Atom or group transfer radical polymerization

Details Atom or group transfer radical polymerization Atom or group transfer radical polymerization

1998-02-04

2003-03-25

Wu, David W. (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S090000, C526S328000, C526S347000, C526S332000, C526S347200, C526S348000

Reexamination Certificate

active

06538091

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns novel (co)polymers and a novel radical polymerization process based on transition metal-mediated atom or group transfer polymerization (“atom transfer radical polymerization”).
2. Discussion of the Background
Living polymerization renders unique possibilities of preparing a multitude- of polymers which are well-defined in terms of molecular dimension, polydispersity, topology, composition, functionalization and microstructure. Many living systems based on anionic, cationic and several other types of initiators have been developed over the past 40 years (see O. W. Webster,
Science
, 251, 887 (1991)).
However, in comparison to other living systems, living radical polymerization represented a poorly answered challenge prior to the present invention. It was difficult to control the molecular weight and the polydispersity to achieve a highly uniform product of desired structure by prior radical polymerization processes.
On the other hand, radical polymerization offers the advantages of being applicable to polymerization of a wide variety of commercially important monomers, many of which cannot be polymerizediby other polymerization processes. Moreover, it is easier to make random copolymers by radical polymerization than by other (e.g., ionic) polymerization processes. Certain block copolymers cannot be made by other polymerization processes. Further, radical polymerization processes can be conducted in bulk, in solution, in suspension or in an emulsion, in contrast to other polymerization processes.
Thus, a need is strongly felt for a radical polymerization process which provides (co)polymers having a predetermined molecular weight, a narrow molecular weight distribution (low “polydispersity”), various topologies and controlled, uniform structures.
Three approaches to preparation of controlled polymers in a “living” radical process have been described (Greszta et al,
Macromolecules
, 27, 638 (1994)). The first approach involves the situation where growing radicals react reversibly with scavenging radicals to form covalent species. The second approach involves the situation where growing radicals react reversibly with covalent species to produce persistent radicals. The third approach involves the situation where growing radicals participate in a degenerative transfer reaction which regenerates the same type of radicals.
There are some patents and articles on living/controlled radical polymerization. Some of the best-controlled polymers obtained by “living” radical polymerization are prepared with preformed alkoxyamines or are those prepared in situ (U.S. Pat. No. 4,581,429; Hawker,
J. Am. Chem. Soc
., 116, 11185 (1994); Georges et al, WO 94/11412; Georges et al,
Macromolecules
, 26, 2987 (1993)). A Co-containing complex has been used to prepare “living” polyacrylates (Wayland, B. B., Pszmik, G., Mukerjee, S. L., Fryd, M.
J. Am. Chem. Soc
., 116, 7943 (1994)). A “living” poly(vinyl acetate) can be prepared using an Al(i-Bu)
3
: Bpy,:TEMPO initiating system (Mardare et al,
Macromolecules
, 27, 645 (1994)). An initiating system based on benzoyl peroxide and chromium acetate has been used to conduct the controlled radical polymerization of methyl methacrylate and vinyl acetate (Lee et al,
J. Chem. Soc. Trans. Faraday Soc. I
, 74, 1726 (1978); Mardare et al,
Polym. Prep
. (
ACS
), 36(1) (1995)).
However, none of these “living” polymerization systems include an atom transfer process based on a redox reaction with a transition metal compound.
One paper describes a redox iniferter system based on Ni(0) and benzyl halides. However, a very broad and bimodal molecular weight distribution was obtained, and the initiator efficiency based on benzyl halides used was about 1-2% or less (T. Otsu, T. Tashinori, M. Yoshioka,
Chem. Express
1990, 5(10), 801). Tazaki et al (
