Star block copolymers branching distribution

An important group of surface-active nonionic synthetic polymers (nonionic emulsifiers) are ethylene oxide (block) (co)polymers. They have been widely researched and some interesting results on their behavior in water have been obtained [33]. Amphiphilic PEO copolymers are currently of interest in such applications as polymer emulsifiers, rheology modifiers, drug carriers, polymer blend compatibilizers, and phase transfer catalysts. Examples are block copolymers of EO and styrene, graft or block copolymers with PEO branches anchored to a hydrophilic backbone, and star-shaped macromolecules with PEO arms attached to a hydrophobic core. One of the most interesting findings is that some block micelle systems in fact exists in two populations, i.e., a bimodal size distribution. 

The results of experimental and theoretical research on water-soluble (nonstoichio-metric) IPECs based on nonlinear (branched) polyionic species (HPE) complexed with oppositely charged linear PEs (GPE) demonstrated that the main feature of such macromolecular co-assemblies is their pronounced compartmentalized structure, which results from a distinctly nonuniform distribution of the linear GPE chains within the intramolecular volume of the branched HPE. In the case of star-shaped PEs or star-like micelles of ionic amphiphilic block copolymers, this com-partmentalization leads to the formation of water-soluble IPECs with core-corona (complex coacervate core) or core-shell-corona (complex coacervate shell) structures, respectively. Water-soluble IPECs based on cylindrical PE brushes appear to exhibit longitudinally undulating structures (necklace) of complex coacervate pearls decorated by the cylindrical PE corona. 

Riess and coworkers [214, 215] have also developed a unique method to synthesize heteroarm, ABC-type, three-armed, star-branched block copolymers as shown in Scheme 30. Poly(styryl)potassium was reacted with a tert-butyldimethylsiloxy-protected, hydroxyethylated 1,1-diphenylethylene (85) to form a siloxy-functionalized polymeric 1,1-diphenylalkylpotassium (86), that was then used to initiate polymerization of ethylene oxide as shown in Scheme30 [214]. Samples of the diblock copolymers, 87, exhibited rather broad molecular weight distributions (Mw/M =1.15-1.16). After removal of the protecting group with tetrabutylammonium fluoride the corresponding... 

The results of the 2G and 3G dendrimer-like star-branched polymers and block copolymers, after fractional precipitation, are summarized in Table 5.2. The resulting polymer all possessed the observed Mn values in good agreement with those calculated, and narrow molecular-weight distributions (M /Mn 1.1). Since the off-center living polymers and the 2G living dendrons used as subunits are sampled during the synthesis and well characterized prior to the synthesis and then reacted with a multifunctional core to synthesize the 2G and 3G polymers, this procedure corresponds to an example of an arm-first process. 

The TMS protective group was quantitatively deprotected by treatment with (C4H9)4NF in THF at room temperature (Scheme 7). SEC profiles of the resulting poly(12) and poly (13) exhibited narrow monomodal distributions similar to those of the original poly(12a) and poly(13a), respectively. Thus, TMS group is capable of protecting the active ethynyl hydrogen of 12 in addition to hydroxyl and amine functions. Since ethynyl and the related C=C bonds have been recently used in click reaction with azides to prepare block copolymers, star-branched polymers, and even hyperbranched... 

The synthesis of a miktoarm star copolymer of the type AnBn has been also demonstrated. The synthesis was performed via ATRP using divinylbenzene, as the core cross-liking agent. PEO macroinitiator chains were utilized for the polymerization of divinylbenzene forming a star polymer, with a random number of branches. The above star polymer was used as a multi-functional initiator for the polymerization of methacrylate monomers. Therefore, the synthesis of an amphiphilic miktoarm star copolymer was realized [54]. Finally, the hydrolysis of the protected methacrylate block led to the preparation of the desired DHBCs, namely the PEOn-PMAA stars. SEC analysis of the preeursor PEOn-PMMA copolymer revealed a relatively broad molecular weight distribution. Nevertheless, this is a good example for the synthesis of A Bn double hydrophilic star copolymers. 

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