Abstract
In nature, a sapling can grow into a big tree under irradiation of sunlight. In chemistry, a similar concept that a small molecule only exposing to sunlight grows into a hyperbranched macromolecule has not been realized by now. The achievement of the concept will be fascinating and valuable for polymer synthesis wherein sunlight is inexpensive, abundant, renewable, and nonpolluting. Herein, we report a new strategy in which small monomers can directly grow into big hyperbranched macromolecule under irradiation of sunlight without any catalyst.
Highlights
In nature, a sapling can grow into a big tree under irradiation of sunlight
The thiol can be activated into thiyl radical(3) by sunlight[22,23], and the radical attacks an alkyne to form an intermediate(4) with an alkene group, an alkyene group, and a thiol group
The alternate thiol-yne and thiol-ene click reactions should eventually produce a hyperbranched polymer with a larger number of peripheral alkyne groups and 100% degree of branching if the formed alkene groups always have much higher reactivity than the remained alkyne groups regardless of the factors of concentration and steric hindrance
Summary
A sapling can grow into a big tree under irradiation of sunlight. In chemistry, a similar concept that a small molecule only exposing to sunlight grows into a hyperbranched macromolecule has not been realized . Some significant progresses in photosynthesis are to employ photo-catalysts with good abilities of absorbing visible light for sensitizing organic molecules to achieve photochemical reactions or photo-polymerizations[7,8,9,10,11,12,13,14,15,16,17,18]. Inspired from nature, we report a novel sunlight-activated thiol-yne and thiol-ene strategy to produce hyperbranched polymers from rationally-designed small molecules. The molecules containing both thiols and alkyne or alkene groups are in situ generated from ring-opening of alkyne or alkene -containing thiolactone monomers by amino monomers. The thiols are activated into thiyl radicals under irradiation of sunlight, and the thiyl radicals react with alkyne or alkene groups to obtain the hyperbranched polymers
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