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Thermoplastic poly(urethane-siloxane)/organoclay nanocomposites (TPU NCs) with different hard segment content (20–55 wt. %) were prepared by in situ polymerization in the presence of organically modified montmorillonite as a nanofiller (Cloisite 30B; 1 wt. %). Hydroxyl-terminated ethoxypropyl- poly(dimethylsiloxane) was used as soft segment, while 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol were the hard segment components. The study of the influence of the hard segment content on the functional properties of TPU NCs was performed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water contact angle and water absorption tests. The results revealed that TPU NCs with the increasing hard segment content exhibit higher values of degree of microphase separation, melting temperature of the hard segments, degree of crystallinity, storage modulus (except for TPU NC-55), but lower thermal stability and hydrophobicity. TPU NC films were hydrophobic and their free surface energy was in the range from 17.7 to 24.9 mJ m-2. This work highlights how the composition of TPU NCs would affect their functional properties and provide an additional composition intended for designing advanced TPU NC materials for special biomedical applications.

Nanocomposites based on aliphatic polyurethanes have recently attracted a lot of attention regarding economical and ecological aspects, due to their improved thermal and mechanical properties. The aim of this paper was to investigate the influence of silica nanoparticles, differing in size and specific surface, on thermal stability and degradation, lifetime and mechanical characteristics of the obtained nanocomposites. Two series of nanocomposites based on aliphatic polyurethanes were obtained by using a single-step procedure and by addition of silica nanoparticles of types A380 or N999 at different loadings (0,0 0.15, 0.5, 1,0 and 3.5 wt.%). It was found that the increase in heating rate caused shifting of the onset temperature to higher values (from 283 to 312 °C). According to the shape of DTG curves, it was observed that the degradation mechanism of prepared nanocomposites consists of two overlapping processes, related to the scission of hard and soft building blocks. Based on DTG results, the addition of larger N999 silica nanoparticles induced lower thermal degradation, shifting the maximum rate temperatures of the first and second degradation stages to lower values, and caused the change in the degradation mechanism. Addition of smaller silica nanoparticles (A380) did not significantly affect the mechanism of the degradation reaction, indicating homogeneity of the obtained nanocomposites. The presence of A380 nanoparticles improved thermal stability of nanocomposites, by increasing the onset temperature from 286 °C for the pristine elastomer to 303 °C for the sample containing 3.5 wt.% of silica. Existence of interactions of A380 silica nanoparticles with hard and soft phases was observed, based on the increase in the maximum rates of the first and second degradation steps. The activation energy of thermal degradation of polyurethanes modified with A380 silica nanoparticles was obtained by using the Flyn-Wall and Toop models. Dependence of the activation energy and the lifetime of nanocomposites based on aliphatic polyurethanes on the silica content were estimated. The highest Ea values (determined for 1 and 5 % weight loss) were found for nanocomposites containing 0.5 and 0.15 wt. % of A380 silica nanoparticles (121 and 161.2 kJ/mol). A negative effect of the silica addition on mechanical properties of nanocomposites was observed. The polyurethanes containing smaller SiO2 particles (A380) had a higher tensile strength, elongation at break and hardness as compared to the elastomers filled with larger silica nanoparticles (N999). [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45022]

Reinforcing of elastomers by the addition of various nanofillers has led to significant improvements in elastomer properties, and therefore, to the increase of potentials for use as suitable materials for special applications. The aim of this study was to investigate the effects of combinations of two active fillers (carbon black and synthesized silica (50/0; 35/15; 25/25; 15/35; 0/50; phr)) on the morphology, curing, as well as thermal, dynamic-mechanical and mechanical properties of nanocomposites based on the styrene-butadiene rubber as the network precursor. Based on SEM results, the largest agglomerates were observed in the structure of the nanocomposite containing 25 phr of carbon black and 25 phr of SiO2. Determination of curing characteristics indicated that the minimum torque at 100, 150 and 160°C had higher magnitudes for the compounds with silica filler, which is in accordance with the tendency of SiO2 to form filler-filler interactions. Values of the scorch time and the optimal time of crosslinking increased by increasing the silica phr content in the fillers mixture. It could be thus supposed that the fraction of occluded and trapped chains in the structure of elastomer reinforced by SiO2 is higher due to the almost 2-fold higher value of the silica NDBP number as compared to the NDBP number of carbon black particles. On the basis of MDSC results, it was assessed that the addition of combined active fillers had negligible effects on the glass transition temperature, registered at about -47°C for all tested samples. The obtained DMA data, concerning storage moduli in the temperature range from -20 to 0°C, (characteristic for "Payne" effect) are very significant for predictions of the properties of the tyre tread such as the slip resistance on the road on ice and in the wet conditions. The increase of silica content in the combined filler induced a decrease of the dynamic mechanical loss factor of prepared nanocomposites in the temperature range from 40 to 80°C. The obtained results are very important for the structuring of elastomeric materials aimed for production of tyres with reduced rolling resistance and fuel consumption. The elastomer containing the highest content of carbon black showed the highest value of the tensile strength (21.8 MPa). The abrasion resistance of the synthesized nanocomposites increased as the silica content was reduced in the combined fillers. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 45022]

