Poly(oxymethylene) crystals grown in the polymerization of trioxane initiated with perchloric acid in nitrobenzene

Summary Nascent crystalline poly(oxymethylene) (POM) was synthesized by cationic polymerization of trioxane with anhydrous perchloric acid in nitrobenzene solution. The high polarity of the solvent enabled to obtain high molecular weight polymer. Also the yield obtained indicates that the polymerization reached the expected thermodynamic ceiling-equilibrium. The participation of free oxy carbenium ions from growing POM-chains are relevant on the mecha nism of polymerization and crystallization. After an induction period, hexagonal single crystals of POM are formed whose macro conformation correspond to extended chain crystals. Thermal da ta is in agreement with this morphology, typical of a simultaneous polymerization and crystallization. The spiral growth of the crystals proceeds by a catalyzed crystal growth process.     

Morphology of nascent polyoxymethylene obtained by polymerization of trioxane in nitrobenzene solution

The morphology of the crystal structure of nascent polyoxymethylene (POM) obtained by cationic polymerization of trioxane in nitrobenzene was investigated by optical and electron microscopy. It was found that the morphology depends on temperature and conversion of polymerization at constant initial monomeric concentration (1.5 mol/l). Morphological changes were observed near the equilibrium concentration of trioxane in nitrobenzene (1.5 mol/l, 35°C). At lower temperatures (10–30°C), thin lamellar crystallites, organized in spherulites, are formed by successive polymerization and crystallization. At higher temperatures (40–90°C), thick crystallites organized in oval structures are formed by simultaneous polymerization and crystallization. Peculiarities of crystal formation of POM, obtained by simultaneous and successive polymerization and crystallization, are discussed.     

In Situ polymerization in binary polymer/monomer mixtures: A novel route to polymeric composites

The formation of a polymer/polymer composite by solid-state polymerization of trioxane (TOX) crystals grown within binary trioxane/polycaprolactone or trioxane/poly(oxythylene) mixtures is reported. At present, such composites have been formed with trioxane-rich (hypoeutectic) mixtures. It is observed that in this composition range, much higher yields are obtained through thermal orientation of the TOX crystals which result in very highly ordered systems as revealed by optical and electron microscopy. These POM-rich composites were not, however, amenable to mechanical testing.     

Poly(alkylene oxide) ionomers: 1. Copolymerization of trioxane by gas phase mixing of comonomers and initiator

Uniform copolymers of trioxane with 1,3-dioxolane and ethyl glycidate of various comonomer compositions were prepared. A special reactor was used which allowed mixing of comonomers and initiator in the gas phase above the polymerization temperature of the mixture. Polymerization was accomplished by rapidly quenching the initiated mixture to dry ice temperature, giving polymer yields in excess of 80%. The polymers were either base treated or endcapped with propionic anhydride to obtain stable materials. The copolymers of trioxane and ethyl glycidate were treated with sodium hydroxide in aqueous dioxane at 85°C to give polyoxymethylene (POM) ionomers. The polymeric sodium salts could also be exchanged to other alkali salts of POM ionomers with various alkali chlorides while the polymers were either in suspension or in film form. Treatment of the sodium salts with acetic acid gave the free POM carboxylic acids. All polymers were characterized by their inherent viscosity, infra-red spectrum and p.m.r. spectrum.     

Interfacial reaction and its influence on phase morphology and impact properties of modified‐polyacetal/thermoplastic polyurethane blends