Mem. Fac. Eng
., Osaka City Univ., vol. 30 (1989), pages 103-113) disclose a redox iniferter system based on reduced nickel and benzyl halides or xylylene dihalides. The examples earlier disclosed by Tazaki et al do not include a coordinating ligand. Tazaki et al also disclose the polymerization of styrene and methyl methacrylate using their iniferter system.
These systems are similar to the redox initiators developed early (Bamford, in
Comprehensive Polymer Science
, Allen, G., Aggarwal, S. L., Russo, S., eds., Pergamon: Oxford, 1991, vol. 3, p. 123), in which the small amount of initiating radicals were generated by redox reaction between (1) RCHX
2
or RCX
3
(where X=Br, Cl) and (2) Ni(0) and other transition metals. The reversible deactivation of initiating radicals by oxidized Ni is very slow in comparison with propagation, resulting in very low initiator efficiency and a very broad and bimodal molecular weight distribution.
Bamford (supra) also discloses a Ni[P(OPh)
3
]
4
/CCl
4
or CBr
4
system for polymerizing methyl methacrylate or styrene, and use of Mo(CO)
n
to prepare a graft copolymer from a polymer having a brominated backbone and as a suitable transition metal catalyst for CCl
4
, CBr
4
or CCl
3
CO
2
Et initiators for polymerizing methyl methacrylate. Organic halides other than CCl
4
and CBr
4
are also disclosed. Mn
2
(CO)
10
/CCl
4
is taught as a source of CCl
3
radicals. Bamford also teaches that systems such as Mn(acac)
3
and some vanadium (V) systems have been used as a source of radicals, rather than as a catalyst for transferring radicals.
A number of the systems described by Bamford are “self-inhibiting” (i.e., an intermediate in initiation interferes with radical generation). Other systems require coordination of monomer and/or photoinitiation to proceed. It is further suggested that photoinitiating systems result in formation of metal-carbon bonds. In fact, Mn(CO)
5
Cl, a thermal initiator, is also believed to form Mn—C bonds under certain conditions.
In each of the reactions described by Bamford, the rate of radical formation appears to be the rate-limiting step. Thus, once a growing radical chain is formed, chain growth (propagation) apparently proceeds until transfer or termination occurs.
Another paper describes the polymerization of methyl methacrylate, initiated by CCl
4
in the presence of RuCl
2
(PPh
3
)
3
. However, the reaction does not occur without methylaluminum bis(2,6-di-tert-butylphenoxide), added as an activator (see M. Kato, M. Kamigaito, M. Sawamoto, T. Higashimura,
Macromolecules
, 28, 1721 (1995)).
U.S. Pat. No. 5,405,913 (to Harwood et al) discloses a redox initiating system consisting of Cu
II
salts, enolizable aldehydes and ketones (which do not contain any halogen atoms), various combinations of coordinating agents for Cu
II
and Cu
I
, and a strong amine base that is not oxidized by Cu
II
. The process of Harwood et al requires use of a strong amine base to deprotonate the enolizable initiator (thus forming an enolate ion), which then transfers a single electron to Cu
II
, consequently forming an enolyl radical and Cu
I
. The redox initiation process of Harwood et al is not reversible.
In each of the systems described by Tazaki et al, Otsu et al, Harwood et al and Bamford, polymers having uncontrolled molecular weights and polydispersities typical for those produced by conventional radical processes were obtained (i.e., >1.5). Only the system described by Kato et al (
Macromolecules
, 28, 1721 (1995)) achieves lower polydispersities. However, the polymerization system of Kato et al requires an additional activator, reportedly being inactive when using CCl
4
, transition metal and ligand alone.
Atom transfer radical addition, ATRA, is a known method for carbon-carbon bond formation in organic synthesis. (For reviews of atom transfer methods in organic synthesis, see Curran, D. P.
Synthesis
, 1988, 489; Curran, D. P. in Free
Radicals in Synthesis and Biology
, Minisci, F., ed., Kluwer: Dordrecht, 1989, p. 37; and Curran, D. P. in
Comprehensive Organic Synthesis
, Trost, B. M., Fleming, I., eds., Pergamon: Oxford, 1991, Vol. 4, p. 715.) In a very broad clas

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