Stereo-defects present in stereo-regular polymers often diminish thermal and mechanical properties, and hence suppressing or eliminating them is a major aspirational goal for achieving polymers with optimal or enhanced properties. Here, we accomplish the opposite by introducing controlled stereo-defects to semicrystalline biodegradable poly(3-hydroxybutyrate) (P3HB), which offers an attractive biodegradable alternative to semicrystalline isotactic polypropylene but is brittle and opaque. We enhance the specific properties and mechanical performance of P3HB by drastically toughening it and also rendering it with the desired optical clarity while maintaining its biodegradability and crystallinity. This toughening strategy of stereo-microstructural engineering without changing the chemical compositions also departs from the conventional approach of toughening P3HB through copolymerization that increases chemical complexity, suppresses crystallization in the resulting copolymers, and is thus undesirable in the context of polymer recycling and performance. More specifically, syndio-rich P3HB (sr-P3HB), readily synthesized from the eight-membered mesodimethyl diolide, has a unique set of stereo-microstructures comprising enriched syndiotactic [rr] and no isotactic [mm] triads but abundant stereo-defects randomly distributed along the chain. This sr-P3HB material is characterized by high toughness (U T = 96 MJ/m 3 ) as a result of its high elongation at break (>400%) and tensile strength (34 MPa), crystallinity (T m = 114 °C), optical clarity (due to its submicron spherulites), and good barrier properties, while it still biodegrades in freshwater and soil.
Biodegradable polyhydroxyalkanoate (PHA) homopolymers and statistical copolymers are ubiquitous in microbially produced PHAs, but the step-growth polycondensation mechanism the biosynthesis operates on presents a challenge to access welldefined block copolymers (BCPs), especially higher-order tri-BCP PHAs. Here we report a stereoselective-chemocatalytic route to produce discrete hard−soft−hard ABA all-PHA tri-BCPs based on the living chain-growth ring-opening polymerization of racemic (rac) 8-membered diolides (rac-8DL R ; R denotes the two substituents on the ring). Depending on the composition of the soft B block, originated from rac-8DL R (R = Et, n Bu), and its ratio to the semicrystalline, high-melting hard A block, derived from rac-8DL Me , the resulting all-PHA tri-BCPs with high molar mass (M n up to 238 kg mol −1 ) and low dispersity (Đ = 1.07) exhibit tunable mechanical properties characteristic of a strong and tough thermoplastic, elastomer, or a semicrystalline thermoplastic elastomer.
While hydrocarbon solvents such as alkanes are ineffective
in extraction
of polar substances such as phenols from water, polymeric alkanes
such as poly(α-olefin)s (PAOs) when modified with phase-anchored
hydrogen bond-accepting polyisobutylene (PIB) additives can be designed
so that these hydrocarbon solvent systems efficiently extract many
phenols from water. Phenols such as bisphenol-A (BPA), 4-chlorophenol,
2,4-dichlorophenol, 2-naphthol, and alkyl- or aryl-substituted phenols
are sequestered from water with >95% efficiency. For example, using
a PIB oligomer with imidazole as a terminal group as an additive at
a concentration of 0.1 M in a PAO that is a hydrogenated trimer of
1-decene (PAO432), >99% of the BPA present in an aqueous
solution of deionized water containing 200 mg of BPA/L of water is
extracted into the PAO phase. With PIB-imidazole in PAO432 at 0.6 or 1.0 M, an array of other chlorinated, brominated, and
alkylated phenols, which were typically initially present between
200 and 500 mg/L water, were additionally extracted with >95% efficiency.
Using 0.3 M PIB-imidazole in PAO432, other bisphenols such
as phenolphthalein and fluorescein at concentrations of ca. 3 mg/L
in water could be reduced to concentrations of <20 or 2 μg/L,
respectively. While very polar phenols with methoxy, hydroxy, and
amino substituents are less efficiently extracted, most of these phenols
could ultimately be extracted and sequestered with >80% efficiency.
PAO432/PIB-imidazole phases that contain sequestered phenol
can be recycled by mixing the PAO phase with solid NaOH. This regenerates
the starting PAO432/PIB-imidazole mixture. Recycling of
these nonvolatile PAO solvent systems for at least five cycles is
described. Substituted imidazoles bound to PIB were also shown to
be similarly effective sequestering agents for phenols.
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