The cationic polymerization of 1,3,5‐trioxane, 1,3‐dioxolane and a small amount of 2‐hydroxyacetic acid (HAA) was carried out, and the resulting modified‐polyacetal (POM) was blended with thermoplastic polyurethane (TPU) in melt. The results of ¹H NMR analysis indicated that HAA was almost incorporated in the modified‐POM, and that the resulting carboxyl end‐group and hydroxyl end‐group in the modified‐POM reacted with TPU during the melt blending. There were many boundary layers between the cavities and matrix in the modified‐POM/TPU (82/18 by weight) blend that was etched with tetrahydrofuran (THF), and the diameter of the cavities became ～0.3–1 μm long when the blending time reached 10 min. The results of scanning electron microscopic (SEM) observation and dynamic mechanical analysis (DMA) indicated that the modified‐POM/TPU blend had a good compatibility because of the interfacial reaction between the modified‐POM and TPU phase in the blend. The modified‐POM/TPU blend exhibited higher Charpy impact strength when compared with a normal‐POM/TPU blend; the toughness of the modified‐POM/TPU blend attributed to the good compatibility between the two phases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4375–4382, 2006     

On the Fine Structure of Shish-Kebabs in Injection Moulded Polyethylene

Abstract

The fine structure of melt-crystallized shish-kebabs is investigated by means of TEM, SAXS, DSC and RS. In addition to the well known two morphological entities (shish and kebab), a third entity called “transitional zone” has been detected by TEM and two independent SAXS maxima. The transitional zone is characterized by a crystal morphology somewhere in between the shish and kebab crystals and a comparatively high connectivity of molecules along those crystals. In situ SAXS experiments at elevated temperatures reveal the change of the size of this zone with crystallization conditions.     

Thermoplastic Polyurethane-Encapsulated Melamine Phosphate Flame Retardant Polyoxymethylene

Due to its “unzipping” degradation mode and poor compatibility with most other flame retardants, polyoxymethylene (POM) is the most difficult flame-retarded polymer among macromolecular materials. In this project, we took advantage of thermoplastic polyurethane (TPU) resin, which possesses good compatibility with POM, serving as an encapsulation layer, and the carrier resin of the nitrogen-phosphorus composite flame retardant melamine phosphate to achieve even and fine dispersion of the flame retardant particles in the POM matrix. The improved morphology of the dispersion phase can markedly modify the flame retardancy and good mechanical performance. Additionally, the encapsulation of TPU avoids direct contact of the flame retardant with POM, thus also advantageous to the enhancement of its material performance. Moreover, as an efficient formaldehyde absorbent and toughening agent, TPU itself can greatly improve the flame retardancy, thermal stability, and toughness of the flame retardant POM. Therefore, this method provides a simple and effective method to prepare flame retardant POM with good comprehensive performance.     

Mechanical behavior of polytetrafluoroethylene around the room-temperature first-order transition

The effect of the room-temperature first-order transition on the plastic yield behavior of polytetrafluoroethylene (PTFE) has been investigated. Stress-strain curves were measured at different strain rates and temperatures. Tensile creep under constant dead load was also measured as a function of temperature and stress level. The effect of degree of crystallinity was investigated by using both a rapidly quenched and slow-cooled polymer. Observations were extended to large deformations, so that the phenomenon primarily observed was plastic yield rather than linear viscoelastic behavior. The curve of yield stress vs. temperature in the temperature range from –50 to +68°C was found to be almost identical with the curve of elastic modulus vs. temperature; the yield stress shows a marked local decrease at the first-order transition. The yield elongation was almost constant (at about 5%) over this same range, which is in accord with the above result. The more highly crystalline polymer is always more rigid than the less crystalline polymer at small deformations, but above 19°C its stress-strain curve shows a “cross-over” in stress level with the curve of the less crystalline polymer as extension increases. That is, above 19°C the less crystalline polymer shows a more rapid rate of “strain hardening”, even though the strain-hardening effect is pronounced in both polymers. Attempts to apply time-temperature superposition to creep data at different temperatures were partially successful; the lateral shifts required corresponded to an activation energy of approximately 80 kcal. The experimental observations suggest a model of the solid-state structure of PTFE which could be described as an “elastic-plastic network”, in which crystalline domains are connected by elastic amorphous regions, and in which the crystalline domains can flow plastically at sufficiently high stress or temperature.     

