Stereocomplexed Functional and Statistical Poly(lactide-carbonate)s via a Simple Organocatalytic System

The stereocomplexation of polylactide (PLA) has been widely relied upon to develop degradable, sustainable materials with increased strength and improved material properties in comparison to stereopure PLA. However, forming functionalized copolymers of PLA while retaining high crystallinity remains elusive. Herein, the controlled ring-opening copolymerization (ROCOP) of lactide (LA) and functionalized cyclic carbonate monomers is undertaken. The produced polymers are shown to remain crystalline up to 25 mol % carbonate content and are efficiently stereocomplexed with homopolymer PLA and copolymers of opposite chirality. Polymers with alkene and alkyne pendent handles are shown to undergo efficient derivatization with thiol–ene click chemistry, which would allow both the covalent conjugation of therapeutic moieties and tuning of material properties

Stereocomplexed Functional and Statistical Poly(lactide-carbonate)s via a Simple Organocatalytic System

The stereocomplexation of polylactide (PLA) has been widely relied upon to develop degradable, sustainable materials with increased strength and improved material properties in comparison to stereopure PLA. However, forming functionalized copolymers of PLA while retaining high crystallinity remains elusive. Herein, the controlled ring-opening copolymerization (ROCOP) of lactide (LA) and functionalized cyclic carbonate monomers is undertaken. The produced polymers are shown to remain crystalline up to 25 mol % carbonate content and are efficiently stereocomplexed with homopolymer PLA and copolymers of opposite chirality. Polymers with alkene and alkyne pendent handles are shown to undergo efficient derivatization with thiol–ene click chemistry, which would allow both the covalent conjugation of therapeutic moieties and tuning of material properties

Isoselective Ring-Opening Polymerization of rac-Lactide From Chiral Takemoto’s Organocatalysts:Elucidation of Stereocontrol

Despite significant advances in organocatalysis, stereoselective polymerization reactions utilizing chiral organocatalysts have received very little attention, and much about the underlying mechanisms remains unknown. Here, we report that both commercially available (R,R)- and (S,S)-enantiomers of chiral thiourea-amine Takemoto’s organocatalysts promote efficient control and high isoselectivity at room temperature of the ring-opening polymerization (ROP) of racemic lactide by kinetic resolution, yielding highly isotactic, semicrystalline and metal-free polylactide (PLA). Kinetic investigations and combined analyses of the resulting PLAs have allowed the stereocontrol mechanism, which eventually involves both enantiomorphic site control and chain-end control, to be determined. Moreover, epimerization of rac-LA to meso-LA is identified as being responsible for the introduction of some stereoerrors during the ROP process

Influence of chain topology (cyclic versus linear) on the nucleation and isothermal crystallization of poly(L-lactide) and poly(D-lactide)

In this paper, ring closure click chemistry methods have been used to produce cyclic c-PLLA and c-PDLA of a number average molecular weight close to 10 kg/mol. The effects of stereochemistry of the polymer chains and their topology on their structure, nucleation and crystallization were studied in detail employing Wide Angle X-ray Scattering (WAXS), Small Angle X-ray Scattering (SAXS), Polarized Light Optical Microscopy (PLOM) and standard and advanced Differential Scanning Calorimetry (DSC). The crystal structures of linear and cyclic PLAs are identical to each other and no differences in superstructural morphology could be detected. Cyclic PLA chains are able to nucleate much faster and to produce a higher number of nuclei in comparison to linear analogues, either upon cooling from the melt or upon heating from the glassy state. In the samples prepared in this work, a small fraction of linear or higher molecular weight cycles was detected (according to SEC analyses). The presence of such “impurities” retards spherulitic growth rates of c-PLAs making them nearly the same as those of l-PLAs. On the other hand, the overall crystallization rate determined by DSC was much larger for c-PLAs, as a consequence of the enhanced nucleation that occurs in cyclic chains. The equilibrium melting temperatures of cyclic chains were determined and found to be 5 ºC higher in comparison with values for l-PLAs. This result is a consequence of the lower entropy of cyclic chains in the melt. Self-nucleation studies demonstrated that c-PLAs have a shorter crystalline memory than linear analogues, as a result of their lower entanglement density. Successive self-nucleation and annealing (SSA) experiments reveal the remarkable ability of cyclic molecules to thicken, even to the point of crystallization with extended collapsed ring conformations. In general terms, stereochemistry had less influence on the results obtained in comparison with the dominating effect of chain topology.“UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13–4E–1726” and “Mineco MAT2014-53437-C2-P”, 'Ministerio de Economia y Competitividad (MINECO), code: MAT2015-63704-P (MINECO/FEDER, UE) and by the Eusko Jaurlaritza (Basque Government), code: IT-654-13. O.C acknowledges financial support from the European Commission and Région Wallonne FEDER program (Materia Nova) and OPTI²MAT program of excellence, by the Interuniversity Attraction Pole Program (P7/05) initiated by the Belgian Science Policy office and by the FNRS-FRFC. OC is Research Associate of the F.R.S.-FNRS. Organic Synthesis and Mass Spectrometry Laboratory thanks F.R.S.-FNRS for the financial support for the acquisition of the Waters QToF Premier and Synapt-G2Si mass spectrometers and for continuing support. Finally, all authors would like to acknowledge Research and Innovation Staff Exchange (RISE) H2020-MSCA-RISE-2017-778092, project BIODEST for promoting cooperation between the Mons team and the UPV/EHU team

