Molecular and kinetic design for the expanded control of molecular weights in the ring-opening metathesis polymerization of norbornene-substituted polyhedral oligomeric silsesquioxanes

• Published in: Polymer chemistry Vol. 9; no. 42; pp. 5179 - 5189
• Main Authors: Chae, Chang-Geun, Yu, Yong-Guen, Seo, Ho-Bin, Kim, Myung-Jin, Kishore, Mallela Y. L. N., Lee, Jae-Suk
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.11.2018
• Subjects: Chemical synthesis; Clustering; Control rods; Metathesis; Molecular conformation; Molecular weight; Monomers; Morphology; Polyhedral oligomeric silsesquioxane; Polymer chemistry; Polymerization; Polynorbornene; Self-assembly; Spacers; Substitutes; Thin films
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/C8PY00870A

Cube-like polyhedral oligomeric silsesquioxane (POSS) is a promising candidate for isotropically bulky pendants to expand the dimensional limit of polymer main chains. This paper presents molecular and kinetic insights into the controlled synthesis of rod-like POSS-containing polynorbornenes. Ring-opening metathesis polymerization (ROMP) was performed on three norbornene-substituted POSS monomers with different spacers. For monomers possessing non- and amide functionalities at the spacers, ROMP at the maximum concentration ([M] 0 = 0.4 M) led to 100% conversion, predictable molecular weights ( M n ≤ 1236 kDa) and low dispersities ( Đ ≤ 1.20) in homopolymers. Scaling analysis for POSS-containing polynorbornenes revealed an unusual finding, namely, that the periodic clustering of POSS pendants favored by long flexible spacers (16-atom chains) enhanced the rigidity of polynorbornene main chains, leading to their rod-like conformation. Kinetically optimized ROMP allowed the subsequent addition of a macromonomer to create POSS-bottlebrush copolymers (POSSBBCPs). These POSSBBCPs self-assembled into thin films to form ordered nanostructures with diverse morphologies and periodicities greater than 100 nm.