Non-crystalline Polymers Research Articles

LLDPE/TiO2 nanocomposites produced from different crystallite sizes of TiO2 via in situ polymerization

Nano-TiO2 particles with a range of crystallite sizes were synthesized by a conventional sol-gel method, and then used as nanoparticle substrates in the synthesis of LLDPE/TiO2 nanocomposites via in situ polymerization of ethylene/1-hexene with zirconocene/MMAO catalyst. It was found that the size of the nano-TiO2 crystallite nanoparticles can influence the catalytic activity in the polymerization system. The larger nano-TiO2 crystallites provided better catalytic activity in the polymerization system due to more space for monomer attack. In addition, by thermo-gravimetric analysis, it can be seen that the larger nano-TiO2 crystallites also exhibited lower interaction with available MMAO. Consequently, the MMAO reacted more efficiently with the zirconocene catalyst during the activation process, and enhanced polymerization catalysis. All the polymer nanocomposites products did not have well defined melting temperature indicating non-crystalline polymers. This is due to the high amount of hexene incorporation (based on 13C NMR). The difference in crystallite sizes of the nano-TiO2 also affected how 1-hexene became incorporated into the polymer nanocomposites. The smaller crystallite size of nano-TiO2 allowed greater 1-hexene incorporation due to depression of the reactivity of the ethylene. The contribution of this work helps develop a better understanding of the role of nano-TiO2 in the catalytic activity of the polymerization system and in the microstructure of the polymer composite product. However, this study only considers work on the laboratory scale, so for commercial application of these results, it is necessary to scale up the polymerization process. It is only at this stage, that other physical properties, such as the mechanical properties of these materials can be sensibly determined.

Construction, Characterization and Biological Activity of Chiral and Thermally Stable Nanostructured Poly(Ester-Imide)s as Tyrosine-Containing Pseudo-Poly(Amino Acid)s

In this paper we studied the synthesis of biodegradable optically active poly(ester-imide)s containing different amino acid residues in the main chain. These pseudo-poly(amino acid)s were synthesized by polycondensation of N,N′-(pyromellitoyl)-bis-l-tyrosine dimethyl ester as a diphenolic monomer and two chiral trimellitic anhydride-derived diacid monomers containing s-valine and l-methionine. The direct polycondensation reaction of these diacids with aromatic diol was carried out in a system of tosyl chloride (TsCl), pyridine (Py) and N,N′-dimethylformamide (DMF) as a condensing agent. The structures and morphology of these polymers were studied by FT-IR, 1H-NMR, powder X-ray diffraction, field emission scanning electron microscopy (FE-SEM), specific rotation, elemental and thermogravimetric analysis (TGA) techniques. TGA profiles indicate that the resulting PEIs have a good thermal stability. Morphology probes showed these polymers were noncrystalline and nanostructured polymers. The monomers and prepared polymers were buried under the soil to study the sensitivity of the monomers and the obtained polymers to microbial degradation. The high microbial population and prominent dehydrogenase activity in the soil containing polymers showed that the synthesized polymers are biologically active and microbiologically biodegradable. Wheat seedling growth in the soil buried with synthetic polymers not only confirmed non-toxicity of polymers but also showed possibility of phyto-remediation in polymer-contaminated soils.

Piezoelectric Properties of Non‐Polar Block Copolymers

Most polymers are typical dielectric materials, but recent research in our group has shown that nanostructured block copolymer morphologies exhibit new and unexpected electroactive behavior. We present herein the fi rst study of converse piezoelectric properties in non-crystalline polymer systems, consisting of non-polar monomers, and evaluate its evolution with temperature to yield detailed information on electric fi eld‐ polymer interaction on a molecular level. The observed properties should hold generally and suggest that block copolymers may provide a valuable new route to piezoelectric materials. So far, mostly inorganic, perovskite structured ceramics, many of them titanate derivatives such as lead zirconate titanate (PZT), dominate the fi eld of commercial piezoelectric applications. Nanogenerators, fi eld-effect transistors, strain, and optoelectronic sensors are only few of many applications for this interesting class of materials. [ 1 , 2 ] Whilst the piezoelectric properties of many of these crystals and ceramics are well

