Interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) composed of two or more chemically distinct networks are not only intrinsically interesting as examples of macromolecular chemical topological isomerism but are in practice useful means of controlling mutual miscibility and phase morphology in crosslinked polymers. We will first review briefly the synthesis and properties of such IPN systems. This will be followed by an outline of a phenomenological theory of the phase stability and linearised theory of spinodal decomposition of binary, chemically quenched, low crosslink density IPNs recently developed by K. Binder and the author. Finally, we will discuss some aspects of the synthesis of ternary IPNs and the thermochromic properties of IPNs containing a crosslinked polydiacetylene.     

Interpenetrating polymer networks of polyurethane and furfuryl alcohol. I. Morphology and mechanical properties

Polyurethane/furfuryl alcohol (PU/FA) interpenetrating polymer networks (IPNs) were synthesized from furfuryl alcohol using p-toluene sulfonic acid as a catalyst and blocked NCO-terminated PU prepolymer with m-xylylenediamine (MXDA) as a chain extender. From IR spectrum analysis it was found that the major reactions in the PU/MXDA/FA system are the polymerization of PU/MXDA and the self-polymerization of FA. The tensile strengths of PU/FA IPNs that contain 5 p.h.r. PU are greater than those of the pure components. The flexural strength, flexural modulus, Shore D hardness and HDT decrease and the notched Izod impact strength increases with the polyurethane content. The compatibility of the compounds in these PU/FA IPNs was investigated by dynamic mechanical analysis and scanning electron microscopy. It was found that glass transition temperatures are shifted inwardly which indicated that the PU/FA IPNs were semicompatible. It was confirmed from scanning electron micrography that the system was heterogeneous.     

Interpenetrating polymer networks of photocrosslinkable cellulose derivatives

A series of interpenetrating polymer networks has been prepared from two cellulose derivatives, one of which contains cinnamate groups and the other containing randomly substituted cinnamate and allyl groups. The latter derivative forms a crosslinked network in less than 5 min on exposure to ultraviolet radiation and can be used to make amorphous interpenetrating polymer networks containing 50% by weight loading level of crosslinked vinyl polymers. The syntheses of both derivatives and the thermal properties and film morphologies of their interpenetrating polymer networks are discussed. © 1996 John Wiley & Sons, Inc.     

Interpenetrating polymer networks. II. Sunlight-induced polymerization of multifunctional acrylates

Protective coatings and glass laminates have been readily obtained by sunlight-curing of acrylate monomers dispersed in a poly(methyl methacrylate) matrix or in a styrene–butadiene rubber, in the presence of an acylphosphine oxide photoinitiator. The polymerization reaction was followed by infrared spectroscopy and by gel fraction measurements and was shown to proceed extensively within minutes. As expected, the inhibitory effect of atmospheric O₂ on such radical-initiated reactions was less pronounced in solid than in liquid samples. The monomer, photoinitiator, and plasticizer concentrations were found to have a strong influence on the rate of polymerization, the final degree of conversion, and the hardness of the sun-cured polymer. The adhesion of the cured coating on glass was substantially improved by the addition of an acrylate-grafted organosol silica. To produce strongly adhesive glass laminates, a photocurable acrylate resin was poured between two coated glass plates and exposed to sunlight for a few seconds. The same formulation can serve as a light-sensitive quick setting glue to bond glass to a variety of materials [polycarbonates, poly(vinyl chloride), aluminium, and steel]. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2269–2282, 1998     

Interpenetrating polymer networks of bismaleimide and polyurethane-crosslinked epoxy

This study prepared an interpenetrating polymer network of bismaleimide and polybutylene adipate-based polyurethane-crosslinked epoxy (BMI/PU-EP IPN) using the simultaneous bulk polymerization technique. Infrared spectra analysis was also performed to identify the polyurethane-crosslinked epoxy (PU-EP). Also investigated herein were the mechanical properties including tensile strength, fracture energy, and Izod impact strength of various bismaleimide content in PU-EP matrix. In addition, differential scanning calorimetry and thermogravimetric analyses of the BMI/PU-EP IPN were conducted as well. Analyses results demonstrate that the bismaleimide was dissolved primarily in the polyurethane domains of the epoxy matrix to form a compatible system, thereby increasing the mechanical strength of the BMI/PU-EP IPNs. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 529–536, 1998     

