Abstract
Several alkali metal salts that activated 18-crown-6 were applied as initiators of β-butyrolactone anionic ring-opening polymerization in tetrahydrofuran at room temperature. Some of them, i.e., Ph2PK, Ph3HBK, (Me3Si)2NK, and t-BuOK, deprotonate the monomer which results in macromolecules with trans-crotonate starting group. Other salts, for example, MeOK, i-PrOK, PhCH2OK, and CbK (Cb denotes carbazolyl group), deprotonate monomer or open its ring in the acyl-oxygen position. After ring-opening KOH forms as intermediate and initiates further polymerization. Ph3CK and monopotassium salt of ethylenediaminetetraacetic acid also deprotonate monomer and open its ring, however, in the alkyl-oxygen position. Monopotassium salts of glycolic acid, diglycolic acid, or malonic acid initiate polymerization mainly by ring opening in the alkyl-oxygen position. It results in the formation of polymers with two reactive terminal groups. The salts used react with the monomer as strong bases, nucleophilic bases, or nucleophiles. It determines unsaturation of the polymers obtained in the wide range of 2–100 mol%.
Highlights
Lactones are important monomers, which are polymerized by ring-opening mechanism giving biodegradable polyesters [1, 2]
Monopotassium salts of glycolic acid, diglycolic acid, malonic acid, and ethylenediaminetetraacetic acid were applied for synthesis of polyfunctional reactive poly(β-butyrolactone)s
The series of signals at m/z 844.9 to 2736.6 represents potassium adduct ions of macromolecules with hydroxyl and methoxycarbonyl end groups. The former formed at the early stage of the polymerization and the latter resulted from quenching of potassium carboxylate end growing species with MeI
Summary
Lactones are important monomers, which are polymerized by ring-opening mechanism giving biodegradable polyesters [1, 2]. Similar effect was observed by Kircheldorf et al [8] for β-butyrolactone (β-BL) polymerization in the presence of the same initiator Contrary to these results, Jedliński et al [12] stated that MeOK and t-BuOK activated with 18-crown-6 (18C6) initiates β-PL and β-BL polymerization exclusively by nucleophilic ring opening in the acyloxygen position. All potassium alkoxides (except t-BuOK), monopotassium salts of carboxylic acids as well as Ph3CK and CbK were synthesized in the reaction of appropriate substrate with KH activated with 18C6 in THF solution at 20 °C. Molar masses and dispersities of polymers were obtained by means of size exclusion chromatography (SEC) on a Shimadzu Prominance UFLC instrument at 40 °C on a Shodex 300 mm × 8 mm OHpac column using tetrahydrofuran as a solvent. Data were acquired in continuum mode until acceptable averaged data were obtained and were analyzed using Shimadzu Biotech Launchpad program
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