Interpenetrated Network Research Articles

Hydrogen-bond-directing effect in the ionothermal synthesis of metal coordination polymers

Four new cobalt coordination polymers, (EMIm)[Co2(TMA-H)2(44bpy)3]Br 1, (EMIm)[Co(TMA-H)(44bpy)2](44bpy)Br 2, (EMIm)[Co(TMA)(Im-H)]3 and (EMIm)2[Co(TMA)2(TED-H2)] 4, were prepared from 1-ethyl-3-methyl imidazolium bromide (EMIm-Br). All the compounds have similar two-dimensional cobalt trimesate (TMA) coordination layers but different three-dimensional supramolecular architectures that contain one of three potentially ditopic amines, 4,4'-bipyridine (44bpy), imidazole (Im-H) and triethylenediamine (TED). Two-fold interpenetration of hydrogen-bonding networks was found for 1, 2 and 4. The coordination layers of 1 and 2 are neutral while 3 and 4 have anionic molecular assemblies. The use of organic amines, that act as supramolecular bridging ligands, introduces hydrogen-bond-directing effects in the ionothermal synthesis of metal coordination polymers. Hydrogen bonding helps to align the packing between the coordination layers and control the formation of 3D supramolecular networks. In 1, hydrogen bonds between the ionic species within the channels direct the alignment of non-directional electrostatic interactions between EMIm+ and Br(-) ions, which is a rare case of a hydrogen-bond-templating effect of ionic liquids in ionothermal synthesis.

Properties and Aggregate Structure of Unsaturated Polyester/Phenolic Resin Blends

In this study, unsaturated polyester resin (UP) is blended with resole type phenolic resin, co-crosslinking process performed and the resin blends show miscibility and interpenetration network (IPN) structure. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are employed to examine the aggregate structure of crosslinked network of the UP/phenolic resin blend. Tensile fractured sections of the resin blends are observed using scanning electronic microscopy (SEM) to shed light on their miscibility. Tensile and flexural tests were also conducted to examine the mechanical properties of the UP/phenolic resin blends. The results show that UP20/Ph80 and UP40/Ph60 resin blends have well-formed Interpenetrating Network (IPN) structures while phase separation is observed for UP60/Ph40 resin blend. Finally, thermal cure of UP80/Ph20 resin blend is incomplete, thus showing immiscibility. The mechanical properties of all resin blends at different mixing proportions deviate from a linear relationship and show a concave curve, indicating the non-additive effect of blending.

Photocurable silica hybrid organic–inorganic films for photonic applications

We report the preparation of hybrid organic–inorganic films deposited by dip-coating from a base-catalyzed sol containing tetraethoxysilane and 3-methacryloxypropyltrimethoxysilane as the silicon source, and ethyl-2,4,6-trimethylbenzoylphenylphosphinate as the photoinitiator. The films were cured with a UV lamp, obtaining a change in refractive index upon UV irradiation through the formation of an interpenetrated silica-methacrylate network. The refractive index increased of Δn = 14 × 10−3 after UV treatment. The synthesis is simple and reproducible and yields films with optical quality which can be useful as materials for applications in optics and information storage.

Highly Interpenetrated Supramolecular Networks Supported by N⋅⋅⋅I Halogen Bonding

Halogen bonding (XB) has been used to assemble tetrakis(4-pyridyl)pentaerythritol (tetradentate XB acceptor) with different alpha,omega-diiodoperfluoroalkanes (bidentate XB donors) or tetrakis(4-iodotetrafluorophenyl)pentaerythritol (tetradentate XB donor). The remarkable linearity of the XB formed, the rodlike character of alpha,omega-diiodoperfluoroalkanes and the mutual complementarities of pentaerythritol partners, translate the three-dimensional character of the XB acceptor into open primary networks, which interpenetrate to avoid the presence of voids and to ensure segregation of the modules. Two-dimensional (2D) square 4(4) layers (sql) with fourfold and fivefold interpenetration, as well as an eightfold diamondoid network (dia) of class Ia and a remarkable tenfold dia network of class IIIa, have been obtained.

