Glass Transition Temperature Of Poly Research Articles

Synthesis, Chain Flexibility, and Glass-Transition Temperature of Poly (2,2-Diphenylethyl Methacrylate)

Six poly(2,2-diphenylethyl methacrylate) samples, with relatively low polydispersity index ( M w / M n :1.2-1.4) and M w ranging from 14.4 2 10 4 to 184.4 2 10 4 , were prepared by free-radical polymerization and fractionation. The dilute solution properties of the samples were studied by low-angle laser-light scattering in THF at 25C and viscometry in a thermodynamically good solvent (toluene at 25C) and in a -solvent (p-xylene at 22C). Differential scanning calorimetry was used for the T g determination. The results are compared with those reported for poly(2-phenylethyl methacrylate) and poly(diphenylmethyl methacrylate).

Simulation study of the glass transition temperature in poly(methyl methacrylate).

The glass transition in syndiotactic poly (methyl methacrylate) has been studied through atomistic molecular dynamics simulations performed at temperatures in the range from 297 K to 684 K. The mean squared deviations of atoms, monomers, and molecules from their initial positions were analyzed by means of a technique that separates the effects of diffusive motion from the underlying vibrational motion. The diffusive motion shows a novel power-law variation with time, with an exponent that varies continuously from 0.5 below the glass transition temperature T(g) to 1 at high temperatures. The self part of the van Hove correlation functions for both hydrogen atoms and monomers shows structural arrest at the lowest temperature studied. A second peak in the atomic van Hove correlation is attributed to rotation of the CH3 group.

Glass Transition Temperatures of Poly[(methyl methacrylate)-co-(butyl acrylate)]s Synthesized by Atom-Transfer Radical Polymerization

Glass transition temperatures Tg of methyl methacrylate/butyl acrylate copolymers obtained by means of atom-transfer radical polymerization are measured using differential scanning calorimetry. Due the nature of this polymerization method an increase in molecular weight is produced as the reaction progresses, which gives rise to an increase in Tg. Simultaneously, a composition gradient with the enrichment of butyl acrylate causes a decrease in Tg. These opposite effects almost compensate each other and, therefore, no influence on the molecular weight at M̄n < 10000 is found. This fact allows the application of the Johnston's equation and the Mayo-Lewis terminal model to describe and predict the variation in Tg with copolymer conversion for the copolymers and under the experimental conditions investigated.

Influence of various drugs on the glass transition temperature of poly(vinylpyrrolidone): a thermodynamic and spectroscopic investigation

Purpose: To determine the influence of hydrogen bonding and solubility parameter on the glass transition temperature ( T g) of various drug–poly(vinylpyrrolidone) blends. Methods: The T g of PVP films containing either acetaminophen, naproxen, salicylamide, carbamazepine, griseofulvin or propranolol hydrochloride were measured using differential scanning calorimetry. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction was used to characterize the specific interactions between the drug–PVP blends and the physical state of the films, respectively. The total solubility parameter and its individual components were calculated using the method of Van Krevelen. Results: Salicylamide displayed the greatest plasticizing effect, depressing the T g to the minimum. This was consistent with the FTIR data, which indicated the presence of hydrogen bonding with PVP. Griseofulvin showed the least plasticizing effect due to lack of interaction with PVP. All the drugs except griseofulvin were amorphous within the film up to 30% (w/w) drug composition. The correlation between the various components of the solubility parameters and the plasticizing effect of drugs was very poor. Conclusions: Spectroscopic investigation for the presence of interaction between the drugs and PVP proved to be extremely predictive of the plasticizing effect of various drugs. In contrast, solubility parameters appeared to be far less sensitive indicators of drug–PVP miscibility.

