MALDI-TOF characterization of highly cross-linked, degradable polymer networks

Multifunctional anhydride monomers were synthesized and photopolymerized to form highly cross-linked, degradable networks. The networks were synthesized from monomers and oligomers of dimethacrylated sebacic acid of varying molecular weight, as well as under varying reaction conditions. The cross-linked polymers were subsequently degraded in phosphate buffered saline, and the degradation products, sebacic acid and poly(methacrylic acid), were isolated. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to characterize the absolute molecular weight distribution of the Linear poly(methacrylic acid) degradation product, especially as a function of the network evolution (i.e., double-bond conversion), rate of initiation, and monomer size, MALDI-TOF results, supported by H-1 NMR, showed that the distribution of kinetic chain lengths was relatively narrow, with average lengths shorter than calculated from experimentally measured rate data, indicating the influence of diffusion-controlled kinetics as well as chain transfer. Furthermore, the average kinetic chain length shifted to lower values with increasing initiation fate and double-bond conversion. Since multifunctional monomer polymerizations are extremely complex and notoriously difficult to characterize due to the insoluble nature of the resulting cross-linked polymer structure, this work demonstrates, for the first time, how these degradable monomers can provide further insight and characterization of multifunctional monomer polymerizations.