Τετάρτη, 17 Ιουλίου 2019

Macromolecular Research

Effect of the Monomer Ratio on the Properties of Melt-Polymerized Polycarbonate

Abstract

In this study, the effects of bisphenol A (BPA) and diphenyl carbonate (DPC) molar ratio, on the properties of melt-polymerized polycarbonate (PC) were investigated. The molecular size distribution theory proposed by Flory was applied, to melt polymerization of PC to predict physical properties, affected by the molar ratio of BPA and DPC. A terminal OH group affected the viscosity of PC at high temperatures, leading to instability during processing. With increase in the DPC/BPA molar ratio, terminal OH content decreased, albeit different from the theoretical predicted value, because of the volatilization of DPC. Additionally, BPA residual amount was affected by BPA and DPC molar ratio. BPA is regulated in countries because of its similarity to estrogen, and BPA residues can be predicted and managed by using the Flory equation. 

Correlation Between Shear-Flow Rheology and Solution Spreading During Spin Coating of Polysilane Solutions

Abstract

The effect of side groups on rheological properties of different polysilanes in solution phase is investigated and correlated, with radial uniformity of estimated thickness of wet films. The polymethylphenylsilane homopolymer has shear rate-dependent flow properties in the interval 0.2-0.8 s-1 and relaxation time of 0.53 s. This behavior is changed for the copolymer containing methylphenylsilylene units, which becomes less sensitive to shear deformation as a result of chain reduced mobility, with the highest relaxation time of 1.54 s and flow activation energy of 27.08 kJ/mol, combined with the smallest deviation from constant viscosity (~0.02 Pa·s). Such Newtonian flow leads to higher uniformity of the wet film thickness profile alongthe radial position of the spin-coating wafer, comparatively with the other polysilane solutions. Higher spinning times (>60 s) and lower spinning speeds (<590 rpm) are also favorable, to obtain polysilane films with constant thickness. Molecular modeling was performed to investigate polysilane conformation in solution, and its interaction with toluene molecules. The studied polymer solutions have slightly higher work of adhesion to indium tin oxide, and polyethylene terephthalate (around 143 mN/m) substrates, in regard with glass and silicon (around 140 mN/m). 

Fabrication of Randomly Stooped Polymer Nanohairs Using Scattered Electron Flood under Ambient Condition

Abstract

Despite attractive applications of randomly oriented nanostructures with high aspect ratio, their fabrication suffers from both complicated processes and lack of materials. In this letter, we present a simple but effective method for the fabrication of randomly stooped polymeric nanohairs havinghigh aspect ratio under ambient condition by using scattered electron flood. High aspect ratio vertical nanohairs prepared by nano-molding process exhibited randomly stooped geometry after the electron irradiation. Fourier transform infrared spectroscopy and Monte Carlo simulation revealed that radiolysis of polymeric nanohairs by scattered electrons in ambient air allowed directionally random distribution of shrinkage of the nanohairs, resulting in randomly stooped nanohair structures. 

Facile and Affordable Process to Control Shell Thickness of Polydopamine-Assisted Polystyrene/Silver Core-Shell Particles

Abstract

We prepared polystyrene (PS)/silver (Ag) core-shell particles with an excellent electrical conductivity in a facile, affordable and eco-friendly way. As core particles, monodisperse PS particles were synthesized by the process of dispersion polymerization. Then, the PS particles were coated with polydopamine (PDA) through the spontaneous oxidative polymerization of dopamine to produce PDA-coated PS particles. In essence, it is noted that the catechol and amine groups of PDA coated on PS particles can weakly reduce metallic ions. As a secondary reducing agent with an affordable price, glucose was therefore added to promote the reduction of metallic ions. Herein, the effect of glucose concentration on the Ag shell thickness of PDAassisted PS/Ag core-shell particles was investigated. The degree of Ag reduction increased with an increase characteristically in glucose concentration, resulting in the increase of Ag shell thickness. Notably, a thick and uniform Ag shell layer could be plated on PDA-coated PS particles, which were noted to have rendered excellent electrical conductivity. When the glucose concentration of 55 mM was applied, the electrical conductivity of the PS/Ag core-shell particles reached as high as 7.8×105 S/m, which was almost close to that of conductive metals.
 

Preparation of Thin-Layer Graphene Using RAFT Polymerization and a Thiol-Ene Click Reaction

Abstract

In this paper, functionalization of graphene is conducted through click reactions for its effective dispersion. The poly(sodium 4-styrenesolfonate) (PSS) was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The chain end dithioester group of RAFT-polymerized PSS was reduced to a thiol and used to couple PSS to graphene oxide (GO) via a thiol-ene click reaction. An aqueous dispersion of reduced GO with PSS (PSS-rGO) resisted sedimentation due to steric effects and charge-charge repulsion between the PSS attached to rGO. Atomic force microscopy showed that the PSS-rGO mixture was composed of dispersed particles of thin-layer (1.5 nm thick) graphene. Thickness of the PSS-rGO was close to that of GO. This indicates that there was no significant re-aggregation during GO reducing process.
 

High-Performance Fluorinated Ethylene-Propylene/Graphite Composites Interconnected with Single-Walled Carbon Nanotubes

Abstract

Herein, we report a novel method for the fabrication of highly conductive fluorinated ethylene-propylene (FEP)/graphite nanocomposites for high-temperature bipolar plates (BPs) by incorporating the well-dispersed single-walled carbon nanotube (SWCNT) as a secondary filler in the FEP matrix. The SWCNTs were pre-dispersed with FEP powder by sonication in ethanol and subsequently mixed with graphite powder by ball milling. The composite BPs were prepared from the mixed powder by compression molding. The resulting FEP/graphite/SWCNT nanocomposite containing 80 wt% graphite (500 µm particles) and 0.1 wt% SWCNT exhibited high electrical conductivity (210 S cm−1) superior to that of the composite devoid of SWCNTs (120 S cm−1) by modulating the electrical transportation pathways between graphite particles through the SWCNTs. A small amount of the incorporated SWCNTs (0.1 wt%) also improved chemical inertness to phosphoric acid. Hence, the prepared FEP/graphite nanocomposites with SWCNTs as a secondary filler exhibited a robust performance for application as high-temperature BPs for phosphoric acid fuel cells.
 

