scholarly journals Anchor Effect in Polymerization Kinetics: Case of Monofunctionalized POSS

Polymers ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 515 ◽  
Author(s):  
Agnieszka Marcinkowska ◽  
Dawid Przadka ◽  
Beata Dudziec ◽  
Katarzyna Szczesniak ◽  
Ewa Andrzejewska
Keyword(s):  
Volume Fraction ◽  
Gel Permeation Chromatography ◽  
Polymerization Kinetics ◽  
Point Of View ◽  
Rate Coefficients ◽  
Anchor Effect ◽  
Scanning Calorimetry ◽  
Molar Ratios ◽  
Transmission Electron ◽  
Free Volume Fraction

The effect of the anchoring group on the detailed polymerization kinetics was investigated using monomethacryloxy-heptaisobutyl POSS (1M-POSS). This compound was copolymerized with lauryl methacrylate (LM) as the base monomer, at various molar ratios. The process was initiated photochemically. The polymerization kinetics were followed by photo-DSC and photorheology while the polymers were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). For comparison, a methacrylate containing the branched siloxy-silane group (TSM) was also studied. It was found that the modifiers with a bulky substituent have a dual effect on the termination process: (i) At low concentrations, they increase the molecular mobility by increasing the free volume fraction, which leads to an acceleration of the termination and slows the polymerization; while (ii) at higher concentrations, they retard molecular motions due to the “anchor effect” that suppresses the termination, leading to acceleration of the polymerization. The anchor effect can also be considered from a different point of view: The possibility of anchoring a monomer with a long substituent (LM) around the POSS cage, which can further enhance propagation. These conclusions were derived based on kinetic results, determination of polymerization rate coefficients, and copolymer analysis.

Characterization of bi-layered magnetic nanoparticles synthesized via two-step surface-initiated ring-opening polymerization

2015 ◽  
Vol 87 (11-12) ◽  
pp. 1085-1097 ◽  
Author(s):  
Li Wang ◽  
Stefan Baudis ◽  
Karl Kratz ◽  
Andreas Lendlein
Keyword(s):  
Magnetic Nanoparticles ◽  
Ring Opening ◽  
Average Molecular Weight ◽  
Polymer Networks ◽  
Gel Permeation Chromatography ◽  
Degree Of Crystallinity ◽  
Scanning Calorimetry ◽  
H Nmr ◽  
Transmission Electron

AbstractA versatile strategy to integrate multiple functions in a polymer based material is the formation of polymer networks with defined nanostructures. Here, we present synthesis and comprehensive characterization of covalently surface functionalized magnetic nanoparticles (MNPs) comprising a bi-layer oligomeric shell, using Sn(Oct)2 as catalyst for a two-step functionalization. These hydroxy-terminated precursors for degradable magneto- and thermo-sensitive polymer networks were prepared via two subsequent surface-initiated ring-opening polymerizations (ROPs) with ω-pentadecalactone and ε-caprolactone. A two-step mass loss obtained in thermogravimetric analysis and two distinct melting transitions around 50 and 85°C observed in differential scanning calorimetry experiments, which are attributed to the melting of OPDL and OCL crystallites, confirmed a successful preparation of the modified MNPs. The oligomeric coating of the nanoparticles could be visualized by transmission electron microscopy. The investigation of degrafted oligomeric coatings by gel permeation chromatography and 1H-NMR spectroscopy showed an increase in number average molecular weight as well as the presence of signals related to both of oligo(ω-pentadecalactone) (OPDL) and oligo(ε-caprolactone) (OCL) after the second ROP. A more detailed analysis of the NMR results revealed that only a few ω-pentadecalactone repeating units are present in the degrafted oligomeric bi-layers, whereby a considerable degree of transesterification could be observed when OPDL was polymerized in the 2nd ROP step. These findings are supported by a low degree of crystallinity for OPDL in the degrafted oligomeric bi-layers obtained in wide angle X-ray scattering experiments. Based on these findings it can be concluded that Sn(Oct)2 was suitable as catalyst for the preparation of nanosized bi-layered coated MNP precursors by a two-step ROP.

