Polymers absorption

The first synthetic polyglycoHc acid suture was introduced in 1970 with great success (21). This is because synthetic polymers are preferable to natural polymers since greater control over uniformity and mechanical properties are obtainable. The foreign body response to synthetic polymer absorption generally is quite predictable whereas catgut absorption is variable and usually produces a more intense inflammatory reaction (22). This greater tissue compatibihty is cmcial when the implant must serve as an inert, mechanical device prior to bioresorption. 

The molecular process termed permeation is the most fundamental physical means by which fluid can pass right through an elastomer or other polymer. Absorption and permeation, besides being interrelated, both depend on two other phenomena associated with fluid-polymer interactions, as follows ... 

For this purpose, stabilization efficiency was defined as 1-As/Aq, where As and Aq represent the increase in absorbance in the blue spectral region (yellowing) in the presence and absence of stabilizer, respectively. The resulting stabilization efficiencies were found to decrease substantially over relatively short exposure times (ca. 40% decrease between 10 and 25 hrs irradiation). Difference absorption spectra obtained during accelerometer exposure exhibited a new absorption band at ca. 300 nm which overlapped strongly with polymer fluorescence (required for efficient RET quenching) and weakly with polymer absorption (screening).1... 

An important point concerning the spectra in Figure 3.71 is that at intermediate doping levels three principal absorption bands can be seen, at c. l.OeV, 2.7eV and 3.6eV, that are not simply the superposition of the as-grown and neutral polymer absorptions. The authors interpreted this observation in terms of the homogeneous doping of the film throughout its bulk, not just the oxidation of the surface layer or the layer next to the electrode. 

Polythiophenes functionalized with monosaccharides have been evaluated for their ability to detect the influenza virus and E. coli (Baek et al. 2000). Copolymers of thiophene acetic acid 10 and carbohydrate-modified thiophenes 11 have been prepared via iron(III) chloride mediated polymerization. Addition of influenza virus to a sialic acid containing copolymer resulted in a blue shift of the polymer absorption maximum, resulting in an orange to red chromatic transition. Mannose-containing polythiophenes underwent color changes upon the addition of the lectin ConA or E. coli cells that contain cell surface mannose-binding receptors. A similar biotinylated pol5hhiophene afforded a streptavidin responsive material (Paid and Leclerc 1996). 

The close correspondence between the absorption spectrum in solution and the photocurrent spectrum of the adsorbed dye is by no means found in all cases. The adsorbed state can be different in structure from the solution state which is seen in a different photocurrent spectrum. It has been found e. g. that polymers are formed in the adsorbed state. This is a well known phenomenon for cyanine dyes 50-5b where polymer bands are found in the absorption spectrum of the adsorbed molecules. An example is given in the photocurrent spectra of Fig. 15. One sees that with increasing amount of adsorbed dye — no equilibrium adsorption was reached during this experiment — the polymer absorption band appears in the photocurrent. 

Name of polymer Absorption bandsa of pure polymer films, cm1 Absorption bands in LDPE matrix cm1 Corresponding chemical group Assignment13... 

The technique is more diagnostic in terms of detail, because the IR spectra are dominated by intense polymer absorptions, which cannot be eliminated completely by computer subtraction. 

The polymer absorption is intense ap 555 7.5 x 105 cm-1 for light polarized parallel to the PA chains and the dichroic ratio is 25. The polymer is not fluorescent. 

There is an early report in the literature claiming absence of the autocatalytic reaction enhancement in TS if the reaction is induced by UV-excitation of the monomer crystal. The implication would be that thermal and UV-polymerization involve different mechanisms. Later on, however. Chance and Patel found this to be an artifact caused by the neglect of spatially inhomogeneous absorption by polymer molecules which effectively competes with monomer excitation at increasing conversion and prematurely terminates the reaction. Although it is difficult to correct X(t)-curves obtained under UV-excitation for polymer absorption quantitatively, particularly if irradiation is done with unpolarized non-monochromatic light, it turns out that there is a qualitative agreement between X(t)-curves obtained under y-and UV-irradiation. Application of this correction, however, does not solve the puzzle why in case of y- or UV-polymerization of TS, the reaction rate increases less dramatically with conversion, than observed upon thermal conversion. 

A direct measure of the optical absorption coefficient a is the optical density OD defined by OD = log Iq/I = 0,434od (Iq and I are the incident and the transmitted light intensities and d is the thickness of the crystal). Weak polymer absorption in the range from 600 to 400 nm is present in the original monomer crystals due to weak thermal polymerization reactions. The absorption of the linear polymer molecules (which are homogeneously distributed within the partially polymerized monomer diacetylene crystals) increase during UV-irradiation at room temperature due to photopolymerization reactions. In contrast to the monomer absorption, the polymer... 

The intense absorption lines of the photoproduct series A to E obtained by UV-irradiation at low temperature are shown in Fig. 4a This spectrum represents a difference spectrum, where the original spectrum of the monomer crystal, certaining a small amount of polymer has been substracted. Therefore only the effect of the UV-irradiation is shown in the Figure. In the same spectra lines b, c and d of a weaker series a to e are also present. For comparison the low temperature optical absorption of the polymer chains is shown in Fig. 4b. In a simple picture one would expect the positions of the optical absorption of the intermediates to be situated between the monomer and polymer absorption. However, lines D and E are below the polymer absorptions. In contrast to the absorptions at room temperature the polymer chain absorptions at low temperatures are split into doublets. This splitting is caused by a structural phase transition The phase transition occurs at 170 K and results in a doubling of the unit cell in alignment with the chain direction. A corresponding doublet structure is also present in all absorptions of the reaction intermediates described in this paper, however, their intensity ratios are less than 1 10 and therefore in most cases a resolution of the weak lines is possible only after very intense UV-irradiation. 

The DR and AC intermediates of the photopolymerization reaction are stable only at low temperatures. At temperatures above about 100 K they react to form long macromolecules by subsequent addition of monomer molecules. The 10 K optical absorption spectra of Fig. 17 show the result of the thermal reaction as a function of the time at 100 K The initial spectrum showing only the dimer A absorption has been prepared at 10 K by only one UV-excimer laser pulse at 308 nm. Only pure thermal addition polymerization reactions are observed within the DR-series A, B, C,. .. No chain termination reactions are detectable in the optical spectra. The final product P is situated in the vicinity of the final polymer absorption. 

Here, the transport rates depend on the partition coefficient Kfp only. The solute concentration in the membrane can often be related to the gas phase partial pressure using Henry s law or a similar equilibrium relationship. At higher pressures, vapor-liquid equilibrium or gas-polymer absorption data are necessary to determine the concentration gradient in the membrane. 

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