Stabilization of Selected Polymers

Relative Thermal Stability of Selected Polymers Based on the Temperature at Which Their Half-Life Th Is 30 min... 

TABLE 11.1 Effect of Antioxidants on the Long-Term Stability of Selected Polymers... 

J. Lo, Flammability and Photo-stability of Selected Polymer Systems, Doctoral Dissertation, Polytechnic Institute of... 

Food Additives and Contaminants 15, No.l, 1st Jan. 1998, p.93-9 SYSTEMATIC STUDY ON THE STABILITY OF SELECTED POLYMER ANTIOXIDANTS IN EU OFFICIAL AQUEOUS AND ALTERNATIVE FOOD SIMULANTS USING HPLC Demertzis P G Franz R... 

This material was first synthesized in the middle 1960s by E.I. Du Pont de Nemours and Co., and was soon recognized as an outstanding ion conductor for laboratory as well as for industrial electrochemistry. The perfluorinated polymeric backbone is responsible for the good chemical and thermal stability of the polymer. Nation membrane swollen with an electrolyte solution shows high cation conductivity, whereas the transport of anions is almost entirely suppressed. This so-called permselectivity (cf. Section 6.2.1) is a characteristic advantage of Nation in comparison with classical ion-exchange polymers, in which the selective ion transport is usually not so pronounced. 

The heat of reaction for vinyl polymers affects the thermal stability of the polymer during extrusion, and the thermal stability is related to the ceiling temperature. The ceiling temperature is the temperature where the polymerization reaction equilibrium is shifted so that the monomer will not polymerize, or if kept at this temperature all the polymer will be converted back to monomer. From thermodynamics the equilibrium constant for any reaction is a function of the heat of reaction and the entropy of the reaction. For PS resin, the exothermic heat of reaction for polymerization is 70 kj/gmol, and the ceiling temperature is 310 °C. Ceiling temperatures for select polymers are shown in Table 2.5. 

TABLE 2. Emulsion stability of selected amphiphilic copolymers prepared by adding 1.5 g of a selected experimental polymer to an oil/water mixture and blending at 90° C to 100° C. 

In order to increase the selectivity and efficiency of extraction, novel stationary phases have been developed, particularly in trace analysis. Cyclodextrins, graphi-tized carbon blacks, and conductive polymers such as polypyrrole and poly aniline have been investigated [73]. Sol-gel polymers also seem to be interesting. A particularly important feature is the high thermal stability of these polymers [74]. Recent applications for analysis of biological samples have been described in several articles [75-81]. Review articles present recent developments in methodology, the SPME technique [82-84], and novel coatings [85, 86]. 

Introducing a functional ester group that enables selective photocrosslinking without destruction of the polymer backbone can improve the stability of the polymers without changing the sensitivity to direct laser structur-... 

The lack of the melt processing activity of HAS means that they do not contribute to the conventional melt processing formulations consisting of hindered phenols and aromatic phosphites. A properly selected combination of processing stabilizers and HAS has, however, a favourable effect on the LTHS and light stability of the polymer during the longterm application [129,135]. 

Adams, M. R. Carton, A. Far-Ultraviolet Degradation of Selected Polymers. In Polymer Durability Degradation, Stabilization, and Lifetime Prediction Clough, R. L., Billingham, N. C., Gillen, K. T., Eds. Advances in Chemistry Series 249 American Chemical Society Washington, DC, 1996 pp 139-158. 

The selection of polymers and polymer blends for use as specific materials requires the consideration of how these will withstand the environmental conditions to which these will be subjected. The long term stability of a polymer will depend on its aging characteristics both physical and chemical. 

Organic polymer adsorbents such as polystyrene, polyacrylic ester, phenolic and phenolic amine resin without functional groups (contrary to ion exchange resins) are advantageous because properties (pore volume, pore width, specific inner surface, polarity) can be adjusted in wide ranges. By this way the selective separation of polar and nonpolar substances can be achieved. The thermal stability of these polymers is limited to 180°C. 

These concerns can be addressed partially through the use of mixed-matrix membranes [77-79]. Dispersing the microporous material in the form of small particles within a polymeric matrix simplifies membrane formation dramatically. Mixed matrix materials possess transport properties intermediate between those of the polymer matrix and the microporous particle and operating temperatures are limited by the thermal stability of the polymer matrix. However, proper selection of the matrix, control of particle volume fraction, and development of a membrane formation process can yield materials with properties that approach those of the particles [77-78]. Special attention must be given to the particle-polymer interface. If the interface morphology is uncontrolled, the matrix may 1) not wet the particle leaving a non-selective void around the particle, 2) enter the particle and block pores, or 3) rigidify around the particle and block access to it [79]. 

The secondary benzoate (4) is labile below 300°C whereas the primary benzoate (3) is stable. Both the model compounds were found to be labile at 300°C. Hence it can be concluded that the stability of the polymers is direcdy related to the stability of the respective benzoates. Tliis study clearly shows the effect of one weak link per chain on the polymer properties. An additional route to secondary benzoates is discussed below under termination. In related studies on styrene we have established that both the cyanoisopropyl radicals (from AIBN) and t-butoxy radicals are much more selective in this system and add virtually exclusively to the tail to give polymers tliat are thermally stable. 

Similar to the behavior of Nafion, poly(ester sulphonic acid) ionomers selectively exclude anionic species and large particles, but cations and neutral molecules are permeable. Of the three Eastman Kodak AQ 29, AQ 38, and AQ 55 polymers, AQ 55 (see the polymer backbone in Fig. 11.12) is the most studied and most applied in biosensor preparation. Wang and coworkers described have features of this polymer as an electrode material, including strong affinity toward hydrophobic counterions, prevention of electrode fouling from proteins, stability of the polymer film on the electrode, ability to preconcentrate catalysts in the film, and lowering the overpotential of many species difficult to oxidize or reduce. Several workers also showed that this poly(ester sulphonic acid) polymer is very stable as an organic phase electrode material. ... 

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