Morphological Behavior of Compositionally Gradient Polystyrene–Polylactide Bottlebrush Copolymers

Abstract

Morphological behavior of PS−PLA bottlebrush copolymers with a compositional gradient along the backbone was investigated by small-angle X-ray scattering (SAXS) analysis and compared to that of their block copolymer analogs. Side chain-symmetric gradient copolymers with varying volume fractions were prepared by one-step ring-opening metathesis polymerization of the corresponding exo-and endo-norbornenefunctionalized macromonomers of similar lengths. The morphological map constructed using the SAXS data revealed a wide cylindrical morphology window, including for symmetric compositions, well-ordered lamella morphologies at very low PS volume fractions, and the formation of a rare bicontinuous gyroid morphology. In addition to the highly asymmetric nature of the morphology diagram, the domain spacings obtained for gradient bottlebrush copolymers were significantly smaller (by 30−40%) than the corresponding bottlebrush block copolymer analogs, which was attributed to a nonperpendicular orientation of the gradient bottlebrush backbone at the domain interface. Side chain-asymmetric gradient bottlebrush copolymers were synthesized from PS and PLA macromonomers of different lengths and were demonstrated to assemble into well-ordered cylindrical and lamella morphologies. The results of these studies demonstrate that the gradient interface plays an important role in determining molecular packing during bottlebrush copolymer self-assembly. A rich morphological behavior of the gradient bottlebrush copolymers combined with their "user-friendly" onestep synthesis provides a robust and versatile platform for nanostructured material-design and fabrication.

Random copolymerization of macromonomers as a versatile strategy to synthesize mixed‐graft block copolymers

“…This gradient composition can be better visualized by plotting the instantaneous copolymer composition as a function of total macromonomer conversion (Figure 1C), which, according to the terminal model (Equations S2‐5), is calculated by the rate of each macromonomer's incorporation at any given time. Note that while the kinetic experiments indicated a slight gradient composition along the backbone, the gradient was not as steep as in the gradient copolymers synthesized by the Rzayev group via the copolymerization of exo ‐Nb‐PS and endo ‐Nb‐PLA, in which the exo ‐Nb‐PS polymerized 29 times faster than the endo ‐Nb‐PLA, with reactivity ratios r 1 = 5.0 and r 2 = 0.19 20 …”

“… a assuming ρ PS = 1.04 g/cm 3 and ρ PLA = 1.25 g/cm 3 20b,24 . Calculated based on 1 H‐NMR of the purified products. …”

Mesoscale Modeling of Agglomeration of Molecular Bottlebrushes: Focus on Conformations and Clustering Criteria

“…For a chosen architecture and chemical nature of a bottlebrush, its conformation can be tuned either by regulating the solvent quality or by regulating the concentration of bottlebrushes in solution. The phase separation and agglomeration processes in blends and solutions incorporating MBBs-as well as migration of bottlebrushes to the interfaces and surfaces in multi-phase systems-introduce further complexity, so that the resulting behavior depends on the interplay between the contributions from the components with various affinities [22][23][24][25]. The self-assembly process can also be tailored by external stimuli, such as temperature, pH, ionic strength, and external fields [2,[26][27][28][29].…”

Complete Photonic Band Gaps with Nonfrustrated ABC Bottlebrush Block Polymers

“…In addition to molecular parameters present in linear architectures like block fractions and Flory−Huggins χ parameters, bottlebrush polymers can be designed with different grafting densities, 33 side-chain lengths, 36−39 shapes, 40−42 and composition gradients. 43,44 Multiblock architectures, such as ABC triblock bottlebrushes, have also begun to be explored. 34,45,46 This vast range of parameters permits nearly endless variation in the design of bottlebrush polymers and should permit the selfassembly of a wide range of different phases.…”

“…34,45,46 This vast range of parameters permits nearly endless variation in the design of bottlebrush polymers and should permit the selfassembly of a wide range of different phases. Though the phase behavior of bottlebrush polymers across this vast parameter space is still being explored, all classical phases, including lamellar, 22−24,33,34,37−39 cylindrical, 21,36,37,43,44 spherical, 21,39 and gyroid morphologies 44 have been observed in bottlebrush block polymers, albeit with varying degrees of order. A major challenge in the self-assembly of 3D photonic crystals with bottlebrush polymers is the absence of design rules or theories that can predict which combinations of molecular parameters will yield a desired phase.…”