The mechanical properties of nanocomposites obtained by incorporation of fairly uniform hematite nanorods (α-Fe2O3 NRs) into epoxy resin were studied as a function of the content of the inorganic phase. A thorough microstructural characterization of the α-Fe2O3 NRs and the nanocomposites was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM measurements revealed rod-like morphology of the nanofiller with a uniform size distribution (8.5 nm×170 nm, diameter×length). High-magnification TEM and AFM measurements indicated agglomeration of α-Fe2O3 NRs embedded in the epoxy resin. Stress at break, strain at break, elastic modulus and tensile toughness of the nanocomposites were compared with the data obtained for pure epoxy resin. Significant influence of nanofiller on the mechanical properties of epoxy resin, as well as on the glass transition temperature, could be noticed for samples with low contents of the inorganic phase (up to 1 wt. %). [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 45020]

Segmented thermoplastic polyurethane copolymers (PURs) were synthesized using 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol as the hard segment and α,ω-dihydroxy-poly(propylene oxide)-b-poly(dimethylsiloxane)-b-poly(propylene oxide) (PPO-PDMS) as the soft segment. The content of incorporated soft segments in PURs varied in the range from 40 to 90 wt.%. The structure, molecular weights and crystallinity of obtained copolymers were monitored by FTIR, 1H, 2D NMR spectroscopy, GPC and DSC analysis, respectively. Surface free energy analysis indicates the presence of hydrophobic (siloxane) groups on the surface, giving highly hydrophobic nature to the obtained PURs films. Water absorption measurements showed that the increase of the hydrophobic PPO-PDMS segment content, led to the decrease of percentage of absorbed water in copolymers. SEM and AFM analysis revealed that copolymers with lower content of PPO-PDMS segments have higher microphase separation between segments. The results obtained in this work indicate that synthesized PURs based on PPO-PDMS, demonstrated proper surface and morphological properties with a great potential for variety of applications such as hydrophobic coatings in biomedicine. [Projekat Ministarstva nauke Republike Srbije, br. 172062]

In this work, epoxy hybrid materials were synthesized by addition of thermoplastic segmented aliphatic polyurethanes with good elastic properties. The modified epoxy samples were obtained by curing of previously homogenized mixture of prepared polyurethane melts, epoxy resin and crosslinking agent Jeffamine D-2000. The influence of different weight content of polyurethanes (5, 10 and 15 wt. % compared to pure epoxy resin) as well the influence of different hard segments of elastomers (20, 25 and 30 wt. %) on the curing of modified epoxy systems was studied. The curing was followed by differential scanning calorimetry (DSC), in dynamic regime from 30 to 300°C, at three heating rates (5, 10 and 20°C/min). With the increase of hard segments content of polyurethanes added in higher concentration (10 and 15 wt. %) into epoxy matrix, the temperature of maximum ratio of curing was shifted to lower values (from 205 to 179°C). Obtained DSC data were analyzed using two integral methods (Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose) and one differential kinetic model (Friedman). The significant differences were observed in the second part of the epoxy curing (for the reaction degrees higher than 60 %), where the values of activation energies remarkably increase. The addition of polyurethane elastomers retarded the curing process due to decreased mobility of reactant molecules caused by higher viscosity of reaction mixture. By detailed analysis of determined kinetic parameters, it is concluded that the influence of slow diffusion is more pronounced in the presence of thermoplastic polycarbonate-based polyurethanes, which confirmed their effect on the mechanism of epoxy curing. The highest tensile strength and hardness showed the DGEBA modified with the polyurethane with highest hard segment content. Increasing the hard segment content of polyurethane and its concentration in matrix, the tensile strength of modified epoxy was increased. The elongation at break of modified epoxy samples was significantly improved by addition of polycarbonate-based polyurethanes with low hard segment content, due to higher content of flexible soft segment chains. [Projekat Ministarstva nauke Republike Srbije, br. III 45022), i Pokrajinski Sekretarijat za nauku i tehnološki razvoj (projekat 114-451-2396/2011-01). Autor iz Praga duguje zahvalnost „the Grant Agency of the Czech Republic“ (Czech Science Foundation, project No. P108/10/0195).]

