60/500,609, filed September 5,2003, which is hereby incorporated by reference into the subject application in its entirety.

[0002] The government may have certain rights in the present invention pursuant to a grant from the Department of Energy, Grant No. DE-FG02-97ER14807.

[0003] All patents, patent applications and publications cited herein are hereby incorporated by reference in their entirety. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art as known to those skilled therein as of the date of the invention described and claimed herein.

[0004] Copyright Statement: copyright in the text and graphic materials contained in this disclosure is owned by Columbia University of New York. The materials contained in this disclosure may be used, downloaded, reproduced or reprinted, provided that this copyright notice appears in all copies and provided that such use, download, reproduction or reprint is for noncommercial or personal use only. The materials contained in this disclosure may not be modified in any way.

FIELD OF THE INVENTION [0005] This invention relates to polymerization methods with mononuclear metal hydrides and mononuclear metalloradical chain transfer catalysts.

BACKGROUND OF THE INVENTION [0006] The commercial production of polymers by free radical polymerization is practical only with molecular weight control. High initiator concentrations or high temperatures limit molecular weight, but they are expensive. Techniques involving chain transfer agents are also being developed to control the molecular weight of polymer, but traditional chain transfer agents must be used stoichiometrically. Known chain transfer agents, such as thiols, suffer from several additional disadvantages, including odor problems and broad molecular weight distribution of the polymer, because molecular weight is controlled by termination and reinitiation. Improved chain transfer agents are therefore of interest in the field of polymer chemistry.

[0007] There has recently been much interest in catalytic chain transfer agents, which are additives that cause repeated chain transfer. Chain transfer catalysts avoid the use of thiols and allow the formation of vinyl-terminated polymers and oligomers, which are useful, for example, in the production of macromonomers.

[0008] For a general metalloradical Me the catalytic chain transfer process is demonstrated by reactions 1 and 2, where M-H is the metal hydride derived from the metalloradical M* that reacts with a monomer unit to start a new chain. ktr (g) Chain Transfer 3 4 + C02CH3 Reinitiation [0009] The polymer left after chain transfer (shown in reaction 1) will have a terminal vinyl group, and its molecular weight will be significantly lower than that produced by radical polymerization under the same conditions in the absence of the chain transfer catalyst.

[00010] Accordingly, there is great interest in new and effective chain transfer catalysts, which are useful in commercial processes for free radical polymerization, especially the free radical polymerization of methyl methacrylate. There is also great interest in developing new and effective ways of carrying out free radical polymerization.

SUMMARY OF THE INVENTION [00011] The present invention is directed to polymerization methods, comprising contacting a monomer with at least one mononuclear metal hydride, wherein the metal is selected from the group consisting of chromium, molybdenum, tungsten, vanadium, and iron, or a combination thereof; provided that the mononuclear metal hydride is not (ri5- C5Ph5) Cr (CO) 3H.

[00012] The invention is also directed to polymerization methods, comprising admixing a polymerization intermediate with a chain transfer catalyst, wherein the chain transfer catalyst comprises at least one mononuclear metalloradical, wherein the metal is selected from the group consisting of Cr, Mo, W, V, and Fe, or a combination thereof; provided that the chain transfer catalyst is not (rl5-C5Ph5) Cr (CO) 3*, thereby forming a polymerization product.

DETAILED DESCRIPTION OF THE INVENTION [00013] The present invention is directed to polymerization methods, comprising contacting a monomer with at least one mononuclear metal hydride, wherein the metal is selected from the group consisting of Cr, Mo, W, V, and Fe, or a combination thereof ; provided that the mononuclear metal hydride is not (q5-C5Ph5) Cr (CO) 3H. In one embodiment, the polymerization method occurs in the absence of an initiator.

[00014] In one embodiment, the metal is selected from the group consisting of Cr, Mo, and W, or a combination thereof, and the mononuclear metal hydride is less sterically hindered than a mononuclear pentaphenylcyclopentadienyl metal hydride and is sufficiently sterically hindered to prevent dimerization of the metal.

