Polymer studies

Wen X, Tolbert W A and DIott D D 1992 Multiphonon up pumping and moleoular hot spots in superheated polymers studied by ultrafast optioal oalorimetry Chem. Phys. Lett. 192 315-20... 

The first living polymer studied in detail was polystyrene polymerized with sodium naphthalenide in tetrahydrofuran at low temperatures ... 

Polymers. Studies to determine possible exposure of workers to residual epichl orohydrin and ethylene oxide monomers in the polymers have been done. Tests of warehouse air where Hydrin H and Hydrin C are stored showed epichl orohydrin levels below 0.5 ppm. Air samples taken above laboratory mixing equipment (Banbury mixer and 6" x 12" mill) when compounds of Hydrin H or C were mixed gave epichl orohydrin levels below detectable limits, and ethylene oxide levels less than 0.2 ppm, well below permissible exposure limits (46). A subacute vapor inhalation toxicity study in which animals were exposed to emission products from compounded Parel 58 suggests that no significant health effects would be expected in workers periodically exposed to these vapors (47). 

PEs, as other polymers, exhibit nonlinear behavior in their viscous and elastic properties under practical processing conditions, i.e., at high-shear stresses. The MFI value is, therefore, of little importance in polymer processing as it is determined at a fixed low-shear rate and does not provide information on melt elasticity [38,39]. In order to understand the processing behavior of polymers, studies on melt viscosity are done in the high-shear rate range viz. 100-1000 s . Additionally, it is important to measure the elastic property of a polymer under similar conditions to achieve consistent product quality in terms of residual stress and/or dimensional accuracy of the processed product. 

The three polymers studied display remarkable physical aging effects [24], with a strong increase of modulus and changes in the location and intensity of the glass transition. This phenomenon is exemplified in Fig. 17 where the changes of dynamic moduli in a PDEB sample aged for 14 months are very apparent. 

The polymers studied and the experimental procedure were described in the last section. The samples were made of the same PC-TLCP composite and the pure TLCP Vectra A950, respectively. To study the influence of sample forms and geometries on mechanical constants, plate samples (80 x 80 x 2 mm-) were also injection molded with a film gate. Tensile samples were then cut from the plate in the longitudinal (//) and transverse... 

The performance of such a probe can be demonstrated for polymer studies by heating a phantom sample up to 460 °C. The sample was made from a PTFE plug, two pieces of a PVC hose and a silicon rubber hose. The deformation and the... 

The mechanisms of photochemical degradation of a polymer are rather difficult to study as the observed degradation is typically a result of the effect of light on the contaminants in the polymer rather than the pure polymer. Studies typically look for the degradation products, either low molecular weight volatiles or radicals, or work to identify the wavelength of light absorbed by the system via spectroscopic methods. 

Figure 15 Molecular structures of conjugated polymers studied by Birgerson and co-workers [108],...

Propylene oxide is a surface active monomer structurally similar to ethylene oxide and therefore of interest as a SHM W-SP, but with more than ten repeating units this polymer is not water soluble. A compositional isomer methyl vinyl ether is water soluble the adsorption behavior of this polymer (PMVE) is illustrated in Figure 4. At 1 ppm the rate of 7T increase is linear over three hours. The diffusion rate could be calculated if the W-SP s molecular weight were monodispersed. The polymer studied had a Gaussian molecular weight distribution, which is true of essentially all W-SPs even after attempts have been made to... 

The relevance of these concepts to polymer studies will now be considered. 

The physico-chemical changes induced in polymers following exposure to radiation can be studied by a range of spectroscopic techniques. Recent developments in instrumentation and data analysis procedures in electronic, vibrational and magnetic resonance spectroscopies have provided considerable new insights into polymer structure and behaviour. The application of these spectroscopic methods in polymer studies are reviewed with emphasis on their utility in investigations of radiation effects on macromolecules. 

Infrared (IR) spectroscopy has been widely used in polymer studies for the assignment of molecular structure and for monitoring changes in the arrangement of chemical bonds (1.8-11). 

FTIR instruments offer advantages in speed and higher signal-to-noise ratios compared to dispersive IR spectrometers. These advantages combined with the facility for extensive data processing have seen the FTIR technique find increasing applications in polymer studies (11). 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

Experimentally the sample is placed in a strong magnetic field and, rather than the frequency being scanned at a constant field strength to detect absorption of radiation, in practice the frequency of exciting radiation is kept constant and the magnetic field flux is varied. Both ESR and NMR spectroscopy have found widespread application in polymer studies and several excellent texts describing the techniques are available (1,17-19). 

Polymer Properties. The modified polymers do exhibit some interesting properties. Water solubility is lost at 15% or less degree of substitution altho the polymers are at least partially soluble in acetic acid above about 25% degree of substitution. Solubility in butyrolactone also occurs above about 50% degree of substitution but the polymers are not soluble in xylene or methanol regardless of the degree of substitution. All polymers studied were soluble in DMSO, dimethylacetamide, dimethylform-... 

Of the polymers studied the methylated polyamides B and C are both biodegradable and photodegradable. Their use in agriculture are being studied. 

The periodontal pocket is another site for drug delivery in the oral cavity. Needleman et al. [46] investigated three mucoadhesive polymers (cationic chitosan, anionic xanthan gum, neutral polyethylene oxide) in vitro, using organ cultures, and in vivo in patients on their periodontal and oral mucosa. Of the polymers studied, chitosan displayed the longest adhesion in vitro and on the periodontal pockets, and the shortest adhesion on oral mucosa. 

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