Transition Temperatures Of Polymers Research Articles

Organic additives in gel-tape casting of ceramic powders – A novel approach to the problem of elasticity and cracking of thin tapes

Polymerization reactions are frequently used in fabrication of a wide range of ceramic components, from 3D elements (gelcasting, UV-curing), through thin tapes (gel-tape casting) to porous samples (mechanical foaming coupled with gelcasting). The analysis of the properties of organic additives used in these techniques as well as factors which influence the polymerization reaction in ceramic suspension are seldom described in the scientific literature. For this reason this paper presents the properties of selected monomers and polymers with influence on the elasticity of zirconia tapes obtained by gel-tape casting. The measured parameters were as follows: glass transition temperature of polymers with and without external plasticizers, wetting angle of ceramic substrates by monomers, and viscoelastic properties of zirconia slurries. The issues of oxygen inhibition, polymerization rate and polymerization shrinkage with influence on unwanted cracking of thin tapes are also discussed. The location of polymeric binder in green bodies was analyzed by SEM.

Chemical Modification of Glycidyl Methacrylate Copolymers with Alcoholes Containing Pyridine Groups

Abstract. In this work the homopolymer and copolymers of glycidyl methacrylate (GMA) with ethylmethacrylate (EMA), methylacrylate(MA) and ethylacrylate (EA) were synthesized by free radical polymerization using azobis(isobutyronitrile) (AIBN) as initiator at 70 ±10C. Then, copolymers of glycidyl methacrylate have been modified by incorporation of 2-(2-pyridile)ethanol by the ring opening reaction of the epoxy groups. The polymers were characterized by 1H-NMR and FT-IR. Presence of bulk the 2-(2-pyridile)ethanol groups in polymer side chains leads to an increase in the rigidity and glass transition temperature of polymer as shown by DMTA analysis. The research demonstrated that the synthesized modified polymer could successfully remove heavy metals from solution. With the incorporation of the 2-(2-pyridile)ethanol groups in the polymer side chains, a series of novel modified polymer containing new properties are obtained, that can find some applications in polymer industry.

Polymers Based on Norbornene Derivatives

This study presents the influence of exo,exo-N,N’- hexylene-di(5-norbornene-2,3-dicarboximide) on the degree of cross-linking and glass transition temperature of the polymers obtained from a mixture of dimethyl esters of exo,exo- and endo,endo-5-norbornene-2,3-dicarboxylic acid. It was found that exo,exo-N,N’- hexylene-di(5-norbornene-2,3-dicarboximide) can be used as a cross-linking agent in ROMP. Addition of the cross-linking agent leads to an increase in the degree of cross-linking polymers. The glass transition temperature of polymers increases with concentration increasing of the crosslinking agent.

Monoacryloyl esters of carbohydrates: Synthesis, polymerization and application in ceramic technology

The article presents the interdisciplinary research among organic synthesis, chemistry of polymers and ceramic technology. It presents the synthesis of monoacryloyl esters of fructose and glucose that is 1-O-acryloyl-d-fructose and 3-O-acryloyl-d-glucose, conditions of their polymerization and application in shaping of advanced ceramic powders by the so called gelcasting method. The paper presents the influence of carbohydrate esters on the viscosity of Al2O3 suspensions and microstructure of final ceramic samples. The results showed that synthesized esters of saccharides can play the role of organic monomers able to polymerize in situ and self-cross-linking compounds in gelcasting. The paper presents the proposed structure of polymeric network which is formed from acryloyl ester of glucose during gelcasting process. The paper describes rheological behaviour of slurries composed of synthesized substances and A2O3 powders, wetting angles of alumina substrate by synthesized compounds, differences in glass transition temperatures of polymers and the microstructure of obtained final ceramic samples.

