Effect of Chirality on π-Stacking in Styrene and Maleimide Alternating Copolymers

Abstract

The effect of different chiral sequences in alternating copolymers of styrene and maleimide, poly(styrene-alt-dimethyl-N,N-propylamide) (SMI) was studied. The methods used for the SMI also applied to the general class of alternating copolymers of styrene and various maleimides. Only racemo-diisotactic polymers can associate into complexes because of the symmetrically distributed phenyl groups and maleimide monomers. This polymer is isotactic with respect to the chiral site of the styrene monomers (R, S) and isotactic with respect to the chirality of the maleimide [racemo (RR, SS)]. The maleimide, racemo (SS or RR) chirality, and the complementary S or R chirality in the styrene moiety form the repeating unit of racemo-diisotactic SMI. Structural deviations from the isotactic configurations induces an asymmetry in the distribution of styrene monomers and introduce bends in the polymer backbone, which prevent association through pi-stacking interactions. Semiempirical PM3 calculations on the SMI polymer have shown that this pi-stacking occurs when the polymers are separated by a distance about 10 A, and each pi-stacking pair formed from the styrene monomers has a stabilization energy of about 12 kJ/mol.

Amphiphilic Copolymers for Versatile, Facile, and In Situ Tunable Surface Biofunctionalization

“…The design concept of our AP platform specifically referred to two previously reported properties of styrene-maleic anhydride/acid copolymers (SMAs): 1) the almost linear conformation at neutral pH that favors π-stacking and hydrophobic interactions of the styrene units and supports self-association as well as surface affinity (an effect caused by a stabilizing H-bond between the protonated carboxyl group and the neighboring, deprotonated carboxyl group of the diacid, [31,32] ) and 2) the fact that SMAs with a styrene to maleic acid ratio of 2:1 to 3:1 strongly interact with hydrophobic membrane proteins. [34,35] Accordingly, we selected the 10-30, 80-30, and 120-30 backbone types with an optimal styrene to MA ratio of 2.3:1 and PEGylated the SMAs upon reaction of the anhydride with an amine terminated PEG to introduce a stable amide bond. [36] By selecting a P EG /S-ratio ≥ 8 we could avoid self-association (see Figure 1A) while providing a rather pH-independent solubility (data not shown) and linear conformation stabilized by hydrogen bond formation between the remaining, over a large pH range (pH > 3.5) deprotonated carboxylic acid group, and the NH-group of the amide bond.…”

Recent advances in alternating copolymers: The synthesis, modification, and applications of precision polymers

“…Dimethyl-N, N-propylamide imidized SMAh was found to self-assemble to nanotubes, which were said to arise from the π-stacking of the styrenes and the van der Waals interactions between the maleimide units [122]. Theoretical studies showed that only racemo-diisotactic configuration of imidized SMAh polymer could form complexes by π-stacking, when the phenyl groups and maleimides are symetrically distributed [123].…”

Synthesis of comb‐like dispersants and a study on the effect of dispersant architecture and carbon black dispersion

“…31 Figure 1 (bottom) shows the 1 H NMR spectrum of the PIB-alt-MAH copolymer with long PIB tails; the peaks associated with the vinyl ether end group have disappeared and the aromatic peaks have coalesced into a large multiplet at 7.32-7.11 ppm (d and e), possibly due to π-π stacking of adjacent phenyl rings. 32 This phenomenon is also manifested in a significant downfield chemical shift of the ultimate methylene group of the PIB tail (c).…”