Synthesis and Physical Properties of Proton Conducting Polymer Electrolytes Comprising PAM Cross-Linked Flexible Spacers

Abstract

The design of novel proton exchange membranes with high conductivity and better dimensional stability has become increasingly important due to the need for applications in different devices. The present work shows the acid-doped and crosslinked polyacrylamide (PAM) networks including flexible spaces. To this end PAM was modified with 1,4-butanediol diglycidyl ether (BG) to form PAM35BG and PAM50BG networks, which would afford more space for protonated solvents. The reaction of PAM with BG was monitored by FTIR and 13C CP-MAS NMR. The polymer electrolytes were produced by acid doping at several stoichiometric ratios with respect to the monomer repeat unit of a host polymer. The resulting materials exhibited better thermal, chemical, and electrochemical stabilities and had distinct Tg values. Additionally, the pores of the PAM-BG materials were filled with H3PO4 to get PAM35BG0.5H3PO4 and PAM50BG1.0H3PO4. The doping enhanced the proton conductivities of the membranes as high as 0.003 S/cm at 120 °C under an anhydrous atmosphere. The proton diffusion mechanism and the dielectric relaxation were further examined using the complex modulus formalism, M*.
 

Maleinized Hyperbranched Polyol Polyester: Effect of the Content of Maleic Anhydride in the Structural, Thermal and Rheological Properties

Abstract

The aim of this work is to obtain the material that, in the future, may become a better alternative, as a functionalizing agent, to maleic anhydride (MA), or a crosslinking agent with the least amount of functional groups. To achieve that goal, a hyperbranched polyester polyol (HBP) of the second generation (HBP2G) was modified with MA to obtain HBP2GMA. The effects of the proportion of MA in the structural, thermal, and rheological properties of the HBP2GMAs were evaluated. Furthermore, these properties were compared with those of the HBP2G. A reduction in the intensity of peak corresponding to the OH stretching of HBP2G was observed with the increase in the extent of HBP2G modification by the analysis of the infrared (IR). HBP2GMAs showed a peak at 3030 cm-1 in their IR spectra, which was due to the -CH=CH- stretching of MA. This was further assessed by 1H NMR analysis. The number of MA units grafted into HBP2G was between 4 and 9, indicating a high degree of functionality. All materials possessed viscosity values below 34.94 Pa·s at 110 °C, which were dependent on the grade of the modification percentage (MP) and the molar content of MA grafted into HBP2G. Mass spectrometry analysis demonstrated the formation of products by the esterification reaction between the HBP2G and MA. The thermal stability of the HBP2GMAs determined as the decomposition temperature (Td) was between 258 and 281 °C which was better than that of the HBP2G. 

Phosphate-Functionalized Stabilized F127 Nanoparticles: Introduction of Discrete Surface Charges and Electrophoretic Determination of Aggregation Number

Abstract

Pluronic F127 forms spherical micelle with a defined number of molecules aggregated in aqueous environments. Such self-assembled micelles dissociate into unimers below certain concentration and temperature. We stabilized the micelles by semi-interpenetrating network (sIPN) formation within the hydrophobic core in the presence of a fluorescent dye. Additionally, by varying the mixing ratio of negatively charged and pristine F127s we prepared thermally stable polymeric nanoparticles with discrete surface charges within nearly same sizes. Using the nanomaterials with prescribed number of charges, we demonstrate that the electrophoretic mobility of nanoparticles is solely depending on number of surface charges. Finally, the aggregation number (Nagg) of F127 was further determined by electrophoresis. 

Synthesis and Antibacterial Activities of Boronic Acid-Based Recyclable Spherical Polymer Brushes

Abstract

Crosslinked poly(4-vinylbenzyl chloride) (PVBC) microbead was prepared by suspension polymerization. Various spherical polymer brushes (SPBs) were produced by grafting polymeric chains on their surfaces via surface initiated-atom transfer radical polymerization (SI-ATRP) using 4-vinylphenyl boronic acid (VPBA), 2-(dimethylamino)ethyl methacrylate (DMA), and quaternized DMA (QDMA). PVBC-g-PDMA, PVBC-g-PQDMA, PVBC-g-PVPBA, PVBC-g-P(VPBA-b-DMA), PVBC-g-P(VPBA-co-DMA) and PVBC-g-P(VPBA-b-QDMA) SPBs were characterized using nuclear magnetic resonance spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Antibacterial activities of the synthesized SPBs were investigated against Escherichia coli and Staphylococcus aureus in nutrient and nutrient free media. Although PVBC-g-P(VPBA-b-DMA) SPB provided high antibacterial activity in the nutrient containing media due to its antibacterial, anti-biofilm and anti-QS properties, PVBC-g-P8QDMA SPB was found to be more effective in nutrient free media. Considering repeatable antibacterial activity, the PVBC-g-P(VPBA-b-8QDMA) SPB has advantageous over PVBC-g-P(VPBA-b-DMA) and PVBC-g-P8QDMA SPBs for long-term applications such as wastewater treatment in fluidized bad system.
 

Δεν υπάρχουν σχόλια:

Δημοσίευση σχολίου