Synthesis, characterization, and glass transition temperature of poly(styrene‐b‐butyl methacrylate) block copolymers by stable free radical polymerization

AbstractThe synthesis of controlled polystyrenes with different molecular weights has been performed in the presence of 1‐phenyl‐1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethane (PETEMPO). The polystyrenes have served as macroinitiators for the formation of poly(styrene‐b‐butyl methacrylate) block copolymers. Using differential scanning calorimetry (DSC) it has been shown that all block copolymers synthesized do not present phase segregation. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 14–21, 2001

Study of the transition temperatures and acid–base properties of poly (methyl methacrylate) adsorbed on alumina and silica, by using inverse gas chromatography technique

The study of phenomena transitions in polymers is of vital importance in material sciences and more particularly when polymers are adsorbed on oxides. In a previous study, we determined the glass transition temperatures of poly (methyl methacrylate) (PMMA) adsorbed on alumina, by using the inverse gas chromatography (IGC) at infinite dilution. This technique proved to be an excellent technique to determine not only the glass transitions, but also β-transition and liquid–liquid transitions of polymers adsorbed on solid substrates. In this paper, we also used the IGC technique to determine the second order transitions of the systems PMMA/SiO 2 and PMMA/Al 2O 3, at various covered surface fractions and for various tacticities of the polymer (atactic, isotactic and syndiotactic). The maxima of the dispersive component of the surface energy γ s d of our two systems, obtained by IGC at infinite dilution, indicated clearly the presence of transition temperatures (glass or local transitions). In general, we observed with PMMA, three principal maxima that reflect the changes in motions leading to reorganisation and rearrangement of the various groups or chain segments of the polymer. The change in the retention mechanism of the probes at the transition temperatures is attributed to an increased molecular mobility of the polymer segments, allowing for the penetration of the probes into the polymer layer. The study of the chemical physical properties of PMMA/SiO 2 and PMMA/Al 2O 3, revealed an important difference in the acidic and basic behaviour, in Lewis terms, of oxide covered by various concentrations of PMMA. This study also highlighted an important effect of the tacticity of the polymer on the acidic basic character of PMMA adsorbed on oxides.

Relation between microstructure and glass transition temperature of poly[(methyl methacrylate)‐co‐(ethyl acrylate)

AbstractThe glass transition temperature of a series of samples of the poly[(methyl methacrylate)‐co‐(ethyl acrylate)] copolymer, synthesized at low conversion, were calculated theoretically using the equations of Barton and Johnston. The values obtained are more precise when the probabilities of the compositional diads are derived from the 13C NMR data instead of the classical method utilizing reactivity ratios. This can be observed more clearly when the copolymer samples are synthesized at high conversion. Introduction of configuration (tacticity) at the diad level confirms the above observations and slightly improves the calculated values of Tg compared to the initial formulae which were only taking into account the compositional sequences of the copolymer.© 2001 Society of Chemical Industry

Bulk Properties of Poly(macromonomer)s of Increased Backbone and Branch Lengths

We measured dynamic shear moduli of poly(macromonomer)s of an increased backbone chain length and those bearing branch chains of increased branch length up to the critical molecular weight for the intermolecular chain entanglement, Mc, of a linear polystyrene as functions of frequency and temperature using a parallel-plate rheometer. The poly(macromonomer)s were prepared from ω-methacryloyloxyethyl polystyrene macromonomers (MA-PSt)s or ω-vinylbenzyl polystyrene macromonomers (VB-PSt)s. It was revealed that a great increase in the backbone length caused the poly(macromonomer)s to show a weak rubbery plateau region in the master curves of the storage modulus G‘, where the molecular weights of the branch chains were smaller than Mc. The plateau modulus was much lower than that observed for the linear polystyrenes. On the other hand, the poly(macromonomer)s with polystyrene branches are nearly equal to the Mc, and a very short backbone chain showed a clear rubbery plateau region. The glass transition temperature of poly(macromonomer)s in the region without the chain entanglement decreased with decreasing branch length but remained almost constant over the wide range of the backbone length.

