Formation of linear polymers in confined intranetwork space during synthesis of sequential semi-interpenetrating polymer networks

Sequential semi-interpenetrating polymer networks based on polyurethanes with different crosslink densities and linear polystyrene, poly(butyl methacrylate), and poly(methacrylic acid) have been studied. For the parent polyurethanes, the molecular mass of chain segments between crosslink junctions is estimated by the Flory-Rehner method. The kinetics of formation of linear polymers in semi-interpenetrating polymer networks is investigated as a function of the crosslink density of the polyurethane network. The molecular-mass distributions of linear polymers developed in semi-interpenetrating polymer networks are examined by size-exclusion chromatography. The relationship between the kinetics of formation of linear components under the conditions of confined space and their molecular mass is established.     

The interaction parameter of crosslinked networks and star polymers

Recent results on blends containing star polymers have revived the interest on the interaction parameters of structures that contain junctions between chains, a matter which can be connected with the earlier studies on the influence of crosslinks on the interaction parameters of polymer networks and gels. Here, we review results on crosslinked networks and star polymer solutions together with the more recent work on star polymer blends. The review covers swelling and elastic deformation of gels, differential vapour sorption between crosslinked and uncrosslinked polymers, osmotic equilibrium of gels and of star polymer solutions, and neutron scattering of polymer blends containing star polymers. In the systems reviewed, the interaction parameters of stars and networks differ from those of linear chains, and the difference is attributed mainly to entropic effects.     

From the conformation of a single molecule to physical networks in highly interacting polymers: A small-angle neutron study

Small-angle neutron scattering has been used to study the conformation and structure of highly interacting macromolecules in complex fluids. The evolution of the structure has been investigated from the conformation of a single molecule through an association process to the formation of physical networks. Two highly interacting polymers, an ionic polymer (consisting of a perfluorinated backbone and an ionizable hydrophilic side chain dissolved in water/alcohol mixtures) and rodlike, highly conjugated phenylene ethylene molecules (dissolved in toluene), have been studied. Highly interacting polymers often form relatively long lasting physical networks with increasing polymer concentration. The driving force, however, is system-specific, and so are the micellar systems and physical networks formed. Although the two families of polymers under consideration are entirely different chemically, their strong interaction, either ionic or through π–π coupling, results in similarities in the complex fluids formed when they are dissolved in solutions. These include elongated configurations in dilute solutions, association into micelles, and eventually coalescence into physical networks. The ionic polymers form durable stable networks, whereas the rodlike polymers form a fragile, gel-like phase. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3165–3178, 2004     

Sequential semi-interpenetrating polymer networks based on polyurethane and polystyrene

The formation of microheterogeneous sequential semi-interpenetrating polymer networks based on network polyurethanes with different molecular masses of chain segments between crosslinks and a linear polystyrene has been studied by DSC and small-angle X-ray scattering. It has been shown that variation in the molecular mass of polymer segments between polyurethane network junctions affects the formation of the linear component of semi-interpenetrating polymer networks. As a result, the material structure may change in a wide range from a nearly single-phase system to a two-phase one. SAXS measurements indicate that there is a cymbate dependence between the degree of segregation of components of sequential semi-interpenetrating polymer networks and their microheterogeneous structure on the internetwork space. Two hierarchical heterogeneity levels are found to exist in polymer networks, and the features of each of these levels are analyzed.     

Liquid crystal polysiloxane networks as materials for molecular imprinting technology: memory of the mesomorphic organization

A novel approach to the synthesis of molecularly imprinted polymers via non-covalent linkages has been studied. It relies on the use of thermotropic side group liquid crystal polymer networks. The polysiloxane networks obtained after extraction of the template preserved the mesomorphic organization set up in the presence of the guest molecule. A first batch rebinding analysis was performed: this study revealed that the imprinted polymer has a much greater affinity for the template molecule than has the non-imprinted polymer, and a significant selectivity.     

Liquid crystal polysiloxane networks as materials for molecular imprinting technology: memory of the mesomorphic organization

A novel approach to the synthesis of molecularly imprinted polymers via non-covalent linkages has been studied. It relies on the use of thermotropic side group liquid crystal polymer networks. The polysiloxane networks obtained after extraction of the template preserved the mesomorphic organization set up in the presence of the guest molecule. A first batch rebinding analysis was performed: this study revealed that the imprinted polymer has a much greater affinity for the template molecule than has the non-imprinted polymer, and a significant selectivity.     

