Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1997-09-22
1999-11-02
Mosley, Terressa
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528176, 528194, C08G 6400
Patent
active
059772913
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to copolyesters and in particular to those having hydroxy acid repeating units.
Polycondensed hydroxyacids, especially those of R-stereospecific configuration made microbiologically, have recently become commercially available. Of these, poly-3-hydroxybutyric acid homopolymer (PHB) is capable of a high level of crystallinity, but melts at the relatively high temperature 174-180.degree. C., at which loss of molecular weight is relatively rapid. Copolymers (PHBV) containing 3-hydroxyvalerate units at eg 3-30 mol percent melt at a lower temperature and are correspondingly more stable during melt-processing, but they crystallise more slowly.
We have now found that the crystallisation behaviour can be influenced favourably by bringing the repeating units together in a special configuration.
ACCORDING TO THE INVENTION a hydroxycarboxylic acid copolyester of R-stereospecific configuration contains a majority of first repeating units capable of forming a highly crystalline high-melting homopolyester and a minority of second repeating units capable when randomly copolycondensed with said first repeating units of lowering the melting point of said homopolyester:
characterised by one or more of the following features: 15.degree. C., than that of the corresponding random copolyester; 0.9, especially less than 0.5, of that of the corresponding random copolyester; of the corresponding random polyester of 20% higher molecular weight; longer than correspond to their over-all molar proportionality.
The repeating units in the copolyesters preferably include the residues of 3-hydroxybutyric acid (HB) and other hydroxy acids especially 4-hydroxybutyric acid (4HB) or 3-hydroxyvaleric acid (HV). Preferably HB units are in a majority, especially at least 70, especially at least 80, for example 70-98 mol percent of the total units. If desired, the minority units may be of more than one chemical formula. Polyesters containing HB and HV units are referred to hereinafter as "PHBV".
The molecular weight of the polyesters is typically in the range 100000 to 2000000, conveniently 150000 to 1000000. It appears that acceptable mechanical properties are obtainable at molecular weights lower than have been necessary when using random copolyesters of a similar over-all chemical composition.
The invention provides also processes for making the copolymers particularly by fermentation, characterised by controlling the distribution of repeating units by reference to the pattern of feeding substrates corresponding to the respective repeating units,
In such a process the following procedures are used: repeating units. Generally a predetermined fraction of the intended consumption of each substrate is fed over a period of time and then withheld until its concentration in the medium is about zero; that is, has fallen to a level between 1% of its maximum fed concentration and the level at which the organism has begun to net-consume its store of polyester. The changeover point may be the same or different for the respective feedstocks. The first feedstock fed may be the majority feedstock or the minority feedstock. The materials actually fed may be chemically 100% of one feedstock or may be a mixture of chemical compounds all producing the same repeating unit, or may be a mixture preponderantly producing one repeating unit but with a small proportion--for example 0.01 to 1.0% w/w producing another. The feed times of each feedstock can be for example in the range 0.5 to 20 h, depending on how great a departure from randomness is required. cell growth is limited; the limiting nutrient is preferably phosphorus, rather than nitrogen but is fed at a concentration permitting a moderate cell growth during polyester lay-down; for the moderate cell growth.
The microorganism used in the fermentation may be any capable of laying down a crystallisable copolyester. When the copolyester is PHBV with PHB in the molar majority, the organism is suitably a bacterium of the genera Alcaliaenes, Athiorhodium, Azotobacter, Bacillus, Nocardia, Pseudo
Cox Michael Kenneth
Hammond Timothy
Wood John Christopher
Bond Gary M.
Monsanto Company
Mosley Terressa
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