Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae from 1,4-butanediol and the results compared with previous studies on Nylons 4 6 and 6 8. In 2N 2(N + 1) Nylons, the lengths of the two alkane segments are equal and two different hydrogen-bonded sheet schemes are possible: progressive or alternating shear. At room temperature, Nylons 8 10 and 10 12 adopt the progressive scheme and the adjacent re-entry folds in the crystals must be in the alkane chain segments. In contrast, Nylons 4 6 and 6 8 lamellae, crystallized from the same solvent, exhibit the alternating hydrogen bonding scheme and each adjacent re-entry fold must contain an amide group. The transition in the chemical nature of the lamellar surface, from the amide fold to the alkane fold, occurs in passing from Nylon 6 8 to 8 10. Thus, the progressive hydrogen-bonded sheet/alkane fold structure is energetically more favorable, provided the alkane-folding geometry is sufficiently relaxed; this comes with increasing alkane segment length. For each hydrogen-bonded sheet structure there are still two principal intersheet stacking modes in lamellar crystals: the progressively sheared R-phase or the alternatingly sheared β-phase, both of which have been found in the 8 10 and 10 12 Nylons. The 2N 2(N + 1) Nylons have the choice of four possible structures. The melting points of solution grown crystals of Nylons 4 6, 6 8, 8 10, and 10 12 decrease with decreasing intrachain amide density. When lamellar crystals of these Nylons are heated, the two characteristic interchain diffraction signals move together and meet at their Brill temperature; for Nylon 10 12 it appears to be close to the melting point.
Poly(ester amide)s are an emerging group of biodegradable polymers that may cover both commodity and speciality applications. These polymers have ester and amide groups on their chemical structure which are of a degradable character and provide good thermal and mechanical properties. In this sense, the strong hydrogen-bonding interactions between amide groups may counter some typical weaknesses of aliphatic polyesters like for example poly(-caprolactone). Poly(ester amide)s can be prepared from different monomers and following different synthetic methodologies which lead to polymers with random, blocky and ordered microstructures. Properties like hydrophilic/hydrophobic ratio and biodegradability can easily be tuned. During the last decade a great effort has been made to get functionalized poly(ester amide)s by incorporation of -amino acids with hydroxyl, carboxyl and amine pendant groups and also by incorporation of carbon-carbon double bonds in both the polymer main chain and the side groups. Specific applications of these materials in the biomedical field are just being developed and are reviewed in this work (e.g., controlled drug delivery systems, hydrogels, tissue engineering and other uses like adhesives and smart materials) together with the main families of functionalized poly(ester amide)s that have been developed to date.
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