Compatibility of cross-linked polymers with plasticizers by glass transition temperature measurement and swelling tests

To elucidate the compatibility of polymer and plasticizer components of binders a study of polymer–plasticizer interactions by differential scanning calorimetry (DSC) and swelling tests was conducted. The glass transition temperatures (T_g's) of mixtures of polymers and plasticizers, both cured and uncured, were determined with a DSC technique. Results with the PEG polymer systems were complicated by the partial crystallization of the polymer from the polymer/plasticizer mixtures. The PGA polymer system did not exhibit this behavior. However, the T_g's of cured PGA with various plasticizer mixtures made complicated departures from linearity (plots of T_g versus weight fraction of plasticizer) that indicated polymer–plasticizer interaction. By using least-squares analysis of data plotted by the equation Values of the interaction parameter K were determined for cured PGA in various plasticizer systems. These K values are in good agreement with the molecular flexibility of the plasticizers based on their molecular structure. The results of swelling tests are discussed to elucidate further the nature of the interaction of these polymers with plasticizers. Calculated polymer-plasticizer interaction values (χ) from the swelling tests correlated with the solubility parameter (δ) for a given class of polymer (polyether, polyester) and plasticizer (nitrate ester, ether-type). The efficiency of a plasticizer in reducing the T_g of a polymer (below the linearly interpolated value) was found not to be related to the swelling behavior of the polymer in the plasticizer.     

23Na NMR in urethane cross-linked polyether solid polymer electrolytes

Sodium triflate/polyether urethane polymer electrolytes ranging in concentration from 0.05 molal to 1.75 molal have been investigated via ²³Na static solid-state NMR. Room temperature spectra and spin lattice relaxation times were consistent with a single narrow resonance indicating the presence of only mobile ionic species. The concentration and temperature dependence of relaxation times, chemical shifts, and linewidth have been investigated. The results suggest either a single species or rapid exchange between a number of species (even at temperatures below the glass transition temperature, T_g). The linewidth decreases with increasing concentration of ions and remains temperature independent below T_g. Below T_g a maximum quadrupolar interaction constant of 2 MHz is calculated. The addition of plasticizer to the polymer electrolyte causes significant chemical shift changes that depend on the solvent donicity of the plasticizer. The linewidth and T₁ relaxation times also depend on the T_g of the plasticized systems. Previous ²³Na NMR literature results are reviewed and qualitative models developed to account for the variation in results. © 1994 John Wiley & Sons, Inc.     

Glass temperature depression of polymer by use of mixed solvents: A colligative property

The entropy theory of glasses is used to determine the glass temperature depression by a multicomponent low molecular weight plasticizer (diluent). The glass temperature, T_g, is calculated as a function of pressure, P, the mole fractions, m_i, of the plasticizers, and the degree of polymerization p. One finds, provided there is no phase separation, that to a good approximation, the initial glass temperature depression is a function of the total mole fraction of plasticizer. Moreover, the glass temperature depression for small plasticizer molecules is found to be nearly a universal function of the plasticizer mole fraction (it depends on no other plasticizer variable), and to vary inversely as the number of flexible bonds per monomer unit of the polymer. A useful approximation is found, γdT_g/dm₁ = −3T_g, where m₁ is the total mole fraction of diluent on a per monomer of polymer basis, and γ is the number of flexible bonds per monomer. Although these results agree with experimental data in the literature, a more definitive experimental test is needed. © 1996 John Wiley & Sons, Inc.     

Prediction of the glass transition temperature for compatible polymer blends of varying compositions

Compatible polymer blends have been found to have widespread commercial applications. The simplest criterion for judging polymer—polymer miscibility in the solid state is the glass transition temperature (T_g), which can vary widely according to blend composition for a compatible system.Recently, an equation which predicts the T_g of intimate mixtures of compatible polymers has been derived, based on classical thermodynamics. Only a knowledge of the T_g and heat capacity increment (ΔC_p) of each pure component is required to predict the T_g at any composition.In this paper, the validity of this entropy-based relationship is investigated for a variety of commercial compatible polymer blends, including some based on poly(vinyl chloride), polystyrene, and poly(2,6-dimethyl-,4-phenylene oxide). The T_g and ΔC_p of each pure component are measured with a Perkin-Elmer DSC-2 differential scanning calorimeter, are predicted glass transition temperatures are compared with those observed experimentally.     

