For a linear polymer molecule, the total chain length l depends on the bond length between chain atoms d, the total number of bonds in the molecule n, and the angle between adjacent backbone chain atoms θ, as follows: l = n d s i n (θ/2) furthermore, the average end-to-end distance for a series of polymer molecules r is equal to: r = d (n)^1/2 for a linear polytetrafluoroethylene determine: a. the number-average molecular weight for l=2000 nm; b. the number-average molecular weight for r=17 nm.