[00015] In another embodiment, the metal is selected from the group consisting of V, Fe, or a combination thereof, and the mononuclear metal hydride is more sterically hindered than a mononuclear cyclopentadienyl metal hydride and is sufficiently sterically hindered to prevent dimerization of the metal.

[00016] In one embodiment of the present invention, the mononuclear metal hydride is of the formula QxMLyH ; wherein M is selected from the group consisting of Cr, Mo, W, V, and Fe, or a combination thereof; wherein Q is cyclopentadienyl, tris (pyrazolyl) borate, or tetrakis (pyrazolyl) borate, each optionally substituted with aliphatic, aryl, or a combination thereof; each L is independently a ligand; x is 0 or 1 ; and y satisfies the valence of M. In another embodiment, M is Cr. In one embodiment, M is Fe.

[00017] In another embodiment, Q is selected from the group consisting of pentamethylcyclopentadienyl, pentaisopropylcyclopentadienyl, pentaphenylcyclopentadienyl, tris (pyrazolyl) borate, and tris (3,5-dimethylpyrazolyl) borate. In another embodiment, Q is pentamethylcyclopentadienyl.

[00018] In one embodiment, Q is pentamethylcyclopentadienyl and L is a small phosphine.

In another embodiment, Q is pentamethylcyclopentadienyl and L is dppe.

[00019] In another embodiment, the mononuclear metal hydride is selected from the group consisting of (q5-C5Me5) Cr (CO) 3H ; (rl5-C5Me5) Cr (CO) 2 (PMe3) H; (#5-C5Me5)Cr(CO)2(PEt3)H; (#5-C5Me5)Cr(CO)2(P(OMe)3)H; (#5-C5Me5)Cr(CO)2(P(OEt)3)H; (#5-C5Ph5) Cr (CO) 2 (PMe3) H (#5-C5Ph5)Cr(CO)2(PEt3)H; (#5-C5Ph5)Cr(CO)2(P(OMe) 3) H; (#5-C5Ph5)Cr(CO)2(P(OEt)3)H; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 3H; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (PMe3) H; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (PEt3) H; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) H; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) H; (tris (pyrazolyl) borate) Mo (CO) 3H; (tris (pyrazolyl) borate) Mo (CO) 2 (PMe3) H; (tris (pyrazolyl) borate) Mo (CO) 2 (PEt3) H; (tris (pyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) H; (tris (pyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) H; (tetrakis (pyrazolyl) borate) Mo (CO) 3H; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (PMe3) H; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (PEt3) H; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) H; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) H; [ ( -C5Mc5) V (CO) 3H]- ; [ (T15-C5Me5) V (CO) 2 (PPh3) H]- ; [(#5-C5Me5) V (CO) 2(PMe3)H]-; [(#5-C5Me5)V(CO)2(PEt3)H]-; [ (il5-C5Me5) V (CO) 2 (P (OMe) 3) H]-; [(#5-C5Me5) V (CO) 2 (P (OEt) 3) H] ; <BR> <BR> <BR> <BR> [(#5-C5H5)V(CO)3H]-; [(#5-C5H5)V(CO)2(PPh3)H]-;<BR> <BR> <BR> <BR> <BR> <BR> <BR> [(#5-C5H5)V(CO)2(PMe3)H]-; [(#5-C5H5)V(CO)2(PEt3)H]-; [ (115-C5H5) V (CO) 2 (P (OMe) 3) H]-; [(#5-C5H5)V(CO)2(P(OEt)3)H]-; [(rl5-C5Ph5) V (CO) 3H] ; [ (#5-C5Ph5) V (CO) 2 (PPh3) H]- ; [(#5-C5Ph5)V(CO)2(PMe3)H]-; [(#5-C5Ph5)V(CO)2(PEt3)H]-; [(#5-C5Ph5) V (CO) 2 (P (OMe) 3) H] ; [ (Ti'-C5Phs) V (CO) 2 (P (OEt) 3) H]- ; [HV (CO) 5 (PPh3) 1- ; and [HV (CO) 4(dppe)]-; (#5-C5Ph5)Fe(CO) 2H (#5-C5Me5)Fe(CO)2H; (#5-C5H5)Fe(CO)2H; (#5-C5Ph5)Fe(dppe)H; (#5-C5Me5)Fe(dppe)H; (#5-C5H5)Fe(dppe) H ; or a combination thereof.