Kadanoff-Baym Approach to Entropy Production inO(N) Theory with Next-to-Leading Order Self-Energy

Left in a dry. atmosphere for a while, gels become glasslike dehydrated substances. We investigated the dehydration process of some gels by adopting simultaneous time-resolved measuring method of weight and other properties. The feature during the dehydration process was different depending on the properties of the network and solvent in gel. Besides, in the DTA measurements of the dehydrated egg white gel, we observed an endothermic peak of which the intensity and peak position increased with elevating heating rate, similar to the glass transition in the non-crystalline polymers.

Crosslinking of Trimethylene Carbonate and D, L‐Lactide (Co‐) Polymers by Gamma Irradiation in the Presence of Pentaerythritol Triacrylate

High-molecular-weight (co)polymers of trimethylene carbonate and D,L-lactide are efficiently crosslinked using PETA during gamma irradiation. Form-stable networks with gel contents of 86 ± 5 to 96 ± 1 are obtained from non-crystalline (co)polymers. Glass transition temperatures and elastic moduli of the networks can be varied by adjusting the copolymer composition. The PETA-containing (co)polymer networks are not cytotoxic. Upon incubation in macrophage cultures for 14 d, all (co)polymer films and PETA-containing network films erode to varying extents, showing that these materials can be degraded by cell-mediated erosion processes. This method is very useful for the facile preparation of TMC- and DLLA-containing form-stable networks from high-molecular-weight polymers.

Pseudo-poly(amino acid)s: study on construction and characterization of novel chiral and thermally stable nanostructured poly(ester-imide)s containing different trimellitylimido-amino acid-based diacids and pyromellitoyl-tyrosine-based diol

A new class of chiral and potentially biodegradable poly(ester-imide)s (PEI)s as pseudo-poly(amino acid)s (PAA)s bearing natural amino acids in the main chain was synthesized. In this investigation, N,N′-(pyromellitoyl)-bis-(L-tyrosine dimethyl ester) as a biodegradable optically active diphenol and synthesized trimellitic anhydride-derived dicarboxylic acids containing different natural amino acids such as S-valine, L-methionine, L-leucine, L-isoleucine, and L-phenylalanine were used for direct polyesterification. With the aim of tosyl chloride/pyridine/N,N′-dimethylformamide system as a condensing agent, the new optically active PEIs were obtained in good yields and moderate inherent viscosity up to 0.42 dL/g. The obtained polymers were characterized with FT-IR, 1H-NMR, X-ray diffraction (XRD), field emission scanning electron microscopy, elemental, and thermogravimetric analysis techniques. These polymers show high solubility in organic solvents, such as N,N′-dimethyl acetamide, N-methyl-2-pyrrolidone, and sulfuric acid at room temperature, and are insoluble in solvents, such as methylene chloride, cyclohexane, and water. Morphology probes showed these pseudo-poly(amino acid)s were noncrystalline and nanostructured polymers. On the basis of thermogravimetric analysis data, such PAAs are thermally stable and can be classified as self-extinguishing polymers. In addition due to the existence of amino acids in the polymer backbones these pseudo-PAAs not only are optically active but also are expected to be biodegradable and therefore could be classified under eco-friendly polymers.

Influence of ordering change on the optical and thermal properties of inflation polyethylene films

Changes of thermal diffusivity inside femtosecond laser-structured volumes as small as few percent were reliably determined (with standard deviation less than 1%) with miniaturized sensors. An increase of thermal diffusivity of a crystalline high-density polyethylene (HDPE) inflation films by 10–20% from the measured (1.16 ± 0.01) × 10 −7 m 2 s −1 value in regions not structured by femtosecond laser pulses is considerably larger than that of non-crystalline polymers, 0–3%. The origin of the change of thermal diffusivity are interplay between the laser induced disordering, voids’ formation, compaction, and changes in molecular orientation. It is shown that laser structuring can be used to modify thermal and optical properties. The birefringence and infrared spectroscopy with thermal imaging of CH 2 vibrations are confirming inter-relation between structural, optical, and thermal properties of the laser-structured crystalline HDPE inflation films. Birefringence modulation as high as Δ n ∼ ± 1 × 10 −3 is achieved with grating structures.