Different aliphatic dicarboxylates affected assemble of new coordination polymers constructed from flexible–rigid mixed ligands

In this article, seven coordination polymers: [Cd(C 5H 6O 4)(C 10H 8N 2)] n ( 1), [Zn(C 5H 6O 4)(C 10H 8N 2)] n ( 2), [Cd(C 6H 8O 4)(C 10H 8N 2)] n ( 3), {[Mn(C 10H 8N 2)(H 2O) 4] (C 4H 4O 4)·4H 2O} n ( 4), [Mn 5(C 4H 4O 4) 4(O)] n ( 5), [Cd(C 4H 4O 4)(C 10H 8N 2)(H 2O)] n ( 6) and [Zn(C 6H 6O 4)(C 12H 8N 2)(H 2O)] n ( 7) were synthesized and characterized by single-crystallographic X-ray diffraction. Compounds 1 and 2 are two-dimensional layers connected by glutarate anions and 4,4′-bpy. Unlike compounds 1 and 2, compound 3 is a two-fold interpenetration network. Compound 4 is a one-dimensional chain-like structure, which is further extended to two-dimensional supramolecular layer structure with hydrogen bond. During the synthesis of compound 4, to our surprise, we got compound 5; compound 5 is an interesting three-dimensional network composed of pentanuclear Mn(II) building units and succinate anions. Compound 6 is also a two-dimensional supramolecular layer structure composed of one-dimensional chain-like structure with hydrogen bonds and Π–Π interactions. Compound 7 is also a one-dimensional chain-like structure, which is further connected with the same kind of interaction to generate two-dimensional supramolecular layer structure. Furthermore, compounds 1 and 2 both exhibit fluorescent property at room temperature.

Removal of Cd(II), Hg(II), and Pb(II) ions from aqueous solution using p(HEMA/chitosan) membranes

AbstractAn interpenetration network (IPN) was synthesized from 2‐hydroxyethyl methacrylate (HEMA) and chitosan, p(HEMA/chitosan) via UV‐initiated photo‐polymerization. The selectivity to different heavy metal ions viz Cd(II), Pb(II), and Hg(II) to the IPN membrane has been investigated from aqueous solution using bare pHEMA membrane as a control system. Removal efficiency of metal ions from aqueous solution using the IPN membranes increased with increasing chitosan content and initial metal ions concentrations, and the equilibrium time was reached within 60 min. Adsorption of all the tested heavy metal ions on the IPN membranes was found to be pH dependent and maximum adsorption was obtained at pH 5.0. The maximum adsorption capacities of the IPN membrane for Cd(II), Pb(II), and Hg(II) were 0.063, 0.179, and 0.197 mmol/g membrane, respectively. The adsorption of the Cd(II), Hg(II), and Pb(II) metal ions on the bare pHEMA membrane was not significant. When the heavy metal ions were in competition, the amounts of adsorbed metal ions were found to be 0.035 mmol/g for Cd(II), 0.074 mmol/g for Hg(II), and 0.153 mmol/g for Pb(II), the IPN membrane is significantly selective for Pb(II) ions. The stability constants of IPN membrane–metal ions complexes were calculated by the method of Ruzic. The results obtained from the kinetics and isotherm studies showed that the experimental data for the removal of heavy metal ions were well described with the second‐order kinetic equations and the Langmuir isotherm model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Construction of a Three-fold Parallel Interpenetration Network and Bilayer Structure Based on Copper(II) and Trimesic Acid

Solvothermal reactions of Cu(NO3)2·3H2O with trimesic acid (H3BTC) at different pH conditions yield two coordination polymers of [Cu3(BTC)2(H2O)3(NH3)4]n·2nH2O (1) and [Cu4(BTC)2(OH)2(H2O)2(NH3)4]n (2). Crystal structural analysis reveals that complex 1 exhibits a three-fold parallel interpenetration network and complex 2 shows a two-dimensional bilayer structure. Crystal data are orthorhombic, space group Pbcn, a = 11.242(3) A, b = 16.963(4) A, c = 13.898(4) A, Z = 4 for 1 and monoclinic, space group C2/c, a = 18.887(4) A, b = 10.761(2) A, c = 14.488(3) A, β = 126.100(3)°, Z = 4 for 2.

