Question

1. Calculate the molecular weight of two macromolecules: the first is a polybutadiene, and the second is a polyisoprene. If both possess a degree of polymerization of 1000, comment on the differences in molecular weight.

Answer 1

Molecular mass of butadiene = 54.09 g/ mol

Molecular mass of isoprene = 68.12 g/ mol

Formula used :- D.P. = Mn, Molecular weight of Polymer I m Molecular weight of monomer dearie of polymerization Butadiene monomer I Isoprene Monomer D.P. = 1000 = Mn 54.09 DP = 1000 = Mn 68.12 Mn = 54.09x1000 – 54090 Mn = 68.12X1000 = 68,120

Importance of high molecular weight of polymer

1) increases the impact resistance of the material means how far a polymer can be stretched before rupturing.

2) Increases the chemical resistance

3) increases the viscosity of the material

Lower Molecular Weight polymers ( polybutadiene)low viscosity due to lack of chain entanglement and can flow easily.

So as molecular mass increases properties get better such as increased strength, low chemical stress and also increases the crack resistance making polyisoprene a better polymer than polybutadiene.