[00020] In another embodiment, the mononuclear metal hydride is selected from the group consisting of (q5-C5Me5) Cr (CO) 3H; (q5-C5Me5) Cr (CO) 2 (PMe3) H; (#5-C5Me5)Cr(CO)2(P(OMe) 3) H (#5-C5Ph5)Fe(CO)2H; (#5-C5Me5)Fe(dppe) H ; or a combination thereof. In one embodiment, the mononuclear metal hydride is (#5-C5Me5) Cr (CO) 3H.

[00021] In one embodiment, the monomer comprises an acrylate or styrene. In another embodiment, the monomer comprises methyl methacrylate.

[00022] In addition, the invention is also directed to polymerization methods, comprising admixing a polymerization intermediate with a chain transfer catalyst, wherein the chain transfer catalyst comprises at least one mononuclear metalloradical, wherein the metal is selected from the group consisting of Cr, Mo, W, V, and Fe, or a combination thereof; provided that the chain transfer catalyst is not (n5-C5Ph5) Cr (CO) 3s, thereby forming a polymerization product. In another embodiment, admixing the polymerization intermediate with the chain transfer catalyst results in controlling the molecular weight of the polymerization product.

[00023] In one embodiment, the metal is selected from the group consisting of Cr, Mo, and W, or a combination thereof, wherein the mononuclear metalloradical is less sterically hindered than a mononuclear pentaphenylcyclopentadienyl metalloradical and is sufficiently sterically hindered to prevent dimerization of the metal.

[00024] In another embodiment, the metal is selected from the group consisting of V, Fe, or a combination thereof, wherein the mononuclear metalloradical is more sterically hindered than a mononuclear cyclopentadienyl metalloradical and is sufficiently sterically hindered to prevent dimerization of the corresponding metalloradical.

[00025] In one embodiment of the present invention, the chain transfer catalyst is of the formula QXMLy ; wherein M is selected from the group consisting of Cr, Mo, W, V, and Fe, or a combination thereof ; wherein Q is cyclopentadienyl, tris (pyrazolyl) borate, or tetrakis (pyrazolyl) borate, each optionally substituted with aliphatic, aryl, or a combination thereof ; each L is independently a ligand; x is 0 or 1 ; and y satisfies the valence of M. In another embodiment, M is Cr. In one embodiment, M is Fe.

[00026] In another embodiment, Q is selected from the group consisting of pentamethylcyclopentadienyl, pentaisopropylcyclopentadienyl, pentaphenylcyclopentadienyl, tris (pyrazolyl) borate, and tris (3,5-dimethylpyrazolyl) borate. In another embodiment, Q is pentamethylcyclopentadienyl.

[00027] In one embodiment, Q is pentamethylcyclopentadienyl and L is a small phosphine.

In another embodiment, Q is pentamethylcyclopentadienyl and L is dppe.

