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Block polyester copolymers by ring opening polymerization employing new catalysts

a novel Mg-based catalyst and method for PLA polymerization. The method is an easy “one-pot” process, is very fast, and allows for the manufacturing of complex PLA polymers with 5 and 6 blocks vs. the commonly available 2 and 3 blocks. This in turn, allows for improved characteristics of the PLA polymers.

The Technology

Poly(lactic acid) (PLA) is a biodegradable polymer prepared by the catalyzed ring opening polymerization of lactide. An ideal catalyst should enable a sequential polymerization of the lactide enantiomers to afford stereoblock copolymers with predetermined number and lengths of blocks. The invention includes a magnesium based catalyst that combines very high activity with a true-living nature, which gives access to PLA materials of unprecedented microstructures.

Full consumption of thousands of equivalents of L-LA within minutes gave PLLA of expected molecular weights and narrow molecular weight distributions. Precise PLLA-b-PDLA diblock copolymers having block lengths of up to 500 repeat units were readily prepared within 30 min, and their thermal characterization revealed a stereocomplex phase only with very high melting transitions and melting enthalpies. The one pot sequential polymerization was extended up to precise hexablocks having ‘dialed-in’ block lengths.

The Need

Poly(lactic acid) (PLA) is a plastic material derived from annually-renewable resources, which decomposes post-consumption to non-toxic materials. PLA is produced by the catalysed ring opening polymerization (ROP) of lactide.

PLA is attracting considerable current interest and has found various commodity (packaging, fibres, etc.) and biomedical (sutures, stents, tissue engineering, drug release) applications. The most advanced microstructural varieties of PLA are block-copolymers, such as stereo-diblock PLLA-PDLA, or PEG-PLLA that may offer higher tensile strength and melting temperature, or controlled rate of drug release, respectively. Substantial worldwide effort is dedicated to the development of methodologies that would enable the fabrication of PLA block-copolymers of precise microstructures, since these are expected to be suitable for various advanced applications. Yet, the potential of PLA-based materials is far from being fully exploited, since the ability of the current technology to produce precise as well as sophisticated block-copolymers is limited.

Applications

The technology may have significant impact on a wide array of applications from cheaper and more durable utensils and packages, to larger penetration in the automotive and HW markets, as well biomedical application such as drug delivery, tissue engineering and bio-degradable bone implants.

Advantages

  • Using of nontoxic and bio-compatible metals; such as zinc magnesium and calcium
  • Method that leads to stereo-regular polymers of the desired isotactic-type,  and fine tuning of catalyst performance by variations of the ligand structure and the metal
  • Using of metal complexes in catalysis process adding more control to the catalysis process, in addition of high activity and appreciable stereo-selectivity

Patents

2 PCT applications were filed: PCT/IL2017/050161 published as WO2017/137990 and PCT/IL2017/050735 as WO2018/002941.