The Inconsistency in Adsorption Properties and Powder XRD Data of MOF-5 Is Rationalized by Framework Interpenetration and the Presence of Organic and Inorganic Species in the Nanocavities

MOF-5 is the archetype metal-organic framework and has been subjected to numerous studies the past few years. The focal point of this report is the pitfalls related to the MOF-5 phase identification based on powder XRD data. A broad set of conditions and procedures have been reported for MOF-5 synthesis. These variations have led to materials with substantially different adsorption properties (specific surface areas in the range 700 to 3400 m(2)/g). The relatively low weight loss observed for some as synthesized samples upon solvent removal is also indicative of a low pore volume. Regrettably, these materials have all been described as MOF-5 without any further comments. Furthermore, the reported powder XRD patterns hint at structural differences: The variations in surface area are accompanied by peak splitting phenomena and rather pronounced changes in the relative peak intensities in the powder XRD patterns. In this work, we use single-crystal XRD to investigate structural differences between low and high surface area MOF-5. The low surface area MOF-5 sample had two different classes of crystals. For the dominant phase, Zn(OH)2 species partly occupied the cavities. The presence of Zn species makes the hosting cavity and possibly also adjacent cavities inaccessible and thus efficiently reduces the pore volume of the material. Furthermore, the minor phase consisted of doubly interpenetrated MOF-5 networks, which lowers the adsorption capacity. The presence of Zn species and lattice interpenetration changes the symmetry from cubic to trigonal and explains the peak splitting observed in the powder XRD patterns. Pore-filling effects from the Zn species (and partly the solvent molecules) are also responsible for the pronounced variations in powder XRD peak intensities. This latter conclusion is particularly useful for predicting the adsorption properties of a MOF-5-type material from powder XRD.

Synthesis and Micromechanical Properties of Flexible, Self-Supporting Polymer−SiO2 Nanofilms

Large-scale, self-supporting ultrathin films composed of an elastomeric polyacrylate network interpenetrated by a silica (SiO2) network were synthesized and characterized. The organic network was first photopolymerized and the silica structure was subsequently developed in situ in the preformed organic gel. Composition and morphology of the hybrid interpenetrated network (IPN) nanofilms were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy and compared with the case of zirconia (ZrO2) hybrid IPN reported earlier. Young modulus, ultimate tensile strength, and ultimate tensile elongation were determined for different organic/inorganic molar ratios and give some insights on how the composition of the nanofilms influence their robustness and self-supporting properties.

Molecular Cage, One‐Dimensional Tube and Two‐Dimensional Polycatenane obtained from Reactions of Flexible Tripodal Ligand 1,3,5‐Tris(imidazol‐1‐ylmethyl)‐2,4,6‐trimethylbenzene with Copper Salts

AbstractThree novel copper complexes, [CuII(titmb)(N3)2]·0.5H2O (1), [CuI3(titmb)2](ClO4)3 (2), and [CuII(titmb)(SO4)]·2.2H2O (3), were obtained by reactions of flexible tripodal ligand 1,3,5‐tris(imidazol‐1‐ylmethyl)‐2,4,6‐trimethylbenzene (titmb) with the corresponding copper(II) salts using hydrothermal method and their structures were determined by X‐ray crystallography. Complex 1 exhibits a one‐dimensional (1D) tube‐like chain structure, while the 2 possesses a M3L2 molecular cage‐like structure, in which the copper atom has a valence of +1, indicating that the CuII is reduced to CuI under the hydrothermal condition. Complex 3 has a polycatenated network structure with inclined interpenetration of (6,3) networks. Ligand titmb adopts a cis,cis,cis‐conformation in all of the three complexes. The results indicate that the anions play important roles in the structure of the complexes. In addition, complex 2 was further investigated by electrospray massspectrometry.

