Characterization and degradation of poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks

Poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks (PMPS–PMMA IPNs) were prepared by in situ sequential condensation of poly(methylphenylsiloxane) with tetramethyl orthosilicate and polymerization of methyl methacrylate. PMPS–PMMA IPNs were characterized by infrared (IR), differential scanning calorimetry (DSC), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The mobility of PMPS segments in IPNs, investigated by proton spin–spin relaxation T₂ measurements, is seriously restricted. The PMPS networks have influence on the average activation energy E_a,av of MMA segments in thermal degradation at initial conversion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1717–1724, 1999     

Binary frontal polymerization: A new method to produce simultaneous interpenetrating polymer networks (SINs)

We report a new method for the preparation of a simultaneous interpenetrating polymer network (SIN) using a thermal propagating front of two independent and noninterfering polymerization mechanisms. The system consists of the free radical crosslinking of triethylene glycol dimethacrylate (TGDMA) and the amine/BCl₃ · amine curing of diglycidyl ether of bisphenol A (DGEBA). The front velocity dependence on the percentage of each monomer shows a minimum at 45% TGDMA. Temperature profile measurements indicate that a single reaction front propagates. A colored opaque material is produced, but SEM and TEM analysis were inconclusive whether phase separation occurred. Samples as large as 5 cm in diameter were prepared with this method. We conclude that this method should be especially suited for preparing large samples of IPNs in which significant phase separation occurs. © 1997 John Wiley & Sons, Inc.     

On the mechanism of polymerization of cyclic esters induced by tin(II) octoate

Mechanism of initiation and propagation in polymerization of ϵ‐caprolactone and L,L‐dilactide induced with tin(II) octoate (Sn(Oct)₂) and Sn(Oct)₂/n‐butyl alcohol system is presented. Tin(II) alkoxide bond formation is required in reaction of Sn(Oct)₂ with hydroxyl group containing compound to form a true initiator. Then tin(II) alkoxide end group is an active centre in the further propagation.     

Pseudo interpenetrating polymer networks and interpenetrating polymer networks of zeolite 13 X and polystyrene and poly(ethyl acrylate)

Free-radical polymerization of liquid styrene and ethyl acrylate with or without ethylene dimethacrylate crosslinker in the presence of zeolite 13 X produces interpenetrating polymer networks (IPN's) or pseudo IPN's in which polymer chains have grown and filled internal pores of the zeolite. A variety of methods of characterization including, solubility studies, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), ¹³C solid-state nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS) provide supporting evidence for this. The polymer chains within the internal pores do not exhibit a bulk glass transition. This is part of a larger study of the glass transition of polymers confined to cavities or pores of various sizes.     

Morphology and mechanical properties of styrene–butadiene–styrene/poly(methyl methacrylate–co-n-butyl acrylate) interpenetrating polymer networks

A series of interpenetrating polymer networks (IPNs) based on styrenic triblock copolymer, polystyrene-b-polybutadiene-b-polystyrene (SBS), and random copolymer of methyl methacrylate (MMA) and n-butyl acrylate (nBA) were prepared. Corresponding semi-IPNs of the same composition without a crosslinking agent were also synthesized for comparison, and toluene was used as a common solvent to investigate the influence of the presence of the common solvent during the IPN synthesis. Throughout the compositions of IPNs tested, SBS appears to form a continuous phase and the domain size decreases gradually with the increase in SBS concentration. IPNs are found to have finer domain sizes than semi-IPNs because of the higher intermixing between polymers. The microstructure of SBS could be observed using highly magnified transmission electron microscopy (TEM). The dynamic mechanical behavior of the IPNs shows the inward shifting of two glass transition peaks, corresponding to polybutadiene phase of SBS and p(MMA–co-nBA) phase respectively, which indicates enhanced intermixing. The increase in loss tangent of styrene blocks of SBS by the addition of common solvent indicates the structural change of the microstructure in SBS, and this structural change can also be confirmed through the observation of the morphology of SBS-rich phase with higher magnification. © 1997 John Wiley & Sons, Ltd.     

