A Rigid, Chiral, Dendronized Polymer with a Thermally Stable, Right‐Handed Helical Conformation

Abstract

First- and second-generation dendronized polymethacrylates PG1 and PG2 carrying chiral 4-aminoproline-based dendrons were obtained on the half-gram scale in high molar masses (PG1: M(n)=5 x 10(6) g mol(-1), PG2: M(n)=1x10(6) g mol(-1)) by spontaneous (radical) polymerization of the corresponding vinyl macromonomers. NMR spectroscopic studies on PG2 together with its unprecedented high glass transition temperature (T(g)>200 degrees C, decomp) and structural parameters provided by atomistic MD simulations show this polymer to be rather rigid. Optical rotation and CD measurements revealed that PG2 adopts a helical conformation that remains unchanged over wide ranges of temperature and solvent polarity. It is also retained when the polymer is deprotected (and thus positively charged, de-PG2) at its terminal amino groups, by which the mass and steric demand of the dendrons is reduced by roughly 50 %. Molecular dynamics simulations on models of PG2 reveal its helical conformation to be right-handed, irrespective of backbone tacticity, and initial results also indicate that de-PG2 retains the right-handedness.

Doubly dendronized chiral polymers showing thermoresponsive properties

“…Since the same protocol was applied as in the previous report for the proline-based couplings where no racemation occurs, 16,20 these chiral macromonomers were expected to possess high stereoisomeric purity.…”

“…This is different from the G2 polymer constructed solely with 4-aminoproline units, which possesses amplified chirality from the monomer, and can adopt left-handed helix conformation mainly due to the stable conformation of the rigid chiral dendrons. 16 The thermal stability of the chiroptical properties of P1 and P3, also examined by CD spectroscopy, relates to both the chirality of the proline core and their phase transition temperatures. For the polymer P1, the signal intensities decrease with the increase of temperature, whether it is below or above its T cp .…”

“…15 We recently reported that polymers carrying rigid proline dendrons can induce the ordered arrangement of the pendants along the polymethacrylate backbone. 16 With slightly flexible dendrons from lysine, polymers can show ordered chiroptical properties with high generation dendron pendants.…”

Internal organization of macromonomers and dendronized polymers based on thiophene dendrons

“…36,37 Thus, the NH groups of the 4-aminoprolines were found to form this kind of interaction with the amide oxygen atoms of either the neighbor or the same repeat unit, enhancing the stability and stiffness of the right-handed helical conformation.…”

Dendronized Polymers with Aromatic Sulfonimide Dendrons

“…For polymers 1, 2, and 3 the corresponding values are >200, [16] þ 67, [2a] and < À80 8C, [17] respectively. The fact that the T g values of PG1(CH3) and PG2(CH 3 ) are right in between that of polymers 1 and 2 confirms the qualitative assessment given in Figure 1 which is based on the inverse relation of segment length between the branching unit and T g .…”