Preparation and Property of Al87Ce3Ni8.5Mn1.5 Nanophase Amorphous Composites

2011 ◽  
Vol 412 ◽  
pp. 263-266
Author(s):  
Hong Wei Zhang ◽  
Li Li Zhang ◽  
Feng Rui Zhai ◽  
Jia Jin Tian ◽  
Can Bang Zhang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Single Phase ◽  
Volume Fraction ◽  
Material Structure ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Transmission Electron ◽  
Different Temperatures

The higher mechanical strength of Al87Ce3Ni8.5Mn1.5 nanophase amorphous composites has been obtained with two methods. The first nanophase amorphous composites are directly produced by the single roller spin quenching technology. The method taken for the second nanophase amorphous composites is at first to obtain amorphous single-phase alloy, followed by annealed at different temperatures .The formative condition, the microstructure, the particle size, the volume fraction of α-Al phase and microhardness of nanophase amorphous composites etc have been investigated and compared by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The microstructure of composites produced by the second method is higher than the former, the fabricated material structure of the system is more uniform and the process is easier to control.

Hardness evolution of Al–Cr–N coatings under thermal load

2008 ◽  
Vol 23 (11) ◽  
pp. 2880-2885 ◽  
Author(s):  
Herbert Willmann ◽  
Paul H. Mayrhofer ◽  
Lars Hultman ◽  
Christian Mitterer
Keyword(s):  
Thermal Load ◽  
Structural Changes ◽  
Single Phase ◽  
Volume Fraction ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Al Content ◽  
Annealing Temperatures ◽  
Transmission Electron

Microstructure and hardness evolution of arc-evaporated single-phase cubic Al0.56Cr0.44N and Al0.68Cr0.32N coatings have been investigated after thermal treatment in Ar atmosphere. Based on a combination of differential scanning calorimetry and x-ray diffraction studies, we can conclude that Al0.56Cr0.44N undergoes only small structural changes without any decomposition for annealing temperatures Ta ⩽ 900 °C. Consequently, the hardness decreases only marginally from the as-deposited value of 30.0 ± 1.1 GPa to 29.4 ± 0.9 GPa with Ta increasing to 900 °C, respectively. The film with higher Al content (Al0.68Cr0.32N) exhibits formation of hexagonal (h) AlN at Ta ⩾ 700 °C, which occurs preferably at grain boundaries as identified by analytical transmission electron microscopy. Hence, the hardness increases from the as-deposited value of 30.1 ± 1.3 GPa to 31.6 ± 1.4 GPa with Ta = 725 °C. At higher temperatures, where the size and volume fraction of the h-AlN phase increases, the hardness decreases to 27.5 ± 1.0 GPa with Ta = 900 °C.

scholarly journals Thermal analysis of postcured aramid fiber/epoxy composites

2021 ◽  
Vol 60 (1) ◽  
pp. 479-489
Author(s):  
Konstantinos Karvanis ◽  
Soňa Rusnáková ◽  
Ondřej Krejčí ◽  
Alena Kalendová
Keyword(s):  
Thermal Resistance ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Thermomechanical Analysis ◽  
Mechanical Analysis ◽  
Aramid Fiber ◽  
Point Of View ◽  
Creep Recovery ◽  
Aramid Fibers ◽  
Scanning Calorimetry

Abstract In this study, aramid fiber-reinforced polymer (AFRP) composites were prepared and then postcured under specific heating/cooling rates. By dynamic mechanical analysis, the viscoelastic properties of the AFRP composites at elevated temperatures and under various frequencies were determined. Thermomechanical analysis (TMA), in the modes of creep-recovery and stress–relaxation tests, was also performed. Furthermore, differential scanning calorimetry was also used, and the decomposition of the AFRP composites, aramid fibers, and pure postcured epoxy, in two different atmospheres, namely, air atmosphere and nitrogen (N2) atmosphere, was explored by the thermogravimetric analysis (TGA). From this point of view, the aramid fibers showed remarkably thermal resistance, in N2 atmosphere, and the volume fraction of fibers (Φf) was calculated to be Φf = 51%. In the TGA experiments, the postcured AFRP composites showed very good thermal resistance, both in air and N2 atmosphere, and this characteristic in conjunction with their relatively high T g, which is in the range of 85–95°C, depending on the frequency and the determination method, classifies these composites as potential materials in applications where the resistance in high temperatures is a required characteristic.

Understanding the Compromise between Strength and Exfoliation Corrosion in High Strength 7000 Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 455-460 ◽  
Author(s):  
T. Marlaud ◽  
B. Baroux ◽  
Alexis Deschamps ◽  
J.L. Chemin ◽  
C. Hénon
Keyword(s):  
Corrosion Resistance ◽  
Volume Fraction ◽  
High Strength ◽  
Precipitate Size ◽  
Scanning Calorimetry ◽  
X Ray Scattering ◽  
Transmission Electron ◽  
Size Evolution ◽  
Zn Content ◽  
Zn Alloy

The microstructural evolution has been investigated in three alloys of the 7000 series possessing increasing zinc contents by combining small-angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy, in order to gain understanding on the evolution of the compromise between yield strength and corrosion resistance. We show that the three materials show qualitatively identical precipitation sequences; however the precipitated volume fraction is shown to increase in parallel to the Zn content. Moreover, the precipitate size evolution is faster in the high Zn alloy. The precipitate composition is inferred to vary in the three materials, and this difference is shown to explain the differences in calorimetric behavior, precipitation kinetics and corrosion resistance.