The transparency of polyurethane-poly(methyl methacrylate) interpenetrating and semi-interpenetrating polymer networks

Various combinations of polyurethane (PUR) and poly(methyl methacrylate) (PMMA) were prepared as interpenetrating polymer networks (IPN) or semi-IPNs. In the latter, either the PUR or the PMMA component was crosslinked. The optical transmissions of these materials were measured as a function of the crosslink degrees of both phases. The role of the PUR chain extender, poly(oxypropylene) glycol, is discussed. It is concluded that any means which increases the degree of phase dispersion favours the transparency of PUR/PMMA based IPNs and semi-IPNs.     

A review of kinetic studies on the formation of interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) are unique alloys of crosslinked polymers. This article reviews the studies on kinetic effects involved in IPN formation. Several investigators have studied the effect of kinetics of curing reactions on the morphology and properties of IPNs. It was found, in general, that the faster the rates of the respective chain extension and crosslinking reactions are and the closer they are to simultaneity, the more homogeneous are the IPNs. Other investigations revealed that the individual components sometimes can polymerize more rapidly in the IPN than alone, due to a “solvent effect” of the IPN. Effects of changing reaction variables, such as NCO/OH ratio, composition activators and temperature were used to study reaction kinetics as well as phase morphology by the Fourier transform infrared technique. Thermochemical techniques have been utilized to study the kinetics of IPN formation which influence phase separation. Small-angle X-ray scattering and small-angle neutron scattering techniques were used to estimate the extent of microheterogeneity of the phase domains in a study of the kinetics of phase separation in the IPNs.     

A comparative study of polyurethane-poly(methyl methacrylate) interpenetrating and semi-1 interpenetrating polymer networks

Polyurethane(PUR)-poly(methyl methacrylate) (PAc) semi-1 interpenetrating polymer networks of various compositions have been prepared. They show several differences from the corresponding full IPN's. Thus, the rate of polymerization of the acrylic phase is lower. Transparent plates are also more difficult to obtain. Both effects are ascribed to the absence of the crosslinking agent of the second phase. The composition also plays a role in transparency. Solvent extraction shows that, with increasing PUR content, more PAc remains entrapped in the PUR network. The transition behaviour indicates that the phases are less entangled in semi-IPN's than in IPN's. Consequently, the effect of crosslinking or not crosslinking the second component is very important with regard to the properties of PUR/PAc combinations.     

Catalytic promiscuity of an iron(II)–phenanthroline complex

A mononuclear iron(II) complex, [Fe(phen)₃]Cl₂ ( 1 ) (phen =1,10‐phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X‐ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5‐di‐tert ‐butylcatechol (3,5‐DTBC) through radical pathways with a significant turnover number (k _cat =3.55 × 10³ h⁻¹) and exhibits catechol dioxygenase activity towards the same 3,5‐DTBC substrate at room temperature in oxygen‐saturated ethanol medium. The existence of an isobestic point at 610 nm from spectrophotometric data indicates the presence of Fe³⁺ −3,5‐DTBC adduct favouring an enzyme–substrate binding phenomenon. Upon stoichiometric addition of 3,5‐DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate‐to‐iron(III) ligand‐to‐metal charge transfer bands (575 and 721 nm) are observed and the in situ generated catecholate intermediate reacts with dioxygen (k _obs =9.89 × 10⁻⁴ min⁻¹) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a substrate activation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.     

