Weight Average Molecular Calculator

Weight Average Molecular Weight Formula:

\[ M_w = \sum (w_i \times MW_i) \]

Weight Average Molecular Weight (M_w):

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1. What is Weight Average Molecular Weight?

The weight average molecular weight (M_w) is a way to characterize the molecular weight distribution of a polymer sample. It gives more weight to the heavier molecules in the distribution compared to the number average molecular weight.

2. How Does the Calculator Work?

The calculator uses the weight average molecular weight formula:

\[ M_w = \sum (w_i \times MW_i) \]

Where:

\( M_w \) — Weight average molecular weight (g/mol)
\( w_i \) — Mass fraction of component i
\( MW_i \) — Molecular weight of component i (g/mol)

Explanation: The weight average molecular weight is calculated by summing the products of each component's molecular weight and its corresponding mass fraction.

3. Importance of Weight Average MW

Details: The weight average molecular weight is particularly important in polymer science as it is sensitive to the presence of high molecular weight species. It affects physical properties like viscosity and mechanical strength.

4. Using the Calculator

Tips: Enter the molecular weight and mass fraction for each component. The sum of all mass fractions must equal 1. You can add more components as needed.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between M_w and M_n?
A: M_w (weight average) is more sensitive to higher molecular weight molecules, while M_n (number average) gives equal weight to all molecules regardless of size.

Q2: When is weight average molecular weight used?
A: It's particularly important for properties that depend more on the mass of the molecules than their number, such as melt viscosity and mechanical strength.

Q3: What does a high M_w/M_n ratio indicate?
A: A high ratio indicates a broad molecular weight distribution, while a ratio close to 1 indicates a narrow distribution.

Q4: How is M_w measured experimentally?
A: Common methods include light scattering and size exclusion chromatography with appropriate detectors.

Q5: Why is M_w important for polymers?
A: Many polymer properties (like viscosity and strength) depend more on M_w than M_n, making it a critical parameter for material performance.