Dendritic macromonomers copolymerization

It is also possible to introduce polymerizable groups at the focal point of dendritic macromolecules and a number of authors have demonstrated the synthesis of novel hybrid dendritic-linear block copolymers by this methodology [69-73]. Initial experiments in the use of the dendritic macromonomers involved the preparation of a series of polyether dendrimers, such as the third generation derivative, 37, which contains a single styrene at its focal point [74]. Copolymerization of 37 with styrene then affords a hybrid block copolymer, 38, in which... 

Hawker and Frechet [50] prepared a dendritic macromonomer using the convergent-growth route to prepare a polyether dendron. The dendron core functional group (R in Scheme 9) was a hydroxymethyl group that was reacted with chloromethylstyrene to form the styrene-functionalized dendritic macromonomer. This macromonomer was copolymerized with slyrene monomer using standard free-radical polymerization conditions. 

The core first method has been applied to prepare four-arm star PMMA. In this case selective degradation of the core allowed unambiguous proof of the star structure. However, the MWD is a little too large to claim that only four-arm star polymers are present [81], Comb PMMAs with randomly placed branches have been prepared by anionic copolymerization of MMA and monodisperse PMMA macromonomers [82], A thorough dilute solution characterization revealed monodisperse samples with 2 to 13 branches. A certain polydispersity of the number of branches has to be expected. This was not detected because the branch length was very short relative to the length of the backbone [83]. Recently, PMMA stars (with 6 and 12 arms) have been prepared from dendritic... 

These were obtained by copolymerization of styrenic macromonomers containing dendritic pendant groups with styrene [16a] with a later extension to methacrylate-type copolymers [16b]. As these studies were carried out with... 

The variety of branched architectures that can be constructed by the macromonomer technique is even larger. Copolymerization involving different kinds of macromonomers may afford a branched copolymer with multiple kinds of branches. Macromonomer main chain itself can be a block or a random copolymer. Furthermore, a macromonomer with an already branched or dendritic structure may polymerize or copolymerize to a hyper-branched structure. A block copolymer with a polymerizable function just on the block junction may homopolymerize to a double comb or double-haired star polymer. 

The DB of branching can be modified by special synthetic approaches, as demonstrated by the NMR quantification of subunits. Copolymerization - for example, the addition of bifunctional monomers AB - resulted in an increase in linear units and, therefore, in a decrease of the DB [109-112]. An enhancement of DB was realized, for example, by employing a slow monomer addition technique [113], the polymerization of prefabricated dendron macromonomers [56, 114], and by a stepwise addition of the monomer mixture for the (A2 + B3) approach [92]. Whereas dendritic and terminal units are essential for a dendritic structure, in the case of hb polymers the content of the linear units can vary greatly. To date, few examples of AB2 hb polymerizations have been reported were the linear unit is a chemically labile structure that either breaks down to the initial educts, or reacts immediately with a further terminal unit to form the stabile dendritic unit. Thus, a hb polymer containing only T and D units is formed, with 100% DB [35,115-119]. 

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