Interplay of Hydrogen Bonds in Assembling (4,4)-Coordination Networks: Transformations from Open to Interpenetrated Networks via Anion Exchange

Open (4,4)-coordination networks were shown to assemble via N-H···O hydrogen bonds in two different ways: the usual offset packing via /?-sheet hydrogen bonds and an unprecedented trigonal packing. Both of the structures have continuous channels that are occupied by guest molecules (nitrobenzene or EtOH and H 2 O) which account for 37% or 28% of the crystal volume. Interestingly, these complexes have shown an ability to exchange ClO 4 - with PF 6 - ions and transform into the doubly interpenetrated varieties.

Weak Interactions in the Crystal Structures of Tetraacetylenes Derived from Pentaerythrityl Tetraphenyl Ether

Tetrakis(4-ethynylphenyl)methane (7) is known to crystallize as an interpenetrated diamondoid network held together in part by weak C⋮CH···C⋮C interactions that define characteristic cyclic quartets of ethynyl groups. To test the ability of this motif to direct the crystallization of more flexible molecules, we synthesized a series of tetraacetylenes derived from pentaerythrityl tetraphenyl ether, and we solved their structures by X-ray diffraction. Pentaerythrityl tetrakis(4-ethynylphenyl) ether (4) and the more rigid analogue 7 crystallize isostructurally, even though their cores are significantly different in size and flexibility. This observation shows that C⋮CH···C⋮C interactions may have value in engineering molecular crystals. However, widely different structures are obtained by crystallizing pentaerythrityl tetrakis(3-ethynylphenyl) ether (5) and pentaerythrityl tetrakis(4‘-ethynyl-1,1‘-biphenyl-4-yl) ether (6), despite their close similarity to tetraacetylene 4. The unpredictably varied behavior ...

Monomers, chains, ladders, and two-dimensional sheets: Structural diversity in six new compounds of Zn(II) with 4,4′-bipyridine

Six new zinc(II)–4,4′-bipyridine coordination polymers with diverse structural topologies are reported. The reaction of one equivalent of zinc(II) perchlorate hexahydrate with three equivalents of 4,4′-bipyridine (bipy) under hydrothermal conditions produces a mixture of [Zn(4,4′-bipy) 2(H 2O) 4](ClO 4) 2 · 2(4,4′-bipy) ( 1), [Zn 3(4,4′-bipy) 4(OAc) 4](ClO 4) 2 · 2(H 2O) ( 2), and [Zn 3(4,4′-bipy) 3(OAc) 4(H 2O) 2](ClO 4) 2 · (H 2O) ( 3) (OAc = acetate), for which single crystals can be isolated. Compound 1 contains sheet-like arrays of discrete monomers co-crystallized with uncoordinated bipy molecules to form extended triangular channels containing counterions. Compounds 2 and 3 consist of acetate-bridged zinc trimers linked by bipy to form three-leg ladders that are isolated in 3 and further linked by bipy into two-dimensional networks in 2. The reaction of one equivalent of zinc(II) perchlorate hexahydrate with 1.5 equivalents of bipy in dimethyl sulfoxide yields single crystals of [Zn(4,4′-bipy)(ClO 4)(H 2O)(OH)] ( 4) and [Zn(4,4′-bipy)(DMSO) 4](ClO 4) 2 ( 5) while crystals of [Zn(4,4′-bipy) 3(DMSO) 2](ClO 4) 2] · 2(4,4′-bipy) · (H 2O) ( 6) are obtained from DMSO with three equivalents of bipy. Compound 4 is a mutually interpenetrated network of hydrogen-bonded, one-dimensional Zn–bipy zig-zag chains and compound 5 exists as isolated, linear chains. Compound 6 also contains linear chains, linked in three-dimensions by π-stacking interactions between bipy ligands and guests.

