Prepolymerization Time Research Articles

The Preparation and Performance of Epoxy/Acetylene Carbon Black Wave-Absorbing Foam.

The epoxy foam material filled with an absorbing agent effectively absorbs electromagnetic waves. In this study, epoxy resin was used as the matrix, and acetylene carbon black was used as the magnetic absorbing agent to prepare an absorbing foam material (epoxy/CB). The microstructure of acetylene carbon black (CB) and its distribution in epoxy resin, as well as the effects of pre-polymerization time and CB content on the foam structure, were systematically characterized. Additionally, two dispersion methods, the hot-melt in situ stirring dispersion method and the three-roll milling dispersion method, were studied for their effects on the foaming process and absorbing properties of epoxy/CB. The results showed that with the prolongation of pre-polymerization time, the pore size decreased from 1.02 mm to 0.4 mm, leading to a more uniform pore distribution. Compared to the hot-melt in situ stirring dispersion method, the three-roll milling dispersion method effectively improved the dispersion of CB in epoxy resin, reducing the aggregate size from 300-400 nm to 70-80 nm. The pore diameter also decreased from 0.453 mm to 0.311 mm, improving the uniformity of particle size distribution. However, the absorbing material prepared with the three-roll milling dispersion method exhibited unsatisfactory absorption performance, with values close to 0 dB at mid-low frequencies and around -1 dB at high frequencies. In contrast, the absorbing material prepared with the hot-melt in situ stirring dispersion method showed better absorption performance at high frequencies, reaching around -9 dB.

Study on polymerization kinetics of copolymerized flame-retardant polyamide 66: Apparent rate constant and reaction activation energy

The research of polymerization kinetics and reaction mechanism on flame-retardant polyamide 66 (FRPA66) is of great significance for its industrial production. Here, FRPA66 is prepared by one-step melt polycondensation of nylon 66 salt and a reactive flame retardant DPDA. By exploring the relationship of viscosity-average molecular weight versus reaction time at different polymerization stages, the apparent rate constant of FRPA66 is calculated to be 41.8 dL g−1s−1. Besides, molecular simulation analysis demonstrates that the reaction activation energy of DPDA and nylon 66 salt in pre-polymerization stage is 312.04 kcal/mol, indicating that the pre-polymerization time can be extended to make up for the lack of pre-polymerization power of FRPA66. In the final polymerization stage, reasonable control of releasing pressure and polymerization time can promote the self-condensation of a small part of DPDA, thus improving the molecular weight of FRPA66. Finally, based on the polymerization kinetic and reaction mechanism, FRPA66 containing 5% DPDA can reach V-0 level.

Preparation, Structure and Properties of Epoxy/Carbonyl Iron Powder Wave-Absorbing Foam for Electromagnetic Shielding.

The application of absorbing materials for electromagnetic shielding is becoming extensive, and the use of absorbents is one of the most important points of preparing absorbing foam materials. In this work, epoxy resin was used as the matrix and carbonyl iron powder (CIP) was used as the absorbent, and the structural absorbing foam materials were prepared by the ball mill dispersion method. Scanning electron microscopy showed that the CIP was evenly dispersed in the resin matrix. The foam structures formed at pre-polymerization times of 10 min, 30 min and 50 min were analyzed, and it was found that the cell diameter decreased from 0.47 mm to 0.31 mm with the increase in the pre-polymerization time. The reflectivity of the frontal and reverse sides of the foam gradually tends to be unified at frequencies of 2-18 GHz. When the CIP content increased from 30 wt% to 70 wt%, the cell diameter increased from 0.32 mm to 0.4 mm, and the uniformity of CIP distribution deteriorated. However, with the increase in the CIP content, the absorption properties of the composite materials were enhanced, and the absorption frequency band broadened. When the CIP content reached 70 wt%, the compression strength and modulus of the foam increased to 1.32 MPa and 139.0 MPa, respectively, indicating a strong ability to resist deformation.