Low glass transition temperature polymer electrolyte prepared from ionic liquid grafted polyethylene oxide

In this contribution, we report a new type of poly (ionic liquids) prepared by imidazolium ionic liquids directly grafting onto polyethylene oxide backbone. Different molecular weights of poly (ionic liquids) are obtained with a low glass transition temperature up to −14 °C. The materials as polymer electrolyte achieve a high conductivity around 10−5 S cm−1 at 30 °C and close to 10−3 S cm−1 at 90 °C. High viscosity up to 4000 Pa s at room temperature would minimize the electrolytes leaking in electrochemical devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2104–2110

Effect of thermal lag on glass transition temperature of polymers measured by DMA

This paper investigates the influence of thermal lag on the glass transition temperature of polymers measured under different heating rates during dynamic mechanical analysis (DMA). The E-modulus–temperature curves of a two-component epoxy adhesive and a pultruded glass fiber-reinforced polyester were measured by a DMA machine. Experimental results showed that two kinds of thermal lag result when the heating rate exceeds 0.5°C/min: one between the specimen temperature and the thermocouple of the machine and the other along the length of the specimen. A finite volume model was developed in order to simulate the thermal environment inside the DMA chamber and validate the measured thermal lags. A numerical procedure was adopted to calculate the influence of the thermal gradient along the length of the specimen on the E-modulus–temperature curve. It was found that when the thermal lag effects are excluded, the E-modulus of a specimen decreases with increasing heating rates. This result contradicts reported results obtained using the experimentally derived E-modulus vs. temperature curves, disregarding the influence of the thermal lags, and thus claiming an increase of the E-modulus with increasing heating rates.

Controlling the sub-molecular motions to increase the glass transition temperature of polymers

Employing atomistic molecular dynamics (MD) simulations, we scrutinize the relationship between sub-molecular motions in a glassy polymer and its glass-transition temperature (Tg). This molecular understanding allows us to modify the polymer to manipulate atomistic motions, thereby controlling the glass transition temperature. We demonstrate this using a high performance polymer, HFPE-30, which has applications in aerospace industry. Control over sub-molecular motion is achieved by chemical substitution and it leads to increase in the glass transition temperature without affecting its mechanical properties. The approach laid out here could pave a way to achieve highly cross-linked high temperature polymers with better thermo-chemical stability.

The Influence of the Degree of Crystallinity on the Glass Transition Temperature of Polymers

The influence of the degree of crystallinity of polymers on the glass transition temperature Tg of their amorphous domains is quantitatively analyzed. The analysis is made based on the Mandelkerns ideas [ concerning the restrictive effect of crystallization on the mobility of macromolecules within the amorphous domains. At low degrees of crystallinity, Tg of amorphous domains slowly increases, and then increases much faster at high degrees of crystallinity.

3D Cross-Linked Nanoweb Architecture of Binder-Free TiO2 Electrodes for Lithium Ion Batteries

The nanoweb structure of TiO2 anode, cross-linked between electrospun nanofibers, is directly fabricated on the current collector by utilizing the fluidity of low glass transition temperature polymer, poly(vinyl acetate), at room temperature. This characteristic enables us to fabricate the nanoweb structure by direct electrospinning on the current collector, followed by uniaxial pressing. This proposed structure facilitates electron transport through the direct conducting pathways between TiO2 active materials and current collector as well as provides strong adhesion strength to the current collector without polymeric binders. Consequently, we could achieve stable cycle performance up to 100 cycles and the excellent rate capability of ∼60% at high rate charge/discharge condition of 10 C.

