Dyad and Triad Probabilities in Terpolymers

The chain sequence length distribution of DNA can be represented using the geometric distribution. The mean and variance of the geometric distribution would be expected to depend on the mechanism of formation of polynucleotide sequences. For instance, a terpolymer formed hy free radical polymerization can be modeled with respect to the sequence distribution as follows. Let three termonomers enter a long copolymer chain atMj, M2, and M3 concentrations with reactivity ratios r 2, 21, r23, r 2, 13, 31- Assume that the bond formation order does not matter in the rate, that is, 

FIGURE 11.3 Triad probabilities in SAN copolymer—AAA, AAS, ASA (or SAS), SSA, ASS, and SSS triads as a function of AN mole fraction in copolymer. 

The sequence length of the repeats of monomer 2 in the chain is given by 

For a tetrapolymer with four monomers such as the case for DNA, polynucleotides, 

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