Interpenetrating polymer networks of polyurethane and polystyrene ionomers

Interpenetrating polymer networks (IPNs) and linear blends of polyurethane (PUN) and poly(styrene–acrylic acid) (PSAA), which contain mutually opposite charge groups, i.e., tertiary amine and carboxyl groups, respectively, were synthesized through simultaneous bulk polymerization. Physical and mechanical properties of these IPNs and linear blends are discussed in the present paper. The tensile strength of both PUN/PSAA IPNs and linear blends has shown to increase with an increase of acrylic acid (AA) content in PSAA in any PUN/PSAA composition. A maximum value emerged in both polymer systems with 30 mol % AA in PSAA and the PUN/PSAA ratio of 25/75. A minimum swelling ratio as well as a maximum density was also observed in the IPNs and linear blends, respectively, related to this PUN/PSAA ratio. From dynamic mechanical analysis, two distinct relaxation transitions for the IPN or linear blend without AA in the system have merged into a single broad transition as the AA was introduced into PSAA. Two-Phase morphology was observed from scanning electron microscopy studies for the polymer systems in the absence of charge groups; however, one-phase morphology was observed when the charge groups were introduced.     

Interpenetrating polymer network from blocked isocyanates. I. Structure and properties of polyurethane-urea polyvinyl simultaneous interpenetrating networks

A series of polyurethane-urea/polyvinyl simultaneous interpenetrating polymer networks (SINs) were prepared starting from a mixture of isocyanate prepolymer blocked with N-(1-1′-dimethyl-3-cxobutyl) acrylamide oxime, chain extender, vinyl monomers, and catalysts. Their physical properties and morphology were investigated using differential scanning calorimetry, dynamic mechanical measurements, and small-angle X-ray scattering. The polyurethane-urea networks examined were two-phase in nature. The vinyl network was formed with diacetone acrylamide oxime, trimethylolpropane trimethacrylate, and N-vinyl-pyrrolidone. Calorimetric analyses revealed that the polyether soft segment phase separated within the SINs. At higher temperature, dynamic mechanical measurements demonstrated the presence of only one glass transition temperature (T_g) intermediate in temperature to the T_g of the vinyl network and the T_g of the urethane hard phase. This is indicative of chain entanglement (interpenetration) between the vinyl network and the polyurethane hard segments resulting in a two-phase morphology. Small-angle X-ray scattering analyses provided measurements of diffuse phase boundary thickness, phase mixing, and domain size distribution. Appreciable interfacial thickness was not observed and thus phase mixing occurred within the phases. Domain size distribution indicated that high network constraints hindered the development of domains and limited the phase segregation.     

Interpenetrating polymer networks with controllable intermolecular hydrogen bonding

Summary The effect of introducing simultaneously crosslinking and intermolecular hydrogen bonding into blends of poly(styrene) and poly(butyl acrylate) on miscibility was studied by DSC, TEM and IR. Incorporation of strong proton-donor groups into PS apparently promotes its miscibility with PBA due to hydrogen bonding. Single phase IPN can be prepared but much higher content of the proton-donor is needed in comparison with the corresponding blend without crosslinking. The interlocking structure of the networks appears unfavourable to forming real miscible IPNs.     

Interpenetrating polymer networks derived from epoxide-amine adducts in either polymer network

A new type of interpenetrating polymer network was synthesized via photoinitiated free-radical polymerization of α,ω-methacryloyl terminated macromonomers prepared from epoxide-amine-adducts, followed by thermal addition polymerization of bisphenol-A diglycidyl ether and 4,4′-diaminodiphenylsulfone or 3(4),8(9)-bis(aminomethyl)tricyclo[5.2.1.0.^2,6]decane. The interpenetrating polymer networks are optically transparent and show only one glass transition temperature ranging from -10 to 130°C, as a function of the macromonomer/addition polymer mixing ratio. The presence of a single phase was confirmed by scanning electron microscopy (SEM).     

