Versatile Preparation of Branched Polylactides by Low-Temperature, Organocatalytic Ring-Opening Polymerization in N-Methylpyrrolidone and Their Surface Degradation Behavior

Abstract

We describe how the organocatalytic, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-based lactide ring-opening polymerization can be effectively performed in a very polar solvent, N-methylpyrrolidone (NMP). Due to a low ceiling temperature, this "living" mechanism has been unreported to date, but we here demonstrate that through a combination of low temperature and repeated monomer additions (starve-fed process), this mechanism enables the generation of a plethora of multifunctional homo-and (stereo)block-poly(lactide)s (PLAs) with exquisite control of the molecular weight dispersity (typically Đ < 1.1) and topology (from linear through 4-, 6-, or 8-armed stars and up to ∼140 armed combs). They are scarcely obtainable or inaccessible through more classical synthetic methods due to the poor solubility of multifunctional initiators (polyols) in most organic solvents and monomer melts. In these precisely designed structures, branching significantly altered the nature of the materials' hydrolytic degradation, allowing them to acquire a pronounced surface character (as opposed to the bulk degradation of linear polymers). Finally, we have assessed the amenability of this method to in situ block copolymerization by using the tacticity of PLLA blocks in PLLA-b-PDLLA versus PDLLA-b-PLLA (L-LA polymerized before or after DL-LA) as a sensitive method to detect (stereochemical) defects.

Combined Core Stability and Degradability of Nanomedicine via Amorphous PDLLA-Dextran Bottlebrush Copolymer for Alzheimer’s Disease Combination Treatment

“…The fragment remained more than 90% of its molecular weight after 60 days. It takes months or even years for the PLA- b -PEG copolymer fragments to degrade into small molecules. − …”

Guaiacolate derivatives‐containing sodium complexes as catalysts for l‐lactide polymerization

“…[ 23–25 ] However, for the biological applications of PLA‐based biomaterials, problems such as residual toxic components resulting from the use of toxic metal catalyst in PLA production must be resolved. Suitable alternatives to toxic metal catalysts are organic catalysts [ 26–32 ] or nontoxic metal catalysts, such as group I, [ 33–40 ] group II, [ 41–44 ] group IV, [ 45–49 ] zinc, [ 50–56 ] and aluminum [ 57–62 ] catalysts.…”