Hyperbranched polymers self-condensing vinyl polymerization

Figure 8.5 Schematic representation of the self-condensing vinyl polymerization of an AB -monomerto give a hyperbranched vinyl polymer [19]...

The second generation of hyperbranched polymers was introduced a few years ago when Frechet et al. reported the use of self-condensing vinyl polymerization to prepare hyperbranched polymers by carbocationic systems (Fig. 3) [46]. Similar procedures but adapted for radical polymerization were shortly thereafter demonstrated by Hawker et al. [47] and Matyjaszewski et al. [48]. 

Fig. 3. Schematic description of self-condensing vinyl polymerization used for the synthesis of of hyperbranched polymers based on vinyl monomers as presented by Frechet [52] -(represents a reactive site which can initiate polymerization)...

Hyperbranched polymers can be synthesized in several different ways, the most commonly used being classical condensation reactions. These reactions are made either in bulk or in solution where the A,jB monomers are condensed by themselves or in combination with a By core monomer. The use of a By core monomer improves the control over the molecular weight and dispersity of the hyperbranched polymer. Hyperbranched polymers can also be synthesized by self-condensing vinyl polymerization using vinyl-functional monomers. The introduction of this approach has greatly increased the number of possible monomers that can be used for this type of polymer. 

A wide variety of hyperbranched polymers have been described in the literature. Initially, these were mainly condensation polymers such as polyesters and polyethers since the required monomers were the most readily available. A number of hyperbranched polymers based on vinyl monomers have been described lately after the introduction of self-condensing vinyl polymerization. One structural variation which has been widely employed for hyperbranched... 

The self-condensing copper-catalyzed polymerization of macromonomer of poly(tBA) with a reactive C—Br bond (H-6) affords hyperbranched or highly branched poly(tBA).447 Copolymerization of H-1 and TV-cyclohexylmaleimide induced alternating and self-condensing vinyl polymerization.448 The residual C—Cl bond was further employed for the copper-catalyzed radical homopolymerization of styrene to give star polymers with hyperbranched structures. Hyperbranched polymers of H-1 further serve as a complex multifunctionalized macroinitiator for the copper-catalyzed polymerization of a functional monomer with polar chromophores to yield possible second-order nonlinear optical materials.325... 

Hyperbranched polymers may be prepared by the self-condensing vinyl polymerization (SCVP) [257] of AB star monomers by a controlled free radical process, such as ATRP [258]. The result, under certain conditions, is a highly branched, soluble polymer that contains one double bond and, in the absence of irreversible termination, a large quantity of halogen end groups equal to the degree of polymerization which can be further functionalized [87] (Fig.35). Two examples explored in detail by ATRP are vinyl benzyl chloride (VBC, p-chlo-romethylstyrene) [258] and 2-(2-bromopropionyloxy)ethyl acrylate (BPEA) [259-261] both depicted in Fig. 35. Several other (meth)acrylates with either 2-... 

With appropriate choice of reaction conditions, hyperbranched polymers can be formed by self-condensing vinyl polymerization of monomers that additionally contain the appropriate initiator (NMP, ATRP), when the compounds are called inimers, or RAFT agent functionality. Monomers used in this process include 340, 341 and 342 " " (for NMP), 108 and 344 and related monomers (for ATRP) and 343" (for RAFT). Careful control of reaction conditions is required to avoid network formation. 

Hyperbranched polymers are synthesized in a one-step method, often from AB monomers but also by combining A +B (x>3) monomers or variations of those. Polymerization methods have been applied that involve polycondensation, polyaddition, and ring-opening or self-condensing vinyl polymerization. Even though the one-pot synthetic approach leads to imperfectly branched structures because of uncontrolled growth, it is more suitable for the preparation on a larger scale and thus for commercial use. Nowadays, different... 

Highly branched, so called hyperbranched macromolecules have recently attracted interest, because of their interesting properties, which closely resemble those of dendrimers. Vinyl monomers with pendant initiating moieties, for example, 3-(l-chloroethyl)-ethenylbenzene, have been reported to give rise to hyperbranched polymers in a process termed self-condensing vinyl polymerization [253]. Hyperbranched PIBs have been synthesized by cationic copolymerization of 4-(2-methoxyisopropyl)styrene and IB [254]. Using a similar approach the preparation of arborescent block copolymers of IB and St (arb-PIB-h-PSt) has also been reported (see above) [226]. 

Hyperbranched polymers can be prepared by a variety of techniques, including the polycondensation of AB monomers as originally described by Flory [113], the reaction of A2 + B3 monomers, and self-condensing vinyl polymerization [139-141]. The first report [142] of using click chemistry in the synthesis of hyperbranched materials appeared at about the same time as the initial report for dendrimers prepared using CuAAC however, but much fewer examples have been reported that describe hyperbranched materials involving click chemistry. Nevertheless, these polymers represent an important class of materials, and both CuAAC [142-147] and thiol-ene [148] chemistry have found their way into the hyperbranched hterature. 

Yan, D. Zhou, Z. Muller, A. Molecular weight distribution of hyperbranched polymers generated by self-condensing vinyl polymerization in the presence of a multifunctional initiator. Macromolecules 1999, 32, 245. 

Preparation of hyperbranched polymers using ATRP involves self-condensing vinyl polymerization (SCVP) (Frechet et al., 1995) of AB monomers, which contain two active species, viz., the double bond A group (polymerizable) and the initiating site B. Two main examples explored in detail within the context of ATRP are p-chloromethyl styrene or vinyl benzyl chloride (VBC) and 2-(2-bromopro-pionyloxy) ethyl acrylate (BPEA) (Fig. 11.30). Several other (meth)acrylates with either 2-bromopropionate or 2-bromoisobntyrate gronps have also been used. 

Muller, A.H.E., Yan, D., and Wulkow, M. (1997) Molecular parameters of hyperbranched polymers made by self-condensing vinyl polymerization. 1. Molecular weight distribution. Macromolecules, 30,7015-7023. 

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