Synthesis of poly(ionic liquid)s with high specific surface areas for m-cresol adsorption

Developing ideal adsorbents for moving phenolic compounds from aqueous solutions remains a challenge. Herein, novel poly(ionic liquid)s (PILs) of PIL-Ba-x and PIL-An-5 were prepared via Friedel–Crafts alkylation using benzyl alcohol and aniline auxiliary cross-linking agents, respectively, for the adsorption of m-cresol in the aqueous phase. The specific surface areas and pore volumes of the synthesized PILs can be adjusted by pre-polymerization time, thereby realizing the regulation of the adsorption property of m-cresol. Results showed that the adsorption kinetics of PILs conformed to pseudo-second-order kinetics and reached adsorption equilibrium within 6 min. Their adsorption thermodynamics conformed to the Langmuir models. Based on the fitting data of the Langmuir model, the maximum adsorption capacity of m-cresol by PIL-Ba-5 can reach 228 mg/g. Moreover, the mechanism analysis showed that hydrogen bonding, electrostatic interaction, and π–π interaction promoted the adsorption of m-cresol by PIL-Ba. After the adsorption of m-cresol was separated by anhydrous ethanol, the adsorbent was recovered at least five times, and the removal efficiency was stable.

Effects of Prepolymerization, Temperature, and Hydrogen Concentration on Kinetics of Propylene Bulk Polymerization Using a Commercial Ziegler-Natta Catalyst

The effects of prepolymerization, temperature, and hydrogen concentration on propylene bulk polymerization with a commercial Ziegler-Natta catalyst were investigated, and the apparent polymerization rate constants were estimated by varying reaction temperatures, hydrogen partial pressures, and polymerization methods. It was shown that prepolymerization has different effects on the polymerization rate and isotacticity of the polymer; without prepolymerization, the polymerization rate and isotacticity reach their maximum at 70°C and 80°C, respectively, whereas the polymerization rate and isotacticity with prepolymerization increase with the polymerization temperature in the range of 50-80°C. Moderate prepolymerization time reduced the fine fraction while increasing polymerization rate and isotacticity. Appropriate prepolymerization technique can increase mass transfer performance and fragmentation, which is a promising way to improve polymerization rate, isotacticity index, and fine fraction. Otherwise, insufficient prepolymerization or excessive prepolymerization causes prepolymer particle fragmentation.

A Facile Method for Generating a Smooth and Tubular Vessel Lumen Using a Viscous Fingering Pattern in a Microfluidic Device.

Blood vessels are ubiquitous in the human body and play essential roles not only in the delivery of vital oxygen and nutrients but also in many disease implications and drug transportation. Although fabricating in vitro blood vessels has been greatly facilitated through various microfluidic organ-on-chip systems, most platforms that are used in the laboratories suffer from a series of laborious processes ranging from chip fabrication, optimization, and control of physiologic flows in micro-channels. These issues have thus limited the implementation of the technique to broader scientific communities that are not ready to fabricate microfluidic systems in-house. Therefore, we aimed to identify a commercially available microfluidic solution that supports user custom protocol developed for microvasculature-on-a-chip (MVOC). The custom protocol was validated to reliably form a smooth and functional blood vessel using a viscous fingering (VF) technique. Using VF technique, the unpolymerized collagen gel in the media channels was extruded by less viscous fluid through VF passive flow pumping, whereby the fluid volume at the inlet and outlet ports are different. The different diameters of hollow tubes produced by VF technique were carefully investigated by varying the ambient temperature, the pressure of the passive pump, the pre-polymerization time, and the concentration of collagen type I. Subsequently, culturing human umbilical vein endothelial cells inside the hollow structure to form blood vessels validated that the VF-created structure revealed a much greater permeability reduction than the vessel formed without VF patterns, highlighting that a more functional vessel tube can be formed in the proposed methodology. We believe the current protocol is timely and will offer new opportunities in the field of in vitro MVOC.

