Water content in polymers

M. Watanabe, Y. Satoh, and C. Shimura. Management of the water-content in polymer electrolyte membranes with porous fiber wicks. Journal of the Electrochemical Society 140, 3190-3193 1993. 

T Hatakeyama, K Nakamura, H.Hatakeyama. Determination of bound water content in polymers by DTA, DSC and TG. Thermochimica Acta 123 153-161, 1988. 

Free water (Wj) is shown as peak I on curves III and IV. W( is the unbound water content in polymers whose transition temperature and enthalpy arc equal to those of pure water (curve V). 

Detailed near-infrared spectra of PET exposed to different relative humidities indicated three different subbands of the first overtone of water at 7080 cm 7010 cm and 6810 cm The comparison with the water spectmm of bulk water suggested that most of the water is only weakly bonded with PET (89). The analysis of difference spectra of dry nylon and nylon exposed to different humidities, indicated that there were distinct populations of hydrogen-bonded water in it (90). Recently, Musto et al. (91) investigated the nature of molecular interactions of water in epoxy resins by means of near-infrared spectroscopy as proposed by Eukuda et al. (89,90). They found three subbands at 7076 cm 6820 cm and 6535 cm evidencing two kinds of water adsorbed in the polymer (mobile water localized in micro vide and water molecules firmly bonded to the network). However, hydroxyl groups of epoxy may complicate the analysis of water content in polymers because they absorb also in the same overtone region as water. 

DIES can be used both for qualitative monitoring of chemical reactions in organic materials e.g. curing, drying) and for quantitative measurements e.g. determination of the concentration of polar liquids in materials such as water content in polymers). DIES can be combined with other techniques, such as FTIR, to gain specific molecular information on reactions that take place simultaneously and monitor these reactions. However, only conductivity, a macroscopic property, is measured. Consequently, molecular differentiation between combined reactions cannot be made. A lab-scale experiment in combination with more specific techniques (e.g. FTIR) is necessary to determine quantitatively the specific reactions. Dielectric analysis also measures changes in the properties of a polymer as it is subjected to a periodic field. A general problem in interpretation of dielectric and conductive methods is that they are not specific and are affected by many sources of interferences. These factors may explain the relatively slow introduction of this technique in characterisation of elastomer systems. 

Use the molecular weight ratio to calculate the apparent extent of reaction of the caprolactam in these systems. Is the variation in p qualitatively consistent with your expectations of the effect of increased water content in the system Plot p versus moisture content and estimate by extrapolation the equilibrium moisture content of nylon-6 at 255 C. Does the apparent equilibrium moisture content of this polymer seem consistent with the value given in Sec. 5.6 for nylon-6,6 at 290°C ... 

A very similar behavior has been found by Goren et al.126) in their investigation of the polymer (Lys-Ala-Glu)n. The higher the water content in mixtures with methanol and the more the pH shifts up or down relative to the neutral state, the charge increases and the CD signals assume more the form of the characteristic -structure, thus losing the form of an a-helix. 

Study of the effect of small amounts of water in the liquid, organic phase on the polymerization of bisphenol-A and HFB in several solvents.[14] Solvents were rigorously dried and assayed for water content by potentiometric Karl Fischer titration. A series of polymerizations catalyzed and uncatalyzed in each solvent were carried out in which the water content was increased incrementally. Polymer yields and inherent viscosities were determined as a function of water content in each solvent. The optimal water content expressed as the mole ratio of water to catalyst shows that the necessary water level varies substantially with solvent (see Table V and Figure 1-3). 

Fig. 16. The relationship between the yield of crystalline polymer, microtacticity of raw polymer and water content in the polymerization of propylene oxide-a-d by EtZnNBu ZnEt [Oguni et al. (90)]...

Detected MRI signal should be converted for water content in a polymer electrolyte membrane (PEM). Our group performed a simple approach to relate the image intensity to the water content in the membrane by acquiring a series of MR images of an MEA exposed to water vapor activity, a, that are known to result in specific values of X, as the following equation found in literature.40... 

