Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

Abstract

Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly­(d,l-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N bb α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z (System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C ∞), a proxy for the backbone stiffness, scales with N bb as a function of the grafting density: C ∞ ∼ N bb f(z). The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

Consequences of Grafting Density on the Linear Viscoelastic Behavior of Graft Polymers

“…Figure S13 shows a sketch of the proposed backbone kinking that results in a more "flexible" chain, which is similar to the torsional limitations that Lin et al observed. 13 Figure S13. Cartoon depiction of backbone folding back on itself to space out side chains.…”

Effect of side chain and backbone length on lamellar spacing in polystyrene‐block‐poly(dimethyl siloxane) brush block copolymers

“…Lattice spacings on the order of d 0 = 100 nm are consistently reported in the literature . Several intricate designs of BBCPs are reported with variable graft density, block composition, and side chain chemistries . BBCPs have found practical use as templates for the fabrication of functional materials such as coatings, photonic crystals, scaffolds for well‐ordered nanoparticle arrays, metallo‐dielectric composites, and novel elastomeric materials …”

Synthesis and Applications of Compartmentalised Molecular Polymer Brushes

“…Interestingly,the domain spacing was noted to be insensitive to the backbone length, which suggested the brushes were undergoing phase separation of their side chains,with the backbone confined at the interface between the two polymers and the side chains segregated to opposite sides (i.e.a long the x axis). [52] Increases in the degree of polymerisation of the brush backbone led to increasing domain spacing in the respective thin films,w ith ar emarkable near-linear relationship observed. These lamellar domains had dimensions which depended on the backbone length and were large enough to reflect visible light.…”

“…[52] Increases in the degree of polymerisation of the brush backbone led to increasing domain spacing in the respective thin films,w ith ar emarkable near-linear relationship observed. [52] with permission.C opyright 2017 AmericanC hemical Society.E )The reflectance of the bulk self-assembled thin films is related to the molecularw eight of the compartmentalised brushes. [20a] Thedomain spacing may also be adjusted by altering the self-assembly conditions,s uch as changing the annealing solvent and temperature, [20a] as well as by the blending in of additives (e.g.…”