Advanced composites based on end-capped polyarylene ether nitrile/bisphthalonitrile with controllable thermal curing reaction

A novel polymer was prepared through the combination of phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) and bisphthalonitrile (BPh), applying post-solid phase chemical reaction technology. BPh monomer was firstly pre-polymerized to form BPh prepolymer and then followed by crosslinking reaction with PEN-Ph matrix resin to obtain PEN-Ph/BPh composites. The generated crosslinking structures were confirmed by FTIR and UV including phthalocyanine, triazine, and isoindoline rings. Besides, the effect of BPh pre-polymerization time on the performance of PEN-Ph/BPh composite materials was studied. Tensile strength and modulus highest values of composites exceeded 98.9 MPa and 2.17 GPa respectively as BPh pre-polymerization time reached 30 min, improved by 55.6% and 36.9% in comparison with unpolymerized one. Besides, PEN-Ph/BPh composite films exhibited superior thermal properties (Tg: 278–330 °C, T5% (decomposition temperature of 5 wt%)>500 °C) and maintained excellent dielectric stability over 300 °C, leading to use for electronic fields at elevated temperature.

A self-templating dilution strategy for preparation of hollow concave polystyrene nanoparticles in a styrene/ethanol-water ternary system

Hollow concave polymer particles have attracted wide attention due to their particular properties and applications, however, the controllable synthesis of hollow concave polystyrene nanoparticles (HC-PSNPs) based on soap-free emulsion polymerization via a one-pot method has not been achieved. Herein, based on a styrene/ethanol-water (St/EtOH-H2O) ternary system, a simple green self-templating dilution strategy was established to produce monodisperse HC-PSNPs. In the synthesis, the degree of concavity and opening size of HC-PSNPs can be controlled by adjusting polymerization parameters such as the pre-polymerization time (polymerization time before dilution) and dilution conditions (including dilution ratio and ethanol content of the diluents). Furthermore, one opening or multiple openings in the surface of HC-PSNPs can be controlled by varying the post-polymerization temperature (polymerization temperature after dilution). Based on our results and observations, we propose a plausible mechanism for the formation of HC-PSNPs.

Continuous Differential Microemulsion Polymerization to Prepare Nanosized Polymer Latices in Microreactors

Microreactors are a promising platform for continuous synthesis of polymer latices when combined with emulsion polymerization. However, this application has long been haunted by fouling and clogging problems. In this work, we proposed the strategy of conducting differential microemulsion polymerization in microreactors within a biphasic slug flow and achieved rapid and stable preparation of nanosized PMMA latices (polymeric content as high as 15.7% with average particle size smaller than 20 nm). We started by exploring the temperature thresholds with thermal and redox initiation, the effect of initiator concentration, and the kinetic characteristics of microemulsion polymerization at different temperatures. Then, as for the differential microemulsion polymerization, extensive investigation was made into the effects of the volumetric flow ratio, the prepolymerization time, the initiator concentration, and the solid content of the initial microemulsion. Finally, we compared the differential microemulsion polymerization with the soap-free emulsion polymerization in the slug flow. The striking advantages in the polymerization rate, the average particle diameter, and the size distribution reflected higher density of particle nuclei, larger specific surface area of particles, and the pivotal effect of the persistent particle nucleation in the microemulsion polymerization.

Preparation and Application of Waterborne Polyurethane with Starch as Soft Segment

The preparation of waterborne polyurethane was studied when starch acted as soft segment. The reaction conditions of preparation about the waterborne polyurethane were discussed. The infrared spectrum was used to characterize the copolymer emulsions. At the same time, the applications of the prepared starch-TDI copolymer emulsions were researched on paper coating and wet end addition in this paper. It was showed that the prepolymerization time was 2 hours and the blocking time was 25 minutes. The results of applications showed that the physical properties were improved obviously after coating or wet end addition. In addition, it was found that the coated papers had better enhancement effects than the wet end added papers.

