Optically Active Precision Aliphatic Polyesters via Cross‐Metathesis Polymerization

Abstract

Precision synthesis of optically active poly(lactic‐alt‐caprolactic acid) is realized using cross‐metathesis polymerization (CMP) and hydrogenation. Enantiopure monomers ML and MD are generated through two consecutive esterification reactions. CMP of these two monomers in different feed ratios, followed by hydrogenation, afford saturated polymers HPL, HPD, and HPDL comprising L‐lactic and/or D‐lactic acid and ε‐caprolactone‐derived motifs with alternating sequences. CMP kinetic analysis by nuclear magnetic resonance (NMR) is performed by employing a racemic monomer Mrac. Enantiomeric polyesters HPL and HPD display opposite rotation values and mirror‐imaged cotton effects in circular dichroism (CD) spectra, whereas HPDL derived from equimolar ML and MD shows inactive optical rotation and no CD response. Stereocomplex HPD+HPL is obtained by equimolar mixing of HPL and HPD, since this specimen is the only one to exhibit a sharp melting peak on differential scanning calorimetry (DSC) curve at 45.7 °C. Hence, an amorphous, enantiomerically pure polyester becomes crystalline via stereocomplexation with its complementary enantiomer.

Discrete and Stereospecific Oligomers Prepared by Sequential and Alternating Single Unit Monomer Insertion

“…12 Most importantly, such polymers have the potential to open new opportunities for the development of advanced materials for data storage, [13][14][15][16] catalysis [17][18] and drug delivery. [19][20][21] Various strategies have been proposed for regulating monomer sequence and chain length of synthetic polymers, including condensation chain polymerization, 22 alternating radical polymerization, [23][24][25][26][27][28][29] anionic polymerization, [30][31] ring-opening or cross metathesis polymerization, [32][33][34] atom transfer radical addition (ATRA), [24][25][35][36][37] iterative exponential growth, [38][39][40][41][42][43] single unit monomer insertion 12,[44][45][46][47][48][49][50] and various organic coupling, condensation or "click" addition reactions. 19,[51][52]...…”

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(lactic acid‐ co ‐alanine)s from the melt

“…Zhan et al studied the effects of incorporated poly( d ‐lactide‐ co ‐ ε ‐caprolactone) up to 20 wt% on the mechanical and thermal stability of PLLA . On the other hand, SC crystallization is reported for LA‐based alternating copolymers of poly( l ‐lactic acid‐ alt ‐6‐hydroxycaproic acid)/poly( d ‐lactic acid‐ alt ‐6‐hydroxycaproic acid) and poly( l ‐lactic acid‐ alt ‐glycolic acid)/poly( d ‐lactic acid ‐alt ‐glycolic acid) blends. Table summarizes the reported studies on the effects of random and alternating copolymerization of l ‐ and d ‐lactic acids with comonomers on SC crystallization.…”

Synthesis and stereocomplex formation of enantiomeric alternating copolymers with two types of chiral centers, poly(lactic acid-alt-2-hydroxybutanoic acid)s

“…On the other hand, SC formation took place in enantiomeric alternating copolymer blends of poly(L-lactic acid-alt-6-hydroxycaproic acid) and poly(D-lactic acid-alt-6-hydroxycaproic acid) 66 and of poly(L-lactic acid-alt-glycolic acid) [P(LLA-alt-GA)] and poly(D-lactic acid-alt-glycolic acid) [P(DLA-alt-GA)]. 67 These enantiomeric alternating copolymers which formed SC had the repeating or monomer units of lactic acid-6-hydroxycaproic acid or 6-hydroxycaproic acid-lactic acid and of lactic acid-glycolic acid or glycolic acid-lactic acid.…”