We
report here the synthesis of a novel substituted polyvalerolactone
from the renewable monomer, 4-carbomethoxyvalerolactone (CMVL, two steps from malic acid). The polymerization proceeds to high
equilibrium monomer conversion to give the semicrystalline carbomethoxylated
polyester with low dispersity. The material displays a glass transition
temperature of −18 °C and two melting temperatures at
68 and 86 °C. This polymer can be chemically recycled by either
of two independent pathways. The first (red) cleanly returns CMVL by a backbiting depolymerization from the hydroxy terminus;
the second (blue) uses a base to cleave the polyester in a retro-oxa-Michael
fashion. This affords a methacrylate-like monomer that we have polymerized
radically to a new polymethacrylate analogue. This is a rare example
of a polymer that has been shown to have two independent chemical
recycling pathways leading to two different classes of monomers.
A trifunctional aziridine linker, trimethylolpropane tris(2-methyl-1-aziridinepropionate) (TTMAP), was melt blended with linear poly(lactic acid) (PLA) to make (i) star-shaped PLA and (ii) long chain branched (LCB) PLA by utilizing both pyromellitic dianhydride (PMDA) and TTMAP. Mixing torque evolution during melt processing revealed high reactivity of TTMAP with the carboxyl end group on PLA and low reactivity of PMDA with the hydroxyl end group. Star-shaped PLA exhibited higher viscosity than linear PLA, but no strain hardening in extensional flow; while LCB PLA showed significant extensional hardening. The strain rate dependence of extensional hardening coefficient indicated that concentration of LCB molecules in LCB PLA is low and the possible topological chain structure of those molecules is H-shaped. Unlike current methods used to branch PLA, (e.g., free radical chemistry or the use of an epoxy functional oligomers), our branching strategy produced strain hardening with less increase in shear viscosity. The topological structures of LCB chains by free radical chemistry and epoxy functional oligomers are also discussed.
We report the cationic ring-opening homo- and copolymerization of the 7-membered exocyclic hemiacetal ester 7-methoxyoxepan-2-one (MOPO) to afford poly(7-methoxyoxepan-2-one) [poly(MOPO)] and its copolymers with isobutyl vinyl ether (IBVE).
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