A simple model for cooperative and non-exponential processes in non-crystalline polymers

A quite simple Markov chain model is presented in an attempt to understand several characteristic properties of the structural relaxation in glass-former materials. A second order Markov model is proposed for a small region of the material. Only a few parameters are necessary for the definition of the material in the model equations namely the energy levels accessible to that small region and the transition probabilities between them. The later are considered dependent on the energy levels and the potential barrier heights between them, on temperature, on a reference transition rate parameter and on a cooperativity or memory parameter related to the interaction with the neighbour regions. Isothermal relaxations at different temperatures were simulated with selected values of the model parameters. As a result, non-exponentiality of energy relaxations and its temperature dependence appears directly related to the cooperativity parameter. Markov chain model shows also non-linearity and memory effects, and a transition between two different regimes in the dependence of the relaxation times with temperature.

Morphology development and exclusion of noncrystalline polymer during crystallization in PVDF/PMMA blends

Morphology development during the crystallization of poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends was investigated at various crystallization temperatures ( T C) by means of time-resolved light scattering measurements and atomic force microscopy (AFM). A coarse spherulite obtained at a high T C of 162 °C was found to be developed with a two-step crystallization process. The ordering in the spherulites ( Pr) increased with time at the early stages and then decreased at the later stages. The rate of spherulite growth started to decrease when Pr started to decrease. In contrast, in the compact spherulite obtained at a low T C of 148 °C, Pr decreased monotonously with time while the growth rate was constant. AFM observation revealed that such characteristic crystallization behavior is attributed to the exclusion of PMMA from the crystal growth during the crystallization; i.e., the amount of excluded PMMA becomes larger as the distance from the spherulite center increases and the crystallization temperature rises.

Mechanism of hydrostimulated displacement of aromatic compounds from cellulose triacetate films

The effect of temperature on the rate of desorption into water of naphthalene, diphenyl, benzophenone, para-terphenyl, α-naphthol, stilbene, anthracene, and dibutyl phthalate introduced into cellulose triacetate films was studied. It was shown that in water, the removal rate of these compounds from the films increases sharply as compared to desorption into air. The relation between the activation energies and pre-exponential factors characterizing the desorption rate was found in the form of a compensatory effect. The nature of the compensatory effect is explained by osmotic phenomena due to hydrophobic hydration of the polymer. We conclude that mobile polymeric chains of non-crystalline polymer are structured around water and Ar-compound molecules as sponge-like structures forming fringed nanoporous capsules. The simultaneous presence of molecules of different compounds in the polymer was found to cause osmotic competition for a place in the sponge; water absorbed by the chain sponge enhances the volume pulsations of nanocapsules. It was revealed that diffusion occurs because of thermal fluctuations inducing the reorganization of nanoporous capsules and their movement together with Ar-molecules in the matrix by the principle of peristalsis.

Assessment of the use of industrial by-products for induced reduction of As, and Se potential leachability in an acid soil

Four industrial by-products (phosphogypsum, PG; red gypsum, RG; sugar foam, SF and ashes from the combustion of biomass, ACB) were evaluated as possible amendments for reducing the leachability and bioavailability of As and Se in a metalloid-spiked acidic soil. The treatments were applied as single, double and triple amendments and at two different rates. The effectiveness of the treatments was evaluated after a series of leaching experiments using a chelating agent (DTPA solution) or a weak acidification (acetic acid at pH 4.93). The most effective treatments (ACB and RG, both applied at high rate) were identified by means of Cluster Analysis using the leachability indexes. Different sorption mechanisms involved in the overall reduction of metalloid leachability were identified using scanning electron microscopy (SEM-BSE and SEM-EDS). In the ACB-treated samples, Se was found associated to organic matter aggregates and to Fe compounds. In the RG-treated samples, EDS analyses showed that As and Se were associated to Fe/Ti (hydr)oxides phases which are present not only in the by-product as maghemite and rutile, but also in the soil as hematite and goethite. In addition, the application of RG induced the formation of non-crystalline Al-hydroxy polymers with As and Se in their composition.