Interpenetrating polymer networks from castor oil and dibasic acids

Prepolyesters were obtained from castor oil and dibasic acids, viz oxalic, malonic, succinic, glutaric, adipic, suberic and sebacic acid. These prepolyesters (PPE) were subsequently interpenetrated with methyl methacrylate containing 1% ethylene glycol dimethacrylate as crosslinker by radical polymerization initiated with benzoyl peroxide. The novel PPE poly(methyl methacrylate) PPE/PMMA interpenetrating polymer networks (IPNs) were obtained as powder. They were characterized by solubility behaviour, IR spectral study and thermal behaviour.     

Interpenetrating polymer networks based on polyurethane and organic-inorganic copolymer

The investigation of the features of the formation of interpenetrating polymer networks (IPNs) based on cross-linked polyurethane and organic-inorganic copolymer (OIC) based on hydroxyethyl methacrylate (HEMA) and titanium isopropoxide (Ti(OPrⁱ)₄) was carried out using the IR spectroscopy method. It has been demonstrated that during the synthesis of organic-inorganic IPNs (OI IPNs), three-dimensional cross-linked structures with the inclusion of (-TiO₂-) fragments in the polymer chain of poly(hydroxyethyl methacrylate) are formed. The examinations of the viscoelastic properties and thermal stability of organic-inorganic IPNs by dynamic mechanical (DMA) and thermogravimetric analysis (TGA) showed that the value of M _c decreases with an increase in the content of (-TiO₂-) fragments in OI IPN; in addition, the thermal stability of the obtained hybrid OI IPNs increases significantly compared to the parent systems.     

Interpenetrating polymer networks: A review on synthesis and properties

A review containing 83 references on the chemistry aspects (mechanism and structure–property relationships) for IPN synthesis is presented.     

Interpenetrating polymer networks based on poly(acrylic acid) and gelatin. I: Swelling and thermal behavior

This article describes the synthesis of full and semi-interpenetrating polymer networks (IPNs) based on poly(acrylic acid) and gelatin as polymers 1 and 2, which were crosslinked sequentially using N,N′-methylene bisacrylamide (B_Am) and glutaraldehyde, respectively. Various samples were prepared by taking varying amounts of acrylic acid and gelatin in the initial feed. Sequential IPNs were prepared by first polymerizing and crosslinking acrylic acid in the presence of gelatin using redox initiators (ammonium persulphate and sodium metabisulphite) and B_Am as a crosslinking agent. Gelatin present in the firm gels was then crosslinked using 4% glutaraldehyde. Characterization of these gels was done by measuring their swelling behavior as a function of pH, temperature, and time. Percent swelling increased with increasing amounts of acrylic acid. The swelling ratio was also determined in the pH range of 1 to 12. Acid/alkali or buffers were used for maintaining pH. A significant increase in the percent swelling was observed when pH of distilled water was above 10. On the other hand, in the case of buffer, the swelling ratio increased with increasing the pH, and a maxima was observed at pH 8.4. A further increase in pH resulted in a decrease in the swelling ratio. Thermal and morphological characterization was done using thermogravimetric analyzer and scanning electron microscopy, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 217–227, 2001     

Interpenetrating polymer networks from castor oil based polyurethanes,XI

Under different experimental conditions, various liquid polyurethanes (PU) were synthesized from castor oil and isophorone diisocyanate varying NCO/OH ratio. These polyurethanes were then subsequently interpenetrated with n-butyl acrylate (nBA) monomer and ethylene glycol di-methacrylate as crosslinker by radical polymerization using benzoyl peroxide as an initiator. This leads to the formation of novel PU/PnBA interpenetrating polymer networks (IPNs) by transfer molding. These IPNs were characterized by their resistance to chemical reagents, thermal behavior (TGA), mechanical properties, namely; tensile strength, Young's modulus, elongation at break (%) and hardness (Shore A). The morphology of the IPNs was studied by Scanning Electron Microscopy. The dielectric behavior was computed in terms of electrical conductivities, dielectric constant (ε′), loss tangent (tan δ) and dielectric loss (ε″).     