Development of a new advanced process for manufacturing polyacetal resins. Part III. End-capping during polymerization for manufacturing acetal homopolymer and copolymer

Conventionally, acetal homopolymer or copolymer is obtained by the polymerization of formaldehyde or trioxane, following the end-capping using acetic anhydride or unzipping of the unstable polymer end fraction. First, Asahi Chemical developed a new process to obtain an end-capped polymer during polymerization of highly purified formaldehyde using acetic anhydride as the chain-transfer agent. Use of highly purified formaldehyde and endcapping during polymerization using acetic anhydride as a chain-transfer agent or an endcapping agent will provide a simple process for manufacturing acetal homopolymer. The polymerization mechanism was confirmed by infrared spectroscopy analysis and proton NMR analysis of the polymer obtained. Second, for the acetal copolymer, purified trioxane was copolymerized with ethylene oxide in the presence of methylal, which gave an endcapped polymer with high thermal stability. Two new intermediates from the initiation reaction of the copolymerization, 1,3,5,7-tetraoxacyclononane (TOCN) and 1,3,5,7,10-pentaoxacyclododecane (POCD), were isolated and a new initiation mechanism was proposed. © 1993 John Wiley & Sons, Inc.     

In Vivo Incorporation of Azide Groups into DNA by Using Membrane‐Permeable Nucleotide Triesters

Metabolic incorporation of bioorthogonal functional groups into cellular nucleic acids can be impeded by insufficient phosphorylation of nucleosides. Previous studies found that 5azidomethyl‐2′‐deoxyuridine (AmdU) was incorporated into the DNA of HeLa cells expressing a low‐fidelity thymidine kinase, but not by wild‐type HeLa cells. Here we report that membrane‐permeable phosphotriester derivatives of AmdU can exhibit enhanced incorporation into the DNA of wild‐type cells and animals. AmdU monophosphate derivatives bearing either 5′‐bispivaloyloxymethyl (POM), 5′‐bis‐(4‐acetoxybenzyl) (AB), or “Protide” protective groups were used to mask the phosphate group of AmdU prior to its entry into cells. The POM derivative “POM‐AmdU” exhibited better chemical stability, greater metabolic incorporation efficiency, and lower toxicity than “AB‐AmdU”. Remarkably, the addition of POM‐AmdU to the water of zebrafish larvae enabled the biosynthesis of azide‐modified DNA throughout the body.     

Studies of the fractionation of polyoxymethylene

The precipitation of polyoxymethylene in p-chlorophenol solution and the molecular weight fractionation of the polymer by mechanical agitation were investigated. The agitation of the solution was carried out in a glass vessel with a stirrer, usually at 60°C. After agitation for several minutes a fibrous polymer precipitated. High molecular weight polymer precipitated around the stirrer in an early stage, and therefore the method might be applied to the fractionation of polyoxymethylene. The method was applied to the fractionation of polyoxymethylene prepared in a solid-state and in a solution polymerization of trioxane, catalyzed by BF₃.OEt₂. It was found that the polymer from the solid state contained a small amount of extremely high molecular weight fraction, and that obtained from the solution had a relatively narrow distribution of molecular weight.     

Synthese und Eigenschaften von Polyacetylen

Polyacetylene is important because it can be transferred into metallic conducting phases by treatment with strong oxidizing or reducing agents (“doping”). The influence of the reaction conditions, especially of the polymerization catalyst, are investigated. The polymers obtained under normal conditions are always crosslinked. The morphology is independent of the polymerization method and can be described as an aggregation of lamellar particles with typical dimensions of a few 100 Å. The polymer chains are oriented perpendicular to the surface and chain folding is observed. The crystal structures of cis and trans polyacetylene are given. The consequences of the morphology on the mechanism of doping and charge transport are discussed using general structural principles.     

