Molecular weight dependence of helical conformation of amino acid‐based polyphenylacetylenes

Abstract

A well‐defined living polymerization catalyst, [(nbd)Rh{C(Ph)=CPh2}(PPh3)]/PPh3, produced a series of amino acid based polyphenylacetylene derivatives having a wide range of molecular weights (Mn: 1500–128,800) with relatively narrow polydispersity. On the basis of the CD and UV–vis spectra of the obtained polymers measured in DMF, plotting the [θ] and Kuhn dissymmetry factor, g, against the molecular weight revealed that their predominantly one‐handed helical conformation strongly depended on their molecular weights.

Polymerization of Substituted Acetylenes Using Well‐Defined Rhodium Complex Catalyst. Chirality Transfer and Amplification in Chiral‐Chiral Block and Random Copolymers

“…No chirality amplification was observed when the 1D unit contents were 60% and larger in the block copolymers. In the case of homopolymer [poly( 1L )], 10–15 degrees of polymerization lead to a construction of stable helical structure . The first block could not form a stable helical structure when the 1L unit contents were small.…”

“…In the case of homopolymer [poly(1L)], 10-15 degrees of polymerization lead to a construction of stable helical structure. [21] The first block could not form a stable helical structure when the 1L unit contents were small. On the other hand, the relationships between the 1D unit content and |g| values of the random copolymers were not linear but convex upward (Figure 6b) in a manner similar to those of Figure 4b, likely due to chirality amplification.…”

“…We previously reported that the chirality of poly(1L) increased according to the M n at a low molecular weight region, and leveled off when the degree of polymerization reached around 20-50. [21,28] In the present study, we examined the relationship between the chirality and M n of the second chiral block in the block copolymers. Poly(1L 50 ) and poly(1D 50 ) exhibited almost mirror image CD signals as shown in Figure 2.…”

“…Rh complex catalysts are most widely used for the polymerization of monosubstituted acetylene monomers to give cis‐stereoregular substituted polyacetylenes. Since Tabata and coworkers discovered the efficient catalytic activity of (nbd)RhCl] 2 /Et 3 N (nbd  2,5‐norbornadiene) to the polymerization of phenylacetylene, various well‐defined Rh complex catalysts have been developed to improve the activity and livingness of acetylene polymerizations, including [(nbd)Rh(CCPh)(PPh 3 ) 2 ], [(nbd)RhCl] 2 /PPh 3 /[C(Ph)CPh 2 ], [(nbd)Rh{C(Ph)CPh 2 }{P(4‐X‐C 6 H 4 ) 3 }] (X  F, Cl) and [(nbd)Rh{C(Ph)CPh 2 }(PPh 3 )] . Introduction of chiral substituents as well as high stereoregularity leads to predominantly one‐handed helical conformation of monosubstituted acetylene polymers, which sometimes exhibit chirality amplification, memory, and recognition .…”

“…

RhCl] 2 /Et 3 N (nbd  2,5-norbornadiene) to the polymerization of phenylacetylene, [15,16] various well-defined Rh complex catalysts have been developed to improve the activity and livingness of acetylene polymerizations, including [(nbd)Rh(CCPh) (PPh 3 ) 2 ], [17] [(nbd)RhCl] 2 /PPh 3 / [C(Ph)CPh 2 ], [18] [(nbd)Rh{C(Ph)CPh 2 } {P(4-X-C 6 H 4 ) 3 }] (X  F, Cl) [19,20] and [(nbd) Rh{C(Ph)CPh 2 }(PPh 3 )]. [21,22] Introduction of chiral substituents as well as high stereoregularity leads to predominantly one-handed helical conformation of monosubstituted acetylene polymers, which sometimes exhibit chirality amplification, [23] memory, [24] and recognition. [25] Green and coworkers have reported helical sense control of random copolymers utilizing the competition between structurally different enantiomeric monomer units.

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