Topic
Ceiling temperature
About: Ceiling temperature is a research topic. Over the lifetime, 278 publications have been published within this topic receiving 5242 citations.
Papers published on a yearly basis
1 / 2
Papers
TL;DR: The reversible kinetics of l-lactide bulk polymerization with tin(II) ethylhexanoate was determined over a wide range of temperatures, 130−220 °C, and monomer to initiator molar ratios, 1000−80 000.
Abstract: The reversible kinetics of l-lactide bulk polymerization with tin(II) ethylhexanoate was determined over a wide range of temperatures, 130−220 °C, and monomer to initiator molar ratios, 1000−80 000. Both polymerization and depolymerization are accurately described by a reversible model with a propagation term that is first order in monomer and catalyst. The activation energy of propagation is 70.9 ± 1.5 kJ mol-1. The enthalpy, entropy, and ceiling temperature of polymerization are −23.3 ± 1.5 kJ mol-1, −22.0 ± 3.2 J mol-1 K-1, and 786 ± 87 °C, respectively. Crystallization increases the propagation rate and decreases the apparent monomer equilibrium in proportion to the degree of crystallinity. Natural hydroxyl impurities stoichiometrically control the polymer molecular weight but do not significantly affect the propagation rate.
252 citations
TL;DR: In this paper, a full-scale experimental campaign and a computational fluid dynamics (CFD) study of a radiant cooling ceiling installed in a test room, under controlled conditions, were conducted.
227 citations
TL;DR: It is shown that a metastable polymer, end-capped poly(o-phthalaldehyde), undergoes mechanically initiated depolymerization to revert the material to monomers, suggesting the possibility of smart materials where aging or mechanical damage triggers depolymization, and orthogonal conditions regenerate the polymer when and where necessary.
Abstract: Biological systems rely on recyclable materials resources such as amino acids, carbohydrates and nucleic acids. When biomaterials are damaged as a result of aging or stress, tissues undergo repair by a depolymerization-repolymerization sequence of remodelling. Integration of this concept into synthetic materials systems may lead to devices with extended lifetimes. Here, we show that a metastable polymer, end-capped poly(o-phthalaldehyde), undergoes mechanically initiated depolymerization to revert the material to monomers. Trapping experiments and steered molecular dynamics simulations are consistent with a heterolytic scission mechanism. The obtained monomer was repolymerized by a chemical initiator, effectively completing a depolymerization-repolymerization cycle. By emulating remodelling of biomaterials, this model system suggests the possibility of smart materials where aging or mechanical damage triggers depolymerization, and orthogonal conditions regenerate the polymer when and where necessary.
219 citations
Book•
1 Sep 1976
TL;DR: In this article, three possible conditions for free energy change of polymerization may be summarized as follows: at the ceiling temperature, Tc, ΔG is zero, so that where ΔHp and ΔSp are the enthalpy and entropy changes per monomer unit.
Abstract: I. THE CHILING TEMPERATURE CONCEPT A. Thermodynamic Approach The Gibbs free energy of a system at temperature T is defined as were H is the enthalpy and S the entropy of the system. The free energy change for any polymerization will be, therefore, When the polymer has a lower free energy than the initial monomer, a polymerization can occur spontaneously, and the sign of ΔG is negative. A positive sign for ΔG signifies, therefore, that the polymerization is not spontaneous. When the system is in equilibrium at a certain critical temperature, there is no tendency for polymerization, and, hence, ΔG = 0 [1–3]. This temperature is known as the ceiling temperature. These three possible conditions for free energy change of polymerization may be summarized as follows: At the ceiling temperature, Tc, ΔG is zero, so that where ΔHp and ΔSp are the enthalpy and entropy changes per monomer unit.
199 citations
TL;DR: All addition polymerizations are exothermic and involve a decrease in entropy as discussed by the authors, and all addition polymerization reactions involve a decreasing entropy at the propagation step, at the concentration of monomer (= [m1]) prevailing in the system.
Abstract: ALL addition polymerizations are exothermic and involve a decrease in entropy. The heat of reaction (q = ΔH) and the decrease in entropy (—ΔS) per mole of monomer polymerized really refer to the values of these quantities appropriate to the propagation step, at the concentration of monomer (= [m1]) prevailing in the system*. We may write this reaction conventionally as
167 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2022 | 1 |
| 2021 | 14 |
| 2020 | 11 |
| 2019 | 8 |
| 2018 | 6 |
| 2017 | 11 |