Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From protein or biologically active polypeptide reactant
Patent
1995-08-08
1997-02-04
Acquah, Samuel A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From protein or biologically active polypeptide reactant
528361, 527200, 527202, C09J 312
Patent
active
055998917
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB93/02014 filed Sep. 28, 1993.
This invention relates to a polymer composition and in particular to a crystallisable polymer stabilised in an amorphous or incompletely crystalline state and to processes for preparing a such a polymer composition.
In processing a crystallisable polymer it is sometimes desirable to hold it in an amorphous or incompletely crystalline state while particular operations are carried out. Whereas this can be done by melting the polymer and chilling it, or having plasticiser present, or using it as a solution, it would be convenient if the polymer could be amorphous or incompletely crystalline when stored and at the start, or possibly even at the end, of processing.
It has been suggested (Sanders et al. International Symposium on bacterial polyhydroxyalkanoates, University of Gottingen, 1-5 Jun. 1992; de Koning et al. Polymer Communications 1992, 33 (15), 3292-3294) that one such polymer, polyhydroxybutyrate (PHB), when in the form of the microscopic particles in which it is produced in certain microorganism cells, is amorphous and remains amorphous for long periods, because of the rarity of homogeneous nucleation events in discrete single particles and the mutual isolation of the particles. A possible explanation for this behaviour is that native granules or particles are very small, reaching a maximum diameter of about 0.25 .mu.m in Alcaligenes eutrophus or 0.7 .mu.m in Bacillus megaterium. The expected frequency of homogeneous nucleation within a given granule (f) is very low, on the order of 10.sup.-8 events/second or less. Under the most conservative set of assumptions (granule diameter of 1 .mu.m, nucleation rate of 30 events mm.sup.-3 sec.sup.-1), the predicted half-life of amorphous, granular PHB is 4.4.times.10.sup.7 seconds, or 510 days. Using more realistic assumptions (granule diameter 0.25 .mu.m, nucleation rate at 30.degree. C. of 2.5 events mm.sup.-3 sec.sup.-1), the predicted half life is some 3.4.times.10.sup.10 seconds, in excess of 1000 years. By contrast, when the polymer is harvested from the cell, the natural particle coatings are removed, the particles are allowed to collide and possibly coalesce which opens the possibility for heterogenous nucleation or more frequent homogeneous nucleation to occur and rapid crystallisation ensues. Thus a bulk sample of PHB crystallises rapidly to an extent of 50% or more, at ambient temperature, usually in less than an hour.
It is desirable in certain circumstances to be able to maintain the amorphous nature of the polymer for a significant period of time after the polymer is prepared or harvested. Similarly, it may be desirable to rejuvenate crystallised polymer and maintain it in the amorphous or incompletely crystalline state until ready to be used. The applicants have found that it is possible to maintain the amorphous or incompletely crystalline state of the polymer for significant periods of time if the polymer is maintained in the form of small particles each particle with a coating of surfactant or phospholipid.
Thus, according to the present invention there is provided a polymer composition substantially free of cellular protein comprising a crystallisable polymer in the form of particles having a largest dimension in the range of 0.1 to 5 .mu.m and having on their surface a surfactant other than a sugar-based surfactant having a molecular weight less than 2000 other than a sugar-based surfactant having a molecular weight less than 2000 or a phospholipid, said polymer having a molecular weight M.sub.w of over 50000 and having a crystallisation half life of more than 0.1 day at ambient temperature.
The polymer is especially one which is capable of a relatively high level of crystallinity, for example over 30%, especially 50-90%. Such polymers may be biologically or synthetically produced.
Suitable biologically produced polymers typically include at least one biologically produced polyhydroxyalkanoate (PHA) having units of formula I : Typically C.sub.m H.sub.n contains 2-5 carbon ato
REFERENCES:
Koosha et al: "The Surface and Chemical Structure of Poly(beta-hydroxybutarate) Macroparticles Produced by Solvent Evaporation Process", Journal of Controlled Release, vol. 9, No. 2, 1989, pp. 149-157.
Patent Abstracts of Japan, vol. 014, No. 310, (C-0736) Jul. 4, 1990, & JP,A,02 105 826, see abstract.
Clauss Joachim
George Neil
Horowitz Daniel M.
Hunter Brian K.
Sanders Jeremy K. M.
Acquah Samuel A.
Zeneca Limited
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