Polylactones.: 51.: Resorbable networks by combined ring-expansion polymerization and ring-opening polycondensation of ε-caprolactone or DL-lactide

The ring-expansion polymerization of epsilon -caprolactone (epsilon -CL) was initiated with 2,2-dibutyl 2-stanna-1,3-dioxepane (DSDOP) or 2,2-dibutyl-2-stanna-1,3-dioxaundecane (DSDUC) and the molecular weights of the resulting cyclic polylactones were controlled by the monomer/initiator (M/I) ratio. Addition of benzene-1,3,5-tricarbonyl chloride yielded networks in a one-pot procedure. An analogous series of networks was prepared from a resorbable tricarboxylic acid trichloride based on glycerol and glutaric acid. After extraction of the soluble byproducts all these gels were isolated in yields of 60-90%. After swelling in CDCl3, these gels were so mobile that relatively sharp signals of all protons were detectable, allowing for a determination of the cross-linking density. The glass-transition temperatures (T-g's), melting temperatures (T-m's), melting enthalpies (DeltaH(m) 's), and swelling factors showed the expected dependence on the cross-linking density, i.e., on the M/I ratio of the polymerization process. Four more gels were prepared from racemic DL-lactide, and their glass transition temperatures and swelling factors were measured. These gels were amorphous and consisted exclusively of nontoxic building blocks familiar with the human metabolism.