Polylactones. 51. Resorbable Networks by Combined Ring-Expansion Polymerization and Ring-Opening Polycondensation of ε-Caprolactone or dl -Lactide

The ring-expansion polymerization of ε-caprolactone (ε-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 CDCl 3, 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 (Δ H 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.