The Relationship Between Structures and In Vitro Properties of a Polyanhydride Implant Containing Gentamicin Sulfate

Laboratory scale injection-molding equipment was utilized to fabricate an implant consisting of poly(FAD:SA 1:1) and 20% (w/w) gentamicin sulfate. Characterizations were performed to determine the molecular weight and glass transition temperature of poly(FAD:SA 1:1). A study was carried out to investigate the relationships between the in vitro performance, morphology, and micro-structures of the molded implants. It was found that implants produced with different structures exhibited different physical integrities in water, i.e., cracking or non-cracking. For the non-cracking implants, a skin–core structure formed by an oriented skin layer was observed under a polarized light microscope. The same morphology was not seen in the cracking implants. The crystal orientation in the skin layer of the non-cracking implants was further identified using a wide-angle x-ray diffraction method (WAXD). No crystal orientation could be found in the cracking implants by WAXD. Furthermore, studies were carried out to evaluate the in vitro drug release for implants showing different degrees of integrity in water. The in vitro drug release of the cracking implants was markedly faster than that of the non-cracking implants due to the pronounced initial drug-burst effect as a result of crack formation in the implants.

Synthesis and radical polymerization of N, N-diethyl-α-fluoroacrylamide

N, N-Diethyl-α-fluoroacrylamide (DEFAA) was prepared by the reaction of ethyl α-fluoroacrylate and dimethylaluminum N, N-diethylamide. DEFAA was easily polymerized with dimethyl 2,2 ′-azobisisobutyrate (MAIB) to yield poly(DEFAA) as a white solid. Poly(DEFAA) was soluble in many organic solvents but not in aliphatic hydrocarbons. The polymerization of DEFAA with MAIB was kinetically investigated in benzene. The overall activation energy was estimated to be 64 kJ/mol. The polymerization rate ( R p) at 40°C was given by R p= k[MAIB] 1.0[DEFAA] 1.0. The high order with respect to initiator might be caused by unimolecular termination. The molecular weight (3–10×10 4) of poly(DEFAA) decreased with initiator concentration and temperature and increased with monomer concentration. The tacticities were found by 19 F -NMR spectroscopy as mm=0.32, mr=0.50 and rr=0.18. The glass transition temperature of poly(DEFAA) was 50°C by differential scanning calorimeter. Copolymerization of DEFAA( M 1) and styrene at 50°C in benzene gave the following results: r 1=0.15, r 2=2.59, Q 1=0.18, and e 1=+0.18.

Electric Field Aligned Photo-Polymer Films for Liquid Crystal Display

Oriented photopolymer films were obtained by using electric field alignment of the cinnamoyl side groups near the glass transition temperature of poly(vinyl)cinnamate (PVCN) followed by photo-polymerization using unpolarized UV light. In this way the induced anisotropy could be fixed and was subsequently shown to lead to a well aligned liquid crystal texture. The combination of electric field and UV light offers a solution to the pretilt angle problem for photo-aligned substrates.

Glass transition temperature of poly(vinylchloride) from molecular dynamics simulation: explicit atom model versus rigid CH2 and CHCl groups model

Abstract Glass transition temperature is the most important descriptor of the properties of amorphous polymers. In this study, molecular dynamics (MD) simulation is used to generate volume-temperature (VT) data at constant pressure for poly(vinylchloride) (PVC) over a temperature range that includes the experimental glass transition temperature (Tg) to study the validity of MD simulation in predicting Tg of amorphous polar polymers. PVC contains a polar group (chloride) which induces a partial charge distribution on all atomic sites of the polymer repeat unit. Two types of MD simulation were conducted. In the first type, all atomic sites were explicitly represented in the polymer chain model. In the second type of simulation, the CH2 and CHCl groups were modeled as rigid units to minimize the computational effort. The Tg values obtained from the MD VT curves were slightly displaced upward relative to the experimental Tg. The rigid unit model tends to under estimate the liquid density compared with the explicit atom model. MD simulation seems to be a practical procedure for predicting the Tg of polar polymers. The rigid unit model provides substantial saving in the computational effort without loss of accuracy.

