Objective:
The purpose of this lab is to approximate the frequency of “head to head” occurrences in a polydisperse solution of polyvinyl alcohol (PVOH) using the Flory & Leutner Method. The Flory & Leutner method depends on the notion that a “head to head” linkage is a 1,2 glycol which can be cleaved by periodic acid. Cleavage the links would cause a decrease in the effective mass and intrinsic viscosity of the PVOH sample. Determination of the intrinsic viscosity of PVOH using cleaved and un-cleaved polymer solutions will approximate the ratio between the molar masses of both solutions, which will help to find the ratio between abnormal and normal polymer chain linkages.
Requirements:
- Polyvinyl alcohol
- Potassium periodate
- Viscometer
- Stopwatch
- 100 mL & 250 mL volumetric flasks and beakers
- 10 mL & 50 mL pipette
- Pipette bulb
Procedure:
- Clean viscometer
- Place viscometer in 25 °C thermostat bath
- Prepare an initial PVOH solution (~.9 g/100 mL)
- Prepare an initial cleaved PVOH solution (~.9 g/100 mL) by introducing KIO4
- Prepare half-dilutions of both solutions (~.45 g/100 mL)
- Pipette distilled H2O into viscometer to determine apparatus constant
- Rinse and dry viscometer
- Pipette PVOH solution to upper fiducial mark
- Measure the flow time of PVOH solution from upper to lower fiducial marks
- Repeat for multiple trials
- Rinse and dry viscometer
- Pipette cleaved PVOH solution to upper fiducial mark
- Measure the flow time of cleaved PVOH solution from upper to lower fiducial marks
- Repeat for multiple trials
- Rinse and dry viscometer
Pre-Calculations:
N/A
Critical Steps:
- Avoid foaming of PVOH solutions
- Wash/rinse glassware and viscometer in between each trial because the PVOH solution is a culture media for bacteria and the residue is hard to remove.
Safety:
While PVOH is nontoxic, exposure of the polymer to the eyes or skin can still cause minor irritation. However, the potassium periodic acid, used to cleave abnormal linkages, can cause burns and severe irritation to eyes and skin, so laboratory safety goggles should be worn at all times. Laboratory attire that covers the arms and legs are highly advisable.