Generation of orthorhombic polyoxymethylene in a cationic polymerization system of trioxane

Orthorhombic polyoxymethylene, which was originally found two decades ago in Italy in a polymerization system of aqueous formaldehyde, has been rediscovered in a cationic polymerization system of trioxane designed to grow needle-like polyoxymethylene single crystals. Besides the single crystals obtained in the liquid phase, it has been known that a thin film bearing a number of particles, up to ～ 1 mm diameter, is formed as a by-product on the inner wall in contact with the gaseous phase. X-ray analysis has now revealed that the particles consist essentially of the orthorhombic crystalline form. The morphology has been investigated and the growth mechanism briefly discussed.     

One-step synthesis of electrically conductive polyaniline nanostructures by oxidative polymerization method

A simple, rapid and efficient route to prepare polyaniline nanostructures (PANI-NS) by “one-step chemical oxidative polymerization” method is described. This method possesses advantages in terms of good yield, short reaction time, neat conditions and cost-effectiveness. The morphology of the PANI-NS was investigated by field-emission scanning electron microscopy (FE-SEM). The average diameter of single PANI-NS was calculated to be ～376 nm. Results from UV–visible spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry (CV) reveals the existence of PANI units present in the polymeric nanostructures. Also, electrical conducting property of the PANI-NS was analyzed using four-probe measurement method.     

Polyaniline self‐assembled with DTPA: Facilely tuned morphology and properties

The effects of pH profile and “soft template” during aniline chemical oxidative polymerization (COP) were investigated and evaluated simultaneously with diethylene triamine pentaacetic acid (DTPA) as a structural directing agent. Formation of PANI nanotubes and nanoparticles, smooth microspheres, and urchin‐like microspheres were illustrated by evaluating the pH profile during aniline COP while considering the “soft template” effects of DTPA. PANI nanosheets with two semicurled edges were found in the system producing nanotubes, which provides an evidence for the “curling mechanism” of PANI nanotube formation. With different pH profiles, chemical structures and aggregation structures of the as‐synthesized PANI micro/nanostructures are similar, whereas their conductivity, wettability, Cr (VI) adsorption, and electrochemical behaviors are distinct. The present study indicates that if properly conducted, pH profile adjustment is more effective than “soft template” to control the morphology and to optimize the performance of PANI micro/nanostructures. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42403.     

Amorphous phase and crystalline morphology in blend of two polymorphic polyesters: Poly(hexamethylene terephthalate) and poly(heptamethylene terephthalate)

Crystalline/crystalline blends of two polymorphic aryl-polyesters, poly(hexamethylene terephthalate) (PHT) and poly(heptamethylene terephthalate) (PHepT), were prepared and the crystallization kinetics, polymorphism behavior, spherulite morphology, and miscibility in this blend system were probed using polarized-light optical microscopy (POM), differential scanning calorimetry (DSC), temperature-resolved wide-angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS). The PHT/PHepT blends of all compositions were proven to be miscible in the melt state or quenched amorphous glassy phase. Miscibility in PHT/PHepT blend leads to the retardation in the crystallization rate of PHT; however, that of PHepT increases, being attributed to the nucleation effects of PHT crystals which are produced before the growth of PHepT crystals. In the miscible blend of polymorphic PHT with polymorphic PHepT, the polymorphism states of both PHT and PHepT in the blend are influenced by the other component. The fraction of the thermodynamically stable β-crystal of PHT in the blend increases with increasing PHepT content when melt-crystallized at 100 °C. In addition, when blended with PHT, the crystal stability of PHepT is altered and leads to that the originally polymorphic PHepT exhibits only the β-crystal when melt-crystallized at all T_c's. Apart from the noted polymorphism behavior, miscibility in the blend also shows great influence on the spherulite morphology of PHT crystallized at 100 °C, in which the dendritic morphology corresponding to the β-crystal of PHT changes to the ring-banded in the blend with higher than 50 wt% PHepT. In blends of PHT/PHepT one-step crystallized at 60 °C, PHepT is located in both PHT interlamellar and interfibrillar region analyzed using SAXS, which further manifests the miscibility between PHT and PHepT.     

