Polymer/monomer switches

Keywords Constitutional changes Covalent changes Dynamic covalent chemistry Molecular machines Molecular motors Molecular switches Polymer/monomer switches Reversible polymers Size switches... 

Both molecular machines and polymer/monomer switches are chemical devices that can perform a specific function. Molecular machines achieve a... 

A polymer/monomer (polymer/repeat-unit or polymer/macrocycle) switch may become of practical importance where a polymer decorated with certain groups has specific size-dependent properties that the monomeric units do not have. The modulation of the conversion between polymeric and monomeric (or macrocyclic) states would also result in the modulation of these properties. Moreover, such size switches, represented by polymerization/depolymerization processes that operate under the control of external events, are examples of environmentally-friendly recyclable polymers (reduction of waste treatment). As well, if the polymer has low solubility and the polymer/monomer switch can work in spite of this, then it becomes possible to reversibly generate a precipitating (solid) polymeric material from a liquid solution of monomer. 

Synthetic Molecular Machines and Polymer/ Monomer Size Switches that Operate Through Dynamic and Non-Dynamic Covalent Changes... 

Polymer/Monomer Size Switches Switching Between Small and Large Molecular Sizes... 

Synthetic Molecular Machines and Polymer/Monomer Size Switches... 

Initially, all of the SBR polymer known as GR-S produced during World War II was by the batch process. Later, it was thought that a higher volume of polymer would be needed for the war effort. The answer was found in switching from batchwise to continuous production. This was demonstrated in 1944 at the Houston, Texas, synthetic mbber plant operated by The Goodyear Tire Rubber Company. One line, consisting of 12 reactors, was lined up in a continuous mode, producing GR-S that was mote consistent than the batch-produced polymer (25). In addition to increased productivity, improved operation of the recovery of monomers resulted because of increased (20%) reactor capacity as well as consistent operation instead of up and down, as by batchwise polymerisation. 

YHiile THF is the solvent of choice for ordinary acrylate ester polymers, there are numerous monomers that can be incorporated into those acrylic polymers that cause problems either with solubility or with adsorption onto the stationary phase. In some cases, these problems can be overcome by switching to a solvent other than THF. 

With pure monomer and diluents a polymerization with a half-life of 8 hr has been recorded with these catalysts. There, stability would appear to be indefinite provided water or oxygen are not admitted to the system. In one experiment described in Table XII the monomer feed is switched off after 60 min and the dissolved monomer exhausted from the polymer slurry. If monomer is reintroduced some days later, polymerization begins again without an induction period and the rate was little changed from that previously observed. 

Every polymerization method is limited to a certain type and number of monomers, thus preventing the possibility to synthesize block copolymers with a wide combination of monomers. However, recent advances in polymer synthesis enabled the switching of the polymerization mechanism from one type to another, thereby permitting the preparation of block copolymers composed of monomers that can be polymerized by different techniques. 

The expected contribution of catalysis in this area will derive both from the availability, at low processing costs, of new monomers obtained from biomasses and from the development of an optimized combination of biotechnology processes with classical and new biocatalytic processes. Research priorities for catalysis in the area of polymers from renewable materials for packaging, furniture, domestic water purification and recycling include the need to develop novel catalysts, e.g., for functionalization of polymeric and dendrimeric materials, with side-chain photoactive molecular switches (to be used as smart materials), or the development of multifunctional materials, combining, for example, nanofiltration with catalytic reactivity. 

Originally, vinyl chloride polymers were based on acetylene. The switch to ethylene,chemistry came after the development of the oxychlorination process for vinyl chloride described in Chapter 9. Today very little acetylene-, based vinyl chloride monomer (VCM) processing remains. 

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