The Influence of Amount of Succinic Anhydride in Chain Extension Reaction on Increasing Molecular Weight of Poly(lactic acid)

2013 ◽  
Vol 747 ◽  
pp. 148-152
Author(s):  
Chaichana Piyamawadee ◽  
Duangdao Aht-Ong
Keyword(s):  
Molecular Weight ◽  
Lactic Acid ◽  
Succinic Anhydride ◽  
Gel Permeation Chromatography ◽  
Chain Extension ◽  
Proton Nuclear Magnetic Resonance ◽  
Poly Lactic Acid ◽  
Condensation Polymerization ◽  
Scanning Calorimetry ◽  
Molar Ratios

High molecular weight PLA was successfully synthesized by chain extension reaction of hydroxylated prepolymer using succinic anhydride as a chain extender. Hydroxylated prepolymer was prepared by direct condensation polymerization of L-lactic acid in the presence of 1,4-butanediol. Various molar ratios between hydroxylated prepolymer and succinic anhydride (i.e, 1:1, 1:2, 1:3) were investigated. The results showed that succinic anhydride can help increasing molecular weight of hydroxylated prepolymer approximately up to 47% as characterized by gel permeation chromatography (GPC) technique. Proton nuclear magnetic resonance (1H-NMR) was used to investigate structure of chain-extended PLA. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine thermal properties while the crystallinity was investigated by X-ray diffraction (XRD).

scholarly journals Synthesis and ionic conductivity of siloxane based polymer electrolytes with pendant propyl acetoacetate groups

2018 ◽  
Vol 90 (6) ◽  
pp. 989-999 ◽  
Author(s):  
Omari Mukbaniani ◽  
Witold Brostow ◽  
Jimsher Aneli ◽  
Tamara Tatrishvili ◽  
Eliza Markarashvili ◽  
...  
Keyword(s):  
Specific Conductivity ◽  
Sol Gel ◽  
Gel Permeation Chromatography ◽  
Polymerization Reaction ◽  
Side Chain ◽  
Anion Receptors ◽  
Scanning Calorimetry ◽  
Molar Ratios ◽  
Wide Range ◽  
Electrolyte Membranes

Abstract Hydrosilylation reaction of 2.4.6.8-tetrahydro-2.4.6.8-tetramethylcyclotetrasiloxane (D4H) with allyl acetoacetate at 1:4.1 molar ratios of initial compounds in the presence of platinum hydrochloric acid (0.1 M solution in THF), Karstedt’s catalyst (Pt2[(VinSiMe2)2O]3) and platinum on the carbon have been carried out and D4R type compounds obtained. Reaction order, rate constants and activation energies for hydrosilylation reactions in the presence of Karstedt’s catalyst have been determined. Ring-opening polymerization reaction of D4R in the presence of catalytic amounts of powder-like potassium hydroxide has been carried out. A linear methylsiloxane oligomer with regular arrangement of propyl acetoacetate groups in the side chain has been obtained. The synthesized methylorganocyclotetrasiloxane and oligomers were studied by FTIR, 1H, 13C and 29Si NMR spectroscopy. Comb-type oligomers were characterized by gel-permeation chromatography, wide-angle X-ray diffractometry and differential scanning calorimetry. Solid oligomer electrolyte membranes have been obtained via sol–gel processes involving lithium trifluoromethylsulfonate (triflate) or lithium bis(trifluoromethylsulfonyl)imide. The specific volumetric electrical conductivity of the membranes at room temperature covers a wide range, from 10−10 to 10−4 S · cm−1, and depends on the structures of grafted anion receptors and the polymer backbones. Higher values of the specific conductivity are seen for the membranes containing triflate.

scholarly journals Light-Induced Actuation of Poly(dimethylsiloxane) Filled with Graphene Oxide Grafted with Poly(2-(trimethylsilyloxy)ethyl Methacrylate)

