Three different characterization methods - C-13 NMR spectroscopy, a terminal terpolymerization model, and a probability analysis based on the Poisson distribution-were used to determine the microstructure of random terpolymers. The methods were used to determine the amino acid sequence distribution of random terpolymers prepared from the polymerization of N-carboxyanhydrides that contained L-leucine, beta-benzyl-L-aspartate, and L-valine. Poly(L-leucine-L-aspartic acid-L-valine) [poly(LDV)] was designed as a target specific substrate for the alpha(4)beta(1) integrin that recognizes the tripeptide sequence leucine-aspartic acid-valine (LDV). The presence of the tripeptide sequence LDV within the polymer was determined to be eight LDV triad sequences on average in terpolymers of approximately 100 kDa. (c) 2006 Wiley Periodicals, Inc.