistance, which probably requires the formation of rubbery particles of suitable size. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1649–1659, 1998     

Kinetic study of photoinduced quasi-simultaneous interpenetrating polymer networks

Interpenetrating Polymer Networks (IPNs) based on a dimethacrylate and an epoxide are synthesized by photopolymerization. By varying the relative amount of radical photoinitiator with respect to the cationic one, and by changing the exposure conditions, it was found possible to delay or accelerate the photopolymerization of the methacrylate monomer compared to the epoxide one. The effect of the relative rate of photopolymerization on the final conversion, glass transition, and morphology is discussed. Finally, the increase in shear modulus as a function of irradiation time was investigated by real time ultrasonic reflectometry. An increase in the mechanical properties after the exposure was evidenced as a consequence of the living character of the cationic polymerization.     

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.