Macromolecules, living

We do not yet know whether the cycle of time we are studying is time caused by the submolecular energy exchanges in living macromolecules, and... 

In macroemulsion polymerization, a relatively high surfactant concentration is present so that many small empty (or monomer-swollen) micelles can be formed besides large monomer droplets (Fig. 10.16). Initiation typically occurs in the water phase and after a few propagation steps, the resulting living macromolecule enters a micelle, as the micelles have a much higher surface area than the monomer droplets. This entering process is known as... 

As it will be shown in this paragraph, neither predominantly linear nor predominantly cyclic structures of the isolated, killed macromolecules are the straightforward arguments by themselves for the linear or cyclic growth of the living macromolecules. Indeed, let us consider an assumed equilibrium between living... 

On the other hand the actual kinetic (rate) measurements are not necessary. It has to be remembered, that for this treatment initiation has to be faster than propagation. Polymerization may be living, even if initiation is slower and providing throughout polymerization new generations of the living macromolecules. 

Analytical techniques that utilise biopolymers, ie, natural macromolecules such as proteias, nucleic acids, and polysaccharides that compose living substances, represent a rapidly expanding field. The number of appHcations is large and thus uses hereia are limited to chiral chromatography, immunology, and biosensors. 

M. Cates. Reptation of living polymers Dynamics of entangled polymers in the presence of reversible chain-scission reactions. Macromolecules 20 2289-2296, 1987. 

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

Cao X. and Faust R., Polyisobutylene based thermoplastic elastomer 5. Poly(styrene-b-isobutylene-b-styrene) tri-block copolymers by coupling of living poly(styrene-b-isobutylene) di-block copolymers. Macromolecules, 32, 5487, 1999. 

Yijin X. and Caiyaun P., Block and star-hlock copolymers by mechanism transformation. 3. S-(PTHF-PSt)4 and S-(PTHF-PSt-PMMA)4 from living CROP to ATRP, Macromolecules, 33, 4750, 2000. Feldthusen J., Ivan B., and Mueller A.H.E., Synthesis of linear and star-shaped block copolymers of isobutylene and methacrylates hy combination of living cationic and anionic polymerizations. Macromolecules, 31, 578, 1998. 

Paulo, C. and Puskas, J.E. Synthesis of hyperbranched polyisobutylenes by inimer-type living polymerization. I. Investigation of the effect of reaction conditions. Macromolecules, 34, 734, 2001. 

Allcock HR, Crane CA, Morrissey CT, Nelson JM, Reeves SD, Honeyman CH, and Manners I. Living cationic polymerization of phosphoranimines as an ambient temperature route to polyphosphazenes with controlled molecular weights. Macromolecules, 1996, 29, 7740-7747. 

It appears that none of these process techniques is dominant, at least with the lactide/glycolide materials. Researchers have considerable choices available in regard to fabrication of microspheres from these polymers. The most commonly used procedures employ relatively mild conditions of pH and temperature and are usually quite compatible with the bioactive agents to be entrapped, including proteins and other macromolecules. Only in the case of live virus and living cell encapsulation have serious deactivation problems been encountered and those problems were due to solvents used in the process. 

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