Title: floor temperature
Long Title: IUPAC Gold Book - floor temperature
DOI: 10.1351/goldbook.15401
Status: current

Definition
Temperature below which, in a given chain polymerization, polymer of high molar mass is not formed.

Notes
1) A floor temperature is only observed for entropy-driven chain polymerizations in which \(\Delta H_{\rm{m}} \gt 0\) and \(\Delta S_{\rm{m}} \gt 0\), where \(\Delta H_{\rm{m}}\) and \(\Delta S_{\rm{m}}\) are respectively the enthalpy and entropy change per mole of monomer reacted.
2) Examples of chain polymerizations for which \(\Delta H_{\rm{m}} \gt 0\) and \(\Delta S_{\rm{m}} \gt 0\) are polymerizations of larger cyclic monomers, e.g., elemental sulfur (\(\ce{S8}\)) and octamethylcyclotetrasiloxane [2,2,4,4,6,6,8,8-octamethyl-1,3,5,7,2,4,6,8-tetraoxatetrasilocane], proceeding via ring-opening mechanisms.
3) Above \(T_{\rm{f}}\), \(\Delta G_{\rm{m}} (= \Delta H_{\rm{m}} - T \Delta H_{\rm{m}}) \lt 0\); at \(T_{\rm{f}}\), \(\Delta G_{\rm{m}} = 0\); and below \(T_{\rm{f}}\), \(\Delta G_{\rm{m}} \gt 0\).
4) Because \(\Delta G_{\rm{m}} = 0\) at the floor temperature, \(T_{\rm{f}} = \Delta H_{\rm{m}}/\Delta S_{\rm{m}}\). If \(\Delta H_{\rm{m}}^{\circ}\) and \(\Delta S_{\rm{m}}^{\circ}\) are the enthalpy and entropy changes in the standard state, and the monomer behaves ideally, then \[T_{\rm{f}} = \Delta H_{\rm{m}}^{\circ}/ \{\Delta S_{\rm{m}}^{\circ} + R\ln ([{\rm{M]}}_{0}/c^{\circ})\}\] where \(c^{\circ} = \pu{1 mol dm-3}\) is the standard concentration and \([{\rm{M}}]_{0}\) is the initial monomer concentration. Thus, \(T_{\rm{f}}\) depends on the initial monomer concentration.
5) The symbol \(T_{\rm{f}}(c^{\circ})\) is used to denote the floor temperature when the initial monomer concentration, \([{\rm{M}}]_{0}\), is equal to \(c^{\circ}\).
6) The symbol \(T_{\rm{f}}({\rm{bulk}})\) is used to denote the floor temperature when the initial monomer concentration is equal to its undiluted concentration.

Related Term
- ceiling temperature: https://goldbook.iupac.org//terms/view/15385

Source
- PAC, 2008, 80, 2163. 'Glossary of terms related to kinetics, thermodynamics, and mechanisms of polymerization (IUPAC Recommendations 2008)' on page 2175 (https://doi.org/10.1351/pac200880102163)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15401/html
- json: https://goldbook.iupac.org/terms/view/15401/json
- xml: https://goldbook.iupac.org/terms/view/15401/xml

Citation: Citation: 'floor temperature' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.15401
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Accessed: 2026-04-18T05:09:15+00:00