PEN/BADCy Interlayer Dielectric Films with Tunable Microstructures via an Assist of Temperature for Enhanced Frequency Stability

Low dielectric interlayer films have become an important element to ensure the development of the microelectronics industry. A kind of flexible interlayer dielectrics, polyarylene ether nitrile/bisphenol A cyanate ester (PEN/BADCy) film, with good thermal stability and low frequency dependence, has been developed by solution casting method. Herein, materials were designed to incorporate bisphenol A cyanate ester as a part of blend, contributing to the frequency stability and structural integrity. The morphological study combined with electron microscopy revealed the uniform and flexible microstructure information with controllable morphology through self-polymerization of cyanate esters with different prepolymerization time and curing temperatures. The dielectric films could present high thermal stability with Tg>180 °C. Significant improvement in the dielectric properties was achieved for the dielectric constant and loss was much stabler than neat PEN over the frequency range from 100 Hz to 5 MHz. When the prepolymerization time was 3 h and final curing temperature reached 230 °C, the dielectric constant and dielectric loss of the films were 3.36 and 0.013 at 100 kHz, respectively. The dimensional stability (CTE = 53.67 × 10−6 K−1) was confirmed and considered beneficial to use as an interlayer dielectrics.

SERS-Based Molecularly Imprinted Plasmonic Sensor for Highly Sensitive PAH Detection.

A novel hybrid plasmonic platform based on the synergetic combination of a molecularly imprinted polymer (MIP) thin film with Au nanoparticle (NPs) assemblies, noted as Au@MIP, was developed for surface-enhanced Raman scattering (SERS) spectroscopy recognition of polycyclic aromatic hydrocarbons (PAHs). While the MIP trapped the PAH close to the Au surface, the plasmonic NPs enhanced the molecule's Raman signal. The Au@MIP fabrication comprises a two-step procedure, first, the layer-by-layer deposition of Au NPs on glass and their further coating with a uniform MIP thin film. Profilometry analysis demonstrated that the thickness and homogeneity of the MIP film could be finely tailored by tuning different parameters such as prepolymerization time or spin-coating rate. Two different PAH molecules, pyrene or fluoranthene, were used as templates for the fabrication of pyrene- or fluoranthene-based Au@MIP substrates. The use of pyrene or fluoranthene, as the template molecule to fabricate the Au@MIP thin films, enabled its ultradetection in the nM regime with a 100-fold improvement compared with the nonimprinted plasmonic sensors (Au@NIPs). The SERS data analysis allowed to estimate the binding constant of the template molecule to the MIP. The selectivity of both pyrene- and fluoranthene-based Au@MIPs was analyzed against three PAHs of different sizes. The results displayed the important role of the template molecule used for the Au@MIPs fabrication in the selectivity of the system. Finally, the practical applicability of pyrene-based Au@MIPs was shown by performing the detection of pyrene in two real samples: creek water and seawater. The design and optimization of this type of plasmonic platform will pave the way for the detection of other relevant (bio)molecules in a broad range of fields such as environmental control, food safety, or biomedicine.

Silica particles wrapped with poly(aniline-co-pyrrole) and reduced graphene oxide for advanced microwave absorption

In this work, a novel nanocomposite composed of silica nanoparticles wrapped with a poly(aniline-co-pyrrole) copolymer and reduced graphene oxide (P(ANi-co-Py)/RGO@SiO2) was prepared by an in situ pre-polymerization method and then characterized. The aniline:pyrrole molar ratio was 1:3 and the pre-polymerization time was 30 min before the in situ polymerization of the copolymer nanocomposites occurred. The results revealed that the microwave absorbing performance of the copolymer nanocomposites was significantly improved compared to that of the component homopolymer nanocomposites. The minimum reflection loss of P(ANi-co-Py)/RGO@SiO2, PANi/RGO@SiO2, and PPy/RGO@SiO2 was −40.6, −38.9, and −13.9 dB, respectively. The effective absorption bandwidth of P(ANi-co-Py)/RGO@SiO2 was 5.5 GHz from 12.3 to 17.8 GHz. In contrast, the effective absorption bandwidth of a component homopolymer nanocomposite, such as PANi/RGO@SiO2, was 2.2 GHz (15.8–18 GHz), and for PPy/RGO@SiO2, was only 1.5 GHz (12.4–13 GHz and 16.7–17.6 GHz) in Ku band. The enhanced microwave absorption was mainly contributed to the interfacial polarization in which the interfacial interaction between SiO2 particles, rGO sheets and conducting polymer chains played critical roles.

