Weight-Average Molecular Weight Formula:
From: | To: |
Definition: The weight-average molecular weight (Mw) is a measurement that takes into account the mass of individual polymer chains, giving more weight to heavier molecules in the distribution.
Purpose: It provides a more accurate representation of the polymer's physical properties that depend on the mass of the molecules, such as viscosity and mechanical strength.
The calculator uses the formula:
Where:
Explanation: The number-average molecular weight is adjusted by the probability of finding the repeating unit in the polymer chain.
Details: Mw is particularly important for understanding polymer properties like melt viscosity and elasticity, which are more influenced by the larger molecules in the distribution.
Tips: Enter the number-average molecular weight in kg/mol and the probability (between 0 and 1). Both values must be positive numbers.
Q1: What's the difference between Mw and Mn?
A: Mn is a simple average, while Mw gives more weight to heavier molecules, making it more sensitive to the presence of high-mass chains.
Q2: What does the probability value represent?
A: It represents the chance of finding the repeating unit AB in the polymer chain, affecting the molecular weight distribution.
Q3: When would Mw be significantly higher than Mn?
A: When there's a broad molecular weight distribution with many high-mass molecules present.
Q4: How do I determine the probability value?
A: The probability is typically determined experimentally or through reaction kinetics analysis.
Q5: What units should I use?
A: The calculator uses kg/mol for molecular weights, but you can use any consistent units as long as you're consistent.