Bottlebrush polymers, a type of polymer material with special architectures, exhibit unique properties such as decreased chain entanglement and compact structures, making them attractive for numerous practical applications. The physical properties of these polymers and their overall performance are highly influenced by their conformation. Generally, the conformation of bottlebrushpolymers can be described in terms of size and shape, which are significantly influenced by their architectural parameters like the grafting density, side chain length, backbone chain stiffness and backbone length. To date, numerous characterization methods have been proposed to study the relationship between conformation and architecture of bottleneck polymers in melt, solution and on the solid surface. Whereas most of these methods rely on computer simulations, only a few, such as atomic force microscopy (AFM), offer high resolution and direct visualization of the molecular shape and size, thus allowing for accurate quantification conformation analysis.
Poly (ethylene glycol) (PEG) grafted polymer brushes have recently attracted significant research attention as promising candidates for numerous applications, especially in biomedical science and biotechnology. This can be attributed to the special characters of polymer brushes and special PEG properties. Nevertheless, despite their practical implications, a thorough and detailed understanding of the architecture and conformation PEG grafted polymers is lacking. Additionally, research on the effects of different parameters such as side chain length on the conformation of these polymers is sparse.
To address the limitations above, a group of researchers at the Hengyang Normal University: Dr. Lifen Xiao, Mr. Jie Li, Dr. Gang Peng and Dr. Geng Huang, systematically investigated the relationship between the conformation and architecture of PEG grafted bottlebrush polymers. Their main aim was to study the effects of different parameters, specifically grafting density and side chain length, on their conformation. Their research work is currently published in the journal, Reactive and Functional Polymers.
In their approach, a combination of ring-opening metathesis polymerization (ROMP) and copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was employed to synthesis several PEG grafted polymers having different grafting densities and chain lengths. The polymer conformations were characterized via the atomic force microscopy technique. Finally, the effects of grafting density and side length parameters on the conformation of the synthesized bottlebrush polymers were systematically investigated and discussed in detail.
The results demonstrated the successful synthesis of alkyne-containing polynorbornene backbones P(NB-alkyne)400, P(NB-2alkyne)400, and P(NB-4alkyne)394. AFM images revealed that whereas P(NB-alkyne)400-g-PEG polymers exhibited low grafting density and spherical morphology, P(NB-4alkyne)394-g-PEG and P(NB-2alkyne)400-g-PEG polymers presented a cylindrical morphology due to their ultrahigh grafting density. This demonstrated that the grafting density played a critical role in determining the shape of the resulting bottlebrush polymers. On the other hand, the side length parameter exhibited remarkable effects on the size of the grafted polymers, including the diameter, contour and persistent lengths, width and height. Furthermore, it was worth noting that the PEG polymers with ultrahigh grafting densities and longer side chain lengths could rupture quickly on the mica surfaces.
In a nutshell, the authors reported the synthesis of PEG grafted bottlebrush polymers via a combination of ROMP and CuAAC reaction and subsequent systematic investigation of the effects of grafting density and side chain length parameters. The polymer had different chain lengths and grafting densities. From the results, the grafting density and side chain length significantly influenced the shape and size of the polymers, respectively. In a statement to Advances in Engineering, the authors explained the study will advance understanding of bottlebrush polymer conformations, benefiting the design and synthesis of high-performance polymers for different applications.
Xiao, L., Li, J., Peng, G., & Huang, G. (2020). The effect of grafting density and side chain length on the conformation of PEG grafted bottlebrush polymers. Reactive and Functional Polymers, 156, 104736.