Qingxiang Zhao

Piezoelectricity and ferroelectricity in odd-odd nylons with long alkane segments

Piezoelectricity and ferroelectricity in odd-odd nylon 11,11 and nylon 13,13 are detected. The results indicate that the γ-phase is responsible for the high piezoelectric and ferroelectric response. The piezoelectric strain coefficient, d 33, as high as −3.9 and −4.1 pC/N is obtained at room temperature for stretched nylon 11,11 and nylon 13,13 films, respectively. The coercive electric field, Ec , values of about 55 and 88 MV/m are obtained for nylon 11,11 and nylon 13,13 films, respectively. And a remanent polarization, Pr , about 40 mC/m2 has been found in both films. Compared with nylon 11,11, the lower coercive electric field (Ec ) in nylon 13,13 is attributed to its longer alkyl chains. These odd-odd nylons have the potential in electroactive applications.

Facile synthesis of size-tunable superparamagnetic/polymeric core/shell nanoparticles by metal-free atom transfer radical polymerization at ambient temperature

A facile route to fabricate size-tunable superparamagnetic/polymeric core/shell nanoparticles with uniform distribution was introduced based on metal-free atom transfer radical polymerization at ambient temperature.

Highly water-dispersed superparamagnetic magnetite colloidal nanocrystal clusters from multifunctional polymeric nanoreactors: synthesis and properties

An unconventional but robust strategy to fabricate uniform hybrid inorganic–organic core–shell superparamagnetic magnetite (Fe3O4) colloidal nanoclusters in situ was introduced based on water-soluble multi-arm star-shaped brush-like block copolymers as multifunctional polymeric nanoreactors, composed of poly(ethylene oxide) (PEO) as the main chain, poly(acrylic acid) (PAA) as functional graft chains, and the second PEO block as a shell (i.e., multi-arm star-shaped brush-like block copolymer [(PEO-g-PAA)-b-PEO]18) with different molecular weights and grafting densities. FeCl3 and FeCl2 as precursors of Fe3O4 were loaded into the graft chain PAA template domain of a multi-arm star-shaped brush-like block copolymer [(PEO-g-PAA)-b-PEO]18 polymeric nanoreactors, followed by an in situ reaction to form Fe3O4 nanoclusters. The dimensions of the clusters can be tuned precisely by changing the chain lengths of the PEO backbones of the PAA grafting region. In addition, the density of the subunits can also be tailored by adjusting grafting density of the PAA side chains, determined by the molar ratio of ethoxyethyl glycidyl ether (EEGE) to EO during the anionic copolymerization. The Fe3O4 colloidal nanocrystal clusters with superparamagnetic behavior at room temperature are highly water-dispersed because of the hydrophilic ligands of the surface-tethered PEO polymer shell.

Water-soluble star-shaped brush-like block copolymers: synthesis and application as multicompartment nanoreactors for fabrication of quantum dot colloidal nanocrystal clusters

A series of novel water-soluble multi-arm star-shaped brush-like block copolymers, composed of poly(ethylene oxide) (PEO) as the main chain, poly(acrylic acid) (PAA) as functional graft chains, and a second PEO block as the shell (i.e., multi-arm star-shaped brush-like block copolymer (PEO-g-PAA)-b-PEO) with different molecular weights and grafting density, were rationally designed and synthesized by a combination of anionic copolymerization and atom transfer radical polymerization (ATRP). The anionic ring-opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was conducted first by using α-cyclodextrin (α-CD) with 18 hydroxyl groups and diphenylmethyl sodium (DPMNa) as co-initiator system. The monomer reactivity ratios for EO and EEGE were also determined: r1(EO) = 1.18 ± 0.03 and r2(EEGE) = 0.79 ± 0.01, respectively. Then the resulting multi-arm star-shaped copolymers of poly(EO-co-EEGE) with hydroxyls as end functional groups were utilized as star-shaped macroinitiators to sequentially initiate the anionic ring-opening polymerization of monomer EO for the second block hydrophilic homopolymer PEO chain grown on the first block poly(EO-co-EEGE) arm end, and then the ethoxyethyl groups of the star-shaped block copolymers of poly(EO-co-EEGE)-b-PEO obtained were removed by hydrolysis. The formed multi-arm star-shaped block copolymers of EO and glycidol (Gly) with multi-pendant hydroxymethyls (star-shaped block copolymer poly(EO-co-Gly)-b-PEO) were then esterified by the reaction of the pendant hydroxyl groups of glycidol units of copolymers with 2-bromoisobutyryl bromide, and the resulting star-shaped brush-like macroinitiators were used to initiate the grafting polymerization of t-butyl acrylate (tBA) by ATRP technique. Finally, the tert-butyl ester groups of PtBA grafting side chains were selectively hydrolyzed in trifluoroacetic acid ​(TFA) to obtain the water-soluble multi-arm star-shaped brush-like block copolymer (PEO-g-PAA)-b-PEO. The water-soluble star-shaped brush-like (PEO-g-PAA)-b-PEO, which consisted of a functional PAA domain as the core and a hydrophilic PEO domain as the shell, were exploited as polymeric nanoreactors to structure-direct in situ fabrication of CdSe quantum dots (QDs) colloidal nanocrystal clusters composed of primary CdSe nanocrystals as subunits, with the secondary structures of CdSe nanocrystals. Spherical CdSe colloidal nanocrystal clusters were intimately and permanently capped with hydrophilic PEO chains on the surface to render the resulting clusters with high water dispersible property.