A Novel Huge Diamond‐like Three‐fold Interpenetrated Network of CuI and Crown Ether

AbstractThe quest for mercury sensitive ion exchangers results in a diamondlike network $^{3}_{\infty}\rm [(CUI)_{2}(1,10DT18C6)]$ (1). This is in contrast to the similar well known 44 network $^{2}_{\infty}\rm [(CUI)(1,10DT18C6)]$ described by Röttgers and Sheldrick [1] a 3D strucutre. 1 is accessible by treatment of CuI with 1,10‐dithia‐18‐crown‐6 in acetonitrile solution in a sealed glass tube in the presence of HgI, but it doesn't contain mercury at all. It seems that either the presence of mercury salts or the excess of iodine ions plays a catalytic role, which is not clarified yet. The main building blocks of 1 are distorted cubes of CuI, which are linked with crown ether rods to give an adamantanlike structure. The space inside the diamondlike network is filled by interpenetration with in sum three similar networks. The longest distance between oppositely CuI cubes in the adamantanlike building block is with 44.796(9) Å three times the b axis.

Thermomechanical properties of epoxy/poly(ɛ-caprolactone) blends

In this article we present a study on the properties of epoxy resins blended with poly(e-caprolactone) (PCL). Several blends were prepared with different PCL amounts. The resins used were a diglycidyl ether of bisphenol F (DGEBF) and a triglycidyl p-amino phenol (TGAP) cured by diethyltoluene diamine (DETDA). All the blends were fully characterized through thermal and mechanical testing. The addition of PCL led to high improvement of toughness but it also reduced the glass transition temperature. Analysis of the rheological and thermal data led to the conclusion that miscible IPNs (interpenetrated networks) were formed. The use of the trifunctional resin TGAP with a percentage varying between 20 wt% and 30 wt% proved to be an efficient means for increasing the glass transition temperature of the mixture based on DGEBF/DETDA with 20 wt% of PCL. POLYM. ENG. SCI. 46:1576–1582, 2006. © 2006 Society of Plastics Engineers.

Polysulfonylamine. CLXXIV [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 17 [2] Silber(I)‐di(methansulfonyl)amid: Ein diamantoides Netzwerk aus Ag2N2‐Vierringen und verbrückenden Mesylgruppen

AbstractPolysulfonylamines. CLXXIV. Crystal Structures of Metal Di(methanesulfonyl)amides. 17. Silver(I) Di(methanesulfonyl)amide: A Diamondoid Network of Four‐Membered Ag2N2 Rings and Bridging Mesyl GroupsThe crystal structure of silver(I) dimesylamide (orthorhombic, space group Fddd, Z = 16, Z′ = 1/2, single‐crystal X‐ray diffraction at −140 °C) consists of dinuclear Ag2[N(SO2Me)2]2 complexes, in which the nitrogen atoms are μ2‐bonded to the silver ions at distances of 241.83(15) pm to form planar rhombic Ag2N2 rings; the short Ag···Ag ring diagonal, 285.36(4) pm, is consistent with weak argentophilic interaction. In the packing, the ring centres lie on 222 sites, conferring crystallographic D2 symmetry on the complex and crystallographic C2 symmetry on the anions. Moreover, each complex is connected to four adjacent complexes by centrosymmetric pairs of silver‐oxygen bonds at distances 245.35(13) pm. In the resulting three‐dimensional coordination polymer, the ring centres represent the nodes of a distorted diamondoid network, whereby the high packing efficiency prevents the interpenetration of networks that is frequently observed in diamondoid solids. The primary N2O2 coordination of the cation corresponds to a distorted tetrahedron with bond angles in the range 103.62(3)–118.57(3)°; including the short Ag···Ag contact and four secondary silver‐oxygen contacts at distances of 300.18(13) pm (2×) and 333.10(13) pm (2×), the coordination number is increased to nine.

