Radioactively labeled polymers

Some materials tend to degrade very slowly under stringent test conditions without an additional source of carbon. However, if readily available sources of carbon are added, it becomes impossible to tell how much of the evolved carbon dioxide can be attributed to decomposition of the plastic. The incorporation of radioactive in synthetic polymers gives a means of distinguishing between CO2 or CH4 produced by the metabolism of the polymer, and that generated by other carbon sources in the test environment. By comparison of the amount of radioactive or to the original radioactivity of the 

Problems with handling the radioactively labelled materials and their disposal are issues on the down side to this method. In addition, in some cases it is difficult to synthesise the target polymer with the radioactive labels in the appropriate locations, with representative molecular weights, or with representative morphological characteristics. 

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Variation in the concentration of UDP-D-glucose (over a 1000-fold range) does not cause any change in the structure of the radioactively labeled polymer produced. The reaction rate at high concentrations of substrate is considerable, and this makes possible the production of milligram quantities of solid polymer. The polymer is, however, contaminated with some protein and D-glucose. ... 

The metabohc rate of poly(ester—amide) where x = Q has been studied in rats using carbon-14 labeled polymer. This study indicates that polymer degradation occurs as a result of hydrolysis of the ester linkages whereas the amide linkages remain relatively stable in vivo. Most of the radioactivity is excreted by urine in the form of unchanged amidediol monomer, the polymer hydrolysis product (51). 

In studying two-component polymerization catalysts, beginning with Feldman and Perry (161), a radioactive label was introduced into the growing polymer chain by quenching the polymerization with tritiated alcohols. The use of these quenching agents is based on the concept of the anionic coordination mechanism of olefin polymerization occurring... 

NRA is a powerful method of obtaining concentration versus depth profiles of labelled polymer chains in films up to several microns thick with a spatial resolution of down to a few nanometres. This involves the detection of gamma rays produced by irradiation by energetic ions to induce a resonant nuclear reaction at various depths in the sample. In order to avoid permanent radioactivity in the specimen, the energy of the projectile is maintained at a relatively low value. Due to the large coulomb barrier around heavy nuclei, only light nuclei may be easily identified (atomic mass < 30). 

Urethane linkages between amino groups of a protein and PEG provide a stable attachment, more resistant to hydrolytic cleavage (13). In fact, it was demonstrated on radioactively labeled PEG-derivatives that urethane links are completely stable under a variety of physiological conditions (14). The attachment of PEG to a protein via carbamate was obtained (15,16) using carbonyldiimidazole activated PEG. However, the polymer activated in this manner is not very reactive and therefore very long reaction times (48-72 h at pH 8.5) were required to achieve sufficient modifications. 

Monodisperse microspheres imprinted with theophylline or 17 (3-estradiol were used in competitive radioimmunoassays showing the MIP s high selectivity for the template molecule. In this case the assay is based on the competition of the target molecule with its radioactively labeled analogue for a limited number of antibody binding sites [77,118]. Figure 15 demonstrates that displacing the radioactively marked theophylline from the imprinted polymer was only possible with theophylline as competitor. Structurally related molecules showed effects solely at elevated concentrations [77]. 

Analysis of radioactively labelled end-groups Absolute single determination wide range of mol. wt. Restricted to certain types of polymer requires knowledge of mode of chain termination 1-2... 

Labelled polystyrene-14C (PS-14C) was the adsorbate. Two batches were prepared by an identical procedure with only one of them containing radioactive 14C. The labelled polymer was used for the adsorption measurements, whereas the unlabelled polymer was used for the determination of the solution properties. The polystyrene was prepared by emulsion polymerization of redistilled styrene. In order to remove unreacted monomer the polystyrene was freeze-dried from benzene solution. 

Carbon-14-labelled triethyloxonium hexachloroantimonate, [( 3115)2002115] (SbClg)", 18 (specific activity 1.15 x 10 Bq g ), has been obtained by treating the C-labelled ( 2115)20 Sb l5 complex with ethyl chloride. The salt was used to clarify the mechanism of initiation of polymerization of 2,3,4-tri-O-methyl-L-glucosane (19) , since it has been noted" " " that the incorporation of the radioactive label into the polymer increases with the increase in the degree of conversion of the monomer (at 10. 5% of the equilibrium yield of the polymer, 2.5% of the initial radioactivity of 18 has been... 

In vitro and in vivo release kinetics were compared using two different approaches. In the first approach (the recovery approach) polymer implants containing a radioactively labeled substrate—,4C-labeled bovine serum albumin, /3-[14C]-lactoglobulin, or [3H]-inulin—were implanted subcutaneously into rates (in vivo) or released in phosphate-buffered saline, pH 7.4, at 37°C (in vitro). At various time points, the polymer implants were removed from the rats or the saline. They were then lyophilized to remove residual water and dissolved in xylene. When the polymer dissolved, the unreleased macromolecules precipitated to the bottom of the vial. Water was then added to dissolve the macromolecules scintillation fluid was next added, resulting in a homogeneous translucent emulsion which was counted via liquid scintillation. 

The composition of carbon-chain polymers with monomeric units having widely differing analytical composition, characteristic elements or groups, or radioactive labels can be readily determined. Chemical (microanalysis, functional group determination, etc.) and spectroscopic methods (infrared, ultraviolet, nuclear magnetic resonance, etc.), as well as the determination of radioactivity, yield the average composition of the polymer. The mean composition can also be determined from the refractive indices of solid samples. The composition can be calculated from the principle that the copolymer is considered to be a solution of one unipolymer (from one of the monomeric units) in the other. The composition can also be found by means of the refractive index increment dw/dc in solution, which gives the variation in refractive index with concentration. The mass fraction of the monomeric unit A can be calculated from... 

The problem of determination of the number of active centers as the number of titanium-polymer bonds was formulated for the first time in the pioneering works of Natta [15, 146] for propylene polymerization on catalyst TiCls + AlEts. He used for this purpose cocatalyst AlEt3 labeled by a radioactive isotope in the ethyl group. Active centers of type Cl cTi- CH2CH3 are formed in this case and polymer with a radioactive label obtained on these centers. The number of active centers can be calculated from these data. 

Methods based on introduction of a radioactive label in the growing polymer molecule. 

Iiranunoradiometric assays (IRt4A.) employ a radioactively labeled antibody rather than a labeled antigen. After equilibration of labeled antibody with antigen, the excess free antibody is removed by addition of a massive quantity of im-munoadsorbent. An "immunoadsorbent" is an insoluble polymer to which an antigen or binder is attached. The antibody-immuno-adsorbent complex is readily removed from bound antibody by centrifugation. 

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