Side-chain influence poly

Abe et ah have studied the conformational characteristics of a series of poly[oxy(-l-alkylethylenes)]. In the first paper a comparison of the statistical weights of various conformations in poly(propylene oxide), deduced from the solution properties of isotactic and atactic chains, were compared with conformational weights derived from a potential-energy surface, and an anomeric effect identified with a discrepancy between the two. Flexible side-chains influence the main chain in a manner which is expressible in the statistical weight matrices. The dimensions of these chains are strongly influenced by their tacticity. Polymer chains containing both sulphur and oxygen heteroatoms have received the attention of... 

Furthermore it can be shown that besides the direct influence of hydrophilic and hydrophobic hydration on the conformation, the interaction of charged groups with ions is also strongly influenced by the hydration of the groups involved. Such studies were made largely by using relatively simple poly-a-aminoacids with ionogenic side chains as model substances. 

Unsaturated groups are very interesting for application development because this specific functionality opens up a broad range of possibilities for further (chemical) modification of the polymer structure, and therefore its physical and material properties. The direct microbial incorporation of other functional substituents to the polymer side chains, e.g. epoxy-, hydroxy-, aromatic-, and halogen functional groups, influences the physical and material properties of poly(HAMCL) even further [28,33,35,39-41]. This features many possibilities to produce tailor-made polymers, depending on the essential material properties that are needed for the development of a specific application. 

The poly (amino acid)s with aromatic side chains behave somewhat differently. In poly(phenylalanine) the a-carbon radical is the major radical species observed, but radicals formed by hydrogen atom addition to the ring are also found. Benzyl radicals formed by side-chain cleavage are present, but only in very low yield. In poly (tyrosine) the only radical species observed is the tyrosyl phenoxyl radical formed by loss of the hydroxyl hydrogen. There is no evidence for formation of significant concentrations of a-carbon radicals. Thus, the nature of the substituents can strongly influence the radiation sensitivity of the backbone chain. 

In agreement with the data on poly-a-olefins and poly-vinyl-ethers having the side chain asymmetric carbon atoms in the y-position with respect to the main chain, stereoregularity does not exert a remarkable influence on the rotatory power of poly-acrylates and poly-methacrylates. In fact, according to the quantitative data reported by H. Sobue, K. Matsuzaki, S. Nakano (135), and to the qualitative indications given by Liu, Szuty and Ullmann (64), concerning respectively poly-menthyl-meth-acrylate and poly-(l-methyl-benzyl)-methaciylate, the specific optical activity of the polymers does not vary by more than 30% when varying, within a wide interval, the isotactic triads content of the polymers (Table 18). 

The extension of the Hammett equation to poly-substituted benzene derivatives has been made for side-chain reactions (Jafife, 1953). The essential features of these treatments are the assumptions that the contribution of each substituent is constant and that the influences of the substituents are simply additive. This postulate is usually cited as the additivity principle. In the case of electrophilic substitution, assuming additivity, the equation may be written... 

Besides the above examples, the influence of dipole-dipole interactions between polar side chains (containing a heteroatom in the y position) and backbone amide groups has been shown for polymers such as poly-L-serine (Birshtein and Ptitsyn, 1967). In such eases, the jS-strueture is energetically more favored than the a-helix. 

For crystalline polymers, however, not only the molecular weight and poly-dispersity index are of interest. Besides the degree of crystallinity, there is a specific influence of chain design, i.e., existence, length, and concentration of side chains on the resistance against environmental stress cracking, as will be pointed out in the next section. 

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