Terpolymers, miktoarm star

By using a combination of RAFT and ring opening polymerization (ROP), (polyethylene oxide) methyl ether)(polystyrene)(poly(L-lactide) 3-miktoarm star terpolymers have been successfully synthesized [182]. The synthetic approach involved the reaction of the cw-functionalized - OH group of the poly(ethylene oxide) methyl ether with maleic anhydride under conditions where only one hydroxyl group can be esterified (MPEO). The double bond... 

By utilizing a combination of RAFT and cationic ROP, the synthesis of [poly(methyl methacrylate)][poly(l,3-dioxepane)][polystyrene] miktoarm star terpolymers was achieved [182], The approach involved the synthesis of PS functionalized with a dithiobenzoate group by RAFT polymerization and subsequent reaction with hydroxyethylene cinnamate (Scheme 98). The newly created hydroxyl group was then used for the cationic ring opening polymerization of 1,3-dioxepane (DOP). The remaining dithiobenzoate group was used for the RAFT polymerization of methyl methacrylate. 

Blending of ABC Miktoarm-Star Terpolymers with AB-Diblock Copolymers... 

Besides linear-block copolymers, also blends with miktoarm-star terpolymers have been reported [193]. Blending a PS-arm-PB-arm-P2VP miktoarm-star terpolymer showing hexagonal symmetry with a PS- -P2VP diblock... 

Miktoarm star terpolymers of the type ABC have been prepared by several methods. Iatrou and Hadjichristidis reported the synthesis of a miktoarm star consisting of PS, PI and PB branches radiating from the star center [51]. This was achieved using the chlorosilane method and the step by step linking of the different branches to the trichloromethylsilane, which was the linking agent, as shown in Scheme 19. 

Only one case concerning the synthesis of a miktoarm star quaterpolymer has appeared in the literature. It consists of four different branches, namely PS, po-ly(4-methyl styrene) (P4MeS), PI and PB [35]. The reaction sequence for the preparation of this miktoarm star is presented in Scheme 23. The procedure was similar to the one adopted for the synthesis of the ABC-type terpolymers by the chlorosilane method. The characteristic of this method is that two of the arms were incorporated to the linking agent by titration. Consequently the order of addition plays an important role for the preparation of well defined products. PS was chosen to react first with an excess of SiCl4, followed after the evaporation of the excess silane, by the titration with the more sterically hindered P4MeS so that only one arm can be incorporated in the star. The moderately hindered PILi anion was then added by titration, followed by the addition of the fourth arm, which is the least sterically hindered PBLi anion so that complete linking can be achieved. The reaction sequence was monitored by SEC and these results in combination with the molecular and spectroscopic characterization data showed that well defined quaterpolymers were prepared. 

The morphological investigation of a three miktoarm star terpolymer was first reported by Hadjichristidis et al. [81]. A SIB miktoarm star with MWs of the arms PS 20.7 K/PI 15.6 K/PBd 12.2 K and a volume fraction of PS equal to 0.4 formed PS cylinders in a polydiene matrix. Due to the low molecular weights the polydiene arms formed one phase. The cylinders are in contrast to the lamellae expected for diblock copolymers but the behavior is analogous to the behavior of I2S and S2I miktoarm stars of the same composition. 

Yamauchi K, Takahashi K (2003) Microdomain morphology in an ABC 3-miktoarm star terpolymer a study by energy-filtering TEM and 3D electron tomography. Macromolecules 36 6962-6966... 

A (PI)(PS)(PDMS) miktoarm star terpolymer was synthesized by the same method.97 The (PI)(PS)Si-(CH3)C1 macromolecular linking agent was prepared as previously mentioned, followed by the addition of the living PDMSLi chains to give the desired product. Also in this case a well-defined polymer with narrow molecular weight distribution was obtained. 

Dumas et al.124 125 have developed a procedure for the synthesis of ABC miktoarm star terpolymers containing amphiphilic branches. Styrene was polymerized in THF at —78 °C using cumylpotassium as initiator. The living chains were then reacted with 1 - [4- (2 - tcrt- b i ityld imethylsiloxy) ethyl] phenyl-1 -phen-ylethylene, as illustrated in Scheme 52. The living center was then used to initiate the polymerization... 

Using the chlorosilane approach, Iatrou and Hadjichristidis synthesized 3-miktoarm star terpolymers of the ABC type [232] and 4-miktoarm star copolymers and quaterpolymers of the A2B2 and ABCD type [233], respectively. The synthesis of the ABC star was based on the following reactions (Scheme 76). 

In fact,Stadler and co-workers [252] recently synthesized an ABC 3-miktoarm star terpolymer having arms of PS, PI, and PMMA using the approach shown in Scheme 84. After purification this polymer exhibited 1= 1.13 as measured by SEC. Unfortunately no absolute characterization was performed. 

In contrast to miktoarm stars, linear triblock terpolymers are comprised of three blocks with different chemical natures arranged in a sequential manner. In this case two junction points exist between blocks within the same chain inducing additional constraints in the arrangement of the blocks in an ordered mesostructme. In analogy to ABC miktoarm stars, the ordered... 

Recent advances in polymer chemistry, in particular, in controlled radical polymerization, have enabled the synthesis of complex macromolecular architectures with controlled topology, which comprise chemically different (functional) blocks of controlled length in well-defined positions. Block co- and terpolymers, molecular and colloidal polymer brushes, and star-like polymers present just a few typical examples. Furthermore, miktoarm stars, core-shell stars and molecular brushes, etc. exemplify structures where chemical and topological complexity are combined in one macromolecule. 

Junnila S, Houhenov N, Hanski S, latrou H, Hirao A, Hadjichristidis N, Ikkala O (2010) Hierarchical smectic self-assembly of an ABC miktoarm star terpolymer with a helical polypeptide arm. Macromolecules 43 9071-9076... 

Scheme 30.15 Synthesis of a four-miktoarm star quar-terpolymer by coupling two unique block copolymers containing complementary click functionality at each block junction. Reproduced with permission from Ref. [110] 2008, Wiley Periodicals, Inc.

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