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Citation: Chunhua Wang, Wenzhi Wang, Xianggang Li. Discussion on calculation methods for the number-average degree of polymerization in polycondensation reactions within polymer chemistry[J]. University Chemistry, ;2026, 41(7): 385-393. doi: 10.12461/PKU.DXHX202506101 shu

Discussion on calculation methods for the number-average degree of polymerization in polycondensation reactions within polymer chemistry

School of Packaging Engineering, Hunan University of Technology, Zhuzhou 412007, Hunan Province, China

Corresponding author: Chunhua Wang, wangchunhua@hut.edu.cn
Received Date: 27 June 2025
Revised Date: 27 August 2025

To address the pedagogical challenge of calculating the number-average degree of polymerization $\left(\overline{X_n}\right)$ in polycondensation reactions, this study systematically derives and analyzes the formulas involved in two distinct calculation approaches for different polycondensation systems. The functional group molar ratio ($r$) method proves exclusively applicable to linear polycondensation. For $\mathrm{aAa}+\mathrm{bBb}+\mathrm{Cb}$ and $\mathrm{aRb}+\mathrm{Cb}$ systems, the monofunctional Cb must first be converted to an equivalent bifunctional monomer with matching endcapping effects before determining $r$. When b groups are in excess, Cb's end-capping effect corresponds to bBb; conversely, with excess a groups, it mirrors aRb. The average functionality ($\bar{f}$) method demonstrates broader applicability, suitable for both linear and crosslinked polycondensation systems, with $\bar{f}$ being directly calculable from its definition. The integration of rigorous formula derivations with practical application examples has yielded significant improvements in teaching outcomes.
- Polycondensation reaction,
- Number-average degree of polymerization,
- Molar ratio of functional groups,
- Average functionality
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