Design and synthesis of interpenetrating polymer networks for second-order nonlinear optics

There has been a tremendous recent interest in the development of second-order nonlinear optical (NLO) polymeric materials for photonic applications. However, a major drawback of second-order NLO polymers that prevents them from being used in device applications is the instability of their electric field induced dipolar alignment. The randomization of the dipole orientation leads to the decay of second-order optical nonlinearities. Numerous efforts have been made to increase the stability of the second-order NLO properties of polymers. The search for new approaches to develop NLO polymers with optimal properties has been an active research area since the past decade. A novel approach, combining the hybrid properties of high glass transition temperatures, extensively extensively crosslinked networks and permanent entanglements, based on interpenetrating polymer networks (IPN) is introduced to develop stable second-order NLO materials. Two types of IPN systems are prepared and their properties are investigated. The designing criteria and the rationale for the selection of polymers are discussed. The IPN samples show excellent temporal stability at elevated temperatures. Long-term stability of the optical nonlinearity at 100°C has been observed in these materials. Temporal stability of the NLO properties of these IPNs is synergistically enhanced. Relaxation behavior of the optical nonlinearity of an IPN system has been studied and compared with that of a typical guest/host system. The improved temporal stability of the second-order NLO properties of this IPN system is a result of the combination of the high rigidity of the polymer backbones, crosslinked matrices and permanent entanglements of the polymer networks. A slight modification of the chemical structure resulted in an improvement of the optical quality of the sample.     

Semi-interpenetrating polymer networks of polyurethane and poly(vinyl chloride)

Summary A series of semi-interpenetrating polymer networks (semi-IPN) of polyurethane (PU) and poly(vinyl chloride) (PVC) has been obtained by prepolymer method and characterised by FTIR; morphological features were examined by SEM-EDS. It has been found that PVC spherical aggregates are dispersed in the PU matrix, but Cl atoms location indicates partial miscibility of both polymers at the interphase which is probably due to hydrogen bonding and/or dipole-dipole interactions. The PVC component influences the phase behaviour of PUs hard segments, as evidenced by DSC results. Thermogravimetric analysis (TG) reveals a complex, multi-step decomposition process with the main mass loss at 503-693 K, while the DTG maxima are located between 540 and 602 K.     

Interpenetrating polymer networks from polyurethanes and methacrylate polymers. II. Interpenetrating polymer networks with opposite charge groups

Interpenetrating polymer networks (IPNs) with opposite charge groups (tertiary amine and carboxyl groups) made from polyurethanes and methacrylate polymers have been synthesized and their properties and morphology, studied. With increasing carboxyl group concentration the mechanical properties and compatibility between the component networks were significantly improved, possibly because of the negative (or zero) free energy produced by the interaction contribution between the tertiary amine groups in the polyurethanes and the carboxyl groups in the methacrylate polymers determined by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The improved molecular mixing in these IPNs was thought to be due to the influence of the opposite charge groups in these systems.     

Polymer networks functionalized with low-valent phosphorus cations

In this work, we show that polymer networks composed of tertiary alkyl phosphines can be cleanly functionalized with phosphino-phosphonium or triphosphenium cations. Methods for functionalizing the polymers range from halide abstraction of commercially available reagents, to ligand exchange from simple to make reported compounds, and finally, macromolecular ligand design guided by observations made at the molecular level to accommodate the formation of kinetically favored triphosphenium cation functionalized networks. The synthesis, comprehensive characterization, and comparison of the new polymers to molecular analogues is outlined. It is shown the addition of the low valent phosphorus centers to the polymer network has the effect of tuning material physical properties.     

