The oral administration of peptide drugs is well known to be precluded by their digestion in the stomach and small intestine. As a new approach to oral delivery, peptide drugs were coated with polymers cross-linked with azoaromatic groups to form an impervious film to protect orally administered drugs from digestion in the stomach and small intestine. When the azopolymer-coated drug reached the large intestine, the indigenous microflora reduced the azo bonds, broke the cross-links, and degraded the polymer film, thereby releasing the drug into the lumen of the colon for local action or for absorption. The ability of the azopolymer coating to protect and deliver orally administered peptide drugs was demonstrated in rats with the peptide hormones vasopressin and insulin.

A series of cross-linking agents of azobenzene with amide and sulfonamide spacer groups were prepared. Several homo-and copolymers were prepared with the azo cross-links by radical polymerization using AIBN initiator. The polymers undergo typical photochemical cis-trans isomerism to varying degrees. The thermal relaxation data indicate the importance of the structural and steric environment surrounding the cross-links. For example, a bulky phenyl substituent next to azobenzene seems to retard the photoisomerization. The nature of the polymeric matrix and the molecular weight did not affect the degree of isomerization, and the cis-trans cycle could be carried out without any fading. There was also no photo viscosity effect.

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