[00028] In another embodiment, the chain transfer catalyst is selected from the group consisting of (ii-CsMe5) Cr (CO) 3* 5-C5Me5) Cr (CO) 2 (PMe3)-; (q5-C5Me5) Cr (CO) 2 (PEt3) q ; (S-C5Mes) Cr (CO) 2 (P (OMe) 3) #; (#5-C5Me5)Cr(CO)2(P(OEt) 3) #; (#5-C5Ph5)Cr(CO)2(PMe3)#; <BR> <BR> <BR> <BR> (i1-CsPh5) Cr(CO)2(PEt3)#; (#5-C5Ph5)Cr(CO)2(P(OMe)3)#; (#5-C5Ph5)Cr(CO)2(P(OEt)3)#; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 3p ; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (PMe3)# ; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (PEt3)-; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) p ; (tris (3,5-dimethylpyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) p ; (tris (pyrazolyl) borate) Mo (CO) 3* ; (tris (pyrazolyl) borate) Mo (CO) 2 (PMe3) @ ; (tris (pyrazolyl) borate) Mo (CO) 2 (PEt3)# ; (tris (pyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) * ; (tris (pyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) @ ; (tetrakis (pyrazolyl) borate) Mo (CO) 3@ ; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (PMe3) @ ; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (PEt3)# ; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (P (OMe) 3) * ; (tetrakis (pyrazolyl) borate) Mo (CO) 2 (P (OEt) 3) * ; [ (In 5-C5Me5) V (CO) 3#] ; [ (#5-C5Me5) V (CO) 2 (PPh3) ; [ (#5-C5Me5) V (CO) 2 (PMe3) #]-; [(#5-C5Me5) V (CO) 2 (PEt3)#]-; [(#5-C5Me5) V (CO) 2 (P (OMe) 3) l ; [(#5-C5Me5) V (CO) 2 (P (OEt) 3)#]-; [(#5-C5H5)V(CO)3#]-; [(#5-C5H5) V (CO) 2 (PPh3) #]-; [(#5-C5H5)V(CO)2(PMe3)#]-; [(#5-C5H5) V (CO) 2 (PEt)#]-; [ ( '-C5Hs) V (CO) 2 (P (OMe) 3)#]-; [(#5-C5H5) V (CO) 2 (P (OEt) 3)#]-; [(#5-C5Ph5) V (CO) 3*] ; [ (#5-C5Ph5) V (CO) 2 (PPh3)#]-; [(#5-C5Ph5) V (CO) 2 (PMe3) #]-; [(#5-C5Ph5) V (CO) 2 (PEt3) #]-; [(#5-C5Ph5) V (CO) 2 (P (OMe) 3) *]-; <BR> <BR> <BR> [(#5-C5Ph5)V(CO)2(P(OEt)3)#]-; [V(CO)5(PPh3)#]-; [V(CO)4(dppe)#]-; (#5-C5Ph5)Fe(CO)2#; (#5-C5Me5) Fe (CO) 2#; (#5-C5H5)Fe(CO)2#; (#5-C5Ph5)Fe(dppe)#; (#5-C5Me5)Fe(dppe)#; (#5-C5H5) Fe (dppe) * ; or a combination thereof.

[00029] In another embodiment, the chain transfer catalyst is selected from the group consisting of (rl5-C5Me5) Cr (CO) 3* ; (r -C5Me5) Cr (CO) 2 (PMe3)# ; and (-C5Me5) Cr (CO) 2(P(OMe)3)#; (#5-C5Ph5)Fe(CO)2#; (#5-C5Me5)Fe(dppe)#; or a combination thereof. In one embodiment, the chain transfer catalyst is (#5-C5Me5) Cr (CO) 3*.

[00030] In one embodiment, the polymerization intermediate comprises an acrylate or styrene. In another embodiment, the polymerization intermediate comprises methyl methacrylate.

[00031] In another embodiment, the polymerization intermediate is generated by reaction with an initiator. In one embodiment, the initiator is selected from the group consisting of AIBN, benzoyl peroxide, and acetyl peroxide, or a combination thereof.

[00032] The term"free radical polymerization"is used herein to mean polymerization that occurs via one or more free radicals. A"free radical"is used herein in its ordinary sense to mean a species that contains one or more unpaired electrons.

[00033] The term"polymerization intermediate"is used herein to mean an intermediate having an unpaired electron. In one embodiment, a polymerization intermediate is generated by reacting a monomer with an initiator. A polymerization intermediate can also be referred to, for example, as a polymer chain-carrying intermediate or a growing polymer chain.

[00034] The term"initiator"is used herein to mean a compound that forms free radicals when treated with heat or light.

