Enantiomeric Block Copolymers Research Articles

Synthesis and properties of multi-armed enantiomeric polylactide-polycaprolactone block copolymers

The degradability of degradable polymers is the most important property to determine the lifetime of commercial applications. To control degradation rate and thermal properties, enantiomeric block copolymers with lactide and hydroxyl terminated multi-armed polycaprolactone were synthesized. Thermal properties of various copolymers were determined by DSC and TGA measurements and the morphological changes during enzymatic degradation were identified by atomic force microscopy. The rate of enzymatic degradation of copolymers was faster than that of each homopolymer while the formation of the stereocomplex between the enantiomeric PLAs (L, D type) resulted in the improvement of thermal properties and retardation of enzymatic degradation.

Strengthening of hydrogels made from enantiomeric block copolymers of polylactide (PLA) and poly(ethylene glycol) (PEG) by the chain extending Diels–Alder reaction at the hydrophilic PEG terminals

Mixtures of furan (F)-terminated AB diblock copolymer of F-PEG-PLA and ABA triblock copolymer of PLA-PEG-PLA (PEG: poly(oxyethylene), PLA: poly(l-lactide) (PLLA) or poly(d-lactide) (PDLA) depending on the enantiomeric block chain) having different compositions were readily synthesized by ROP of l- and d-lactides using partially furanylated PEGs as the macro initiators. Mixed micelle solutions of the enantiomeric copolymer mixtures (F-PEG-PDLA/PDLA-PEG-PDLA + F-PEG-PLLA/PLLA-PEG-PLLA) were prepared in the presence and absence of a coupling agent 1,8-bis(maleimido)diethylene glycol (BMG). Both the BMG-free and BMG-added mixed micelle solutions underwent sol–gel transition, and in which the gel strength was found to become much higher in the BMG-added micelle solutions, reaching a level of 11 kPa. These hydrogel systems were thought to be controlled by the dual cross-linking mechanisms for the gel formation: stereocomplex formation between the enantiomeric PLA blocks and Diels–Alder coupling of the furanyl terminals on PEG blocks with BMG. These sol–gel systems producing strengthened gels are versatile for use as injectable scaffolds in the tissue engineering.

Synthesis and properties of stereo mixtures of enantiomeric block copolymers of polylactide and aliphatic polycarbonate

AbstractABA triblock copolymers of polylactides (PLA: A) and aliphatic polycarbonates (APC: B) were prepared by ring‐opening polymerization of d‐ and l‐lactides with poly(hexamethylene carbonate) diol and poly(hexamethylene/pentamethylene carbonate) diol (PHPC) as macro‐initiators. The enantiomeric copolymers with similar block sequences (PLLA‐APC‐PLLA and PDLA‐APC‐PDLA) were mixed in a 1:1 weight ratio to form a stereocomplex of PLA blocks. The resultant stereo mixtures were found to be more thermally stable (up to 200 °C) than the single block copolymers. Polymer films of the stereo mixtures PLLA‐PHPC‐PLLA/PDLA‐PHPC‐PDLA exhibited higher elongation and lower modulus. It was therefore evident that the present enantiomeric block copolymer system can be applicable as a novel thermoplastic elastomer that is environmentally friendly in terms of its biobased nature and the use of carbon dioxide as feedstock. © 2014 Society of Chemical Industry

Thermoplastic elastomers based on poly(lactide)–poly(trimethylene carbonate-co-caprolactone)–poly(lactide) triblock copolymers and their stereocomplexes

Triblock copolymers of poly(l-lactide)–poly(trimethylene carbonate-co-caprolactone)–poly(l-lactide) and poly(d-lactide)–poly(trimethylene carbonate-co-caprolactone)–poly(d-lactide) were prepared by sequential ring-opening polymerizations. These polymers are thermoplastic elastomers (TPEs) with good tensile properties and excellent resistance to creep. In equimolar blends of these enantiomeric copolymers, stereocomplexation between the enantiomeric poly(lactide) segments occurs. Due to the enhanced phase separation, the specimens of stereocomplex have even better resistance to creep than the enantiomeric block copolymers.

Chiroptical Properties of Homopolymers and Block Copolymers Synthesized from the Enantiomeric Monomers N-Acryloyl-L-Alanine and N-Acryloyl-D-Alanine Using Aqueous RAFT Polymerization

Chiral homo- and block copolymers based on the enantiomeric monomers N-acryloyl-l-alanine (ALAL) and N-acryloyl-d-alanine (ADAL) were prepared directly in water using controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymerization of the chiral monomers proceeded in a controlled fashion producing the respective homopolymers, block copolymers, and a statistical copolymer with targeted molecular weights and narrow molecular weight distributions. The chiroptical activity of these biomimetic polymers and their analogous model compounds was investigated using circular dichroism (CD). P(ALAL) and P(ADAL) were shown to be optically active exhibiting mirror image CD spectra. In addition, statistical and enantiomeric block copolymers prepared at 1:1 stochiometric ratios exhibited virtually no optical activity.

Stereocomplex formation in enantiomeric diblock and triblock copolymers of poly (ε-caprolactone) and polylactide

Enantiomeric diblock and triblock copolymers from caprolactone and lactide with various compositions were synthesized using alcohol/tin octoate as initiator system. Stereocomplexes were formed between pairs of enantiomeric block copolymers and their thermal properties examined. The melting temperatures of the crystalline PCL and PLA phases are depending on the composition of block copolymers. A raise of approximately 55°C of the temperature of PLA phase is observed in the blends as a consequence of stereocomplex formation as well in diblock as in triblock copolymers.