Effect of Molecular Weight, Crystallinity, and Hydrophobicity on the Acoustic Activation of Polymer-Shelled Ultrasound Contrast Agents

Polymer-shelled microbubbles are applied as ultrasound contrast agents. To investigate the effect of the polymer on microbubble preparation and acoustic properties, polylactides with systematic variations in molecular weight, crystallinity, and end-group hydrophobicity were used. Polymer-shelled cyclodecane filled capsules were prepared by emulsification, and the cyclodecane was removed by lyophilization to obtain hollow capsules. Complete removal of cyclodecane from the microcapsules was only achieved for short chain (about M(w) 6000) crystalline polymers. The pressure threshold for acoustic destruction of the microbubbles was found to increase with molecular weight. Noncrystalline polymers showed a higher threshold for destruction than crystalline polymers. Hydrophobically modified short chain crystalline polymers showed the steepest increase in acoustic destruction after the threshold as a function of the applied pressure, which is a favorable characteristic for ultrasound mediated drug delivery. Microcapsules made with such polymers had an inhomogeneous surface including pores through which cyclodecane was lyophilized efficiently.

Computer simulation of geminate recombination in non-crystalline polymer solids

A computer simulation method is applied to model geminate charge recombination in non-crystalline polymer solids that exhibit charge transport anisotropy due to different intra- and interchain hopping rates. We investigate how the electron escape probability is affected by both the degree of charge transport anisotropy and morphology of polymer systems.

Phosphines as building blocks in coordination-based self-assembly

Although phosphines have been less widely investigated in coordination self-assembly than have N- and O-donor ligands, interesting and unusual chemistry has been observed from their study in this context. This includes the selective formation of large rings, unsaturated as well as complete coordination cages, solvent- and anion-dependent aggregation, in addition to ring-opening polymerisation to give crystalline or non-crystalline coordination polymers. Important aspects which underpin this chemistry include (i) soft donor character, (ii) pyramidal geometry at the donor atom, (iii) highly bulky and irregular shapes, (iv) the applicability of (31)P NMR spectroscopy, and (v) their relevance to organometallic chemistry and homogeneous catalysis. In this critical review, findings which precede the concept of self-assembly as adopted by synthetic chemists as well as the latest 'supramolecular' chemistry of phosphines are discussed together in an attempt to give the current state of the topic in its historical context. Finally, some aspects and opportunities which may be of interest in the future are suggested (107 references).

Liquid/Liquid Interfacial Polymerization To Grow Single Crystalline Nanoneedles of Various Conducting Polymers

Single crystalline nanoneedles of polyaniline (PANI) and polypyrrole (PPY) were synthesized using an interfacial polymerization for the first time. The interfacial crystallization of conductive polymers at the liquid/liquid interface allowed PANI and PPY polymers to form single crystalline nanocrystals in a rice-like shape in the dimensions of 63 nm x 12 nm for PANI and 70 nm x 20 nm for PPY. Those crystalline nanoneedles displayed a fast conductance switching in the time scale of milliseconds. An important growth condition necessary to yield highly crystalline conductive polymers was the extended crystallization time at the liquid/liquid interfaces to increase the degree of crystallization. As compared to other interfacial polymerization methods, lower concentrations of monomer and oxidant solutions were employed to further extend the crystallization time. While other interfacial growth of conducting polymers yielded noncrystalline polymer fibers, our interfacial method produced single crystalline nanocrystals of conductive polymers. We recently reported the liquid/liquid interfacial synthesis of conducting PEDOT nanocrystals; however, this liquid/liquid interfacial method needs to be extended to other conductive polymer nanocrystal syntheses in order to demonstrate that our technique could be applied as the general fabrication procedure for the single crystalline conducting polymer growth. In this report, we showed that the liquid/liquid interfacial crystallization could yield PANI nanocrystals and PPY nanocrystals, other important conductive polymers, in addition to PEDOT nanocrystals. The resulting crystalline polymers have a fast conductance switching time between the insulating and conducting states on the order of milliseconds. This technique will be useful to synthesize conducting polymers via oxidative coupling processes in a single crystal state, which is extremely difficult to achieve by other synthetic methods.