[00035] The term"initiation"or"reinitiation"is used herein to mean the formation of free radicals, for example, by homolytic cleavage of a bond.

[00036] The term"chain transfer catalyst,""chain-transfer catalyst, "or"catalytic chain transfer agent"is used herein to mean additives that cause repeated chain transfer.

[00037] The term"mononuclear"is used herein to mean a metalloradical that provides sufficent steric hindrance to prevent dimerization of the metal or metalloradical. In one embodiment, the mononuclear metalloradical provides sufficient steric hindrance to prevent the formation of strong metal-carbon bonds' [00038] The term"ligand"is used herein to mean one or more atoms, ions, or molecules that donate electrons to a metal. One of skill in the art will understand that the number of ligands coordinated to a metal will be appropriate to satisfy the valence of the metal.

[00039] The term"small phosphine"is used herein to mean a phosphine that is less bulky that triphenylphosphine. For example, the cone angle of the small phosphine will be smaller than the cone angle of triphenylphosphine.

[00040] The term"aliphatic"is used herein to mean a straight-chain or branched Cl-Ci2 carbon chain that is completely saturated or that contains one or more units of unsaturation.

An aliphatic group optionally contains one or more substituents as will be apparent to those of skill in the art.

[00041] The term"aryl"is used herein to mean monocyclic, bicyclic or tricyclic ring systems having a total of five to fourteen ring members, wherein at least one ring in the system is aromatic and wherein each ring in the system contains 3 to 8 ring members. The term aryl also includes ring systems in which one or more ring members is a heteroatom. An aryl group optionally contains one or more substituents as will be apparent to those of skill in the art.

[00042] The term"Cs"is used herein to mean the chain transfer constant, kir/kp.

[00043] The term"Mn"is used herein to mean number-average molecular weight, which may be determined by gel permeation chromatography.

[00044] The term"Mw"is used herein to mean weight-average molecular weight, which may be determined by gel permeation chromatography.

[00045] The term"AIBN"is used herein to mean azobisisobutylnitrile.

[00046] The term"MMA"is used herein to mean methyl methacrylate.

[00047] The term"PMMA"is used herein to mean poly (methyl methacrylate).

[00048] The term"Me"is used herein to mean methyl.

[00049] The term"Ph"is used herein to mean phenyl.

[00050] The term"iPr"is used herein to mean isopropyl.

[00051] The term"Cp"is used herein to mean cyclopentadienyl.

[00052] The term"Cp*"is used herein to mean pentamethylcyclopentadienyl.

[00053] The term"Cp&num "is used herein to mean pentaphenylcyclopentadienyl.

[00054] The term"Tp"is used herein to mean tris (pyrazolyl) borate.

[00055] The term"Tp*"is used herein to mean tris (3,5-methylpyrazolyl) borate.

[00056] The term"Tp"'is used herein to mean tetrakis (pyrazolyl) borate.

[00057] The term"cod"is used herein to mean cycloocta-1, 5-diene.

[00058] The term"dppe"is used herein to mean 1, 2- (bisdiphenylphosphino) ethane.

[00059] The term"about"is used herein to mean approximately, roughly, around, or in the region of. When the term"about"is used in conjunction with a numerical range, it modifies that range by extending the boundaries above and below the numerical values set forth. In general, the term"about"is used herein to modify a numerical value above and below the stated value by a variance of 20 percent up or down (higher or lower).

[00060] As used herein, the word"or"means any one member of a particular list and also includes any combination of members of that list.

Metalloradicals and Free Radical Polymerization [00061] Catalysis of chain transfer has been described previously for Co (II) chelate systems (Enikolopyan, N. S. et al. J. Polym. Sci., Polym. Chem. Ed. l9Xl, 19, 879; Gridnev, A. A. , Ittel, S. C. , Wayland, B. B. , Fryd, M. Organometallics 1996, 15, 5116; Gridnev, A. A., Ittel, S. C. Chem. Rev. 2001, 101, 3611). Mo (III) chain transfer catalysts have also been reported (Grognec, E. L. , Claverie, J. , and Poli, R. J. Am. Chem. Soc. 2001, 123, 9513).