From polymer to polyelectrolyte: Studies of star-branched poly(ethylene oxide) with lithium functional groups

Star-branched poly(ethylene oxide) with PG-PPO core has been synthesized. The branched structure had on average 18 poly(ethylene oxide) arms with average molecular weight of 1680. The chain ends were capped with OH groups which were then substituted with lithium-containing P(O)(OLi)2, COOLi and SO3Li groups. The substitution level ranged from 30% to 95%. Characterization of physical properties was carried out by various methods, including differential scanning calorimetry and impedance spectroscopy. The results show that polymers with functional groups containing lithium are characterized by relatively high ionic conductivity. The highest ionic conductivity, reaching 8×10−6S/cm at 20°C was obtained for polymer with P(O)(OLi)2 groups, which demonstrates possibility of using these polymers as polyelectrolyte. It has been also found, that the presence of end groups can decrease crystallinity and lower glass transition temperature of polymer. Electrolytes formed by adding LiN(CF3SO2)2 salt to polymers with functional groups containing lithium had higher ionic conductivity and lower glass transition temperature than electrolytes based on polymer without such groups.

Surface energy control of soluble polyimide gate insulators by copolymerization method for high performance pentacene thin-film transistors

We have synthesized a series of surface energy controlled soluble polyimide (PI) gate insulators (KSPI-C1, KSPI-C3, and KSPI-C5) by one-step copolymerization method of the monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4,4-diaminodiphenylmethane, and 1-(3,5-diaminophenyl)-3-octadecylpyrrolidine-2,5-dione (DA-18-IM). The long alkyl chain containing DA-18-IM monomer was used to control the surface energy of PI polymers. Fully imidized PI polymers were found to be completely soluble in organic solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, etc. Thermal gravimetric analysis exhibited that all polymers are stable up to more than 432°C with only 5wt.% weight loss. The glass transition temperatures of polymers are found to be between 208°C and 242°C by differential scanning calorimetry measurement. Thin films of all polymers could be fabricated at only 150°C and a pentacene thin-film transistor (TFT) with KSPI-C3 as a gate dielectric was found to exhibit the highest field effect mobility of 0.53cm2/Vs. Surface energy controlled PI polymers are promising candidates for gate dielectrics for organic TFTs.

Synthesis, characterization and protonation study of novel poly(thioether imide)s based on aromatic heterocyclic diimide

Novel poly(thioether imide)s were synthesized by 2,5-dimercapto-1,3,4-thiadiazole, and aromatic heterocyclic chlorodiimids through nucleophilic substitution reaction as alkali catalysts were presented. The poly(thioether imide)s exhibited good thermal property. The glass transition temperatures of polymers were around 373 °C, and 10% weight loss temperatures were in the range of 450–500 °C in nitrogen/air atmosphere. Meanwhile, the chloroform dilute solutions of these polymers could show strong UV-vis absorption peaks at about 289 nm. After being protonated by inorganic acids (HCl), the new shoulder absorption peaks were observed at 350 nm. The PL absorption bands of polymer solutions were in the region of 350–550 nm, which showed the green-yellow fluorescence.

FORMULATION AND EVALUATION OF SUSTAINED RELEASE LIQUISOLID TABLETS OF METOPROLOL SUCCINATE

L iquisolid technique is the novel concept of drug delivery via the oral route . This technique is applied to poorly water soluble, water insoluble or liphophilic drugs. According to the new formulation method of liquisolid compacts, liquid medi cations such as solutions or suspensions of water insoluble drugs in suitable non - volatile vehicles can be converted into acceptably flowing and compressible powders by blending with selected powder excipients. The present research endeavor is directed t owards the development of liquisolid compact for the production of sustained release tablet of water - soluble Metoprolol succinate . Liquisolid compacts were prepared by using Tween 80 as the liquid vehicle or non - volatile solvent , Avicel PH 102 as absorbing carrier and Aerosil 200 as adsorbing coating material. The prepare d liquisolid systems were evaluated for their micromeretic properties and possible drug excipients interactions. P - XRD analysis confi rmed that no change in crystallinity of Metoprolol succi nate Liquisolid compacts . The DSC and IR spectra analysis study ruled out no any significant interaction between the drug and excipients used in preparation of Metoprolol succinate Liquisolid compacts. The tableting properties were falling within acceptabl e limits. The in vitro dissolution study confirmed reduction in d rug release from Liquisolid compacts compared to conventional matrix tablet , in - vivo study was carried out to check the plasma drug concentration . Tween 80 has plasticizer effect by which it can reduce the glass transition temperature of polymer and impart flexibility in sustaining the release of drug from liquisolid matrices. The results showed that wet granulation had a remarkable impact on the release rate of Metoprolol succinate from liqui solid compacts, reducing the release rate o f drug from liquisolid compacts. Key wo rds : Metoprolol succinate, Liquisolid Tablets , Sustained Release, Avicel.

