The invention provides elastomeric polymer networks and
semi-interpenetrating networks in which a linear PEA, PEUR or PEU polymer
is crosslinked by ester or alpha-amino-acid containing cross-linkers that
polymerize upon exposure to active species. Bioabsorbable elastomeric
internal fixation devices fabricated using such polymer networks and
semi-interpenetrating networks are useful for in vivo implant and
delivery of a variety of different types of molecules in a time release
fashion. Alpha-amino-acid containing ester amide cross-linkers are also
provided by the invention.