Mechanical and Tribological Properties of Nylon 1212 Modified with Brown Corundum Ash and Solid Lubricants

Brown Corundum Ash(BCA) was used to modify nylon 1212(PA1212), which is produced during the production of electric fused brown corundum alumina and will causes serous environmental pollution if it is not recycled. In order to improve the tribological property of PA1212 composites, Graphite, MoS2 and PTFE were used. The composites were prepared by a twin-screw extruder through melt intercalation. The mechanical properties and the wear resistance of the PA1212/Brown Corundum Ash/graphite/MoS2/PTFE composite were studied. The shearing area of composite and the worn surfaces were examined by scanning electric microscope (SEM).

Optical Activity of Homochiral Polyamides in Solution and Solid State: Structural Function for Chiral Induction

In this work, we have explored a simple and facile approach to prepare optically active helical polyamides. The hydroxyl groups of l-TA and d-TA were protected by O-alkoyl ester, and the resulting enantiomers, l-2,3-di-O-acetyl-tartaric acid (l-ATA) and d-2,3-di-O-acetyl-tartaric acid (d-ATA) crystals, were obtained. A pair of aliphatic homochiral polyamides of PA-l and PA-d are prepared using l-ATA, d-ATA, and achiral 1,11-undecanediamine as building blocks via interfacial polycondensation. PA-l and PA-d display negative and positive mirror circular dichroism (CD) spectra images in both solution and solid state. Moreover, the polyamides in solid state display different CD signals and stronger optical activity compared to those in ethanol and even the related chiral monomers in solid state, which was due to the helical conformation of the polyamides in solid state. Scanning electron microscopy results indicated that the aggregations of PA-l express left-handed helical sense, whereas those of PA-d express right-handed helix. In addition, the induced CD signals from the chiral conformation of the backbone become weaker when increasing the temperature from 0 to 60 °C in dilute solution. Either of the polyamides displays relatively stable CD images in solid state when elevating the temperature from 0 to 90 °C.

An unconventional route to fabricate highly pure α-Al2O3 nanocrystals with tunable surface chemistry based on a semi-aromatic polyamide with pyridine rings as a functional matrix

An unconventional but robust route to fabricate highly pure α-Al2O3 colloidal nanocrystals with tunable surface chemistry and dimensions was introduced based on semi-aromatic polyamide (PA6Py) with pyridine rings as a functional matrix. The surface ligands of α-Al2O3 nanocrystals can be tuned by choosing different carboxyl-terminated polymers (e.g., PS and PEO).

Synthesis of ABC Star-Shaped Copolymers via a Combination of Controlled Polymerization Techniques

Two kinds of ABC-type miktoarm star copolymers, poly(α-methylstyrene)-poly(ethylene oxide)-poly(ethoxyethyl glycidylether) (PMS-PEO-PEEGE) and poly(α-methylstyrene)-poly(ethylene oxide)-polyglycidol (PMS-PEO-PG), were synthesized via a combination of anionic polymerization with ring-opening polymerization. Firstly, The poly(α-methyl styryl lithium) (PMS－Li+) was capped by EEGE to form the functionalized poly(α-methylstyrene) with both an active ω-hydroxyl group and an ω’-ethoxyethyl-protected hydroxyl group. Secondly, the PMS-b-PEO block copolymers, star(PMS-PEO-PEEGE) and star(PMS-PEO-PG) copolymers were obtained by the ring-opening polymerization of EO and EEGE via the variation of the functional end group, respectively. Finally, the ethoxyethyl group on the PEEGE arm was hydrolyzed. The obtained miktoarm star copolymers and intermediates were characterized by proton nuclear magnetic resonance (1H-NMR) and size exclusion chromatography (SEC).

Poly(Ethylene Oxide)-B-Poly(ε-Caprolactone) Amphiphilic Block Copolymers: Synthesis and Self-Assembly

A series of amphiphilic block copolymers mPEO-b-PCL with different PCL molecular weight were successfully prepared by combination of anionic ring-opening polymerization with coordination-insertion ring-opening polymerization. Firstly, the linear mPEO was prepared by anionic ring-opening copolymerization of EO with 2-(2-methoxyethoxy) ethoxide potassium as the small molecule initiators, then the mPEO as the macroinitiator was used to initiate the ring-opening polymerization of CL, in the absence of Sn(Oct)2 as the catalyst, and amphiphilic block copolymers mPEO-b-PCL were obtained. By changing the ratio of monomer and macroinitiator, prepared a series of different molecular weight mPEO-b-PCL. The structure of intermediates and final products were characterized by 1H NMR and GPC. The critical micelle concentration (cmc) of the final copolymer was measured. In addition, the sizes and morphologies of the obtained micelles at different PCL chains were studied with Laser nano-particle size analyzer and transmission electron microscopy (TEM).

Synthesis, Characterization and Isothermal Crystallization Kinetics of Poly(Dodecamethylene Terephthalamide)

A kind of semi-aromatic polyamide, poly(dodecamethylene terephthalamide) (PA12T) was synthesized via a three-step reaction of terephthalic acid and 1,12-dodecanediamine. The structure of the prepared PA12T was characterized by Fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (1H-NMR). The thermal behaviour of PA12T was determined by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Melting temperature (Tm), glass transition temperature (Tg) and decomposition temperature (Td) of PA12T are 311°C, 144°C and 429°C, respectively. Isothermal crystallization kinetics of PA12T have been investigated in the temperature range of 270-280°C using DSC. The activation energies (ΔE) were determined to be -170.4 kJ/mol for the isothermal crystallization processes by the Arrhenius’ methods.