Star polymers dispersity

A comment should be made on the dispersity of star polymers. If the arms each have a most probable distribution 2), dispersity of the star... 

ATRP is a very potent method for preparing block copolymers by sequential monomer addition as well as star polymers using multifunctional initators. Furthermore, it can be applied also in heterogenous polymerization systems, e.g., emulsion or dispersion polymerization. In Example 3-15 the ATRP of MMA in miniemulsion (see also Sect. 2.2A.2) is described. 

Figure 13.22 Damping functions hf y) and hs y) for the fast and slow relaxation processes of a 15 wt% solution of a micelle-forming polystyrene-polyisoprene diblock copolymer (molecular weights, respectively, of 14,000 and 29,000) in a low-molecular-weight (A/ = 4,000) polyisoprene. Damping functions for linear and star polymers and for silica dispersion are shown for comparison. (From Watanabe et al. 1997, with permission from Macromolecules 30 5905. Copyright 1997, American Chemical Society.)...

Poly (amidoamine) dendrimers (PAMAM) are new interesting class of star polymers. They have mono dispersive, well defined and developed three-dimensional structures comprising functional groups at high concentration. In its core they have amidic groups. Structurally modified PAMAM dendrimers with 1,8-naphthalimide derivatives are fluorescent dendrimers and they can be applied as effective and selective sensors for different metal cations and protons in organic solvents. This property can be nansferred to other polymer matrixes (for example textiles). 

A comment should be made on the dispersity of star polymers. If the arms each have a most probable distribution (M ./M,-2), dispersity of the star polymers is expected to be l + l/<3, where a is the number of arms of the star polymer, simply as a consequence of statistical averaging. " This explains why polymers formed by conventional radical polymerization with termination by combination i.e. 2 arms) have =1.5. When wc additionally take into... 

Three-layered nanoparticles containing an hbPG core and cross-linked block copolymers based on N-isopropyl acrylate and N,N-dimethylaminoethyl acrylate as the respective arms were synthesized and proved to be thermoresponsive. ° Chu and co-workers" reported electrically conductive core-shell nanoparticles based on poly(n-butylacrylate-b-polystyrene) multiarm star polymers. The PS segments were converted to poly(p-styrenesulfonate) (PSS), thus generating amphiphilic tmimolecular micelles. Then the oxidative propagation of 3,4-ethylenedioxythiophene (EDOT) on the PSS chains was carried out by counterion-induced polymerization to produce a stable aqueous dispersion of the respective PEDOT complex. 

That the tube reorganization is important for star polymers is indicated by another experiment. Kan et found that the relaxation time of a star polymer dispersed in a crosslinked system is by orders of magnitude larger than that in the melt, while for linear polymers the former is larger only by a factor of 2 or 3. 

Discuss feasible routes for the synthesis of narrow-disperse (a) four-armed star polymer, core-(PCLso)4 (where CL = caprolactone) and (b) four-armed star diblock copolymer, core-(PCLso-fc-PStso)4 (where PSt = polystyrene). Calculate the theoretical molecular weights of the star (co)polymers. [Ans. (a) 22,936 (b) 44,332.]... 

Fig. 3.26. A comparison of reduced-viscosity master curves for nearly mono-disperse linear and star polymers.

Living polymerizations afford a variety of options to control polymer size, dispersity, composition, and shape (architecture), as well as allowing specific and defined placement of useful chemical functionalities within these macromolecules. Common strategies for attaching chemical functionalities include the use of functional initiators and post-polymerization reactions. In addition, the absence of chain termination allows access to complex polymeric architectures, which may include block copolymers, multiblock polymers, star polymers, and bottlebrush copolymers. 

Rempp has used a living PS precursor of low molar mass that is made either in a polar solvent, tetrahydrofuran (THF) [82], or in a nonpolar solvent [57]. Here again a living precursor initiates the polymerization of a small amount of DVB, whereupon the cores are formed, as in an arm-first process (Scheme 8). Each core contains as many active sites as there are branches surrounding it. In spite of their low molar mass, the protection the branches exerts on the cores is efficient and prevents the formation of aggregates. The living star polymer solution is molecularly dispersed. Subsequently, the active sites located in the cores are used to initiate the polymerization of another suitable monomer, whereupon a new set of branches (of different chemical nature or not) is generated from the cores. 

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