Structure of microemulsion-ABA triblock copolymer networks

Structural equilibrium properties of transient networks formed by microemulsion droplets and ABA triblock copolymers in solution have been studied by Monte Carlo simulation. The droplets were represented by soft spheres, and the polymers were represented by junctions connected by harmonic bonds with an angular potential regulating the intrinsic chain stiffness. The interaction parameters were selected such that the end A-blocks were localized inside the droplets and the middle B-block in the continuous phase. The influence of (i) the polymer concentration, (ii) the polymer stiffness, and (iii) the contour length of the middle B-block on the formation and the structure of the microemulsion-polymer network were investigated using polymer end-to-end separation probability distribution functions, droplet radial distribution functions, droplet-droplet nearest-neighbor probability distribution functions, and network connectivity indicators. An increase of the polymer-droplet number ratio had a strong impact on the network formation. Under typical conditions and at an intermediate polymer-droplet number ratio, (i) the fraction of polymers forming bridges between droplets increased from essentially zero to unity and (ii) the fraction of polymers that were forming loops decreased as the ratio of the polymer end-to-end separation and the surface-to-surface separation between neighboring droplets for a hypothetical homogeneous droplet distribution was increased from 0.5 to 2. For long and flexible polymers, a mesoscopic segregation triggered by a depletion attraction between droplets appeared, and, furthermore, for sufficiently stiff chains, only bridge conformations occurred. The percolation probability could be represented as a function of the average droplet cluster size only, across all systems.     

An investigation of the interconnection between topological characteristics of physical and chemical networks of anhydride adamantane-containing epoxy polymers

The interconnection between topological characteristics of chemical and physical networks of adamantane-containing epoxy polymers of anhydride curing is studied. It is shown that the introduction of adamantane fragments into the network of an epoxy polymer by different methods affects the glass-transition point and stress-strain properties. The changes in polymer properties depending on the concentration of modifying agents are analyzed during comparison of the frequency parameters of the networks of chemical bonds and engagements within a cluster model of the structure of the polymer amorphous state.     

Electrical conductivity of iodine doped pseudo interpenetrating polymer networks

The iodine doped pseudo interpenetrating polymer networks (PIPN's) of both conjugated and non-conjugated linear polymers in less conducting crosslinked polymer networks may possess modest DC conductivities, σ, of the order of the iodine doped bulk polymers. There is evidence that critical percolation occurs in PIPN's and that these materials possess a quasi-one dimensional character unlike the iodine doped bulk polymers, e.g. the σ of the iodine doped PIPN's increases from about 120 K to 4 K with decreasing temperature. We provide a simple partial (near and somewhat below room temperature) theory and summarize conductivity and resonance Raman spectroscopic studies.     

Topologically interpenetrating elastomeric networks

Several partially interpenetrating polymeric networks (IPN) were made by combining chemically different linear elastomers. The polymer combinations were deposited as films from aqueous emulsions made by mixing the individual emulsions in equal proportions. The films were crosslinked to form two superimposed networks. In two cases, the networks were cleanly separated by hydrolysis of one of the component networks to demonstrate that there was no chemical interaction between the polymers. Measurement of crosslink density showed that, in most cases, partial interpenetration does occur as evidenced by an effective crosslink density of the IPN's greater than the arithmetic mean of the crosslink densities of the component networks. The swelling ratios, densities, and stress–strain properties were determined. For one of the network combinations, a poly(urethane–urea) and a poly(butadiene–acrylonitrile), a series of IPN's varying in polymer composition was made. The swelling ratios and densities are close to the arithmetic means; however, both the tensile strength and crosslink density exhibit a maximum at about 70% poly(butadiene-acrylonitrile). The maximum tensile strength is actually significantly higher than that of either of the component polymers. The elongations all approach that of the poly(urethane–urea), the more extensible material, except for compositions approaching 100% poly(butadiene–acrylonitrile), which exhibit a very low extensibility.     

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one‐pot procedure. The synthesis involved the use of a monofunctional initiator and the four‐step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm‐first” star polymers; (iii) monomer, to form secondary arms and give “in‐out” star polymers; and, finally (iv) branch unit again, to interconnect the “in‐out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm‐first” and the “in‐out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.     

