Increasing of the solvent-polymer affinity results in more expanded polymer coils, which, in turn, provides for higher resistance to the solution flow. Thus, the index of power (a) is growing with increasing of the solvent affinity towards the polymer. Usually a polymer sample is polymolecular (polydisperse), i.e. it contains macromolecules of different molecular weights. Accordingly, polymer samples are characterized by average molar masses (depends on the way of averaging). Thus, a viscosity-average molar mass can be Mv found from the Mark-Kuhn-Houwink equation using experimentally determined [] and reference data for and K a. Polydispersity (or heterogeneity) index of a polymer sample can be determined as the ratio of its viscosity-average molar masses found in solvents significantly differing in their affinity towards the polymer. In this task you will find the polydispersity index of a polystyrene sample by capillary viscometry using toluene (K=0.017 ml/g, and methyl ethyl ketone (K=0.039 ml/g, a=0.69) All constants are given for 25 a=0.57). °С. Chemicals and reagents: Polystyrene (number-average molar mass of about 100 000) solution in toluene, 10g/L, 25 mL Polystyrene (number-average molar mass of about 100 000) solution in methyl ethyl ketone, 10g/L, 25 mL Toluene, 50 mL Methyl ethyl ketone, 50 mL Table of Chemicals Compound State R-Rating S-Provision Solutions in toluene and (C8H8)n, Polystyrene - - methyl ethyl ketone 11 38 48/20 63 65 C7H8, Toluene Liquid 2 29 36/37 46 62 67 C4H8O, Methyl ethyl Liquid 11 36 66 67 2 9 16 ketone Apparatus and glassware: Ubbelohde or other capillary viscometer Graduated cylinder, 10 mL 10 glass vials, 20 mL
Increasing of the solvent-polymer affinity results in more expanded polymer coils, which, in turn, provides for higher resistance to the solution flow. Thus, the index of power (a) is growing with increasing of the solvent affinity towards the polymer. Usually a polymer sample is polymolecular (polydisperse), i.e. it contains macromolecules of different molecular weights. Accordingly, polymer samples are characterized by average molar masses (depends on the way of averaging). Thus, a viscosity-average molar mass Mv can be found from the Mark-Kuhn-Houwink equation using experimentally determined [] and reference data for K and a. Polydispersity (or heterogeneity) index of a polymer sample can be determined as the ratio of its viscosity-average molar masses found in solvents significantly differing in their affinity towards the polymer. In this task you will find the polydispersity index of a polystyrene sample by capillary viscometry using toluene (K=0.017 ml/g, a=0.69) and methyl ethyl ketone (K=0.039 ml/g, a=0.57). All constants are given for 25 °С. Chemicals and reagents: Polystyrene (number-average molar mass of about 100 000) solution in toluene, 10g/L, 25 mL Polystyrene (number-average molar mass of about 100 000) solution in methyl ethyl ketone, 10g/L, 25 mL Toluene, 50 mL Methyl ethyl ketone, 50 mL Table of Chemicals Compound State R-Rating S-Provision (C8H8)n, Polystyrene Solutions in toluene and methyl ethyl ketone - - C7H8, Toluene Liquid 11 38 48/20 63 65 67 2 29 36/37 46 62 C4H8O, Methyl ethyl ketone Liquid 11 36 66 67 2 9 16 Apparatus and glassware: Ubbelohde or other capillary viscometer Graduated cylinder, 10 mL 10 glass vials, 20 mL
Preparatory_problems_IChO_2013.docx