How cyclic chain topology can reduce the crystallization rate of Poly(3- hexylthiophene) and promote the formation of liquid crystalline phases in comparison with linear analogue chains

We have studied how cyclic topology affects the crystallization and morphology of π-conjugated poly(3- hexylthiophene) (P3HT) molecules by comparing linear and cyclic analogues for the first time, with three different chain lengths. We employ a range of experimental techniques including wide-angle X-ray scattering (WAXS), polarized light optical microscopy (PLOM), differential scanning calorimetry (DSC) and a combination of Polarized Light Optical Microscopy (PLOM) and Spectroscopy (S). The crystallization and melting points, melting/crystallization enthalpies, and overall crystallization kinetics of cyclic P3HTs are found to be substantially lower than their linear counterparts. The results are explained by the higher rigidity of cyclic molecules, as predicted by density functional theory (DFT) calculations, in the low molecular weight range explored here, in comparison with linear P3HT chains. Additionally, we have found that cyclic P3HT can form liquid crystalline phases above their crystalline melting points and a new crystal form at lower temperatures. PLOM, WAXS, DSC and PLOM/S results indicate that cyclic P3HTs display bipolar and concentric nematic textures that disappear at a well-defined nematic-isotropic transition temperature. Such liquid crystalline textures are completely absent in the linear P3HTs analogues studied here. We conclude that the cyclic topology induces the formation of liquid crystalline phases as the rigid P3HT oligomers can self-assemble above their crystalline melting temperatures.J.M. acknowledges support from the Provincial Council of Gipuzkoa under the program Fellow Gipuzkoa and “Fomento San Sebastián” in the framework program “Retorno del Talento Local” Donostia up! 2016. We acknowledge the help of Dr. Jaime Martín and Ms. Sara Marina with the combined Microscopy/Spectroscopy measurements. J.M. and A.J.M. acknowledge funding by Mineco MAT2017- 83014-C2-1-P project. N.D. and O.C. are grateful to the Science Policy Office of the Belgian Federal Government (PAI 7/5) and to the Belgian FRFC-FNRS (n°2.4508.12). O.C. is Research Associates of the F.R.S.-FNRS. G.L. is grateful to the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2015026). D.W. and A.J.M acknowledge the support from the National Natural Science Foundation of China (51820105005). All authors gratefully acknowledge the support of the EU through the H2020-MSCA-RISE-2017-778092 BIODEST project. Technical and human support provided by IZO-SGI, SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF) is gratefully acknowledged for assistance and generous allocation of computational resources

Stereoselective ROP of rac- and meso-lactides using achiral TBD as catalyst

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a Pm = 0.88, while meso-LA yields heterotactic PLA (Pm ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from a perfect imbrication of both chiral LA and the propagating chiral end-group interacting with the achiral TBD catalyst