Determination of ultra-low glass transition temperature via differential scanning calorimetry

A novel method was developed to determine the ultra-low glass transition temperature (T_g) of materials through physical blending via differential scanning calorimetry. According to the Fox equation for polymer blends, a blend of two fully compatible polymers has only one T_g. The single T_g is a function of the T_gs of the two simple polymers. Thus, the ultra-low T_g of one material can be obtained from the T_gs of another polymer and their blends. The error of T_g measurements depends on the measurement error of the T_gs for the blends and another polymer. The method was successfully applied to determine the T_gs of acetyl tributyl citrate (ATBC), tributyl citrate (TBC) and poly(ethylene glycol)s (PEG)s with different molecular weights. The T_gs for ATBC, TBC, PEG-4000 and PEG-800 were ?57.0 °C, ?62.7 °C, ?76.6 °C and ?83.1 °C, respectively. For all the samples, the standard deviation of measurements was less than 3.3 °C, and the absolute error of measurements was theoretically not more than 5.3 °C. These results indicate that this method has acceptable precision and accuracy.     

New development on plasticized poly(lactide): Chemical grafting of citrate on PLA by reactive extrusion

New plasticization ways based on low molecular plasticizers from citrates family were investigated to improve the ductility of poly(lactide) (PLA). Grafting reactions between anhydride-grafted PLA (MAG-PLA) copolymer with hydroxyl-functionalized citrate plasticizer, i.e. tributyl citrate (TbC), were so-carried out through reactive extrusion. TributylO-acetylcitrate (ATbC) was used as a non-functionalized reference. Both plasticizers drastically decreased the T_g of PLA. However, the grafting reaction of TbC into MAG-PLA revealed a shift of PLA T_g toward higher values. After 6 months of aging, no phase separation was observed. However, plasticizer leaching was noticed in the case of PLA/ATbC materials, leading to the shift of T_g toward lower temperatures. In contrast, no major leaching phenomenon was noticed in PLA/TbC and PLA/MAG-PLA/TbC blends, indicating that the mobility restriction derived from the hydrogen bonding that can occur between PLA and TbC as well as the grafting reaction of TbC into MAG-PLA enabled to reduce leaching phenomena.     

Performance of gelled-type dye-sensitized solar cells associated with glass transition temperature of the gelatinizing polymers

Poly(methyl acrylate) (PMA), poly(vinyl acetate) (PVAc) and poly(n-isopropylacrylamide) (PNIPAAm) with their respective T_g of 6, 32, and 145 °C were employed to gel the LiI/I₂/tertiary butylpyridine electrolyte system for preparation of the gelled-type dye-sensitized solar cells (DSSC). The light-to-electricity conversion efficiencies of DSSCs gelled by PMA, PVAc, and PNIPAAm were 7.17%, 5.62%, and 3.17%, respectively under simulated AM 1.5 sunlight irradiation, implying that utilizing the polymer of lower T_g to gel the electrolytes leaded to better performance of the DSSCs. Their short-circuit current density and IPCE also showed the similar trend. Electrochemical impedance spectroscopy of the gelled DSSCs revealed that utilizing the polymer of lower T_g resulted in lower impedance associated with the Nernstian diffusion within the electrolytes. The results were consistent with the observation that the molar conductivity of gelled electrolytes was higher as the polymer of lower T_g was applied, which can be justified by Vogel-Tammann-Fulcher (VTF) equation.     

Effect of benzenesulfonamide plasticizers on the glass‐transition temperature of semicrystalline polydodecamide

The effect of various benzenesulfonamide (BSA) plasticizers on the amorphous phase of semicrystalline polydodecamide (PA‐12) has been investigated. MonoBSAs appear as efficient glass‐transition temperature (T_g) depressors because of their miscibility with the host polyamide (PA), low glass transition, and small molecule size. PA‐12's T_g shifts from 50 to about 0 °C at 20 mol % of the most efficient molecules. Comparatively, the more bulky bisBSAs appear to induce less important absolute T_g decreases (30 K at 20 mol %), although these appear as more important when considering the polymer T_g to plasticizer T_g difference. This unexpected observation could be ascribed to both the amide‐sulfonamide interactions and the sterically generated disorder within the polyamide because of the plasticizer molecule's size. Phase‐separation behavior of BSA plasticizers within the host PA has also been investigated. Crystalline phenyl‐SO₂NH₂, for instance, dephased beyond 20 mol % in PA‐12, forming distinct 1–2 micrometer wide crystalline domains as a result of its high propensity to crystallize upon cooling from the melt. By contrast, slow crystallizing N,N‐dimethylBSA, which lacks any specific interaction for PA‐12, remained nevertheless dispersed at a molecular level (metastable state, no phase separation) when vitrification of the host PA‐12 amorphous phase occurred on cooling. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2208–2218, 2002     