Photopolymerization Reactions Using the Photoinitiated Copper (I)‐Catalyzed Azide‐Alkyne Cycloaddition (CuAAC) Reaction

The first bulk photopolymerization of multifunctional alkyne and azide monomers using the CuAAC reaction is successfully carried out from low molecular weight, nonviscous monomer resins. Compared to other traditional step-growth bulk photopolymerization, this approach readily provides crosslinked, high glass transition temperature polymers that incorporate triazole linkages throughout the polymer structure with great temporal control.

Consolidation of suspended particles by using dual ionic thermosensitive polymers with incorporated a hydrophobic component

The flocculation/consolidation of suspended particles using the hydrophobic transition of a thermosensitive polymer is a promising method for sludge dewatering. However, flocculation/consolidation using thermosensitive polymers requires heating of the suspension. Furthermore, although ionic thermosensitive polymers are usually effective for flocculation/consolidation of charged suspended particles, the transition temperature increases when the ionic component is incorporated into the thermosensitive polymer. To alleviate this problem, we proposed the use of dual ionic (i.e. cationic and anionic) thermosensitive polymers. The use of an anionic thermosensitive polymer in combination with a cationic thermosensitive polymer resulted in the formation of a polymer complex. As a result, the transition temperature of the polymer molecules adsorbed on the suspended particles decreased. However, heating of the sludge was still required. In this work, a hydrophobic component was incorporated into the ionic thermosensitive polymers to decrease the transition temperature, and the consolidation of suspended particles using these dual ionic thermosensitive polymers was examined. N-isopropylacrylamide, N,N-dimethylaminopropyl acrylamide, acrylic acid, and N-tert-butylacrylamide (BAAM) were used as the thermosensitive, cationic, anionic, and hydrophobic components, respectively. By incorporating BAAM into either cationic or anionic thermosensitive polymers, the transition temperature of these ionic thermosensitive polymers decreased. The consolidation of kaolin suspension was observed near room temperature by adding the anionic polymer with the incorporated BAAM in combination with the cationic polymer.

Fragility and glass transition temperature of polymer confined under isobaric and isochoric conditions

It is now well established that the glass transition temperature (Tg) of polymers can deviate substantially from the bulk with nanoscale confinement. Understanding the impact of confinement on the Tg of polymers is important but it does not provide information about the temperature dependence of the cooperative segmental dynamics near the Tg, a phenomenon commonly referred to as the dynamic fragility. Here, we measure the dynamic fragility index (m) as well as the Tg of confined poly(4-methylstyrene) (P4MS) under isobaric and isochoric conditions. We accomplish this via variable cooling rate differential scanning calorimetry (DSC) studies on aqueous-suspended and silica-capped P4MS nanoparticles. We observe that both the isobaric (mp) and isochoric (mv) fragilities decrease with confinement. However, Tg decreases and remains constant with isobaric and isochoric confinement, respectively. The importance of interfaces in the observed trends as well as comparisons to prior studies is discussed.

