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Cyclic and linear poly(L-lactide)s by ring-expansion polymerization with Bu2SnO, Oct2SnO, and Bu2SnS
(2023)
To elucidate the usefulness of commercial Bu2SnO as catalyst for syntheses of linear and/or cyclic polylactides L-Lactide was polymerized in bulk with variation of the LA/Cat ratio, temperature and time. Based on a ring-expansion polymerization (REP) mechanism cyclic polylactides (PLAs) with weight average molecular weights in the range of 200,000–300,000 are obtained at the highest temperature (180 °C). Polymerizations at 150 °C yielded crystalline, mainly cyclic polylactides which, after annealing, showed high melting temperatures (up to 197.5 °C) and high crystallinities (>80%). Polymerization at 120 °C confirmed the trend towards more linear chains with lower temperatures but yielded extended-ring crystals showing a “saw-tooth pattern” in the mass spectra. Oct2SnO gave similar results as Bu2SnO. Bu2SnS proved a sluggish polymerization catalyst, but a good transesterification catalyst in solid PLA.
This article describes the elaboration and characterization of diethylphosphonate-containing polymers coated electrodes as sensors for the detection of heavy metalstraces, by electrochemical impedance spectroscopy. Diethylphosphonate groupswere chosen as heavy metals binding sites. Two different series of polymers bearingthese anchoring groups were synthesized. Whereas the diethylphosphonate groupsare directly incorporated in the aromatic macromolecular chain in some polymers, analiphatic spacer is removing the chelating site from the polymer backbone in others.The influence of the macromolecular structure on the sensing response was studied,especially for the detection of Pb2+,Ni2+,Cd2+and Hg2+. Polymer P6, including thehigher amount of diethylphosphonate groups removed from the polymer chain by ashort alkyl spacer gave the higher sensitivity of detection of lead ions, with a detec-tion limit of 50 pM
For the development of selective and sensitive chemical sensors, we have developed a new family of poly(etherphosphoramide) polymers. These polymers were obtained with satisfactory yields by nucleophilic aromatic polycondensation using isosorbide as green resources, and bisphenol A with two novel difluoro phosphinothioic amide monomers. Unprecedented, the thiophosphorylated aminoheterocycles monomers, functionalized with two heterocyclic amine, N-methylpiperazine and morpholine were successfully obtained by nucleophilic substitution reaction of P(S)–Cl compound. The resulting polymers were characterized by different analytical techniques (NMR, MALDI–ToF MS, GPC, DSC, and ATG). The resulting partially green polymers, having tertiary phosphine sulfide with P–N side chain functionalities along the main chain of polymers are the sensitive film at the surface of a gold electrode for the impedimetric detection of Cd, Ni, Pb and Hg. The bio-based poly(etherphosphoramide) functionalized with N-methylpiperazine modified sensor showed better analytical performance
than petrochemical based polymers for the detection of Ni2+. A detection limit of 50 pM was obtained which is very low compared to the previously published electrochemical sensors for nickel detection.
A comparison of tributyltin chloride, dibutyltin dichloride,and butyltin trichloride as catalysts of ring-opening polymerizations(ROPs) of l-lactides at 160°C in bulk reveals increasing reactivity in the above order, but only the least reactive catalysts, Bu3SnCl, yield a uniform reaction product, namely cyclic poly(L-lactide)s with weight average molecular weights (Mw ́s) in the range of 40,000–80,000. A comparison of dimethyltin , dibutyltin , and diphenyltin dichlorides resulted in the following order of reactivity: Me2SnCl2<Bu2SnCl2<<Ph2SnCl2. In this series also, the most reactive catalyst yields cyclic polylactides, but the extent of cyclization varies with the molecular weight. The formation of cyclic polylactides is explained by ROP combined with simultaneous polycondensation involving end-to-end cyclization (ROPPOC method). ROP of meso-lactide at 80 or 60°C yields even-numbered linear chains as main products, a result supporting the ROPPOC mechanism.
Five new catalysts are prepared from dibutyltin oxide and catechol (HCa),
2,3-dihydroxynaphthalene (NaCa), 4-tert-butyl catechol (BuCa), 4-cyano
catechol (CyCa), and 4-benzoyl catechol (BzCa), but only BuCa gives useful
results. When benzyl alcohol is used as an initiator, linear chains having
benzyl ester end groups are formed in a slow polymerization process. In
contrast to cyclic or noncyclic dibutyltin bisalkoxides, neat BuCa yields
cyclic poly(l-lactide)s via a fast ring-expansion polymerization. Under certain
conditions, a high-melting crystalline phase (Tm = 191 °C) is obtained.
At 160 °C and short reaction times even-numbered cycles are slightly
prevailing, but, surprisingly, at 120 °C, odd-numbered cycles are predominantly
formed. These results definitely prove that a ring-expansion mechanism
is operating.