A sulfur-containing polyureaurethane having a refractive index of at least 1.57, an Abbe number of at least 32 both as measured in accordance with ASTM-D542 and a density of less than 1.3 grams/cm 3 as measured in accordance with ASTM-D792, when as least partially cured, that is prepared by the reaction of: (a) a sulfur-containing polyurethane prepolymer; wherein the sulfur-containing polyurethane prepolymer comprises the reaction product of: (i) a polyisocyanate; and (ii) a sulfur-containing active hydrogen material. and (b) an amine-containing curing agent, or (a) a polyisocyanate; (b) a sulfur-containing active hydrogen material; and (c) an amine-containing curing agent; wherein the sulfur-containing active hydrogen material is a polythiol comprising at least one material represented by the following structural formulas and reaction schemes: wherein in (IV'j) and (IV'k) n is an integer from 1 to 20; R 1 and R 3 is C 1 to C 6 n-alkylene, C 2 to C 6 branched alkylene, C 6 to C 8 cycloalkylene, C 6 to C 10 alkylcycloalkylene, C 6 to C 8 arylene, C 6 to C 10 alkyl-arylene, alkyl groups containing ether linkages or thioether linkages or ester linkages or thioester linkages or combinations thereof, --[(CH 2 --) p --X--] q --(--CH 2 --) r --, wherein X is O or S, p is an integer from 2 to 6, q is an integer from 1 to 5, r is an integer from 0 to 10; R 2 is hydrogen or methyl; and wherein n is an integer from 1 to 20; R 1 is hydrogen or methyl; R 2 is C 2 to C 6 n-alkylene, C 2 to C 6 branched alkylene, C 6 to C 8 cycloalkylene, C 6 to C 10 alkylcycloalkylene group C 6 to C 8 arylene, C 6 to C 10 alkyl-arylene, alkyl groups containing ether linkages or thioether linkages or ester linkages or thioester linkages or combinations thereof --[(CH 2 --) p --O--] q --(--CH 2 --) r --, wherein X is O or S, p is an integer from 2 to 6, q is an integer from 1 to 5, r is an integer from 0 to 10. (a) a sulfur-containing polyurethane prepolymer; wherein the sulfur-containing polyurethane prepolymer comprises the reaction product of: (i) a polyisocyanate; and (ii) a sulfur-containing active hydrogen material. and (b) an amine-containing curing agent, or (a) a sulfur-containing polyurethane prepolymer; wherein the sulfur-containing polyurethane prepolymer comprises the reaction product of: (i) a polyisocyanate; and (ii) a sulfur-containing active hydrogen material. and (i) a polyisocyanate; and (ii) a sulfur-containing active hydrogen material. and (b) an amine-containing curing agent, or (a) a polyisocyanate; (b) a sulfur-containing active hydrogen material; and (c) an amine-containing curing agent; wherein the sulfur-containing active hydrogen material is a polythiol comprising at least one material represented by the following structural formulas and reaction schemes: wherein in (IV'j) and (IV'k) n is an integer from 1 to 20; R 1 and R 3 is C 1 to C 6 n-alkylene, C 2 to C 6 branched alkylene, C 6 to C 8 cycloalkylene, C 6 to C 10 alkylcycloalkylene, C 6 to C 8 arylene, C 6 to C 10 alkyl-arylene, alkyl groups containing ether linkages or thioether linkages or ester linkages or thioester linkages or combinations thereof, --[(CH 2 --) p --X--] q --(--CH 2 --) r --, wherein X is O or S, p is an integer from 2 to 6, q is an integer from 1 to 5, r is an integer from 0 to 10; R 2 is hydrogen or methyl; and wherein n is an integer from 1 to 20; R 1 is hydrogen or methyl; R 2 is C 2 to C 6 n-alkylene, C 2 to C 6 branched alkylene, C 6 to C 8 cycloalkylene, C 6 to C 10 alkylcycloalkylene group C 6 to C 8 arylene, C 6 to C 10 alkyl-arylene, alkyl groups containing ether linkages or thioether linkages or ester linkages or thioester linkages or combinations thereof --[(CH 2 --) p --O--] q --(--CH 2 --) r --, wherein X is O or S, p is an integer from 2 to 6, q is an integer from 1 to 5, r is an integer from 0 to 10. (a) a polyisocyanate; (b) a sulfur-containing active hydrogen material; and (c) an amine-containing curing agent;