The ring-opening polymerization of D,L-lactide in the melt initiated with tetraphenyltin

Melt polymerization conditions for D ,L -lactide initiated with tetraphenyltin were studied with regard to polymer molecular weight and weight distributions. “Single” polymerization, “multiple” polymerization (four or eight reactions at the same time), and time-dependent studies are described. Single polymerizations using constant initiator concentrations resulted in a broad scattering of nonreproducible molecular weight values. Multiple polymerizations at constant initiator concentrations, however, resulted in nearly identical molecular weight profiles. Multiple polymerizations at different initiator concentrations did not show an inverse dependency of initiator concentration on polymer molecular weight. Both the single and multiple melt polymerizations resulted in rather broad molecular weight distributions. The presence of hydrolysis products of lactide during the melt polymerization most likely has a detrimental effect on molecular weight. After a short induction period the rather slow polymerization of D ,L -lactide resulted in a maximal molecular weight followed by a slight decrease in molecular weight to a constant value. It is concluded that the polymerization of D ,L -lactide in the melt initiated with tetraphenyltin does not proceed through a “living” mechanism.     

Studies on the preparation of branched polymers from styrene and divinylbenzene

The self‐condensing vinyl polymerization of styrene and an inimer formed in situ by atom transfer radical addition from divinylbenzene and 2‐bromoisobutyl‐tert‐butyrate using atom transfer radical polymerization technique was studied. To study the polymerization mechanism and achieve high molecular weight polymer in a high polymer yield, the polymerization was carried out in bulk at 80°C. Proton nuclear magnetic resonance (¹H‐NMR) spectroscopy and gel permeation chromatography (GPC) coupled with multiangle laser light scattering (MALLS) were used to monitor the polymerization process and characterize the solid polymers. It is proved that the polymerization shows a “living” polymerization behavior and the crosslinking reaction has been restrained effectively due to the introduction of styrene. Polymers with high molecular weight (M_w.MALLS > 10⁵) can be prepared in high yield (near 80%). Comparison of the apparent molecular weights measured by GPC with the absolute values measured by MALLS indicates the existence of branched structures in the prepared polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Optimisation of the synthesis of vancomycin-selective molecularly imprinted polymer nanoparticles using automatic photoreactor

A novel optimized protocol for solid-state synthesis of molecularly imprinted polymer nanoparticles (nanoMIPs) with specificity for antibiotic vancomycin is described. The experimental objective was optimization of the synthesis parameters (factors) affecting the yield of obtained nanoparticles which have been synthesized using the first prototype of an automated solid-phase synthesizer. Applications of experimental design (or design of experiments) in optimization of nanoMIP yield were carried out using MODDE 9.0 software. The factors chosen in the model were the amount of functional monomers in the polymerization mixture, irradiation time, temperature during polymerization, and elution temperature. In general, it could be concluded that the irradiation time is the most important and the temperature was the least important factor which influences the yield of nanoparticles. Overall, the response surface methodology proved to be an effective tool in reducing time required for optimization of complex experimental conditions.     

Polymerization of p-cresyl glycidyl ether catalyzed by imidazoles I. The influence of the imidazole concentration,the reaction temperature,and the presence of isopropanol on the polymerization

The polymerization of p-cresyl glycidyl ether catalyzed by imidazoles has been investigated as a model reaction for the polymerization of technical epoxy resins. The dependence of oligomer yield on time, temperature, and imidazole concentration, the distribution of the polymerization degrees, and the influence of isopropanol have been studied. The reaction rate and the average degree of polymerization are affected by the presence or absence of a secondary nitrogen on the imidazole, i.e., different results are obtained when 2-ethyl, 4-methyl imidazole (EMI) or 1-methyl imidazole (1-MIA) are used. 1-MIA seems to be “precursor” of the catalyst rather than a catalyst by itself. The comparisons of CGE polymerizations catalyzed by 1-MIA in the absence and presence of isopropanol show only quantitative differences: The polymerization in the presence of isopropanol is faster, and the average degree of polymerization is shifted to higher values. The activation energies of CGE polymerizations catalyzed by different imidazoles have been determined.