[00062] Applicants have identified characteristics that can be important for a metalloradical to be an effective chain transfer catalyst. The metalloradical should be thermally stable under conditions of polymerization. In one embodiment, the conditions of polymerization are in the range of about 50 to about 70 °C. In another embodiment, the metalloradical will be stable up to about 70 °C. In one embodiment, the metalloradical will be air stable.

[00063] An effective metalloradical chain transfer catalyst can be mononuclear.

Dimerization of the metalloradical chain transfer catalyst can be prevented by steric or electronic factors, but is not so hindered as to preclude its rapid acceptance of H from a chain-carrying radical such as 3-P, below. The metalloradical chain transfer catalyst can form a weak bond to hydrogen, and can comprise a first-row metal of the periodic chart. Its hydride derivative can be unhindered enough to transfer H readily to monomer, but crowded enough to discourage transfer of a second H to a chain-carrying radical such as 3 (resulting in hydrogenation). /4 M-ktr MH + (1) ) Chain Transfer (@ 3 4 = C02CH3 Reinitiation CO2CH3[00064] Although there is no direct evidence for the actual mechanism of catalytic chain transfer (CCT), a two-step process (equations 1 and 2) has been widely accepted. The instability of Co hydrides has made it difficult to observe the reinitiation step (equation 2) directly, although it has often been said to be fast with Co (II) catalysts (Gridnev, A. A.; Ittel, S. D. Chem. Rev. 2001, 101, 3611-3659).

[00065] However, the Cr hydride (C5Ph5) Cr (CO) 3H is stable enough to be isolated and observed by 1H-NMR and can initiate a radical polymerization of MMA (Abramo, G. P.; Norton, J. R. Macromolecules 2000, 33, 2790-2792). The corresponding metalloradical (C5Ph5) Cr (CO) 3-is known (Hoobler, R. J. et al. Organometallics, 1993, 12, 116).

[00066] In one embodiment, the hydride derivative of the metalloradical be isolable, or at least observable, to permit repeated kinetic measurements on a potential catalyst.

[00067] For example, if one were to design a metalloradical chain transfer catalyst or a hydride that can initiate polymerization in the presence or absence of initiator, the following rules can be applied: [00068] 1. There should be enough steric hindrance to prevent the dimerization of metalloradicals and the hydrogenation of monomer by their hydrides. However, too much steric bulk will decrease the efficiency of the chain transfer catalysts.

[00069] 2. The M-H bond must be sufficiently strically hindered to prevent dimerization of the corresponding metalloradical (i. e. , neither too weak nor too strong), to make H transfer between the metalloradical and the chain-carrying radical reversible.

[00070] 3. The steric bulk should be large enough, and the M-C bond strength should be small enough, to prevent the formation of a strong bond between the metalloradicals and the chain-carrying radical.

[00071] 4. The most advantageous steric bulk can be different for different monomers, depending on the steric and electronic properties of those monomers.

[00072] The invention will be further described with reference to the following examples; however, it is to be understood that the invention is not limited to such examples. Rather, in view of the present disclosure that describes the current best mode for practicing the invention, many modifications and variations would present themselves to those of skill in the art without departing from the scope and spirit of this invention. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Example 1 Advantages of Metal Hydrides [00073] Unlike the unstable hydrides of the known Co (lI) and Mo (m) chain transfer catalysts, (C5Ph5) Cr (CO) 3H is stable and observable by 1H NMR. (C5Ph5) Cr (CO) 3H can initiate the radical polymerization of MMA in the absence of initiator to obtain a vinyl- terminated polymer with an Mn of approximately 6,500, which is close to the Mn (Mn = 8,400) from an AIBN-initiated polymerization in the presence of a similar concentration of (C5Phs) Cr (CO) 3'. IR and UV spectroscopy show that the conversion of (C5Ph5) Cr (CO) 3H to (C5Ph5) Cr (CO) 3 is over 90%. Under the conditions employed, (C5Ph5) Cr (CO) 3* is thus consumed by equation 2 (see above) more rapidly than it is generated by equation 1 (Abramo, G. P.; Norton, J. R. Macromolecules 2000, 33, 2790-2792.