Surface Morphological Evolution of Ultrathin P4VP Films and Generation of Ordered Patterns on Graphite

AbstractThe spin‐coated thin‐film morphology of poly(4‐vinylpyridine) has been studied by AFM; the dark lines or disks (circular holes) in the AFM height images correspond to the depressed regions. An epitaxy‐like “nano‐trench” pattern was observed in the noncrystalline polymer film deposited on the crystalline graphite substrate. The transition from surface‐templated to isotropic dewetting occurs during 3 nm of the film thickness increase. This study presents an example of ordered nanopatterns emerging from the chaotic spin‐coating process. The well‐defined “nano‐trench” morphology offers an opportunity for the study of the nanoconfinement effect and provides a unique means for surface patterning and nanolithography.magnified image

Cellulose alkyl ester/poly(ε-caprolactone) blends: characterization of miscibility and crystallization behaviour

Cellulose valerate (CV)/poly(e-caprolactone) (PCL) blends were investigated to clarify the effect of the degree of substitution (DS) of the cellulose ester component on the miscibility. CVs of DS > 2.15 were miscible with PCL in their amorphous states, as judged from the detection of a single T g by differential scanning calorimetry (DSC). This result and other complementary data for cellulose acetate (CA), propionate (CP), and butyrate (CB) blends with PCL made up a miscibility map as a function of the number N of carbons in the normal acyl substituent as well as of DS. CB of N = 4 and CV of N = 5, the ester side-chains of which make a higher similarity in chemical structure with a repeating unit of PCL, were found to be miscible with the aliphatic polyester at a comparatively lower DS; the critical butyryl DS of ∼1.85 being still lower than 2.15. For PCL-rich compositions of CB(DS > 2.0)/PCL and CV(DS > 2.2)/PCL blends, isothermal melt-crystallization behaviour was characterized by calorimetry and polarized optical microscopy. The CB and CV components gave rise to a marked diminution of the crystallization rate of PCL, as a result of the diluent action of the cellulose esters in the respective miscible, molten mixtures. Through a quantitative analysis of the kinetics, it is suggested regarding the supramolecular morphology that the bulky cellulose esters would be trapped not only on the fold surfaces but also on the growth faces of PCL lamellar crystals, to form a non-crystalline mixed polymer phase in the crystal boundary regions.

Effect of Synthesis Conditions on Composition and Properties of Microspherical Catalyst for Polymerization of Propylene

Experimental data on the influence exerted by the synthesis conditions on the composition and properties of a microspherical catalyst for polymerization of propylene are presented. The possibility of using this catalyst for synthesis of noncrystalline propylene polymers is demonstrated.

Synthesis of Submicrometer Particles of a Stereoregular Polyolefin by Catalysis in Aqueous Dispersion

