Syntheses of diblock copolymers of
isobutylene (IB) with amino
acid-based monomers were carried out by a combination of living carbocationic
and reversible addition–fragmentation chain transfer (RAFT)
polymerizations. Cationic
polymerization of IB followed by hydroboration oxidation produced
hydroxyl end-capped polyisobutylene, which was subsequently converted
into macro-chain-transfer agent (macro-CTA) for the RAFT polymerization
of tert-butyloxycarbonyl (Boc)-protected amino acid-based
monomers such as Boc-l-alanine methacryloyloxyethyl ester
(Boc-l-Ala-HEMA) and Boc-l-leucine methacryloyloxyethyl
ester (Boc-l-Leu-HEMA). The block length and molecular weight
could be controlled while maintaining a narrow molecular weight distribution.
These block copolymers form core–shell type micellar structure
in methanola good solvent for side-chain amino acid block
but bad solvent for polyisobutylene segment. Specific rotation and
circular dichroism (CD) studies indicated the chiral nature of the
block copolymers and revealed that they adopt a stable helical conformation
with predominantly one-handed screw sense in acetonitrile. Removal
of the Boc groups under acidic conditions gave pendant side chain
primary amino groups, and all the block copolymers exhibited “smart”
pH responsiveness and amphiphilic character in aqueous media as confirmed
by 1H NMR, fluorescence spectroscopy, dynamic light scattering
(DLS), atomic force microscopy (AFM), and scanning electron microscopy
(SEM). Block copolymers carrying primary amine groups as pendants
can be useful for postpolymerization modification to prepare other
PIB containing functional materials.
Poly(n-hexyl isocyanate)s (PHICs) with
chiral
moieties at both ends of their polymeric chains were synthesized by
living anionic polymerizations. Such
PHICs were synthesized using a bidirectional initiator (sodium naphthalenide
(Na-Naph)) and terminated with a chiral acid chloride, (S)-2-acetoxypropionyl chloride ((S)-Ct). Na-Naph created a covalent linkage in the middle of the chains
by radical–radical coupling. PHICs containing a chiral moiety
at both ends adopted conformations with an opposite helical sense
in comparison with those PHICs that had the same chiral moiety at
only one end of their chain. By observing these structural differences,
it was hypothesized that such a “helicity inversion”
occurred in the PHICs due to the covalent linkage in the middle of
the chain. Therefore, to prove this assumption about helicity inversion,
a comparison study of the helical behaviors between the PHIC with
the chiral moiety at both ends and the PHIC with the chiral moiety
at only one end was performed. The synthesized PHICs were characterized
using size exclusion chromatography-multiangle laser light scattering
(SEC-MALLS), MALDI-TOF mass spectrometry, NMR spectrometry, and circular
dichroism (CD).
We report for the first time the conformational and structural details of peptide-mimic poly(n-hexyl isocyanate) (PHIC). PHIC is a representative poly(n-alkyl isocyanate)s, which have received significant attention because of their unique stiff chain characteristics and potential applications in various fields. A well-ordered hexagonal close packing structure of PHIC with 8 3 helical conformation was clearly observed in the nanoscale thin films that were selectively annealed with carbon disulfide (CS 2 ). A well-ordered multi-bilayer structure of the polymer with b-sheet conformation was also clearly formed in the films that were selectively annealed with toluene. In addition, a fully reversible transformation between these two self-assembled structures was demonstrated by consecutive annealings with CS 2 and toluene.
Poly(n-hexyl isocyanate) (PHIC) with varying molecular weights were synthesized using a chiral initiator and chiral terminator by living anionic polymerization. In such PHICs, chirality of the initiator plays a decisive role in determining the helical sense of the entire polymeric chain, whereas chirality of the terminator plays a supportive role.
Poly(n-hexyl isocyanate) was synthesized by anionic polymerization using various oxy-initiators, including sodium phenoxide (Na-PO), sodium benzhydroxide (Na-BH), and sodium methoxyphenylethoxide (Na-MPE). We optimized polymerization conditions. To confirm the living natures of the polymerization, we carried out various polymerizations changing mole ratio between monomers and initiators and a postpolymerization by sequential monomer addition method. Our results indicated that the anionic polymerization of n-hexyl isocyanate was not controlled using Na-PO and Na-MPE. However, Na-BH as an initiator is favorable for the living anionic polymerization of n-hexyl isocyanate because it has a dual function in the initiation and in the efficient prevetion of trimerization by reducing the reactivity at the growth chain ends. Polymers were thus synthesized with predictable molecular weights (MW), narrow molecular weight distributions (MWD), and high yields.
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.