Signals Notebook: Why SRU Polymers with Repeat Count 'n' Do Not Display Expanded Molecular Properties

Description

Users observed that SRU polymers with an undefined repeat count (n) do not produce IUPAC-style polymer names, molecular formulas, or molecular weights reflecting repeating units, and that searches may match monomer fragments to polymers.

Solution

Context: The polymer structure in the example has been defined using an SRU (Structure Repeating Unit) where the repeat count is represented as "n". In polymer chemistry, "n" is a symbolic variable indicating that the number of repeating units is undefined or variable, rather than a specific numeric value.

Expected behavior with n (undefined repeat count):

• Molecular Formula is generated from the explicitly defined structural fragment only and does not include expansion of the repeating unit.

• Chemical Name is derived from the fragment and may not conform to IUPAC polymer naming when repeat units are unspecified.

• Molecular Weight is calculated for the displayed fragment only; a full polymer MW cannot be computed without a defined repeat count.

• Structure Searching indexes the polymer using its underlying fragment, so searches for the corresponding monomer/fragment may return the polymer as a match.

How to obtain expanded calculations:

• Replace the symbolic repeat count "n" with a specific numeric value (e.g., 5, 10) to allow the system to incorporate repeating units into the molecular formula and molecular weight.

• Verify that properties update after setting a numeric repeat count.