Stereoregular polyolefins are of vast academic and industrial interest.1 A multitude of polymer microstructures are accessible today via catalyst design. A control of polymer morphology is equally important. Polyolefin particle sizes and structures have been studied intensively in the context of traditional olefin polymerization processes. However, a synthesis of defined submicrometer particles of stereoregular polyolefins remains a challenge, despite the increasing general interest in the preparation of particles and other structures on the length scale of 1 nm to 1 μm (i.e., the colloidal range). Such defined particles, that is individual nonaggregated and thus easy to handle particles could be possible by preparing them in an aqueous dispersion, that is a polymer latex. Beyond the aforementioned fundamental interest in the synthesis of small particles, it can be noted that polymer dispersions are also of practical interest, e.g. for environmentally friendly coatings and paints.2 The early transition metal Ziegler or metallocene catalysts used traditionally for stereospecific olefin polymerization are very sensitive to water.3,4 Late transition metal catalysts are much more water-stable, and they enable the synthesis of polyolefin dispersions by ethylene polymerization in aqueous systems.5,6 However, transition metal catalysts most often polymerize 1-olefins in a nonstereospecific fashion.7 As an approach to the preparation of dispersions of submicrometer particles of stereoregular polyolefins, we have investigated catalytic polymerization in emulsion proceeded by polymer-analogous modification in the dispersed particles. Catalytic polymerization of butadiene with a CS2-modified cobalt catalyst yields latices of syndiotactic 1,2-polybutadiene (1,2-PBD).8 Catalytic hydrogenation9 of such latices seemed a possible route to stereoregular poly(1-butene) dispersions (Scheme 1). To the aqueous 1,2-PBD dispersion, ruthenium(III) tris(2,4-pentanedionate) and triphenylphosphine were added, and the emulsion was submitted to hydrogen pressure. Colloidal stability is fully retained despite the high reaction temperature (vide infra). The 1H NMR spectra of the polymer (Supporting Information, Figure S1) reveals the disappearance of the olefinic protons (5.0-5.5 ppm range), demonstrating complete hydrogenation (> 99%) of the double bonds present in the starting polymer (Table 1, entry 4, 75 bar H2). No metathesis, which could be conceivable,11 is observed. Remarkably already low hydrogen pressures (5 bar) are sufficient to hydrogenate a substantial part of the double bonds of the polymer as seen by NMR and IR (65%, entry 1). At higher pressures an increase of the degree of hydrogenation is observed (entries 2-4) under otherwise identical conditions. Reasonable conversions are only observed at temperatures greater than 100 °C (entry 5). Most likely, this effect relates to the necessity of some softening of the crystalline dispersed particles to facilitate diffusion of the hydrogen substrate and possibly also the catalyst in the initially highly crystalline latex particles. At 150 °C substantial coagulation was observed. Differential scanning calorimetry (DSC) measurements were performed on the isolated polymers obtained by precipitation from the dispersions (cf. Supporting Information, Figure S4). As expected, the high Tm of the 1,2-PBD (190 °C) is reduced by hydrogenation of part of the vinyl groups (65%, entry 1). Complete hydrogenation affords a rubbery, noncrystalline polymer. No thermal transitions are observed, in accordance with the properties expected for syndiotactic poly(1-butene).12 Transmission electronic microscopy (TEM) reveals how the increase of the degree of hydrogenation of the polymer dispersion results in soft particles, by comparison to the hard crystalline particles of the starting 1,2PBD dispersion (Figure 1). Chain scission resulting in substantial molecular weight decrease is a crucial issue for any polymeranalogous modification, albeit it appears unlikely for the reaction studied. GPC reveals no evidence for chain ruptures, e.g. for a >99% hydrogenated polymer (Table 1, entry 4) Mw ) 1.2 × 105 g mol-1 was determined vs Mw ) 1.1 × 105 g mol-1 for the 1,2-PBD starting material (Figure S6). This difference is within experimental error, given that these are apparent molecular weights (determined vs polyethylene standards). One of the remarkable attributes of this catalytic polymer-analogous modification is that it proceeds in * Corresponding author. E-mail: stefan.mecking@unikonstanz.de. Table 1. Hydrogenation Resultsa

Simulation of the Effect of Noncrystalline Species on Long Spacing in Crystalline/Noncrystalline Polymer Blends

A finite element model is used to predict the effect of composition on long spacing (L) in blends of crystalline and noncrystalline polymers. In this model, the diffusive transport of noncrystallizable moieties away from the crystals from which they are excluded is tracked. The effect of the local concentration of noncrystallizable material near the growing interface on the kinetics of crystallization is modeled. Parameters in the model are the Peclet number (Pe), the linear crystallinity (φc), and the overall concentration of noncrystallizable molecules (Co). The overall crystallization rate (T) depends on these three parameters. T is found to exhibit a maximum (Tmax) with respect to φc at given Co and Pe. It is shown that, over a considerable range of Pe and Co, Tmax exhibits either a nearly constant low value nor a nearly constant higher value. It is suggested that Tmax is the operating condition for such crystallization. From this hypothesis, expected values of long spacing are predicted. The dependence of L on Co is found to lie on either of two branches, depending on the value of Pe. Large Pe shows a small effect of Co on L, while high Pe exhibits a relatively large effect. These results agree with observations on blend systems.