High charge carrier mobility in conjugated organometallic polymer networks

The improvement of charge transport in conjugated polymers is a focal point of current research. It is shown here that the carrier mobility can be substantially increased through the introduction of conjugated cross-links between the conjugated chains. Novel organometallic polymer networks based on a poly(p-phenylene ethynylene) (PPE) derivative and Pt0 were synthesized by ligand-exchange reactions between the linear PPE and a low-molecular Pt complex. Time-of-flight measurements revealed ambipolar charge carrier mobilities of up to 1.6 x 10-2 cm2 V-1 s-1 for these materials, which are an order of magnitude higher than those of the neat polymer and represent the highest mobilities yet observed in disordered conjugated polymers.     

Hydrogen-bonded supramolecular polymer networks

The strong dimerizing, quadruple hydrogen-bonding ureido-pyrimidone unit is used to obtain reversible polymer networks. A new synthetic route from commercially available starting materials is described. The hydrogen-bonding ureido-pyrimidone network is prepared using 3(4)-isocyanatomethyl-1-methylcyclohexyl-isocyanate (IMCI) in the regioselective coupling reaction of multi-hydroxy functionalized polymers with isocytosines. ¹H- and ¹³C-NMR, IR, MS, and ES-MS analysis, performed on a model reaction using butanol, demonstrated the formation of the hydrogen-bonding ureido-pyrimidone unit in a yield of more than 95%. The well-defined, strong hydrogen-bonding ureido-pyrimidone network is compared with a traditional covalently bonded polymer network, a multi-directional hydrogen-bonded polymer network based on urea units, and a reference compound. The advantage of the reversible, hydrogen-bonded polymer networks is the formation of the thermodynamically most favorable products, which show a higher “virtual” molecular weight and shear modulus, compared to the irreversible, covalently bonded polymer network. The properties of the ureido-pyrimidone network are unique; the well-defined and strong dimerization of the ureido-pyrimidone unit does not require any additional stabilization such as crystallization or other kinds of phase separation, and displays a well-defined viscoelastic transition. The ureido-pyrimidone network represents the first example of a truly reversible polymer network showing these features. Furthermore, the ureido-pyrimidone dimerization is strong enough to construct supramolecular materials possessing acceptable mechanical properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3657–3670, 1999     

Synthesis and properties of monodisperse polydimethylsiloxane networks

α,ω-Divinyl-terminated polydimethylsiloxane polymers with low polydispersivity were synthesized via anionic polymerization of hexamethylcyclotrisiloxane (D₃). Five “monodisperse” polymers with different molecular weights were hydrosilylated with tetrakisdimethylsiloxysilane in the presence of platinum catalysts and inhibitors to form crosslinked networks. Control studies to determine the effect of platinum, silicon hydride, and heat were performed to verify that no redistribution occurred during hydrosilylation. The properties of these cured samples were characterized chemically by degradation with trifluoromethanesulfonic acid in the presence of hexamethyldisiloxane, infrared spectroscopy, and nuclear magnetic spectroscopy. Mechanical properties were studied by measurements of Shore A hardness, dynamic shear modulus, and tensile modulus. The relationship between the molecular weight of the vinyl polymer and the final properties of the cured networks was measured. © 1993 John Wiley & Sons, Inc.     

Synthesis and sorption ability of telogenated hyper-cross-linked polydivinylbenzene networks

Synthesis and properties of hyper-cross-linked polymer networks prepared by radical polymerization of commercial divinylbenzene in oxylene, a good solvent and a powerful telogen, are reported. The permeability of hyper-cross-linked networks is evaluated by adsorption of bioactive molecules significantly differing in size. High sorption capacity for Cephalosporin C makes the polymers prepared promising for pharmacology and biotechnology.     

Synthesis, processing and properties of conjugated polymer networks

Despite the diverse research activities focused on the chemistry, materials science and physics of conjugated polymers, the feature of conjugated cross-links, which can provide electronic communication between chains, has received little attention. This situation may be a direct consequence of the challenge to introduce such links while retaining adequate processability. Focusing on recent studies of materials for which charge transport or electrical conductivity data are available, this feature article attempts to present an overview of the synthesis, processing and electronic properties of conjugated polymer networks. For the purpose of this discussion, two distinctly separate architectures-featuring covalent cross-links on the one hand and non-covalent organometallic bridges on the other-are treated in separate sections. The available data indicate that cross-linking can have significant benefits for intermolecular charge transfer if the polymers are carefully designed.