Polar, Functionalized Diene-Based Materials. 1. Bulk, Solution, and Emulsion Free Radical Polymerization of 2-Cyanomethyl-1,3-butadiene

The bulk, solution, and emulsion free radical polymerizations of 2-cyanomethyl-1,3-butadiene were studied. Traditional bulk free radical polymerization kinetics were observed, giving polymers with 〈Mn〉 values of 20 × 103−60 × 103 g/mol and polydispersities near 1.5. In solution polymerization, the highest molecular weight (82 × 103 g/mol at 53% conversion) was obtained in tetrahydrofuran, with a broader polydispersity attributed to chain transfer to the solvent. In these two types of polymerizations, the Diels−Alder side product yield was affected by initiator concentration, solvent concentration, and polymerization time. Emulsion polymerization gave the highest molecular weight of poly(2-cyanomethyl-1,3-butadiene) to date of 128 × 103 g/mol in significantly shorter reaction time than bulk or solution reactions. Finally, the polymer microstructure of approximately 95% 1,4 and 5% 4,3 structure was determined, with the percent cis-1,4 (36−45%) varying with the polymerization temperatures. The glass transition temperature of poly(2-cyanomethyl-1,3-butadiene) is near −18 °C, based on the molecular weight and the microstructure.

On the high temperature TSDC peak in poly(ϵ-caprolactone)

The high temperature dielectric relaxation process, observed above the glass transition temperature in poly(ϵ-caprolactone) is studied by Thermally Stimulated Depolarization Currents experiments. The characterization is made by using the windowing polarization technique, decomposing the complex high temperature relaxation into Debye-like peaks. The profile of each peak is then analyzed by using a general kinetic order model, and the origin of the complex relaxation is discussed through the analysis of the parameters obtained from the best fit to the model. The distribution of the trap depths is obtained and their activation energies is found to vary from 0.8 to 1.2 eV. The space charge accumulation is mainly responsible for this relaxation mode in poly(ϵ-caprolactone).

Molecular Model and Analysis of Glass Transition Temperatures for Polymer−Diluent−Salt Systems

Three explicit mathematical models have been developed to predict glass transition temperatures of binary polymer-diluent and polymer-salt systems as well as ternary polymer-diluent-salt systems based on the configurational entropy model and the Flory-Huggins theory. In the presence of salt, the specific ionic interactions of polymer and/or diluent with salts have been taken into account. The validity of the mathematical models were examined against the experimental glass transition temperatures of poly(2-ethyl-2-oxazoline)-propylene carbonate, poly(2-ethyl-2-oxazoline)-silver triflate, and poly(propylene oxide)-lithium iodide as well as poly(2-ethyl-2-oxazoline)-propylene carbonate-silver triflate. The models adequately predict glass transition temperatures depending on the concentrations of the diluent as well as the salt in both binary and ternary systems.

Solid state complexes of poly(L‐lysine) with metal chlorides from the 1st row of the d‐block

AbstractSolid state characterization of poly(L‐lysine)hydrobromide was obtained via differential scanning calorimetry, thermogravimetric analysis, optical microscopy and infrared spectroscopy. The glass transition temperature of poly(L‐lysine)hydrobromide is 178°C. This thermal transition has not been reported previously. Poly(L‐lysine)'s Tg decreases when complexes are produced with the following divalent transition metal chlorides; cobalt chloride hexahydrate, nickel chloride hexahydrate, copper chloride dihydrate and anhydrous zinc chloride. At 10 mol% salt, nickel, chloride decreases Tg by 45°C, and the general trend is Ni2+Co2+Zn2+Cu2+. The depression of poly(L‐lysine)'s Tg correlates well with ligand field stabilization energies for pseudo‐octahedral and pseudo‐tetrahedral dn complexes (n = 7, 8, 10) from the 1st row of the d‐block. However, d9 copper(II) complexes cannot be included in this empirical correlation. Infrared spectroscopic evidence suggests that Co2+, Ni2+ and Zn2+ coordinate to the carbonyl oxygen in the main chain of the polymer. When transition metal ions coordinate to CO, the network of hydrogen bonded amide groups is disrupted, which lowers the glass transition. The amide I region of the infrared spectrum reveals a hydrogen bonded CO stretch @ 1655 cm−1 that is characteristic of poly(α‐amino acid) random coil conformations, and a metal‐ligand coordinated CO stretch @ 1625 cm−1 in complexes with divalent cobalt, nickel and zinc. The amide II region of the infrared spectrum near 1550 cm−1 is also sensitive to the formation of coordination complexes with these d‐block metal chlorides.

