Biodegradable polymers. See

Finally, it may be noted that 4,6-orthoesters obtained for example by reaction of sucrose with ethyl orthoacrylate can be opened to form either the 6- or 4-esters,146 providing convenient starting materials for the preparation of biodegradable polymers (see Scheme 7). 

Optimization of cationic polymers is based on the following motivation to improve the gene transfer efficiency, to make carriers less toxic and more biocompatible. Strategies include the optimization and modification of commonly used polymers such as polylysine or polyethylenimine (see below, this section) and the generation of novel, biodegradable polymers (see Sect. 3.3). 

There are numerous further appHcations for which maleic anhydride serves as a raw material. These appHcations prove the versatiHty of this molecule. The popular artificial sweetener aspartame [22839-47-0] is a dipeptide with one amino acid (l-aspartic acid [56-84-8]) which is produced from maleic anhydride as the starting material. Processes have been reported for production of poly(aspartic acid) [26063-13-8] (184—186) with appHcations for this biodegradable polymer aimed at detergent builders, water treatment, and poly(acryHc acid) [9003-01-4] replacement (184,187,188) (see Detergency). 

See also Biodegradable polymer networks Filled silicone networks Interpenetrating networks (IPNs) Model silicone networks Monodisperse model networks ... 

CO2, a blank compost inoculum without an additional carbon source (polymer sample) is simultaneously tested under the same conditions. The CO2 content of the exhaust air of both vessels is compared. After subtracting the CO2 evolution of the blank inoculum, the CO2 evolution related to the test polymer is monitored and plotted as a biodegradation curve (see Fig. 1). Finally, the activity of the compost inoculum in the controlled composting test is validated using a cellulose reference instead of the polymer. In Fig. 1, the biodegradation curve of Ecoflex is depicted. After 80 days, 90% of the theoretical CO2 evolution is reached. Thus, Ecoflex is ultimately biodegradable according to the ISO standard for compostable polymers (ISO 17088), which requires 90% of the theoretical CO2 evolution within 180 days. 

Eilm products with good mechanical characteristics are only obtained if thermoplastic, plasticized starch has been used. If no plasticizer is used, biodegradable polymers with limited mechanical properties will be obtained. In this case, coextmsion with the base polyester or another polymer is the way to upgrade the mechanical and/or moisture barrier properties (for comparison see Table 6). 

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

Renewable feedstocks can also be used as the raw materials for the synthesis of green, biodegradable polymers. A pertinent example is polylactate, derived from lactic acid which is produced by fermentation (see earlier). Another recent example is the production of polycarbonates by reaction of C02 with (R)-limonene oxide in the presence of a zinc catalyst (Fig. 8.47) [221]. 

Polyvinyl alcohol is a vinyl polymer with a carbon-carbon backbone similar to other polymers such as polyethylene and polystyrene and is widely used as a water-soluble biodegradable polymer in the manufacture of delivery systems for fertilizers, pesticides and herbicides and is also used to manufacture containers and films. To date, only bacteria have been described as causing biodegradation of polyvinyl alcohols with some causing complete degradation of the polymer (see Shimao, 2001 for review). 

In topical formulations, particularly cosmetics, it is used for its softening and conditioning effect on the skin. Lactic acid may also be used in the production of biodegradable polymers and microspheres, such as poly(D-lactic acid), used in drug delivery systems.See also Aliphatic Polyesters. 

The biodegradable polymer blends are often prepared by blending a thermoplastic resin with a biodegradable one (see Table 1.80). Blending must produce dispersion that after disintegration of the biodegradable part the thermoplastic powder will not contaminate the environment. 

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