Synthesis of Molecular Brushes by “Grafting onto” Method:  Combination of ATRP and Click Reactions

• Published in: Journal of the American Chemical Society Vol. 129; no. 20; pp. 6633 - 6639
• Main Authors: Gao, Haifeng, Matyjaszewski, Krzysztof
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 23.05.2007; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; FUNCTIONALIZATION; SHAPED POLY(EPSILON-CAPROLACTONE); EFFICIENT ROUTE; CHEMISTRY; MACROMONOMERS; RING-OPENING POLYMERIZATION; COPOLYMERS; TRANSFER RADICAL POLYMERIZATION; STAR POLYMERS; GRADIENT
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja0711617

Molecular brushes (densely grafted polymers or bottle-brush macromolecules) were synthesized by the “grafting onto” method via combination of atom transfer radical polymerization (ATRP) and “click” reactions. Linear poly(2-hydroxyethyl methacrylate) (PHEMA) polymers were synthesized first by ATRP. After esterification reactions between pentynoic acid and the hydroxyl side groups, polymeric backbones with alkynyl side groups on essentially every monomer unit (PHEMA-alkyne) were obtained. Five kinds of azido-terminated polymeric side chains (SCs) with different chemical compositions and molecular weights were used, including poly(ethylene glycol)-N3 (PEO-N3), polystyrene-N3, poly(n-butyl acrylate)-N3, and poly(n-butyl acrylate)-b-polystyrene-N3. All click coupling reactions between alkyne-containing polymeric backbones (PHEMA-alkyne) and azido-terminated polymeric SCs were completed within 3 h. The grafting density of the obtained molecular brushes was affected by several factors, including the molecular weights and the chemical structures of the linear SCs, as well as the initial molar ratio of linear chains to alkynyl groups. When linear polymers with “thinner” structure and lower molecular weight, e.g., PEO-N3 with M n = 775 g/mol, were reacted with PHEMA-alkyne (degree of polymerization = 210) at a high molar ratio of linear chains to alkynyl groups in the backbone, the brush copolymers with the highest grafting density were obtained (Y grafting = 88%). This result indicates that the average number of SCs was ca. 186 per brush molecule and the average molecular weight of the brush molecules was ca. 190 kg/mol.