Process for the preparation of hydrophobic/hydrophile AB...

Details Process for the preparation of hydrophobic/hydrophile AB... Process for the preparation of hydrophobic/hydrophile AB...

1998-12-04

2001-09-04

Niland, Patrick D. (Department: 1714)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S327900, C525S326100, C525S328900, C525S331900, C525S332100, C525S331200

Reexamination Certificate

active

06284847

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process for the preparation of hydrophobic-hydrophilic AB block copolymers as well as to the AB block copolymer synthesized by the preparation process, and to micellar systems made from the AB block copolymer.
DESCRIPTION OF THE PRIOR ART
According to the state of the art, AB block copolymers are already known in which block A contains monomer units a, which are conjugated dienes, such as 1,3-dienes, and block B contains monomer units b, which are epoxides. Due to the incompatibility of blocks A and B, such polymers form microphase-separated systems as solids while, in most solvents, they form micellar structures (=opposite solubility behavior of blocks A and B in polar and nonpolar solvents).
Thus, the article by M. Gervais and B. Gallot in Makromol. Chem. [Macromolecular chemistry] 178, 1577 (1977) and Dutch patent no. 7,308,061 describe a synthesis of block copolymers having the structure AB and ABA, respectively, whereby A is polybutadiene or polyisoprene and B is polyethylene oxide. In this process, the synthesis takes place in a one-pot reaction by means of the successive addition of dienomer and of ethylene oxide to form mono-functional or bi-functional organo-sodium or organo-potassium initiators in tetrahydrofuran (THF) as the polar solvent.
German patent no. 23 22 079 describes the synthesis of an AB block copolymer wherein A is polybutadiene and B is polyethylene oxide. Here, too, the synthesis takes place in a one-pot reaction by means of the consecutive addition of the monomers butadiene and epoxide to the initiator sec-butyl lithium in benzene. Since this initiator is not capable of polymerizing ethylene oxide, after the addition of the epoxide, potassium tert-butanolate is added. As a result, 20% of the epoxide is polymerized. By means of a nickel catalyst, 95 % of the olefinic double bonds are subsequently hydrogenated.
U.S. Pat. No. 4,254,238 describes the synthesis of graft polymers. Here, the initial polymers are polydienes which are produced according to known methods. Through the reaction of the polydienes with diamines and organo-lithium compounds, polymerization-active centers are created on the initial polymer. The addition of epoxide and the subsequent acidification lead to the formation of functional OH groups on the polymer back-bone. OH groups are de-protonated by a reaction with potassium-organic reagents and, through the addition ethylene oxide, poly(ethylene oxide) blocks are grafted.
The syntheses described by M. Gervais and B. Gallot in Makromol. Chem. [Macro-molecular chemistry] 178, 1577 (1977) as well as in Dutch patent no. 7,308,061 exhibit a very high reactivity on the part of the agents, with the result that chain termination occurs or side chains are formed during the reaction. This gives rise to a non-uniform reaction product that contains molecules with molecule blocks A and/or B which have a non-uniform length and which are not linear but rather branched. Accordingly, these syntheses do not permit a control of the reaction in terms of the precise molecular composition of the target compound.
The synthesis described in German patent no. 23 22 079 yields a reaction mixture that contains lithium ions as well as potassium ions. In this mixture, only 20% of the epoxide is grafted onto the polydiene, as a result of which a large amount of unreacted product remains in the polymer, which then requires a complex purification procedure. This proportion of 20%, however, still contains homopolymer fractions, that is to say, polymer fractions which consist only of epoxide monomer fractions, so that, on the one hand, there is contamination with the homopolymer while, on the other hand, less than 20% is grafted onto block A. A considerably larger quantity of initial material has to be used than is actually converted into the desired product, so that this method entails a great deal of reprocessing and high costs, in addition to which it also creates disposal problems.
The reaction described in U.S. Pat. No. 4,254,238 takes place under very aggressive conditions and is consequently very uncontrolled. For example, chains are cleaved. In addition, lithiated tetramethyl ethylene diamine (TMEDA) and unreacted butyl lithium remain in the solution. Among the reaction products, there is also a fraction of homopoly(ethylene oxide), in other words, a polymer that consists exclusively of epoxide units (alkyleneoxy or ring-opened oxirane units). However, as is shown in the article titled “Synthesis and properties of uniform polyisoprene networks. I. Synthesis and characterization of &agr;,&ohgr;-dihydroxy polyisoprene” in the journal Rubber Chemistry and Technology, volume 49, page 303 (1976), the reaction intermediate products, which only contain two —CH
2
—CH
2
—O side chains, precipitate out of the solution while forming complex compounds with metal ions. The result is a non-uniform product that contains a high proportion of unreacted components and by-products.
None of the methods cited is capable of yielding an AB block copolymer whose chemical properties are clearly defined in terms of its linearity and chain length and which is free of by-products. In Dutch patent no. 7,308,061, the blocks A, which are comprised of the monomeric diene, have a mixed structure made up of 1-4-polymer and 1-2-polymer or 3-4-polymer.
SUMMARY OF THE INVENTION
Therefore, the invention is based on the objective of creating a process for the preparation of AB block copolymers with the monomer units a, which are conjugated diene, and the monomer units b, which are epoxide, a process that yields a product whose structure is clearly defined, whereby the chain lengths of the blocks A and B can be selected at will and can be adjusted by means of the reaction conditions, whereby no branching of the product in the form of side effects occurs and whereby no by-products, such as homopolymers A or B, are formed. Moreover, the blocks A can have a very high proportion of 1,4-polymer. The effort involved for the subsequent purification procedure can be minimal. The process is expected to be expensive.
According to this invention, hydrophobic-hydrophilic AB block copolymers are prepared by producing block A in a first reaction step in a non-polar solvent and block B in a second reaction step in a polar solvent. The resulting AB block copolymer is also an aspect of this invention, as are micellar structures prepared from the copolymer.
According to this invention, hydrophobic-hydrophilic AB block copolymers are prepared by producing block A in a first reaction step in a non-polymer solvent and block B in a second reaction step in a polar solvent. The resulting AB block copolymer is also an aspect of this invention, as are micellar structures prepared from the copolymer.
With the process according to the invention, it is now possible to prepare an AB block copolymer whose blocks A and B have clearly defined chain lengths, also with respect to each other. The product does not exhibit any branching caused by side chains. Now, molecules can be tailor-made as desired so as to meet the required specifications in terms of chain length, molecular weight, polarity proportion and viscosity. The conversion of the initial materials is quantitative, and a product can be made whose block A contains approximately 95% of 1,4-addition product. Depending on the requirements, it is no longer necessary to add equivalent amounts of sodium or potassium organyl for the polymerization of the epoxide—or of the OH groups—which is brought about as a result of the addition of one unit of epoxide to block A. Nevertheless, homogenous growth is attained.
The preparation process according to the invention for AB block coploymers will be described in greater detail below.


REFERENCES:
patent: 4254238 (1981-03-01), Foss et al.
patent: 2322079 C2 (1973-11-01), None
patent: WO 95/18164 (1995-07-01), None
Yu et al., “Efficiency of the sec-Butyllithium/m-Diisopropenylbenzene Diadduct as an Anionic Polymerization Initiator in Apolar Solvents.”Macromolecul

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