Two series of polyurethane films based on hyperbranched polyester of the second pseudogeneration (Boltorn®), 4,4'-methylenediphenyl diisocyanate and two different siloxane prepolymers, α,ω-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and α,ω-dihydroxypropyl-poly(dimethylsiloxane) (HP-PDMS), were prepared by two-step polymerization in solution. The influence of the type and content of soft segment on the morphology, thermomechanical and surface properties of the synthesized polyurethanes was studied by atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and water absorption measurements. It was found that these techniques confirmed existence of microphase separated morphology. Synthesized polyurethanes exhibited two glass transition temperatures and one second relaxation process. The results showed that polyurethanes based on HP-PDMS had higher surface roughness, better microphase separation and waterproof performances. Samples synthesized with lower PDMS content had less hydrophobic surface, but higher crosslinking density and better thermomechanical properties. (Projekat Ministarstva nauke Republike Srbije, br. 172062]

Aliphatic segmented polyurethanes were prepared by one-step procedure in catalytic reaction between polycarbonate diol, hexamethylene-diisocyanate and 1,4-butandiol (as chain extender). The hard segment content TS was varied (17, 24, 30 and 42 wt. %) by changing the ratio of starting compounds. The soft segment is made from flexible aliphatic polycarbonate diol, while hard segments consist of chain extender and diisocyanate component. In order to study the hydrogen bonding formation and phase separation, Fourier transform infrared spectroscopy (FT-IR) was used. Wide angle X-ray scattering (WAXS) was performed to determine a degree of crystallinity and to investigate the phase behavior of prepared elastomers. The effect of TS content on mechanical properties (tensile strength, elongation at break and hardness) was tested. Thermal behavior of prepared novel polycarbonate-based polyurethanes was investigated using differential scanning callorimetry (DSC). It was determined that the elastomer which contains the highest amount of urethane groups in its structure (TS content of 42 wt. %) exhibits the most pronounced phase separation and the highest degree of crystallinity. All prepared polyurethanes exhibit high elongation at break (over 700%). The glass transition temperature Tg of prepared samples was in the temperature region from −39 to −36°C, and it was found to be slightly influenced by the soft segment content. The enthalpy of chain segments relaxation in diffused region between hard and soft domains (detected in the temperature range from 35 to 55 °C) was decreased with the increase of hard segment content. The multiple melting of hard segments (connected with the dissruption of physical crosslinks) appeared above 100 °C. It was found that the melting enthalpy linearly increases with the increase of urethane group content. Sample with 42 wt. % of TS has the highest value of melting enthalpy (41.5 J/g).

Two series of crosslinked poly(urethane-ester-siloxane)s were synthesized from α,ω-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO), 4,4’-methylenediphenyl diisocyanate and Boltorn® hyperbranched polyesters of the second and third pseudo generation, by a two-step polymerization in solution. The effect of the EO-PDMS-EO content and functionality of the applied crosslinking agent on the morphology and surface properties of the prepared poly(urethane-ester-siloxane)s was investigated by FTIR spectroscopy, small-angle X-ray scattering (SAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and water absorption measurement. Different techniques (FTIR peak deconvolution, SAXS and AFM) revealed that decrease of the crosslinking agent functionality and EO-PDMS-EO content promotes microphase separation in the synthesized poly(urethane-ester-siloxane)s. SEM analysis and water absorption experiments showed that due to the hydrophobic character of EO-PDMS-EO and its ability to migrate to the surface of poly(urethane-ester-siloxane)s, samples synthesized with higher EO-PDMS-EO content and crosslinking agent of lower functionality have more hydrophobic surface and better waterproof performances. The obtained results indicate that the synthesis of poly(urethane-ester-siloxane)s based on EO-PDMS-EO and Boltorn® hyperbranched polyesters leads to the creation of networks with interesting morphological and surface properties, which can be easily tailored by changing the content of EO-PDMS-EO segment or functionality of hyperbranched polyester.

