Environment, controlled radical polymerization

Many of the problems in polymer chemistry that some years ago appeared irresolvable are, today, state-of-the-art processes. Examples include the formation of block copolymers by controlled radical polymerization, or the increasingly broad application of transition metal-catalyzed polymerization techniques in aqueous environments. Clearly, polymer synthesis is a highly dynamic art form rather than a mature technological field. ... 

The huge variety of defined nanostmctures and materials that can be fabricated via controlled radical polymerization techniques will probably find applications in a wide field of different research directions. The possibility of combining several building units in one device will enable materials scientists to implement multiple levels of stimuli-responsiveness for the construction of smart materials. Research in biomedicine can be expected to benefit from the ability to generate defined nanopattemed surfaces that can play a central role in biophysical investigations. Also, the potential to create precisely defined confined environments could lead to nanocontainers as delivery vehicles, theranostic agents, or artificial enzymes. 

The conclusion of this study is fliat the kinetics of the free-radical polymerization initiated with highly soluble and mobile photoinitiators are governed primarily by monomer ordering. In contrast, initiator efficiency largely controls the polymerization rate for initiations with builder initiators. These were found to display lower mobility and solubility in liquid crystalline environment. 

Poly(acrylates) and poly(methacrylates) are commercially important polymers with a myriad of uses, including paper and textile coatings, adhesives, caulks and sealants, plasticizers, paint and ink additives, and optical components for computer displays. Since they are derived from monosubsti-tuted and unsymmetrical 1,1-disubstituted vinyl monomers, poly(acrylate) and poly(methacrylate) products with a spectrum of tacticities and thereby mechanical properties are potentially accessible. To date, however, industrially produced materials are generated using free-radical polymerization technology, which offers limited scope for tacticity control. Therefore, there has been much interest in the development of metal-catalyzed routes to these polymers where the coordination environment of the metal offers the potential to influence tacticity. 

Such, G.K., Evans, R.A., and Davis, T.P. (2004) Control of pho-tochromism through local environment effects using living radical polymerization (ATRP). Macromolecules, 37, 9664 9666. 

First, in composites with high fiber concentrations, there is little matrix in the system that is not near a fiber surface. Inasmuch as polymerization processes are influenced by the diffusion of free radicals from initiators and from reactive sites, and because free radicals can be deactivated when they are intercepted at solid boundaries, the high interfacial area of a prepolymerized composite represents a radically different environment from a conventional bulk polymerization reactor, where solid boundaries are few and very distant from the regions in which most of the polymerization takes place. The polymer molecular weight distribution and cross-link density produced under such diffusion-controlled conditions will differ appreciably from those in bulk polymerizations. 

Since plasma contains electrons, ions, photons, radicals, and excited molecules, it becomes important to identify the reactive species controlling the propagating process of the polymerization. A number of workers have reported on kinetic models of plasma polymerization. Our current xmderstanding of the chemical and physical mechanism of the process remains limited because the extreme complexity of the plasma environment resists efforts toward a generalization and characterization. The bulk of the research has been concentrated on establishing the dependence of the macroscopic and spectroscopic properties of the product on the major process variables, e.g., rf power, monomer type, and gas flow rate. 

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