[00074] The stable Cr hydride makes it possible to observe equation 2 directly by treating (C5Ph5) Cr (CO) 3H with MMA (Tang, L.; Papish, E. T.; Abramo, G. P.; Norton, J. R.; Baik, M.-H. ; Friesner, R. A.; Rappe, A. J. Am. Chem. Soc. 2003,10093-10102). From H/D exchange between (C5Ph5) Cr (CO) 3H and MMA-d5, kreuzt was measured as 0. 0017 M-ls-l at 50 °C for the reinitiation step (equation 2, above).

[00075] The reactions between (rl5-C5R5) Cr (CO) 3H (R = Ph, Me, H) with MMA-d5 and styrene-d8 at different temperatures have been studied. H/D exchange between Cr hydrides and MMA-d5 was observed in all experiments, without any hydrogenation of MMA-d5 (equation 3). In the case of styrene competition between hydrogenation and H/D exchange was observed (equation 4). The rate constants are listed in Tables 1 and 2, below. CD2H D2C3 D C5R5Cr (CO) 3H + >=<-C5R5Cr (CO) 3D + or HDC HDC C02CH3 CODHs MMA-d5 MMA-d4 R = Ph, Me, H Sterics have little kD C65 C6D, Ph 6 5 Creinit C5R5Cr (CO) 3H + D (CO) 3. + D. I R Me, Ph D C5R5Cr 4-d8 Sterics have large D Hydrogenation D R Me (Table 1. Values of kreinjta from Isotopic Exchange between (C5R5) Cr (CO) 3H and Excess MMA-ds. <BR> <BR> <BR> <BR> <BR> <BR> kreinit (10-3 M-1s-1<BR> T (K) R=Phb R=Meb R=Hc 333 3.00 (5) 323 1.74 (8) 2.61 (5) 318 1.19 (2) 1.73 (1) 313 0.73 (1) 0.94 (2) 308 0.51 (1) 0.62 (1) 4.0 (2) 303 0.350 (6) 2.5 (1) 298 1.23 (4) 293 0.97 (3) <BR> <BR> <BR> <BR> 288 0.59 (3)<BR> a Obtained using equation 3. Figures in parentheses are standard deviation in least significant<BR> <BR> <BR> digit. b In C6D6. c In toluene-d8.

Table 2. Values of kreinit for (C5R5) Cr (CO) 3H (R = H, Me, Ph) and Excess Styrene-d8 in C6D6. kreinit (10-3 M-1s-1 T (K) R=Phb R=Meb R=Hc 323 18.4 (9) 5.4 (3) 15. 8 (6) 318 10.5 (3) 313 11.8 (7) 4. 6 (2) 6.3 (5) 308 5. 6 (3) 303 7.2 (2) 3.6 (2) 3. 7 (3) a Average of two measurements. b Obtained using top part of equation 4. c Obtained using bottom part of equation 4.

[00076] Comparison of kreinit for the three Cr hydrides at 323K shows a substantial increase in the rate of H transfer as the steric bulk of the hydride complex decreases. In contrast to the observations with MMA, there is little variation in kreinit with the steric bulk of the hydride complex for the polymerization of styrene, presumably because the double bond in styrene has fewer substituents. Completion of hydrogenation by transfer of a second H, to the methyl isobutyryl radical 3 or the a-methylbenzyl radical 4, is not appreciable except in the least crowded case, the C5H5 chromium hydride and styrene. A considerable difference between 3 and 4 is apparent. C6D5 C02CH3 More sterically accessible CO2CH3 HHD to secondH D zizi versus 4 3 [00077] The strength of the Cr-H bond in (C5Ph5) Cr (CO) 3H was determined to be 59.6 kcal/mol by a thermodynamic cycle involving the pKa of the hydride and the redox potential of the anion (the conjugate base of (C5Ph5) Cr (CO) 3H). The Cr-H bond strength of (CsPhs) Cr (CO) 3H is close to those of other Cr hydrides (see Table 3), which implies that the steric bulk on the metal center does not much affect the bond strength.

