A polymer P with a very high initial molecular weight (1 106) is cross-linked by agent A. Each molecule of A brings about one cross-link. The cross-link density is measured by swelling the sample in a perfect Basic Structures of Polymers 47 solvent (whose solubility parameter is equal to that of the polymer). If a 5.00-cm3 sample of P with 0.020 g of A/100 g of P swells to 75.0 cm3, what concentration of A will yield a 5.00-cm3 sample that swells to only 25.0 cm3? Parameter of system = 0.475, V1 = 83.0 cm3/mol. Agent A: FW (M Wt) = 205 g/mol.