Glass Transition Temperature of Poly(tert-butyl methacrylate) Langmuir−Blodgett Film and Spin-Coated Film by X-ray Reflectivity and Ellipsometry

The glass transition temperature (Tg) of poly(tert-butyl methacrylate) (PtBMA) Langmuir−Blodgett (LB) films relative to that of spin-coated films on a silicon substrate is investigated by ellipsometry and X-ray reflectivity. The Tg of spin-coated films on an oxide-free silicon wafer decreases as the film thickness decreases, which is consistent with the majority of the previous reports in the literature. However, the transition temperature of the LB films is nearly independent of the total thickness, that is, the number of accumulated layers, which is much different from the case for spin-coated films. After sufficient thermal annealing of the LB film, it recovers the thermal transition behavior of the spin-coated film with an equivalent thickness. The layer structure of the LB film is deemed to be responsible for the departure from the behavior of the spin-coated film.

Glass-transition temperature of poly(vinylidene fluoride)-poly(methyl acrylate) blends: Influence of aging and chain structure

The glass-transition temperature (T g ) of the poly(vinylidene fluoride) (PVF 2 )-poly(methyl acrylate) (PMA) blends increase with aging time. The T g versus log(time) plots are straight lines whose slope values depend on the head to head (H-H) defect content of PVF 2 samples and on the composition of the blends. The values of polymer-polymer interaction parameters (χ) increase with an increase in the H-H defect of PVF 2 for a fixed composition of the blend. Consequently, the T g of the blend decreases with an increase in the H-H defect of the PVF 2 sample. However, after aging for longer times this decrease of the T g with H-H defects is lower than those of the unaged blends. The possible reasons are discussed.

Poly(aryl ether)s containingo-terphenyl subunits. II. Random poly(ether sulfone)s

The synthesis of new A 2 X-type difluoride monomer, N-2-pyridyl-4',4-bis-(4-fluorobenzenesulfonyl)-o-terphenyl-3,6-dimethyl-4,5-dicarboxylic imide (3), is described. The monomer 3 was incorporated into a series of copoly(aryl ether sulfone)s by polymerization of 4,4'-isopropylidenediphenol and 4,4'-difluorophenylsulfone. The incorporation of monomer 3 had an observable effect on both the glass-transition temperature of poly(aryl ether sulfone)s and the tendency for macrocyclic oligomers to form during polymerization. Replacement of the pyridyl imide group via a transimidization reaction with propargyl amine proceeded quantitatively and without polymer degradation. The acetylene containing copoly(aryl ether sulfone) could be crosslinked by simple thermal treatment, resulting in an increase in the glass-transition temperature and solvent resistance.

Morphology of poly(chloro-p-xylylene) CVD thin films

Poly(chloro-p-xylylene) thin films are shown to have a changing morphology as a function of deposition temperature from spectroscopic ellipsometry and X-ray diffraction measurements. At lower deposition temperatures, the as-deposited polymer exhibited negative birefringence attributed to the presence of amorphous conformationally disordered polymer chains. As the deposition temperature was increased the polymer chains became more conformationally ordered resulting in an increase in the thin film’s birefringence. At higher deposition temperatures, above the polymer’s Tg evidence of crystallinity was apparent from X-ray diffraction results. The increase in the thin film’s birefringence may be attributed to the thermodynamic driving force for crystallization causing the plane of the phenyl group to orient more perpendicular to the plane of the substrate, evidently the more stable conformation for poly(chloro-p-xylylene). After an inert post-deposition anneal at 210°C for 2h, the thin films deposited at lower temperatures showed evidence of higher crystal quality than the above Tg deposited films because of a smaller d-spacing. A decrease in the full width half max of the X-ray diffraction peak was attributed to a large increase in the crystallite size, larger for the films deposited at higher temperatures as a result of a greater degree of crystallinity present in those films as-deposited. Further, comparisons are made between the as-deposited and post-deposition annealed samples in terms of stress, crystalline disorder and crystallite size. In addition, from differential scanning calorimetry measurements, the glass transition temperature of poly(chloro-p-xylylene) was 35°C–36°C and 44°C at heating rates of 0.2°C/min and 5°C/min.