All syntheses that proceed from low-molecular-weight compounds (monomers) to produce high-molecular-weight compounds (polymers) are termed “polymerizations” (i.e., polyreactions). Polymerizations only occur when the appropriate chemical, thermodynamic, and mechanistic requirements are fulfilled.

Principles of Polymerization

Chemically recyclable polymers: a circular economy approach to sustainability

Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as ‘non-polymerizable’ because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol–1 and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL. Bio-derived γ-butyrolactone (γ-BL) is commonly referred to as ‘non-polymerizable’ due to its low strain energy. Now it has been shown that ring-opening polymerization of γ-BL can in fact proceed to high conversions under ambient pressure with a suitable catalyst, producing high-molecular-weight polymers with controlled topologies and complete recyclability.

Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone

Structure and elasticity of non-crystalline polymer networks

Frontal polymerization is a mode of converting monomer into polymer via a localized reaction zone that propagates. Such fronts can exist with free-radical polymerization or epoxy curing. The necessary conditions for the existence of the free-radical frontal polymerization regime are considered. The physicochemical properties of monomers are classified in connection with complications arising in the experiments, including low conversion, convection and bubbles. The density gradient in the reaction zone leading to front decay is the most insidious problem. The analysis of forces that can withstand the Taylor instability allowed us to overcome experimental difficulties and develop approaches to polymerize low-viscosity monomers in the frontal mode. The factors affecting front shape, velocity, conversion, and molecular weight are considered.Historically, frontal polymerization has been performed in neat monomer but we have been able to obtain fronts of very reactive monomers in high-boiling-point solvents including water, DMSO and DMF. Periodic frontal polymerization modes have been observed, including single and multi-point spin modes in which ‘hot spots’(local high-temperature regions) migrate around the front as it propagates. We investigated experimentally the occurrence of the different modes as a function of the initial temperature and the intensity of heat losses and made a qualitative comparison to the results of theoretical analyses based on infinitely narrow reaction zone models.The future directions of research with frontal polymerization are considered, especially with regard to applications to materials synthesis.

Free-Radical Frontal Polymerization: Self-Propagating Thermal Reaction Waves

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.

Hideo Sawada

Papers

Thermodynamics of Polymerization

Thermodynamics of polymerization.