The aim of this work was to determine the influence of clay nanoparticles on thermal properties of segmented polyurethanes based on hexamethylene- diisocyanate, aliphatic polycarbonate diol and 1,4-butanediol as chain extender. The organically modified particles of montmorillonite and bentonite were used as reinforcing fillers. The structure of elastomeric materials was varied either by diol type or chain extender content. The ratio of OH groups from diol and chain extender (R) was either 1 or 10. Thermal properties of prepared materials were determined using modulated differential scanning calorimetry (MDSC). Thermal stability of obtained elastomers has been studied by simultaneously thermogravimetry coupled with DSC. The glass transition temperature, Tg, of soft segments for all investigated samples was about -33°C. On the basis of DTG results, it was concluded that obtained materials were very stable up to 300°C.

Polyethylene (PE) is one of the most widely used polymers in many industrial applications. Biomedical uses seem to be attractive, with increasing interest. However, PE it prone to infections and its additional surface treatment is indispensable. An increase in resistance to infections can be achieved by treating PE surfaces with substances containing antibacterial groups such as triclosan (5-Chloro-2-(2,4-dichlorophenoxy)phenol) and chlorhexidine (1,1'-Hexamethylenebis[5-(4-chlorophenyl)biguanide]). This work has examined the impact of selected antibacterial substances immobilized on low-density polyethylene (LDPE) via polyacrylic acid (PAA) grafted on LDPE by low-temperature barrier discharge plasma. This LDPE surface treatment led to inhibition of Escherichia coli and Staphylococcus aureus adhesion; the first causes intestinal disease, peritonitis, mastitis, pneumonia, septicemia, the latter is the reason for wound and urinary tract infections.

To assist in overcoming the inherent instability of nucleic acid-containing polyplexes in physiological solutions, we have here set out to develop removable nanocoatings for modifying the surface of siRNA-based nanoparticles. Here, N-(2-hydroxypropyl)methacrylamide (HPMA) based copolymers containing carbonylthiazolidine-2-thione (TT) reactive groups in their side chains bound via disulfide spacers to the polymeric backbone were synthesized, and these copolymers were used to coat the surface of polyplexes formed by the self-assembly of anti-Luciferase siRNA with the polycations polyethylene imine (PEI) and poly(HPMA)-grafted poly(l-lysine) (GPL). The coating process was monitored by analyzing changes in the weight-average molecular weight (M(w)), the hydrodynamic radius (R(h)), and the zeta-potential (ζ) of the polyplexes, using both static (SLS) and dynamic (DLS) light scattering methods. The outlined methods resulted in the attachment of, on average, 28 polymer molecules to the surface of the polyplexes, forming a ∼5-nm-thick hydrophilic stealth coating. Initial efforts to develop RGD-targeted coated polyplexes are also described. Atomic force microscopy (AFM) showed an angular polyplex structure and confirmed the narrow size distribution of the coated nanoparticles. The stability of the polymer-coated and uncoated polyplexes was evaluated by gel electrophoresis and by turbidity measurements, and it was found that modifying the surface of the siRNA-containing polyplexes substantially improved their stability in physiological solutions. Using polymer-coated GPL-based polyplexes containing anti-Luciferase siRNA, we finally also obtained some initial proof-of-principle for time- and concentration-dependent target-specific gene silencing, suggesting that these systems hold significant potential for further in vitro and in vivo evaluation.

Polyplexes are polyelectrolyte complexes of DNA and polycations, designed for potential gene delivery. We investigated the properties of new polyplexes formed from cholesterol-modified polycations and DNA. Three complexes were tested; their cholesterol contents were 1.4, 6.3, and 8.7 mol %. UV spectroscopy and fluorescence assay using ethidium bromide proved the formation of polyplexes. The kinetics of turbidity of polyplexes solutions in physiological solution showed that the colloid stability of polyplexes increases with increasing content of cholesterol in polycations. Dynamic, static, and electrophoretic light scattering, small-angle X-ray scattering, and atomic force microscopy were used for characterization of polyplexes. The observed hydrodynamic radii of polyplexes were in the range of 30-60 nm; they were related to the polycation/DNA ratio and hydrophobicity of the used polycations (the cholesterol content). The properties of polyplex particles depend, in addition to polycation structure, on the rate of polycation addition to DNA solutions.

