Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-01-22
2003-01-28
Truong, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S373000, C525S212000, C525S222000, C525S535000
Reexamination Certificate
active
06512081
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the synthesis of dithioesters which can be utilized in a free radical polymerization process with characteristics of a living polymerization. The diothioesters may be monomeric, oligomeric or polymeric. The invention also relates to processes for the synthesis of polymers utilising these dithioesters.
There is increasing interest in methods for producing a variety of polymers with control of the major variables affecting polymer properties. Living polymerizations provide the maximum degree of control for the synthesis of polymers with predictable well defined structures. The characteristics of a living polymerization are discussed by Quirk and Lee (
Polymer International
27, 359 (1992)) who give the following experimentally observable criteria:
“1. Polymerization proceeds until all of the monomer has been consumed. Further addition of monomer results in continued polymerization.
2. The number average molecular weight (or the number average degree of polymerization) is a linear function of conversion.
3. The number of polymer molecules (and active centers) is a constant which is sensibly independent of conversion.
4. The molecular weight can be controlled by the stoichiometry of the reaction.
5. Narrow molecular weight distribution polymers are produced.
6. Block copolymers can be prepared by sequential monomer addition.
7. Chain end-functionalised polymers can be prepared in quantitative yield.”
Thus living polymerization processes can be used to produce polymers of narrow molecular weight distribution containing one or more monomer sequences whose length and composition are controlled by the stoichiometry of the reaction and the degree of conversion. Homopolymers, random copolymers and/or block polymers may be produced with a high degree of control and with low polydispersity.
Syntheses of certain polymers with xanthate or dithiocarbamate end groups from the corresponding disulfides have been described in the literature (see for example, Moad and Solomon “The Chemistry of Free Radical Polymerization”, Pergamon, London, 1995, pp 337-339; Nair and Clouet
J. Macromol. Sci., Rev. Macromol. Chem. Phys.,
1991, C31, 311). Processes have also been described that use these compounds to prepare block copolymers. However, the processes using these compounds are unsuccessful in producing low polydispersity polymers and do not meet many of the criteria for living polymerization as defined above.
WO 98/01478, the entire contents of which is incorporated herein by reference, describes the use of chain transfer agents (CTAs) of the following structure:
in free radical polymerisation processes with living characteristics to provide polymers of controlled molecular weight and low polydispersity.
It has now been found that CTAs of this structure can be prepared in a convenient manner from a single disulphide reagent, or generated in situ in the polymerisation vessel.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a process for the synthesis of dithioesters formula I:
where R is derived from a free radical R. and is selected from the group consisting of optionally substituted alkyl; optionally substituted, saturated, unsaturated or aromatic carbocyclic rings; optionally substituted, saturated, unsaturated or aromatic heterocyclic rings; optionally substituted alkylthio, optionally substituted arylthio; optionally substituted alkoxy; optionally substituted dialkylamino; organometallic species; and polymer chains; R. is a free radical leaving group;
U is independently selected from the group consisting of hydrogen; halogen; and C
1-4
alkyl optionally substituted with one or more substituents independently selected from the group consisting of hydroxy, carboxy, acyloxy, OR″, O
2
CR″ and CO
2
R″;
V is independently selected from the group consisting of hydrogen, halogen, R″, CO
2
H, CO
2
R″, COR″, CN, CONH
2
, CONHR″, CONR
2
″, O
2
CR″ and OR″;
Z is selected from the group consisting of hydrogen, chlorine, optionally substituted alkyl, optionally substituted aryl, optionally substituted alkylthio, optionally substituted alkoxycarbonyl, —CO
2
R″, —CO
2
H, —O
2
CR″, —CONR
2
″, cyano, —[P(═O)(OR″
2
], and —[P(═O)R″
2
];
R″ is independently selected from the group consisting of optionally substituted C
1-18
alkyl, optionally substituted C
2-18
alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted aralkyl, optionally substituted alkaryl, wherein said optional substituents are selected from the group consisting of epoxy, alkoxycarbonyl, aryloxycarbonyl, isocyanato, cyano, silyl, halo and dialkylamino;
and n is 0 or a positive integer,
which process includes contacting a disulphide of the Formula II
with
(i) in the case of n=0, a free radical of the formula R., or
(ii) in the case of n>0, a free radical of the formula R. and at least one monomer of the formula III
R may be selected from any organic group which is derived from the corresponding radical, R., which radical can act as a free radical leaving group. Preferably the radical, R., is capable of initiating free radical polymerisation. Examples of suitable radicals include carbon centred, sulphur centred, and in some circumstances, oxygen or nitrogen centred radicals. Where R is a polymer chain it may be produced by means of free radical polymerisation, or any other means, such as condensation polymerisation.
The term “free radical leaving group” as used herein refers to a group which departs as a free radical during a substitution or displacement reaction.
R may also be derived from a dithioester of formula I generated in situ, or may be derived from an initiating radical or a propagating radical.
Preferably Z is selected to give the C═S bond a high reactivity towards radical addition while not slowing the subsequent rate of fragmentation in the presence of the monomer to the extent that there is an unacceptable retardation of polymerization.
When conducted in the presence of a monomer of formula III the process according to the invention is useful for the preparation of a wide variety of polymer types, including homopolymers, copolymers and block copolymers. Homopolymers may be prepared by using a single monomer of formula III, while copolymers may be prepared by using two or more monomers. Block copolymers may be prepared by contacting a first monomer of formula III with the disulphide of formula II and free radical of formula R. to produce an intermediate homopolymer of formula I, and then contacting the homopolymer with a second monomer of formula III and a free radical of formula R. Further blocks can be add in like manner.
The invention also relates to the used of a disulphide of formula II to provide chain transfer in a free radical polymerization process, and to the use of the disulphide in the preparation of a chain transfer agent of formula I for use in a free radical polymerisation process.
DETAIL OF THE INVENTION
Free radical polymerizations in the presence of chain transfer agents (CTAs) represented by the following structure has been described in Le et al. Int. Patent Appl. WO 98/01478.
Such polymerizations possess the characteristics of a living polymerization in that they are capable of producing polymers of pre-determined molecular weight with narrow molecular weight distribution (low polydispersity), and, by successively adding different monomers, can be used to make block polymers. The process can also be used to produce polymers of more complex architecture, including variously branched homo- and copolymers.
It has now been found that certain materials which are not CTAs of the above structure may nonetheless be utilized as precursor materials to said CTAs and with suitable choice of reaction conditions can be used in a ‘one-pot’ synthesis of CTA and narrow polydispersity polymer.
In particular it has now been found that compounds of Formula II react with free rad
Moad Graeme
Rizzardo Enzio
Thang San Hoa
Bacon & Thomas
E.I. DuPont Nemours and Company
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