Dumbbell shape copolymers

ABA triblock copolymers, sometimes referred to as dumbbell shaped copolymers when B is a linear macromolecule. 

Palm Tree-like and Dumbbell-shaped Copolymers... 

The so-called palm tree-like copolymers consist in an arrangement of nB blocks with one A block of much larger size in a heteroarmed star architecture [8]. These architectures were obtained by sequential copolymerization of norbornenyl-PS macromonomers with a molecular comonomer, namely cyclooctadiene (COD), Scheme 6. Dumbbell-shaped copolymers can be viewed as double stars that are linked through a linear block. They are obtained upon using palm tree-like copolymers to trigger the polymerization of a new amount of PS macromonomers. Scheme 6. 

TABLE 5. Characteristics of (PS)n-b-PB palm tree-type and (PS)n-b-PB-b-(PS)m dumbbell-shaped copolymers. 

The second polymer (sample E) was an ethylene-hexene copolymer which Is slightly branched, and had an My of 211,000 and a nominal density of 0.955 g/cm. Specimens approximately one millimeter thick were prepared from both polymers by molding flat sheets from which dumbbell-shaped bars were cut with a die. The sheets were molded by heating the polymer for ten minutes at 440K In a press at which time the heat was turned off and pressure applied. The polymer was then cooled In the press over... 

Later work by Frechet et al. attempted to prepare ABA diblock copolymers using the same methodology [255]. Two polyether dendrons were connected to a dihydroxy functional TEMPO moiety, which was then used to initiate, as well as control, the polymerization of St and formed dumbbell-shaped block copolymers (Scheme 29). The ABA block copolymers were formed however, there was some initial contamination from mono- and bis-dendritic species, which were removed by column chromatography. In addition, XH NMR analysis determined that the purified ABA triblock copolymers were also contaminated with AB diblock copolymers. This was attributed to the persistent radical effect, as well as inherent problems with the mobility of the bulky dendron counter radical, both of which will result in the AB diblock copolymers. Thermal polymerization may also contribute to diblock formation, as the radicals generated will be trapped by the counter radical dendron, but would not contain the initiating dendron moiety. Pure ABA triblock copolymer was obtained after two purification cycles using column chromatography [255]. 

Scheme 29. Functionalization of a polyether dendron using a dihydroxy-TEMPO moiety followed by the formation of ABA dumbbell-shaped block copolymers with St [255]...

The material used in the study is an isotactic polypropylene copolymer, because it is the polymer that has a better impact resistance-price ratio. To cany out the exprerimental tests 10 dumbbell-shaped samples of typ>e IB were mechanized from a square sheet of side 1000 mm and a thickness of 3 mm of this material. These samples were manufactured according to the standard UNE-EN-ISO 527-2. 

Later work by Frechet et al. attempted to prepare ABA diblock copolymers using the same methodology [255]. Two polyether dendrons were connected to a dihydroxy functional TEMPO moiety, which was then used to initiate, as well as control, the polymerization of St and formed dumbbell-shaped block copolymers (Scheme 29). The ABA block copolymers were formed however, there was some initial contamination from mono- and bis-dendritic species, which were removed by column chromatography. In addition, NMR analysis determined... 

A similar approach was used to construct a unique triblock copolymer having dendritic termini connected by linear segment. The synthesis of the dendritic-fe/oc/c-linear-fetocA -dendritic PS, referred to as the pom-pom structure due to its dumbbell-like shape, results from a convergent anionic polymerization procedure using dichlorodimethyl-silane as a coupling agent [119]. 

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