Heterogeneity of glass transition dynamics in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks

The peculiarities of segmental dynamics over the temperature range of ?140 to 180 °C were studied in polyurethane‐poly(2‐hydroxyethyl methacrylate) semi‐interpenetrating polymer networks (PU‐PHEMA semi‐IPNs) with two‐phase, nanoheterogeneous structure. The networks were synthesized by the sequential method when the PU network was obtained from poly(oxypropylene glycol) (PPG) and adduct of trimethylolpropane (TMP) and toluylene diisocyanate (TDI), and then swollen with 2‐hydroxyethyl methacrylate monomer with its subsequent photopolymerization. PHEMA content in the semi‐IPNs varied from 10 to 57 wt %. Laser‐interferometric creep rate spectroscopy (CRS), supplemented with differential scanning calorimetry (DSC), was used for discrete dynamic analysis of these IPNs. The effects of anomalous, large broadening of the PHEMA glass transition to higher temperatures in comparison with that of neat PHEMA, despite much lower T_g of the PU constituent, and the pronounced heterogeneity of glass transition dynamics were found in these networks. Up to 3 or 4 overlapping creep rate peaks, characterizing different segmental dynamics modes, have been registered within both PU and PHEMA glass transitions in these semi‐IPNs. On the whole, the united semi‐IPN glass transition ranged virtually from ?60 to 160 °C. As proved by IR spectra, some hybridization of the semi‐IPN constituents took place, and therefore the effects observed could be properly interpreted in the framework of the notion of “constrained dynamics.” The peculiar segmental dynamics in the semi‐IPNs studied may help in developing advanced biomedical, damping, and membrane materials based thereon. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 963–975, 2007     

Viscoelastic behavior and phase domain formation in Millar interpenetrating polymer networks of polystyrene

Millar-type interpenetrating polymer networks (IPNs) are composed of two identical networks. In the present case Millar IPNs of polystyrene/polystyrene were prepared where the crosslinker levels of the two networks differed by a factor of 10. Polymer network I contained 0.4% divinylbenzene (DVB) and polymer network II contained 4% DVB, the polymers having the following weight proportions: 75/25, 50/50, and 25/75. A single polystyrene network containing 2.2% DVB was synthesized for comparison with the 50/50 Millar IPN, both containing the same average amount of crosslinker. The creep behavior of the Millar IPNs was found to be dominated by polymer network I, as were the rubbery moduli and swelling behavior in toluene. These results suggested that polymer I domains are more continuous in space and polymer II domains are less continuous. The Donatelli equation predicted polymer II domain sizes of 60 Å to 100 Å for the Millar IPNs. Electron micrographs of specimens containing 1% isoprene in polymer II offered visual evidence for the segregation of polymer II domains from polymer I, and showed that the polymer II domains were, in fact, less continuous. Polymer II domains varied from about 50 to 100 Å in size, as predicted. These results have implications for gelation processes in general.     

Kinetics of the simultaneous oxidation of nickel(II) and sulfur(IV) by oxygen in alkaline medium in Ni(II)–sulfur(IV)–O2 system

In the Ni(II)–S(IV)–O₂ system in the region of pH > 8.4, both Ni(II) and S(IV) are simultaneously autoxidized, and when sulfur is consumed fully NiOOH precipitates. At pH > 8.4, ethanol has no effect on the rate, whereas ammonia strongly inhibits the reaction when pH > 7.0. The kinetics of the reaction, in both the presence and the absence of ethanol, is defined by the rate law where k is the rate constant, K_O is the equilibrium constant for the adsorption of O₂ on ? Ni(OH)₂ particle surface. In ammonia buffer, the factor F is defined by where K, K_OH, K₁, K₂, K₃, and K₄ are the stability constants of NiSO₃, NiOH⁺, Ni(NH₃)²⁺, Ni(NH₃), Ni(NH₃), and Ni(NH₃), respectively. In unbuffered medium, the factor F reduces to The values of k and K^sp were found to be (1.3 ± 0.08) × 10^?1 s^?1 and (4.2 ± 3.5) × 10^?16, respectively, at 30°C. A nonradical mechanism that assumes the adsorption of both SO₃^2? and O₂ on the ? Ni(OH)₂ particle surface has been proposed. At pH ≤ 8.2, Ni(II) displays no catalytic activity for sulfur(IV)‐autoxidation and it is also not oxidized to NiOOH. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 464–478, 2010     

Kinetics and mechanism of cyclic esters polymerization initiated with tin(II) octoate, 1. Polymerization of ε-caprolactone

Kinetics of polymerization of ε-caprolactone (CL) initiated with tin(II) octoate (Sn(Oct)₂) in THF as a solvent at 80°C was studied. The results strongly indicate that polymerization initiated with Sn(Oct)₂ proceeds on the tin(II)-alkoxide bond and are not compatible with a mechanism in which propagation was proposed to proceed by a nucleophilic attack of the … OH ended macromolecules on the monomer-Sn(Oct)₂ complex.     