Study on the in-situ synthesis and the crystallization, mechanical, dielectric properties of Polypropylene/Polybutene-1

Polymeric materials are widely used as capacitor diaphragm materials because of their good pressure resistance, low dielectric loss, good processing performance and good compatibility with devices. In this experiment, the Polypropylene/Polybutene-1 (PP/PB-1) resin was prepared by the reaction of butene-1 polymerization using the modified intermittent bulk polypropylene polymerization reactor. The structure and morphology of the prepared PP/PB-1were characterized by DSC, POM and FT-IR so on. The effects of different prepolymerization time on their crystalline morphology and mechanical properties were investigated. As the polypropylene prepolymerization time becomes longer, the content of Polypropylene in the synthesized polybutene-1 sample increased gradually, and the spherulitic size and nucleation time of polybutene-1 were changed. In addition, the tensile properties of the product were also improved. The PP/PB-1 film was prepared by the film drawing machine using synchronous biaxial stretching method. It was found that when the tensile temperature was 130°C and the tensile rate was 40mm / min, the prepared PP/PB-1 films had the best dielectric properties. At this time, the dielectric constant was 2.9, and the dielectric loss tangent was low (<0.005).

Controlled Hydrolytic Degradation of Polyglycolide–Caprolactone-Based Bioabsorbable Copolymer

Polyglycolide–caprolactone (PGCL)-based copolymer was synthesized from glycolide and caprolactone by ring opening polymerization in the presence of stannous octoate catalyst and diethylene glycol initiator. The effects of prepolymerization time, monomer ratio, monomer-to-catalyst and monomer-to-initiator ratios on per cent weight conversion were optimized. The end-capped copolymer was synthesized to make absorbable sutures having controlled bioabsorbability at different pH levels. It was observed that endcapped absorbable copolymer was more stable at pH 10.0 compared to uncapped absorbable material. End-capped copolymer also retained higher tensile strength compared to uncapped copolymer after 21 days. This phenomenon of controlled hydrolytic degradation of PGCL-based bioabsorbable polymer having terminal group end-capping can be attributed to less availability of hydrophilic end groups facilitating hydrolytic degradation of polymers.

Coagulation performance and mechanism of polyaluminum ferric chloride (PAFC) coagulant synthesized using blast furnace dust

Abstract The research focused on the synthesis and coagulation performance of polyaluminum ferric chloride (PAFC) coagulant in order to explore a comprehensive utilization for blast furnace dust. The optimal conditions for PAFC synthesis were: fifty grams of blast furnace dust reacted with 150 mL hydrochloric acid diluted solution for 3 h at 90 °C and 10 g of aluminum dross reacted with 150 mL hydrochloric acid diluted solution for 2.5 h under room temperature; In co-polymerization stage, the Al/Fe molar ratio = 7:3, basicity B = 1.8, polymerization temperature 60–70 °C, and reaction time (pre-polymerization time of aluminum + copolymerization time of aluminum and iron) 1.0 h + 3.0 h. The main results are as follows: (1) The coagulation tests indicated that self-made PAFC outperformed commercial PAC in turbidity and color removal. (2) Self-made PAFC and flocs generated in water treating process were measured by Scanning Electron Microscopy. Surface charge characteristics of PAFC were measured by Zetasizer 3000HS. Charge neutralization was a very important coagulation mechanism of PAFC in turbidity removal process. And there were other coagulation mechanisms besides charge neutralization such as bridge connection and sweep flocculation, playing significant roles in decolorization process.