The use of anhydride linkages to increase the glass transition temperatures of polymers containing carboxyl end groups: A perspective in powder coatings

A method to increase the glass transition temperature of carboxyl terminated low molecular weight cycloaliphatic polyesters through anhydride linkages is described. Low molecular weight carboxyl terminated cycloaliphatic polyesters, poly(1,4-cyclohexylidenecyclohexane-1,4-dicarboxylate) (PCCD), were synthesized by the polycondensation reaction of cis/trans-1,4-cyclohexane dicarboxylic acid and cis/trans-1,4-cyclohexane dimethanol. The corresponding poly(ester-anhydrides)s were obtained using a mixed anhydride method in melt where the low molecular weight carboxyl terminated cycloaliphatic polyesters were chain extended at the terminal carboxylic acid end groups through reversible anhydride linkages. The poly(ester-anhydrides)s as expected had higher glass transition temperature than the corresponding parent oligomers. PCCD oligomers with no anhydride linkages and PCCD based poly(ester-anhydrides)s with anhydride linkages at comparable molecular weights, had similar glass transition temperatures. However, the latter potentially offer higher reactive group concentration thanks to the reactive anhydride groups. This work was carried out as a proof of concept to show that the glass transition temperature of carboxyl terminated oligomers can be increased by increasing the molecular weight but without sacrificing the reactive group concentration. This approach, the authors suggest, may potentially be used in the design of new carboxyl functional base resins, especially for powder coatings, where both the acid number and glass transition temperature are important.

Synthesis and Characterization of Acrylic Copolymers of 4-Chloromethyl Styrene with Incorporation of Phthalimide Groups and Amination of Resulted Polymers

ChloroMethyl Styrene (CMS) was copolymerized with different monomers such as Methyl MethAcrylate (MMA), Methyl Acrylate (MA), 2-EthylHexyl Acrylate (EHA) by free radical polymerization method at 70 ±1°C using a,a'-Azobis(IsoButyroNitrile) (AIBN) as an initiator. The copolymer compositions were obtained using related 1 HNMR spectra and the polydispersity of the copolymers were determined using Gel Permeation Chromatography (GPC). The amino copolymers were prepared by treating 4-chloromethy styrene copolymers with sodium phthalimide and then with hydrazine monohydrate. The polymers were characterized by 1 HNMR and FT-IR spectroscopic techniques. The glass transition temperature (T g) of all copolymers was determined by Dynamic Mechanical Thermal Analysis (DMTA). Study of DMTA analysis showed that chemical modification of 4-chloromethyl styrene copolymers with phthalimide substituent leads to an increase in the rigidity and glass transition temperature of polymers.

Anisotropic silver nanoparticles as filler for the formation of hybrid nanocomposites

Prismatic and plate-like silver nanoparticles (Ag NPs) were synthesized according to the seed-mediated method. These particles were used as precursors for preparation of homogenous, transparent and colored Ag/poly(vinyl alcohol) (PVA) nanocomposite films with different concentrations of Ag by solution-casting technique. Optical and structural characterization of these nanocomposites includes UV–visible spectroscopy, X-ray diffraction (XRD), FTIR spectroscopy and SEM measurements. Further, the effect of embedded nanoparticles on the thermal properties of the PVA matrix was studied. The value of the glass transition temperature of polymer is found to increase after embedding Ag NPs. Comparison of thermal properties of pure PVA and nanocomposite films showed that the thermo-oxidative stability of polymer slightly increased in the presence of Ag NPs. Furthermore, the effect of the Ag NPs on the crystallinity of polymer was also observed.

Synthesis and electro-optical features of a high T g polymer system with excellent electro-optic activity and thermal stability

Three chromophores with tricyanofuran and tricyanopyrroline electron acceptors were synthesized and doped in high glass transition temperature (T g) polymer poly(N-(4-acetoxylphenyl)maleimide-co-styrene, NAPMI-co-ST). The electro-optic (EO), optical, and thermal properties of the doped poly(NAPMI-co-ST) were characterized and discussed. After being corona poled under 12 kV, this high T g polymer material showed excellent EO activity and thermal stability. The highest EO coefficient (r 33) reached 48.2 pm V−1 (1,310 nm) and could remain 90 % of the original value for 100 h at 85 °C. The EO coefficient was relatively higher compared with other high T g EO polymers. The thermal stability was also very good and the manufacture process was convenient and applicable for device fabrication.