Peculiar kinetics of the complex formation in the iron(III)–sulfate system

The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+$ step and k₂ = 1.1 × 10³ M^?1 s^?1 for the ${\rm FeSO}_4^+ + {\rm SO}_4^{2-} \stackrel{k_2}{\rightleftharpoons}\, {\rm Fe}({\rm SO}_4)_2^-$ step. The mono‐sulfate complex is also formed in the ${\rm Fe}({\rm OH})^{2+} + {\rm SO}_4^{2-} \stackrel{k_{1b}}{\longrightarrow} {\rm FeSO}_4^+$ reaction with the k_1b = 2.7 × 10⁵ M^?1 s^?1 rate constant. The most surprising result is, however, that the 2 FeSO? Fe³⁺ + Fe(SO₄) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO₄) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114–124, 2008     

Unprecedented ferromagnetic interaction in an erbium(III)–copper(II) coordination polymer

Two 3D Ln(III)–Cu(II) coordination polymers [Er₂Cu₃(pydc)₆(H₂O)₆]_n (1) and [Tb₂Cu₃(pydc)₆(H₂O)₆]_n (2) were hydrothermally prepared from pyridine-2,4-dicarboxylic acid (H₂pydc) and characterized by single-crystal X-ray diffraction analysis. The magnetic studies show that an unexpected ferromagnetic interaction between metal centers exists in 1 while 2 behaves as an antiferromagnet.     

Structural modeling and magnetostructural correlations for heterobinuclear Cu(II)–Ni(II) complex

The magnetostructural correlation of model Cu(II)–Ni(II) heterobinuclear complexes was studied by using the broken symmetry approach within the framework of density functional theory. The antiferromagnetic coupling interaction is weakened with the decrease of the dihedral angle between the plane O1CuO2 and the plane O1NiO2 in the core moiety CuO1O2Ni of the model from 180 to 125°, in agreement with the experimental results. The ferromagnetic behavior was also predicted theoretically with dihedral angle less than 125°. The magnetic coupling interaction is reinforced with the increase of the bond angle Cu? O? Ni. The relationship between the magnetic coupling interaction and the spin density localized on the magnetic centers or on the bridging O atoms was investigated. The bond angle Cu? O? Ni for the model with lowest energy was determined and the theoretical value (104°) is a little more than the experimental value (99°). © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

A copper(II)–pyrazole complex cation with imposed symmetry

The reaction of Cu(ClO₄)₂·6H₂O, NaAsF₆ and excess pyrazole yields hexakis­(pyrazole‐κN²)copper(II) bis­(hexa­fluoroarsenate), [Cu(C₃H₄N₂)₆](AsF₆)₂ or [Cu(pzH)₆](AsF₆)₂ (pzH is pyrazole), (I). The analogous hexakis­(pyrazole‐κN²)copper(II) hexafluorophosphate perchlorate complex, [Cu(C₃H₄N₂)₆](PF₆)_1.29(ClO₄)_0.71 or [Cu(pzH)₆](PF₆)_1.29(ClO₄)_0.71, (II), is obtained in a similar fashion, using KPF₆ in place of NaAsF₆. Both compounds contain the hitherto unknown [Cu(pzH)₆]²⁺ complex cation, in which the copper(II) ion lies at the center of a regular octahedron of coordinated N atoms. The cation has crystallographically imposed symmetry. The X‐ray data indicate that the lack of the expected distortion can be accounted for by the presence of either static Jahn–Teller disorder or dynamic Jahn–Teller distortion.