Terrestrial monomers

The ordinary monomer units of PVC are not expected to absorb any terrestrial solar radiation (1>.2>.3 A) Thus, under the usual ambient conditions, photodegradation of the polymer must be initiated by chromophoric impurities. These impurities may simply be structural defects in the PVC itself, or they may be extraneous substances that have been incorporated into the polymer. Several of these potential photosensitizers are discussed in the following sections. 

Fig. 1.9 Terrestrial humic acid model (a) tetramer open form and (b) trimer trapping an additional monomer (Schulten, 2001)...

Polyhydroxybutyric acid (PHB) is a bacterial biopolymer which has gained much interest because of its potential use as a biodegradable plastic material. This compound is produced by various terrestrial bacteria and serves as an energy reservoir. PHB is usually highly polymeric (10,000 monomer units) and is stored in the bacteria as an insoluble material in inclusion bodies that are visible with an electron microscope 1111]. Although PHB has been inten-... 

If a mixture of L- and D-alanine were caused to polymerize, nearly all the polymer molecules would have different structures because their sequences of D-alanine and L-alanine monomer units would differ. To create polymers with definite structures for particular roles, there is only one recourse to build all polypeptides from one of the optical isomers so that the properties will be reproducible from molecule to molecule. Nearly all naturally occurring a-amino acids are of the L form, and most earthly organisms have no use for D-a-amino acids in making polypeptides. Terrestrial life could presumably have begun equally well using mainly D-amino acids (all biomolecules would be mirror images of their present forms). The mechanism by which the established preference was initially selected is not known. 

The natural resins present in native guayule have been extensively studied and include mono-, sesqui-, di-, and triterpene groups, as well as other secondary metabolites (108). Unfractionated guayule resin has shown considerable promise in the areas of wood preservation (in marine and terrestrial environments) (129) and insect antifeedents (termite resistance) (130-132). These resins also show promise as a biobased renewable replacement for petroleum-based monomers and oligomers in adhesives and coatings. Additional profitable uses for the resins include a natural, low toxicity replacement for creosote in wood treatment and for prevention of termite attack. Resin/lignin products, such as additives for phenol formaldehyde resins, may also prove possible. 

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