Process for the polymerization of lactide

Details Process for the polymerization of lactide Process for the polymerization of lactide

1999-10-13

2001-04-10

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S355000, C528S50200C, C528S503000, C525S413000, C525S415000, C525S450000, C264S068000, C264S176100

Reexamination Certificate

active

06214967

ABSTRACT:

FIELD OF INVENTION
The invention relates to a two-step polymerization of lactide to polylactide. The invention in particular relates to a process in the second step of which there is carried out polymerization to a high conversion in conditions in which the mixing of the melt and the evaporation of lactide are avoided.
DISCUSSION OF RELATED ART
In recent years, interest in biodegradable polymers, i.e. biopolymers, has greatly increased, and many companies have made efforts to launch on the market packaging materials, hygiene products, sacks and films for agricultural purposes, and sacks for waste. In particular, various films have gained importance. The use of polymers of lactic acid in these applications has so far been limited by the high price of the polymers and their susceptibility to breaking down during technical processing.
Polyhydroxy acids can be prepared by polycondensation reactions, which are typical in the preparation of polyesters, or by ring-opening polymerization from cyclic lactones. Polyhydroxy acids are thermoplastic polyesters which resemble many conventional polymers.
Polylactides, or condensation polymers based on lactic acid, are for many reasons especially attractive, since their principal degradation product, lactic acid, is a product common in nature, it is not toxic and is used widely in the food and pharmaceutical industries. A high molecular weight polymer can best be produced by ring-opening polymerization from lactide Lactic acid is optically active, and thus its dimer appears in four different forms: L,L-lactide; D,D-lactide; L,D-lactide (mesolactide); and a racemic mixture of L,L- and D,D-lactides. By polymerizing these either as pure compounds or at different blend proportions, polymers are obtained which have different stereochemical structures affecting their resilience and crystallinity and, consequently, also their mechanical and thermal properties. The obtained polymers are usually hard and optically bright.
The ring-opening polymerization of cyclic lactones of hydroxy acids, such as lactide, glycolide, epsilon caprolactone, etc., constitutes technology known per se. The polymerization processes known are various, some examples being patent U.S. Pat. No. 5,378,801 relating to extrusion polymerization, patent publication EP 0 664 309-A relating to two-step polymerization, and patent publication EP 0 499 747-A describing polymerization in a mixing reactor.
It is typical of the prior known art that the residual lactide concentration is high, which hampers the processing of the polymer and, on the other hand, its removal causes additional costs.
SUMMARY OF THE INVENTION
It is an object of the invention to find a method for the polymerization of lactide, preferably to a conversion which is close to the theoretical maximum. The polymerization velocity of lactide depends on many factors, such as the initiator used, the initiator concentration, the polymerization temperature, and the lactide concentration.


REFERENCES:
patent: 5378801 (1995-01-01), Reichert et al.
patent: 5508378 (1996-04-01), Ohara et al.
patent: 0499747 (1992-08-01), None
patent: 0664309 (1995-07-01), None
File WPI, Derwent accession No. 97-061868, Shimadzu Corp: “Prepn. of poly:lactic acid for e.g. drug delivery-by ring opening polymerising lactide, removing unreacted lactide and using in polymerisation”.

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