4-Arm star

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

Fig.9. Predictions of parameter-free theory for G (co) with 0(1) corrections to Gq and Tg as for Fig. 8 and data for a range of 3- and 4-arm star polyisoprenes from [5]. Arm molecular weights in 10 g mol are 11.4,17, 36.7,44,47.5, 95 and 105. The entanglement molecular weight has been taken as 5000 g mol" ...

The viscoelastic properties of solutions of linear and 4-armed star polybutadienes were studied by Osaki and co-workers (117), who compared the storage and loss shear moduli extrapolated to zero concentration with theoretical values. The results for the branched polymer could be accounted for well in terms of the Zimm and Kilb theory (34) a lower value of the hydrodynamic interaction parameter was indicated for the branched polymer than for the linear one, which may be associated with the higher density of polymer segments in the former. 

Wyman and co-workers (120) studied the viscosity of narrow MWD linear and 4-armed star polystyrenes as a function of shear rate. At low shear rates, the star polymers (of MW 204000 and 430000) had low-shear viscosities much lower than linear ones of the same MW it may be remarked that the branch length... 

The ABA-type block copolymers B-86 to B-88 were synthesized via termination of telechelic living poly-(THF) with sodium 2-bromoisopropionate followed by the copper-catalyzed radical polymerizations.387 A similar method has also been utilized for the synthesis of 4-arm star block polymers (arm B-82), where the transformation is done with /3-bromoacyl chloride and the hydroxyl terminal of poly(THF).388 The BAB-type block copolymers where polystyrene is the midsegment were prepared by copper-catalyzed radical polymerization of styrene from bifunctional initiators, followed by the transformation of the halogen terminal into a cationic species with silver perchlorate the resulting cation was for living cationic polymerization of THF.389 A similar transformation with Ph2I+PF6- was carried out for halogen-capped polystyrene and poly(/>methoxystyrene), and the resultant cationic species subsequently initiated cationic polymerization of cyclohexene oxide to produce... 

Fig. 2.4. Real part [G ] and imaginary part [G"] of reduced complex modulus plotted against reduced angular frequency toR for 4 armed star polymer for Zimm-Kilb theory (49). Thick lines are calculated from eigenvalues given in Zimm-Kilb paper solid lines for h- oo and dashed lines for h- 0. Thin lines are calculated from eigenvalues of difference equation with Nb = 100 solid lines for h = 0.25 and dashed lines for h = 0.30 (73)...

Recently the synthesis and characterization of a new star-block architecture, the inverse star-block copolymer, was reported [19].These 4-arm star molecules, with poly(styrene-Msoprene) arms, have two of the arms connected to the silicon atom by the polystyrene (PS) end of the diblock arm while the other two are connected to the central point by the polyisoprene (PI) end (Scheme 4). 

ATRP allows the synthesis of di-block copolymers by sequential (one-pot) or separated steps (two-pot) methods (26). To synthesize di-block, tri-block, 3-and 4-arm star-block copolymers by the two-pot method, a typical ATRP procedure was performed. First, a homopolymer was synthesized as mentioned above and then this was used as a macroinitiator. In addition to the two-pot procedure, one of the tri-block copolymers (P2 in Table 1) was also synthesized by the one-pot ATRP procedure. Once first monomer polymerized to complete conversion, the second monomer was added to the flask under nitrogen to obtain the block copolymers. In both cases, the samples were taken periodically via a syringe to follow the molecular weight of the polymer by GPC and the conversion of polymerization by GC measurements. 

In this study, well-defined PS-6-PEHA di-block, PS-6-PEHA-6-PS and PEHA-6-PS-6-PEHA tri-block, (PS-6-PEHA) 3-arm star-block, (PEHA-6-PS)" and (PS-6-PEHA) 4-arm star-block copolymers were synthesized via ATRP. In order to compare the effect of structures on the baroplastic behavior, some block copolymers were obtained with the replacement of iimer/outer soft segments. Herein, some of the obtained block copolymers and their... 

Figure 3. Images of a) the mold with starting and processed polymers, b) processed baroplastic(PEHAo.4g-b-PSo,3i)" 4-arm star-block copolymer (P6), at different pressures for 1 min at room temperature.

It was also shown that baroplastic materials can be used as a processing aid to process high Tg homopolymer such as polystyrene (PS). To optimize the conditions, polystyrene and baroplastic materials in powder form were blended at different compositions and pressed using compression or extrading at room temperature. The results indicate that a room temperature moldable polystyrene/baroplastic blend can be obtained at 50 wt% baroplastic content with the di-block, tri-block and star-block copolymers. Figure 10 shows that the 50 wt% blend of PS (45K) and 4-arm star-block copolymer (98K, P8) can be... 

Workers have reported the use of silicon tetrachloride to prepare 3 or 4 arm star-block copolymers of butadiene-styrene(17,18) Silicon tetrachloride terminates several living macroanions at a single junction by halogen exchange. A 4-arm star block copolymer is represented below. 

Arm star diblock copolymer Figure 2 Star-block copolymers. 

Two series of 4-arm star polypeptides of y-benzyl-L-glutamate N-carboxyanhydride (NCA) and e-benzyloxycarbonyl-L-lysine NCA were prepared via ROP. A tetra-amino-substituted per-ylene fluoropore was used as the initiator. The polymerization was performed imder dry inert atmosphere conditions and the... 

The method of the multifunctional initiator was used for the synthesis of 3- and 4-arm stars. Trimethylolpropane triacrylate was converted to a silyl enol ether capable of initiating the polymerization of ethyl acrylate to form the corresponding 3-arm star " (Scheme 50). 

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