Thermal Characterization of Polymethyl(α-n-Pentyl)Acrylate

This work presents new results concerning characterization of polymethyl(α-n-pentyl)acrylate polymer by means of thermal analysis. In differential scanning calorimetry investigations, the measured values of T _g, T _f and ΔC _p, i.e. the glass transition temperature, the fictive temperature and the heat capacity step at T _g, show that the polymer can be considered as fragile. Thermogravimetric analysis revealed two mass losses, the first, at low temperature, being associated with the evaporation of water molecules, and the second, at high temperature, corresponding degradation of the polymer. This degradation is a two-step phenomenon. Finally, study of the β and the α transitions by elementary and complex TSDC led to the following values: T _β=?40°C, T _α=36°C, T _c=47°C, τ_c=2.5 s and ΔH=85 to 165 kJ mol^?1.     

Visualization of strain-induced structural rearrangements in amorphous poly(ethylene terephthalate)

A direct microscopic observation procedure is applied to study the deformation of amorphous PET decorated with a thin metal layer when stretching is performed at different draw rates and at temperatures below and above the glass transition temperature T _g. Analysis of the formed microrelief allows stress fields responsible for the deformation of the polymer to be visualized and characterized. When tensile drawing is performed at temperatures above T _g, inhomogeneity of stress fields increases with the increasing draw rate; at high draw rates, the stress-induced crystallization of PET takes place. In the case of drawing the polymer at temperatures below T _g, direct microscopic observations make it possible to visualize the development of shear bands that appear in the unoriented part of the polymer specimen adjacent to the neck. The shear bands are oriented at an angle of about 45° with respect to the draw direction. When necking involves the unoriented part of the polymer, shear bands abruptly change their orientation and become aligned practically parallel to the draw axis.     

Impact of plasticizers and tackifiers on the crystallization of isotactic poly(1-butene)

Crystallization of a semi-crystalline polyolefin in the presence of low molecular weight modifiers was quantified by differential scanning calorimetry and optical microscopy. The polyolefin was a commercial grade of isotactic poly(1-butene) (iPB). Two modifiers were used: an oligomeric plasticizer, designated HOAO, which decreased the glass transition temperature (T_g) of the system, and an oligomeric tackifier, designated HOCP, which increased T_g. Binary iPB/modifier blends containing 10% or 20% by weight of HOAO or HOCP were examined to determine how their addition affects T_g, while ternary iPB/HOAO/HOCP blends containing 10% or 20% by weight of total modifier were examined to determine the effects of dilution by using a ratio of HOAO to HOCP that matched the T_g of iPB. The addition of modifier decreased the nucleation rate, spherulitic crystal growth rate, and final crystallinity of each blend. However, only the nucleation rate showed a dependence on the type of modifier, with nucleation retarded more by HOCP than by HOAO. A Hoffman-Weeks analysis of the melting point as a function of crystallization temperature confirmed that the driving force for nucleation was reduced, and that the effect was larger for HOCP. An Avrami analysis of the bulk crystallization kinetics was consistent with these observations, as the Avrami exponents were in the range of 3-4.     

The estimation of phase modifications in polymers by the method of “molecular probes” in gas chromatography—III. Glass transition behaviour and compatibility in mixtures of poly(methyl methacrylate) with poly(vinyl chloride)

Using the method of “molecular probes” in gas chromatography, glass-transitions in mixtures of poly(methyl methacrylate) with poly(vinyl chloride) are found. The strong variation of T_g for poly (methyl methacrylate) in mixtures with more than 20% of that polymer suggests interactions although T_g for poly(vinyl chloride) remains constant. The existence of a single T_g in mixtures with less than 20% poly(methyl methacrylate), on the other hand, suggests possible compatibility in these mixtures.     

Effects of high-pressure CO2 on the glass transition temperature and mechanical properties of polystyrene

Hydrostatic pressure usually increases the glass transition temperature T_g of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in T_g with pressure as the polymer is plasticized by the environment. Just such a minimum in the T_g of polystyrene (PS) is observed as the pressure of CO₂ gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time-temperature-pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and T_g reach minima, at a CO₂ pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO₂. At the minimum, T_g is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO₂ at the lower temperature. The plasticization effect due to CO₂ can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO₂ gas is a severe plasticizer for polystyrene.     