Interpenetrating polymer networks based on nitrile rubber and metal methacrylates

Interpenetrating polymer networks (IPNs) based on nitrile rubber (NBR) as first component and zinc dimethacrylate (ZnDMA), aluminum trimethacrylate (AlTMA), or zirconium tetramethacrylates (ZrTeMA) as second component were synthesized. Sequential IPNs (SeqIPN) were formed by two routes such as compression molding (CM) and swelling/curing (SC). The IPNs were found to have superior properties compared to metal oxide/hydroxide‐filled NBR. Tensile strength has increased to a large extent while maintaining appreciable elongation. Total crosslink density (covalent and ionic) was found to increase in the order NBR/metal oxide or hydroxide < SeqIPN(CM route) < SeqIPN (SC route). IPNs are found to retain high storage modulus even in the rubbery region. It is observed that change of technique for IPN formation has drastically changed the modulus of the present system. Decrease in tan δ value and inward shifting of peaks were observed because of IPN formation. Morphology of SeqIPN by SC process was found to be more uniform compared to others. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2542–2548, 2006     

Interpenetrating polymer networks derived from silylated soybean oil and polydimethylsiloxane

A series of interpenetrating polymer networks (IPNs) was prepared using various concentrations of silylated soybean oil and polydimethylsiloxane (PDMS) that were cross linked with inorganic silicates. This series of IPNs was prepared from emulsions of silylated soybean oil and PDMS together with colloidal silica and dioctyltin dilaurate catalyst at pH 10. Under these conditions, water soluble silicates reacted with silanols in the oil phase and formed intraparticle siloxane cross links. Upon casting films and evaporation of the water, additional interparticle cross linking were obtained between the coagulating particles to produce entangled networks of soybean oil and PDMS that were further reinforced by fine silica particles. The morphology revealed intimate mixing of the two immiscible components. The mechanical properties depended on the ratio of the soft, flexible PDMS phase and the rigid, brittle cross linked silylated soybean oil phase. These IPNs can be used as high release liners, low friction materials, or as a general protective coating. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2479–2486, 2013     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Interpenetrating polymer networks of polyurethanes and epoxy resin,II. Compatibility and morphology

The interpenetrating polymer networks (IPN) of polyurethanes (PU) and a glycidyl ether of phenol formaldehyde (GEPF) were prepared by a simultaneous polymerization method. The dynamic mechanical properties and morphologies of the IPNs were investigated. It was found that multiphased morphology was formed in the PU/GEPF IPNs. With the PU based on polyester- or polyether-type polyols, the dynamic mechanical analysis (DMA) of these IPNs exhibited various shifts in the loss moduli (E″) of the high and low temperature transition domains depending upon the types and molecular weights of the polyols employed in the PU. Three distinct transition domains were observed as the PU content increased up to a certain level.     

Interpenetrating polymer networks with controllable intermolecular hydrogen bonding: Swelling behavior

Summary The swelling behavior in different solvents of IPNs based on poly(butyl acrylate) and modified polystyrene containing strong proton-donor hydroxyl groups is studied. The experimental data of the volume fractions of the networks in the swollen state V_expt at equilibrium are compared with those expected from the Thiele-Cohen equation (V_TC), which assumes that the two networks are independent and no additional crosslinks form during the formation of the IPNs. For the IPNs without inter-component hydrogen bonding, V_expt in toluene are in good agreement with V_TC. As the hydroxyl content increases, the deviation of V_expt from V_TC increases indicating more crosslinks form in the process of IPN formation. This deviation in the solvents of proton-acceptor type becomes smaller but still apparent. This result implies that hydrogen bonding between the components is destroyed by the solvents but the physical entanglements formed during the formation of the IPNs remain.     

Interpenetrating polymer networks from castor oil-based polyurethanes and polystyrene,XXV

Interpenetrating polymer networks (IPNs) of castor oil-based polyurethanes and polystyrene were prepared by simultaneous polymerization. The liquid prepolyurethanes were formed by reacting the hydroxyl functionality of castor oil with isophorone diisocyanate using different stoichiometric NCO/OH ratios. These prepolyurethanes were mixed with styrene monomer and subsequently polymerized by free radical polymerization initiated by benzoyl peroxide in the presence of the crosslinker 1,4-divinyl benzene. The interpenetrating polymer networks. PU/PS IPNs, were obtained as tough and transparent films by the transfer moulding technique. These IPNs were characterized by the static mechanical properties (tensile strength, Young's modulus and % elongation), thermal properties and morphology. The dielectric relaxation properties (σ, E′, E″ and tanδ) of the IPNs at different temperatures were studied.