The amphiphilic polystyrene- block-poly((sulfamate-carboxylate)isoprene) (PS-PISC) diblock copolymer was synthesized from the precursor diblock copolymer polystyrene- block-isoprene by reaction with chlorosulfonyl isocyanate. The structure and behavior of self-assembled PS-PISC nanoparticles was studied in alkaline and acidic aqueous solutions by a combination of static and dynamic light scattering, analytical ultracentrifugation, atomic force and cryogenic transmission electron microscopies, NMR spectroscopy, potentiometric titration, and fluorometry using pyrene as a polarity-sensitive fluorescent probe. It was found that PS-PISC exists in aqueous solutions in the form of micellar aggregates. The aggregation tendency increases with decreasing effective charge density in the shell, that is, with decreasing pH of the solution, and aggregates found in alkaline aqueous media have much smaller molar masses than those formed in acidic media. The latter are dense, collapsed structures with immobile PISC domains in which most of the COOH and NH 2 (+)SO 3 (-) groups are buried inside of the nanoparticles. The swelling of PISC domains and disentanglement of PISC chains after addition of a base are slow processes occurring on the time scale of days.

In this work we report a new type of pH-responsive micelle-like nanoparticle. Reversible nanoscale structures are formed in solutions of a pH-sensitive hydrophobic polyelectrolyte, poly( N-methacryloyl- l-valine) or poly( N-methacryloyl- l-phenylalanine), and nonionic surfactant (Brij 98) in the presence of hydrochloric acid. The influence of composition and pH on particles size and shape was investigated by a variety of methods. An entity's size and polydispersity could be varied in a broad range making them a perspective candidate as a drug carrier. Unlike the case of typical micelles, our results indicate the presence of cavities in the formed particles. A hypothetical model of a nanoparticle and mechanism of formation are proposed.

Aqueous solutions of self-assembled nanoparticles formed by biocompatible diblock copolymers of poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-PEO) with the same molar mass of the PEO block (5000 g mol-1) and three different molar masses of the PCL block (5000, 13 000, and 32 000 g mol-1) have been prepared by a fast mixing the copolymer solution in a mild selective solvent, tetrahydrofuran (THF)/water, with an excess of water, that is, by quenching the reversible micellization equilibrium, and a subsequent removal of THF by dialysis of the water-rich solution against water. The prepared nanoparticles have been characterized by static and dynamic light scattering and atomic force microscopy imaging. It was found that stable monodisperse nanoparticles are formed only if the initial mixed solvent contained 90 vol % THF. The results show that the prepared nanoparticles are spherical vesicles with relatively thick hydrophobic walls, that is, spherical core/shell nanoparticles with the hollow core filled with the solvent.

Centrifugation was applied to study the transport phenomena in various suspensions of charged colloidal silica particles. Isopycnic focusing of colored density marker beads was used to view the evolution of the density gradient and to determine its steady-state shape from the measured positions of the focused zones. The effect of the ionic and nonionic solutes on the transient and steady states was studied. The experimental results are discussed in relation with the published theoretical dependence of the transport coefficients on the volume fraction of the settling particles. The understanding of the transport phenomena and of the interfering particle interactions governing the formation of the density gradient and the subsequent isopycnic focusing under model static conditions is necessary for the optimization of the isoperichoric focusing field-flow fractionation dynamic experiments, but it should allow a more accurate description of the relaxation phenomena and retention in polarization field-flow fractionation as well. Some previous experimental results concerning the study of the transport phenomena of the charged silica particles in an electric field are exploited here to demonstrate the general character of the observed behavior, independent of the field nature. Copyright 2000 Academic Press.

The kinetics of transport phenomena generated by an electric field and leading to the formation of density gradients in suspensions of charged colloidal silica were studied by using various electrodes. The rate of approach to a steady-state density gradient was found to be much higher when using metallic electrodes (Cu, Fe, and Pt) in comparison with graphite (C) electrodes. Nevertheless, the initial rate with C electrodes was substantially increased by the addition of hydroquinone-quinone because the redox reactions, necessary for electrode-electrolyte current transfer, occur at lower potential compared with the electrolysis of water. On the other hand, the products of oxidation of hydroquinone which accumulate in the system bring about an important decrease of the zeta potential of silica particles and progressive deceleration of their electrophoretic mobility. A detailed study was carried out, by using thin-layer isoperichoric focusing, UV-vis spectrophotometry, and voltamperometry, to explain the observed phenomena which can interfere in electric polarization or focusing field-flow fractionation. Copyright 2000 Academic Press.