Preparation and Properties of Formaldehyde Molecularly Imprinted Polymer and Its Application in Detectiong Formaldehyde in Aquatic Product

Molecularly imprinted polymer( MIP) was prepared by optimized method using formaldehyde as template molecule,α-methacrylic acid as functional monomer,ethylene glycol dimethacrylate as crosslinking agent in chloroform. The imprinted polymer has the best selective adsorption capacity when the molar ratio of template molecular,functional monomer,crosslinking agent is 1∶ 2∶ 20,the prepolymerization time is 4 h,and the polymerization time is 8 h. When the concentration of formaldehyde solution is 2 mmol / L,the adsorption capacity of MIP reaches 12. 40 × 10-2mmol / g. The analysis of squid water sample indicated formaldehyde concentration was 5. 92 mg / Kg. At the same time,formaldehyde was not detected when the test sample was diluted 100 times, while after enriched by MIP solid-phase extraction( MIPSE) the concentration of formaldehyde was 5. 76 mg / Kg. Formaldehyde MIP has high-efficiency in enriching low concentration formaldehyde for sample preparation,and there is no significant difference in the testing results.

Preparation of Urea-Imprinted Cross-Linked Chitosan and Its Adsorption Behavior

A surface molecular imprinting technique was used to prepare a novel molecularly imprinted polymer using urea as the template molecule, chitosan as the functional matrix, epichlorohydrin as the cross-linker, and formaldehyde as the amino-protecting agent. Infrared analysis of the polymer confirmed that urea was successfully imprinted on cross-linked chitosan. On the basis of a single-factor test, Box–Behnken central composite experimental design and response surface methodology were used to optimize the preparation conditions. The optimum preparation conditions included 0.05 mL of acetic acid, 0.79 g of urea, a pre-polymerization time of 2.41 h, 1.63 mL of epichlorohydrin, and 0.6 g of chitosan. The predicted maximum adsorption capacity of urea (9.53 mg/g) was consistent with the experimental value (9.61 ± 0.16 mg/g), which confirmed the accuracy of the response surface method to optimize the preparation conditions of molecularly imprinted polymer. The recycling rate of the molecularly imprinted polymers was up to 84.6%. The molecularly imprinted polymer was used to adsorb urea from a serum sample. The adsorption efficiency had a maximum value of 54.51%.

Effect of Prepolymerization Time on Morphology and Properties of Epoxy-modified Bismaleimide Foams

Abstract Epoxy-modified bismaleimide (BMI) foams were prepared through prepolymerization and foaming. Density-adjustable BMI foams with closed-cell structures were produced. The influence of prepolymerization time on bubble growth and morphology, as well as the compressive and heat resistant properties of the foams, were thoroughly investigated. BMI prepolymerization was an effective method for controlling the bubble growth rate, the bubble size and its distribution, and the foam density. As the prepolymerization time increased, the matrix viscosity, the number of cells per unit volume and the foam density increased, whereas, the bubble growth rate and cell size decreased, and the cell size distribution became narrower. The compressive strength and modulus increased with increasing prepolymerization time. The dimensional stability temperatures of the BMI foams were all above 200°C, as determined by their base materials, and were unaffected by prepolymerization time.

Relationships between synthesis parameters and properties of water expandable polystyrene

Because of the negative environmental impact of volatile hydrocarbon-based blowing agents used in expandable polymers, water has been considered a suitable candidate. Water expandable polystyrene is a polystyrene containing water cells, which may be used as blowing agent. Because of different physical properties of water and volatile hydrocarbons, production conditions and physical properties of expandable polystyrene and water expandable polystyrene are completely different. In this work, water expandable polystyrene was prepared via suspension polymerization of the styrene/polystyrene mixture that contained water droplets as blowing agent. An inverse emulsion system was used to incorporate water into the organic phase. An experimental design was created to investigate the effects of variation of pre-polymerization time, surfactant concentration, suspension stabilizer/suspending agent ratio, suspension stabilizer addition time, and the amount of initial emulsified water on the particle size, distribution of water droplets, and the water content of the final beads. The relationships between the synthesis parameters and the properties of water expandable polystyrene were also studied. Regarding to the expansion behavior of water expandable polystyrene beads, the effect of water content and bead size on the expandability and the foam density were investigated.