Mixed arm star

Miktoarm star (or p-star) polymers are star polymers with branches of different polymers. These polymers are also called heteroarm or mixed-arm star polymers. Their synthesis is more difficult but success has been achieved by sequential coupling [Hadjichristidis, et al., 1999]. To obtain a 3-arm star with one polyisoprenyl (PI) and two polystyryl (PS) branches, polyisoprenyllithium is reacted with an excess of CH3SiCl3 to form the one-arm polymer, the unreacted CH3SiCl3 is removed, and then polystyryllithium is added ... 

Ranganathan K, DengR, Kainthan RIC, Wu C, Brooks DE, KizhakkedathuJN Synthesis of thermoresponsive mixed arm star polymers by combination of RAFT and ATRP from a multifunctional core and its self-assembly in water. Macromolecules 41 4226-4234, 2008. 

The adsorption behavior of fimctionalized linear and three arm star PBd was studied by ellipsometry at 20 C in a mixed solvent of cyclohexane and toluene (50 % by volume) (39/A mixture of cyclohexane and toluene was used. In this mixture... 

ROP can also be used to generate star-shaped block copolymers in a combinatorial manner.Meier et al7 employed a five-arm star-shaped PEG compound as a macroinitiator for the ROP of 8-caprolactone monomer. Using this strategy, the PEG compound formed the core of the star while the outer shell was comprised of polyesters. Polymerizations were performed on a Ghemspeed ASW2000 by mixing monomer and initiator at different ratios and heating to 130 °C. Polymerizations were demonstrated to be reproducible by the low variation in measured MW values in iterative experiments. Moreover, a linear relationship was observed between MWs (calculated by both GPC and NMR) and different [M]/[I]... 

The effect of coupling reaction was considered in the viscoelasticity calculation of three arms star polymer. As mentioned above, the prep>aration of the star polymer accompanies the coupling reaction which mainly generates the dimer. It is obvious that the dimer is in the architecture of H-polymer, therefore the calculations were carried out with mixing three... 

Another approach to synthesize multiarm star block copolymers is based on a combination of CuAAC and the arm-first method (Durmaz et al, 2010). Protected alkyne PS polymers were prepared via ATRP and subsequently crosslinked by a divinyl containing compound. The formed 27-arm star-shaped polymers containing a protected alkyne periphery, was deprotected and subsequently coupled with azide-end-functionalized PEG and PtBuA to form star block or mixed block copolymers. The CuAAC reactions occurred at room temperature for 24 h, surprisingly leading to a full click efficiency. The quantitative character of the latter click reaction at ambient temperatures for such dense polymer structures is in contrast to those obtained by other research groups, as mentioned in previous paragraphs. 

Another ternary solution SPS43 was a 4-arm star PS (Afu =3.0 x 10, M] /Mn 1.10) mixed with a similar molecular weight probe linear PMMA (Muj=3-3 X 10, Muj/Mfi 1.10). The results were very similar to those of LPS98. Figure 10 shows the measured correlation function and the CONTIN... 

Tsitsilianis [93] used DSC to study the phase behavior of (polybutylmethacr-ylate)n(polystyrene)n and (polybutylacrylate)n(polystyrene)n miktoarm stars with varying n. The Tg of the PS phase was found to be much lower than in the homopolymer and the width of the transition was increased. In some cases an intermediate Tg was observed due to the extended interphase region in these materials, as a result of mixing of the different arms in the vicinity of the star cores. 

The term miktoarm (from the greek word fu/crog, meaning mixed), or heteroarm star polymers, refers to stars consisting of chemically different arms. In the past decade considerable effort has been made toward the synthesis of miktoarm stars, when it was realized that these structures exhibit very interesting properties.88-90 The synthesis of the miktoarm star polymers can be accomplished by methods similar to those reported for the synthesis of asymmetric stars. The chlorosilane, DVB, and DPE derivative methods have been successfully employed in this case. Furthermore, several other individual methods have appeared in the literature. The most common examples of miktoarm stars are the A2B, A3B, A2B2, kn >n (n > 2) and ABC types. Other less common structures, like the ABCD, AB5, and AB2C2 are now also available. 

Tuzar and coworkers [294] investigated the micellization behavior of styrene-butadiene star-block copolymers with four arms and polybutadiene inner blocks in the mixed solvent tetrahydrofuran/ethanol, selective for polystyrene blocks. 

Their findings were that star polymers presented a lower surface tension that linear polystyrene and that this value decreased with increasing number of arms. This behavior was explained by a lattice model considering finite compressibility of the chain and density gradient in the polymer blend. Thus this study implied that when mixed with a linear polymer star-shaped macromolecules would segregate to reduce the surface tension. 

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