Porous alginate-Ca 2+ hydrogels interpenetrated with PNIPAAm networks: Interrelationship between compressive stress and pore morphology

Thermo-sensitive porous hydrogels composed of interpenetrated networks (IPN) of alginate-Ca 2+ and PNIPAAm have been obtained. The hydrogels were prepared by cross-linking alginate-Na + with Ca 2+ ions inside PNIPAAm networks. Compressive tests and scanning electron microscopy were used to evaluate gel strength and pore morphology, respectively. IPN hydrogels displayed two distinct pore morphologies under thermal stimuli. Below 30–35 °C, the LCST of PNIPAAm in water, IPN hydrogels were highly porous. The pore size of hydrogel heated above LCST became progressively smaller. Alginate-Ca 2+ and PNIPAAm hydrogels, used as references, did not present such behaviour, indicating that the porous effect is due to IPN hydrogel. It was verified that higher strength is achieved when the hydrogel presents small pore size and the temperature is increased. It is suggested that at temperatures above LCST, the PNIPAAm chains shrink and pull the alginate-Ca 2+ networks back. During shrinking, the polymer chains occupy the open spaces (pores from which water is expelled), and therefore, the hydrogel becomes less deformable when subjected to compressive stress. The results presented in this work indicate that the mechanical properties as well as the pore morphologies of these IPN hydrogels can be tailored by thermal stimulus.

Intermolecular interaction and properties of cross-linked materials from poly(ester-urethane) and nitrochitosan

Two series of semi-interpenetrating polymer network (semi-IPN) films, coded as PUNT and PUN, have been prepared from amorphous nitrochitosan (NCH) and semicrystalline poly(ester-urethane) (PU) cross-linked to the hydroxy groups of tris(hydroxymethyl)propane (TMP) and NCO groups of PU prepolymer, respectively, by a casting method. The effects of different cross-linking methods and NCH content on the crystallization and hydrogen bonding strengths of the films were studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) with the curve fitting method and wide angle X-ray diffraction (WAXD). The miscibility and mechanical properties of the films were measured by dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), density measurement, thermogravimetric analysis (TGA), tensile testing and solvent swelling testing. The results revealed that the degree of crystalline for the semi-IPN films was lower than that of PU, because of the addition of amorphous NCH to destroy the original ordered structure in the PU film. Moreover, the crystal domain formation for the PUNT films cross-linked with TMP can be more easily interrupted than to other self-crosslinked PUN films without TMP, resulting in a new disordered hydrogen bonded band in ATR-FTIR spectra. The PUNT films exhibited better miscibility as well as higher density, thermal stability, tensile strength and water resistance than the PUN films, suggesting an effective interpenetration and dense network structure. The differences between the two series of the films can be attributed to a relatively dense cross-linking network and strong intermolecular hydrogen bonding occurred between NCH and PU in the PUNT films as a result of the reaction cross-linked with TMP. It is noted that with an increase of NCH from 5 to 30% w/w, the thermal stability, tensile strength and water resistance of the PUNT films increased.

