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Exploring Versatile Sulfhydryl Chemistry in the Chain End of a Synthetic Polylactide
journal contribution
posted on 2012-11-13, 00:00 authored by Mijanur
Rahaman Molla, Suhrit GhoshSynthesis of an end-functionalized polylactide by ring-opening
polymerization of lactide monomer using a functional initiator containing
pyridyl disulfide group is reported. Molecular weight of the polymer
determined by GPC matched very well with that determined by end-group
analysis using the UV/vis method, suggesting survival of the end-group
functionality during polymerization. DTT-induced reduction of the
pyridyl disulfide group produced free sulfhydryl group quantitatively
which was utilized for versatile chain-end modifications using various
thiol-mediated high-yielding chemical transformations including thiol–ene,
thiol–maleimide, and thiol–acrylate “click”
reactions. This strategy was further extended to link two macromolecules
by reaction of sulfhydryl-functionalized polylactide and acrylate-terminated
poly(ethylene oxide) (PEO) which produced a block copolymer with an
acid-labile β-thiopropionate linker between the two constituent
blocks. This functional group could be cleaved under mild acidic condition
to produce the individual parent polymers. Further as-synthesized
pyridyl disulfide-terminated polylactide was treated with thiol-functionalized
sugar moiety and n-type semiconducting naphthalene diimide (NDI) chromophore
which also generated quantitative chain-end functionalization by thiol–disulfide
exchange reaction. NDI-functionalized polylactide showed white light
emission due to mixed emission from monomeric and excimer-type species.
Further atomic force microscopic (AFM) studies revealed NDI-functionalized
polymer formed uniform spherical aggregates upon drying of a drop-casted
film on silicon surface possibly due to solvent-evaporation-induced
defined organization of the polymer chain dictated by strong π-stacking
interaction among the NDI chromophores.
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Exploring Versatile Sulfhydryl ChemistrythiolGPCNDI chromophoresAFMchemical transformationslight emissionpyridyl disulfide groupMolecular weightUVblock copolymerPEOSynthetic PolylactideSynthesispolymerizationpolylactidelactide monomeracidic conditionsilicon surfaceChain Endsulfhydryl grouppolymer chainparent polymersconstituent blocks
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