Mikto-arm star polymers

There are two gereral routes to mikto-arm star polymers. The first method makes use of the stepwise addition of living polymers to multifunctional chloro-silane compounds [59-62], The Athens group uses the sequential addition of living polymers to multifunctional chlorosilane compounds under tight stoichiometric control [63, 64],... 

Multiarm polymers (11) can be prepared that still have the reactive functional groups (Z) close to the core. As these are still active, they can be used as sites to initiate the growth of more arms by adding either the same monomer used to prepare (11) or a second monomer to prodnce mikto-arm star polymers, in which the arms have different chemical structures. Thus, an active ended poly(t-butyl acrylate), prepared by ATRP, can be coupled with divinyl benzene to form a multiann star polymer. This structure can be converted to a mikto-arm star polymer by reacting the living ends still present with n-butyl acrylate, and so propagate poly(n-butyl acrylate) chains from the core outward. 

The properties of these polymers have similarities with mikto-arm star block copolymers. 

Finally, Lecomte and coworkers reported the synthesis of mikto-arm star-shaped aliphatic polyesters by implementing a strategy based on click chemistry (Fig. 36) [162]. Firstly, the polymerization of sCL was initiated by a diol bearing an alkyne function. The chain-ends were protected from any further undesired reaction by the esterification reaction with acetyl chloride. The alkyne was then reacted with 3-azidopropan-l-ol. The hydroxyl function located at the middle of the chain was then used to initiate the ROP of sCL and y-bromo-s-caprolactone. Finally, pendant bromides were reacted successfully with sodium azide and then with N, N-dimethylprop-2-yn-l-amine to obtain pendant amines. Under acidic conditions, pendant amines were protonated and the polymer turned out to exhibit amphiphilic properties. 

In addition, 1,1-diphenylalkyllithium sites in the living linked polymer product (100) can initiate polymerization of a second monomer (M ) to generate a heteroarm (or mikto-arm), star-branched polymer, 102 [243, 244). 

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