Equivalence of NH4+, NH2NH3+, and OHNH3+ in Directing the Noncentrosymmetric Diamondoid Network of O−H···O- Hydrogen Bonds in Dihydrogen Cyclohexane Tricarboxylate

The assembly of hexagonal and diamond network architectures from functionalized tectons of trigonal and tetrahedral symmetry, respectively, is an important activity in crystal engineering. We report a novel supramolecular transformation for the synthesis of diamond network structures from the trigonal molecule, 1,3-cis,5-cis-cyclohexanetricarboxylic acid (H3CTA). Crystal structures of some salts of the trigonal anion, H2CTA-, with tetrahedral counterions is analyzed in H2CTA-·NH4+ 1, H2CTA-·MeNH3+ 2, H2CTA-·EtNH3+ 3, H2CTA-·NH2NH3+ 4, and H2CTA-·OHNH3+ 5. The trigonal anion functions as a tetrahedral self-complementary node in the presence of NH4+ counterion (salt 1) via two COOH donors and COO- as a double hydrogen-bond acceptor. The triply interpenetrated diamondoid network of O−H···O- hydrogen bonds in 1 is reproduced in isostructural 3D nets of 4 and 5 by substituting NH4+ by NH2NH3+ and OHNH3+ (Π = 0.025, 0.027). The SHG activity of noncentrosymmetric diamondoid solids 1, 4, and 5 (space group Cc) is comparable to that of the nonlinear optical (NLO) material potassium dihydrogen phosphate (KDP) (0.3 × urea). However, salts 2 and 3 (space groups P21/c and P1̄) have hexagonal and square grid layers of H2CTA- anions because the ammonium cation in these structures is devoid of the fourth strong hydrogen-bond donor group to extend crystal growth to the 3D diamond network. Thus, RNH3+ counterions may be used to control the anionic network of the H2CTA- molecule based on a tetrahedral node in 1, 4, and 5, a trigonal node in 2, and a square node in 3. The function of cyclohexane tricarboxylate as a four-connected node, shown for the first time in a trigonal molecule, is in contrast to the usual role of the trimesate anion as a three-connected node in molecular complexes.

Temperature-sensitive chitosan-poly( N-isopropylacrylamide) interpenetrated networks with enhanced loading capacity and controlled release properties

Interpenetrated polymer networks (IPN) of poly( N-isopropylacrylamide) (PNIPA) and chitosan (two grades) were prepared by free radical polymerisation and cross-linking of PNIPA (700 mM) with bis(acrylamide) (20 mM) in chitosan solutions (1.5 wt.% in acetic acid), and subsequent immersion in glutaraldehyde solutions (0 to 0.7 vol.%) to post-cross-link the chitosan. The amount of chitosan that remained in the IPNs, after washing, was proportional to the glutaraldehyde concentration used in the post-cross-linking step; being only 50% of the theoretical when the post-cross-linking was omitted (semi-IPN). The temperature-induced phase transitions of the IPNs were followed by the changes in the swelling degree and in the thermodynamic parameters (temperature, enthalpy, heat capacity, and width of the transition), which were evaluated using high-sensitivity differential scanning calorimetry (HS-DSC). An increase in the post-cross-linking degree of chitosan caused a decrease in the enthalpy of the transition, and in the absolute value of the transition heat capacity increment (Δ t C p), as well as a broadening of the heat capacity peak. This behaviour is a consequence of the subdivision, in the IPNs, of the PNIPA network in microdomains, some regions of which (surface or outer) cannot be involved in the transitions. On the other hand, changes in pH from 8 to 3 only increased the transition temperature from about 32 to 34 °C, despite the considerable modification that this caused in the ionisation degree of chitosan. The PNIPA/chitosan IPNs had a notably greater affinity for diclofenac than the pure PNIPA hydrogel and were able to sustain the drug release for more than 8 h in 0.9% NaCl solutions or pH 8 phosphate buffer. The IPNs with lower chitosan post-cross-linking degree showed the higher temperature-sensitive release patterns. In contrast, the temperature did not significantly affect the release rate from the most cross-linked IPNs, in which the PNIPA microdomains are smaller and the volume phase transitions are less sharper. Therefore, PNIPA microdomains play an important role in controlling the release process. In summary, the interpenetration of networks with complementary properties, such as those made with PNIPA and chitosan, make it possible to develop drug delivery systems with improved drug loading capacity (owing to chitosan) and sustained release behaviour (owing to PNIPA).