Polymers ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1059 ◽  
Author(s):  
Josef Osicka ◽  
Miroslav Mrlik ◽  
Markéta Ilčíková ◽  
Lukas Munster ◽  
Pavel Bazant ◽  
...  
Keyword(s):  
Surface Modification ◽  
Graphene Oxide ◽  
Gel Permeation Chromatography ◽  
Mechanical Analysis ◽  
Single Step ◽  
Point Of View ◽  
Inert Material ◽  
Ethyl Methacrylate ◽  
Transmission Electron ◽  
On Line

This study serves to combine two approaches into one single step, to achieve a significant improvement of the light-induced actuation capabilities. Graphene oxide (GO) is an inert material, from the electrical and thermal conductivity point of view, and is incompatible with the usually-used poly(dimethylsiloxane) (PDMS) matrix. During surface-modification by surface-initiated atom transfer radical polymerization, the GO was transformed into a conducting and compatible material with the PDMS showing enormous light-induced actuation capability. The GO surface-modification with poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS) chains was confirmed by transmission electron microscopy and thermogravimetric analysis, with an on-line monitoring of gasses using FTIR. The improved compatibility was elucidated using contact angle and dielectric properties measurements. The PHEMATMS shell was investigated using gel permeation chromatography and nuclear magnetic resonance. The improved electric conductivity was measured using the four-point probe method and by Raman spectroscopy. The very important mechanical properties were elucidated using dynamic mechanical analysis, and with the help of thermo-mechanic analysis for the light-induced actuation. The excellent actuation capabilities observed, with changes in the length of around 0.8% at 10% pre-strain, are very promising from the point of view of applications.

Silica/GO hybrids reinforced NR: Better interface interaction and dynamic behavior

2019 ◽  
Vol 52 (7) ◽  
pp. 575-592
Author(s):  
Kaikai Liu ◽  
Yuanyuan Shang ◽  
Liu Yang ◽  
Aihua Du
Keyword(s):  
Mechanical Performance ◽  
Volume Fraction ◽  
High Volume ◽  
Interfacial Interaction ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Interface Interaction ◽  
Transmission Electron ◽  
Strong Interfacial Interaction ◽  
Filler Dispersion

With silica firstly modified by 3-aminopropyl-triethoxysilane (APES), graphene oxide (GO) was prepared by modified Hummer’s method. APES-silica/GO (AsGO) hybrids were fabricated through hydrogen bond to reduce the polarity of silica and GO and increase the compatibility between natural rubber (NR) and AsGO. Subsequently, AsGO was incorporated into NR latex. The interaction between GO and silica in AsGO was characterized by X-ray diffraction, Raman, and Zeta potential. It was confirmed by transmission electron microscopy that the silica was uniformly dispersed on the surface of the GO. The filler–rubber interfacial interaction was thoroughly investigated. The amount of constrained region was quantified through differential scanning calorimetry results, and it showed that the high volume fraction of constrained region is responsible for the strong interfacial interaction. Besides, the mechanical performance, dynamic property, and electrical and thermal conductivity of NR-AsG x were studied. The results showed that the overall performance of NR-AsG x has an optimum value when the GO loading is 1.5 phr, which is due to the good filler dispersion and strong interface interaction.

Effect of boric acid on thermal stability of poly (acrylonitrile-methyl acrylate)

e-Polymers ◽  
2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Na Han ◽  
Xingxiang Zhang
Keyword(s):  
Thermal Stability ◽  
Boric Acid ◽  
Methyl Acrylate ◽  
Gel Permeation Chromatography ◽  
Decomposition Temperature ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molar Ratios ◽  
Thermal Stability Of

AbstractA series of acrylonitrile(AN)-methyl acrylate (MA) copolymers (AN/MA) with molar ratios of 100/0-70/30 were synthesized by water depositing polymerization. One to three percent of boric acid (BA) was adopted as a stabilizer to enhance the thermal stability of AN/MA. The copolymers and the mixtures of copolymers treated with BA were characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (1H NMR), Gel Permeation Chromatography (GPC), Differential Scanning Calorimetry (DSC), Thermogravimetry (TG), X-ray diffraction (XRD) and Optic Microscope. The results show that melting point (Tm), glass transition temperature (Tg) and crystallinity of the copolymer decreased while decomposition temperature (Td) increased with the increase of MA content. Tm of AN/MA dropped to 174 °C and Td rose up to 321 °C when 15 mol% MA was incorporated. It was worthy to note that Tm of the copolymers increased conspicuously after being treated with BA. Stability of AN/MA with a molar ratio of 85/15 containing 1 wt% BA improved remarkably. The mixture can be kept stable up to 30 min at 220 °C.

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