The estimation of phase modifications in polymers by the method of “molecular probes” in gas chromatography—VI. The study of the transitions in poly(ethylene terephthalate)

Multiple transitions have been identified by inverse gas-chromatography for fractions of poly(ethylene terephthalate) with $\text{M}$_n between 1.47 and 2.69 × 10⁴. Depending on the thermal treatment, at least two liquid-liquid transitions T_ll⁽¹⁾ and T_ll⁽²⁾ have been observed in addition to T_g and T_m; this feature is generally considered as characteristic of semi-crystalline polymers. The similarity of the dependence of T_g and T_ll on the molecular weight of the polymer probes suggests a common molecular origin of these phenomena; the fact that T_ll >T_g indicates that the T_ll transitions involve longer chain segments. The melting temperature decreases with increasing molecular weight, suggesting again that the crystallinity and/or the size distribution will enlarge as the molecular weight of the polymer is made higher.     

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.     

Determination of glass transition temperature of poly(ethylene glycol) by spin probe technique

The rotational relaxation data for free nitroxyl radicals in poly(ethylene glycol) samples of mol. wt 3000-22,000 gave for the glass-transition temperature (T_p) a value of ?60°, independent of molecular weight. The rotational activation energy was ～ 2 kJ/mole below T_g and ～ 10 kJ/mole above T_g. This indicated that the mechanism of motion below T_g differs from the above T_g. Evidently the rotating units of polymer are much smaller below T_g than above it. The rotational relaxation time (T) was found to be dependent on the molar volume of PEG (V) and to follow the empirical equations t = A exp (?kV₁) and t = B exp (?kV₁) where V_a and V₁ are the molar volumes (cm³/mol) when T < T_g and T > T_g respectively, and k ～ 1. Therefore the defects in which radicals are located are perhaps the dominant factor determining the dynamic state of probe radicals in polymers at low temperatures.     

DSC investigation of the polystyrene films filled with fullerene

Polystyrene composite films with different content of C₆₀?+?C₇₀ fullerene mix have been obtained from o-xylene solutions. The mass fraction of fullerene was varied from 0.01 to 0.1 mass%. The glass transition temperatures and specific heat capacities in range of 293?C423?K have been determined for the films by DSC method. The plasticization of the polymer is observed in thermal properties of the films under influence of small fullerene additions. The values of T _g and C _P decrease and thermal coefficient of heat capacity b increase as fullerene content increases up to 0.02 mass%. The effect of interaction between polymer and fullerene molecules on thermal properties becomes evident at higher fullerene content in range from 0.02 to 0.1 mass%. At this the values of T _g and C _P increase and b coefficient decrease with increasing content of fullerene. Concentration dependence of C _P and b values is less steep for polymer composite films in elastic state at temperatures above T _g. Molecular interactions in the composites are discussed in view of our-self and literature data.     

Structure-property study of polyimides derived from PMDA and BPDA dianhydrides with structurally different diamines

A series of aromatic diamines were polymerized with two aromatic dianhydrides, pyromellitic dianhydride and 3,3^′,4,4^′-biphenyltetracarboxylic dianhydride, and the resulting poly(amic acid)s were thermally cyclodehydrated to aromatic polyimides. The polyimides were characterized by determining the glass transition temperatures (T_g), thermal stability, coefficients of thermal expansion, and wide-angle X-ray diffraction. Structure-property relationships are elucidated and discussed in terms of the structural fragments in the polymer chain. The PMDA-based polyimides generally revealed a higher T_g than the corresponding BPDA-based analogues. Generally, the dilution of the imide content by the insertion of oxyphenylene segments into the diamines significantly reduced the T_g. The introduction of m- or o-phenylene units into the polymer backbone usually resulted in a decrease in T_g. The attachment of pendant groups on the backbone may lead to decreased or increased T_gs, depending on the structure of pendant groups. As evidenced by X-ray diffraction, the polyimides derived from rigid, rod-like diamines or the diamines having two or three p-oxyphenylene showed a higher crystalline tendency. The presence of aliphatic pendant groups slightly reduced the thermal stability of the polyimides. The other structural changes did not show a dramatic influence on the thermal stability. Some polyimides obtained from p- or m-phenylenediamine had low thermal expansion coefficients below 2×10−5°C⁻¹.     

Thermal and dynamic mechanical investigations on poly[bis(benzimidazobenzisoquinolinones)]

A series of new semi-ladder poly[bis(benzimidazobenzisoquinolinones)], obtained by the polycondensation of dinaphthalene dianhydrides and aromatic tetraamines was investigated by TG, DSC and DMA methods. The influence of polymer structure on the thermal behaviour of the poly[bis(benzimidazobenzisoquinolinones)] was examined. The polymers were found to be thermally stable with T_d > 723 K in air and T_g ranging from 585 to 701 K. A good agreement was obtained in T_g values measured by DSC and DMA methods. It was found that some cross-linking processes occurred at temperatures above T_g. Some of the isothermal ageing curves were used to find the activation energies of isothermal cross-linking and decomposition.