Methacrylic Acid Content in Polymer. One gram of methanol-precipitated, water-washed, dried polymer was dissolved in 100 ml. tetra-hydrofuran (THF) and titrated to a faint pink phenolphthalein end point with 0.055 n-benzyltrimethylammonium hydroxide in THF. The base was standardized by potentiometric titration against 0.01N acetic acid in methanol. The value for a non-acid containing polymer of the same series was used as a blank. All analyses were within 5% of the theoretical value. 

Nanowires of SiC and AI2O3 were synthesized using methods reported earlier in the literature [13, 14]. In a typical preparation of the PVA-SiC NW (0.8 vol%) composite, PVA (1.95 g) and SiC NWs (0.05 g) were added to warm water (50 ml) and the mixture was heated at 70 °C until the polymer dissolved forming a dispersion of the nanowires. The dispersion was dried in Petri dishes at 50 °C over a period of 3 days.3 As the mechanical properties of PVA are sensitive to the water content, the polymer films were stored in a vacuum desiccator with CaCh for at least a week before mechanical testing. Composites with PVA were prepared with 0.2, 0.4 and 0.8 vol% of SiC NWs and 0.4 vol% of AI2O3 NWs. Visual as well as optical microscopic examination of the composite strips indicated uniform distribution of the nanowires throughout the matrix. 

Also the diffusivity of water in polymers is highly dependent on the polymer-water interaction. When a polymer contains many hydrogen-bonding groups (cellulose, poly (vinyl alcohol), proteins, etc., and to a lesser extent synthetic polyamides) the diffusivity increases with the water content. This is explained by the strong localisation of the initially sorbed water over a limited number of sites, whereas at higher water contents the polymer... 

The presence of water is critical for operation but in current PEMFCs proper water management is a delicate issue and poor control can greatly reduce the efficiency of the device. An excess of water can flood the catalyst and porous transport layers impeding the transport of reactants and eventually drowning the fuel cell. At low water content, the polymer electrolyte membrane can become a poor conductor and the reactivity at the electrodes is affected. Local hot spots arising due to the inefficient operation result in early degradation of the cell. ... 

There are a number of useful points to be drawn from this analysis of the water cluster distribution. First, it appears that the cumulative water cluster distribution with a properly chosen cutoff distance is a metric that allows one to see clearly differences in connectivity of the aqueous domain as a function of both water content and polymer architecture. Clearly, Fig. 9(b) shows the connectivity of the aqueous domain moving from many small disconnected clusters to a single sample-spanning cluster as a func-... 

In this work, we have approaehed the understanding of proton transport with two tasks. In the first task, deseribed above, we have sought to identify the moleeular-level stmeture of PFSA membranes and their relevant interfaees as a funetion of water content and polymer architecture. In the second task, described in this Section, we explain our efforts to model and quantify proton transport in these membranes and interfaces and their dependence on water content and polymer architecture. As in the task I, the tool employed is molecular dynamics (MD) simulation. A non-reactive algorithm is sufficient to generate the morphology of the membrane and its interfaces. It is also capable of providing some information about transport in the system such as diffusivities of water and the vehicular component of the proton diffusivity. Moreover, analysis of the hydration of hydronium ion provides indirect information about the structural component of proton diffusion, but a direct measure of the total proton diffusivity is beyond the capabilities of a non-reactive MD simulation. Therefore, in the task II, we develop and implement a reactive molecular dynamics algorithm that will lead to direct measurement of the total proton diffusivity. As the work is an active field, we report the work to date. 

In fact, the surfactant monomeric aggregates and the polymer are mutually exclusive In the range of minimum water content according to the following results. The minimum water content In weight percent. Figure 4, may be expressed as... 

It is obvious that a different factor must be found to explain the sensitivity to dimer formation for maximum water content in the monomeric surfactant aggregates because this phenomenon Is entirely outside the realm of polymers and their entroplc conformational demands. One such factor is the Interaction between aromatic compounds and the polar group of a surfactant. Two examples of such Interaction are described In the next section. 

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