Relationship between Graft Density and the Dilute Solution Structure of Bottlebrush Polymers: An Inter-chemistry Comparison and Scaling Analysis

Abstract

Bottlebrush polymers are an important class of materials which consist of side chains grafted along a linear backbone. There has been a significant effort to understand structure−property relationships of bottlebrush polymers in solution, with experiments and simulations mapping the impact of parameters such as side chain length, backbone length, and concentration. Improvements in the ability to synthetically control the graft density have resulted in greater interest in understanding how the side chain density influences polymer conformation. However, the impact of graft density on bottlebrush polymers with polynorbornene backbones, which are now ubiquitous, remains relatively unexplored. Here, we examine two sets of polynorbornene-based bottlebrush polymers with polystyrene side chains where the graft density varies between 0.4 and 1.0 side chains per norbornene repeat (i.e., 40 to 100% grafted). The solution conformation of these materials in a good solvent, toluene, is probed through small-angle neutron scattering measurements. Fitting these data with a shape-based model allows for the extraction of parameters such as the radius of gyration and the persistence length. Scaling the radius of gyration based on the Flory theory for grafted chains shows that the side chain−side chain interactions have a greater contribution to the polymer conformation compared to the side chain−backbone interactions, in agreement with results from other backbone chemistries. Additionally, there now exist literature studies rich with dilute solution studies of other chemistries, which are used to develop general scaling relationships for both the radius of gyration and the persistence length as a function of the crowding parameter (product of the side chain degree of polymerization and graft density). Several different representations of the crowding parameter are studied to emphasize the importance of the backbone chemistry to the scaling relationships and solution conformation.

Research progress on the conformational properties of comb-like polymers in dilute solutions

“…74 (d) Reduced radius of gyration as a function of the rescaled crowding parameters (N SC z 0 ) for the comb-like chains with different chemical compositions, where N SC = N g , z 0 = s/number of carbons between grafting sites, R g0 is the radius of gyration of backbone. 76 backbone. These findings underscore the importance of selecting specific backbone and sidechain chemical compositions to tailor the polymer's conformation and achieve desired properties in terms of size-mass scaling relationships.…”

“…Recently, Sunday et al prepared several PNB- g -PS comb-like polymer samples by grafting through a method, and analyzed the size and conformation of PNB- g -PS chains under good solvent conditions by SANS characterization. 76 The effects of different chemical compositions on the conformational properties of the comb-like chain were studied by comparing with other systems with different backbones and sidechains. The results show that the sidechain–sidechain excluded volume interaction is stronger than the backbone–sidechain for the different chemical composition of the comb-like chains, but the sidechain–sidechain excluded volume interaction is weaker in the norbornene backbone system compared with the vinyl backbone, which may be attributed to the increased distance between the grafting sites.…”

Bottlebrush Networks: A Primer for Advanced Architectures

“…These differences manifest practically in a number of situations, primarily with regards to maximum elongationsat-break and materials with programmed domain spacings, where the distinction has a dramatic effect: combs are known to stretch further than bottlebrush materials [2,17,[21][22][23] and high grafting densities can have strong effects on the dspacing of bottlebrush block copolymers (which are anticipated to extend to BBNs). [24][25][26][27][28][29][30] Furthermore, the dynamics and elastic modulus of graft copolymer networks has been shown to be strongly dependent upon this classification, with currently unstudied properties (e.g. adhesion, fracture, etc) being anticipated to show a similar dependence.…”

Comparison of Polypentenamer and Polynorbornene Bottlebrushes in Dilute Solution

“…Several experimental, theoretical, and simulation studies have focused on BBs in the melt state, − while other studies have focused on their dilute solution properties. − Typical parameters used to characterize molecular structure in dilute solution include intrinsic viscosity [η], hydrodynamic radius ( R h ), and radius of gyration ( R g ). Combined, these parameters provide sensitized information on the size and shape of a polymer in a chosen solvent/temperature as architectural features are systematically changed.…”