Effect of Macromolecular Skeleton

The environment in which the macromolecule finds itself is important in discussing structure-property relationships. The environment is solvent molecules when the macromolecule is in solution, it is the other polymer molecules in solid state, and at the surface, the vapour or the liquid that are in contact with the surface. The skeleton of the polymer where the flexibility and stability are highly affected and the types of side groups are important in discussing the structure property relationships. The carbon-carbon single bond confirms appreciable flexibility to a polymer chain but, its weakness is its sensitivity to thermooxidative cleavage. The aliphatic carbon-carbon double bond 

Aromatic rings in a polymer skeleton confer rigidity and extended chain character and in aromatic polyamides, polyesters or polyarylenes can also show main chain liquid crystallinity. In Table 6.5, a few examples with their Tg and values are given. 

Oxygen atoms in a hydrocarbon chain give torsional mobility and materials flexibility. Nearby skeletal units have to be taken into consideration as ether linkages are generally stable to hydrolysis and to thermooxidation while polyaldehydes depolymerise readily at moderate temperatures. 

The amide linkage makes the chain stiffer because of the partial double bond character of the N-C bond which causes a possibility for internal and external hydrogen bonding  

Many commercial polyamides are highly crystalline and have repeating units within each crystalline region are inaccessible to water or other reagents. 

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