Molecular Nearly monodisperse polymers

Various authors have obtained this equation with slight differences in the term 6/7c2. The available data on (nearly) monodisperse polymers seem to confirm these rules. For polydisperse polymers, however, the situation is more complicated. For a number of polydisperse polymer samples, experimental values of ii can be found in the literature. These values of ti are always larger than those calculated with Eq. (15.92), using Mw for the molecular mass ... 

Random copolymers can be produced through the much simpler free-radical route which, however, does not allow precise control over the molecular weight and yields a polydisperse polymer. It has been reported recently, however, that nearly monodisperse polymers can be obtained by controlled free-radical polymerizations [2-5]. 

Reactive chains can be obtained by anionic polymerization, followed by attachment of a reactive end-group. This route yields nearly monodisperse polymers with functional groups at their ends, polymers that are very well suited for systematic studies. The synthesis can be quite elaborate, and, for longer chains, the completeness of the end-functionalization is difficult to verify. If the mono-dispersity and the control of the molecular weight of the polymer are not crucial or not possible, more common techniques can be used. They involve either the free-radical synthesis of a polymer incorporating a small fraction of reactive comonomers that will then be distributed along the chain, or the random functionalization of the polymer in the melt (using a free-radical initiator) after the... 

An example is the molecular-weight dependence of zero-shear viscosity as shown in Fig. 4.7 for various nearly monodisperse polymers. As the molecular weight increases above a critical value Me, the viscosity increases much more rapidly than in the low-molecular-weight region below Me, exhibiting the well-known 3.4 power law. ... 

In practice, two approaches have been found to take the molecular-weight distribution into account in comparing Eq. (9.19) with the measured G t) line shapes of nearly monodisperse polymers ... 

A polydispersity of about 2 is typical of high molecular weight condensation polymers. A polydispersity of 1.5-2.0 is typical of the instantaneous molecular weight distribution of a free-radical polymer, but the composite distribution from a moderate- to high-conversion reactor will often be broader than this due to thermal inhomogeneities. Coordination catalysis produces very broad distributions, while some low-temperature, ionic polymerizations can give nearly monodisperse polymers (see Peebles [1] for a comprehensive treatment of molecular weight distributions). 

Recent attempts to prepare 26 by RAFT, however, failed [153]. Double hydrophilic block copolymers of NIPAM and 23e [154], as well as of N,N-diethylacrylamide and 23b [155], were prepared with the CTA benzyl dithiobenzoate, and exhibit LCST and UCST behavior in water. The new polymer 51 is also part of amphiphiUc di- and triblock copolymers [152]. Diblock copolymers with poly(ethylene glycol) methyl ether acrylate, dimethylacry-lamide, or 4-vinylstyrene sulfonate are macrosurfactants with a switch-able hydrophobic block. Triblock copolymers containing additionally 4-vinylbenzoic acid differ in the nature of the hydrophilic part [152]. Near-monodisperse block copolymers of N,N-dimethacrylamide and 49a were synthesized in different ways via macro-CTAs of both monomers as the first step. Such sulfobetaine block polymers form aggregates in pure water but are molecularly dissolved after addition of salt [152,156,157]. 

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