A series of styrenic monomers containing strong donor substituents (i.e., 4-methylstyrene, 4-acetoxystyrene, and 4-tert-butoxystyrene) were tested in sequencecontrolled radical copolymerizations in the presence of acceptor comonomers (i.e., N-substituted maleimide). The copolymers were synthesized by nitroxide-mediated polymerization using the commercially available alkoxyamine BlocBuilder MA. This technique allowed synthesis of copolymers with controlled molecular weights and molecular weight distributions for all monomers. Moreover, a beneficial effect of the donor substituents on the sequence-controlled copolymerization was noted. Indeed, all studied styrenic derivatives led to a very precise incorporation of functional N-substituted maleimides in the copolymer chains. The most favorable donor/acceptor copolymerization was observed with 4-tert-butoxystyrene. This particular monomer was therefore tested in the presence of various functional N-substituted maleimides (i.e., N-benzyl maleimide, 4-(N-maleimido) azobenzene), N-(1-pyrenyl)maleimide, and N-(2-(amino-Boc)ethylene)maleimide). In all cases, sequence-controlled microstructures were obtained and characterized. Moreover, the formed copolymers were hydrolyzed into poly(4-hydroxystyrene-co-N-substituted maleimide) derivatives. In all cases, it was verified that the sequence-controlled microstructure of the copolymers is preserved after hydrolysis.
Sequence-controlled semicrystalline copolymers were prepared by nitroxide-mediated copolymerization of a large excess of octadecylstyrene with small amounts of functional N-substituted maleimides (i.e., N-(n-propyl)maleimide, Nbenzylmaleimide, pentafluorophenyl 4-maleimidobenzoate, 4-(N-maleimido)azobenzene, N-(1-pyrenyl)maleimide, and N-(2-(amino-BOC)ethylene)maleimide). These copolymers were prepared in bulk at 110 °C using the commercial alkoxyamine BlocBuilder MA as initiator and control agent. Time-controlled additions protocols were used to place the N-substituted maleimides at precise chain location along the poly(octadecylstyrene) backbones. Size exclusion chromatography and 1 H NMR studies indicated that well-defined copolymers with controlled monomer sequences, composition, chain length, and molecular weight distribution were formed in all cases. Although possessing an atactic backbone, these polymers exhibit a semicrystalline behavior. The electron diffraction method indicated that the octadecyl side chains form lamellar phases. Moreover, differential scanning calorimetry studies evidenced a melting temperature in the range 40−45 °C and a crystallization temperature around 30−35 °C. It was observed that melting is influenced by the composition and sequence distribution of the copolymers. Thus, small microstructural variations allow a precise control over order−disorder transitions.
Copolymers containing water-soluble poly(ethylene glycol) (PEG) side chains and precisely controlled functional microstructures were synthesized by sequence-controlled copolymerization of donor and acceptor comonomers, that is, styrene derivatives and N-substituted maleimides. Two routes were compared for the preparation of these structures: a) the direct use of a PEG-styrene macromonomer as a donor comonomer, and b) the use of an alkyne-functionalized styrenic comonomer, which was PEGylated by copper-catalyzed alkyne-azide cycloaddition after polymerization. The latter method was found to be the most versatile and enabled the synthesis of high-precision copolymers. For example, PEGylated copolymers containing precisely positioned fluorescent (e.g. pyrene), switchable (e.g. azobenzene), and reactive functionalities (e.g. an activated ester) were prepared.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.