Table 3. BDE of Different Cr Hydrides Cr Hydride BDE, kcal/mol H-Cr (CO) 3 (C5Ph5)a 59. 6 (3) H-Cr (CO) 3 (C5Me5) b 62.3 H-Cr (CO) 3 (C5H5)' 61.5 H-Cr (CO) 2 (PPh3) (C5H5) C 59.8 H-Cr (CO) 2 (PEt3) (C5H5) C 59.9 H-Cr (CO) 2 (P (OMe) 3) (CsHs) c 62.7 aIn CH3CN. bWatkins, W. C.; Jaeger, T.; Kidd, C. E.; Fortier, S.; Baird, M. C.; Kiss, G.; Roper, G. C.; Hoff, C. D. J. Am. Chem. Soc. 1992, 114, 907-914.'The remaining BDE values are from Kiss, G.; Zhang, K.; Mukerjee, S. L.; Hoff, C. D. J. Am. Chem. Soc. 1990, 112, 5657-5658 and are in toluene.

[00078] Thus, chain transfer catalysts should be hindered enough to prevent hydrogenation of the monomers. The M-H bond should be neither too weak nor too strong, to make H transfer between the metalloradical and the chain-carrying radical reversible.

Example 2 Chain Transfer Catalysis by Chromium Metalloradicals and Hydrides [00079] The competition of a general chain-transfer catalyst Me (rate constant ktr, equation 5) with monomer (rate constant kp, equation 6) for a chain-carrying radical 3-P can be assessed by the slope of a Mayo plot (1/DPn versus [monomer], see equation 7). A plot of 1/DPn versus the concentration catalyst divided by the concentration of monomer gives a slope of Cs, or rate of transfer over rate of initiation. In equation 7, DPn is the number average degree of polymerization in the presence of catalyst, and (DPn) o is the number average degree of polymerization in the absence of catalyst. CO '+ c e kip X \3/'< n n+ v 3 CH M1 + kr [Catalyst] D (DPn) o kp [Monomer] [00080] As discussed in Abramo, G. P. , Norton, J. R. Macromolecules 2000, 33, 2790, #5- (C5Phs) Cr (CO) 3* (la) has a Cs value of 984 at 100 °C, a Cs value of 1040 at 70 °C, as determined from the slope of its Mayo plot, and a Cs value of 1500 at 65°C.

Mayo plot for MMA with (C5Ph5) Cr (CO) 2 (PMe3) at 65°C [00081] However, the phosphine and phosphite-substituted derivatives of (C5Ph5) Cr (CO)3# are much less active than (C5Phs) Cr (CO) 3#. Slopes of Mayo plots of MMA at 70 °C give Cs=4 for (C5Ph5) Cr (CO) 2 (PMe3)#, and gives CS=40 for (C5Ph5) Cr (CO) 2 (P (OMe) 3)' (see below).

Mayo plot for MMA with (C5Ph5) Cr (CO) 2 (PMe3)# at 70°C.

Mayo plot for MMA with (CsPh5) Cr (CO) 2P (OMe) 3 at 70°C.

[00082] Without wishing to be bound by theory, applicants believe that the steric bulk on the metal center makes the chain transfer constants decrease significantly. Applicants also believe that the phenyl substituents on (CsPh) Cr (CO) 3' serve only to prevent dimerization.

[00083] Following the methodology of Abramo, the compound Cp*Cr (CO) 3* (lb) is a surprisingly active chain transfer catalyst. Compound 1b is less hindered than la but still largely monomeric because its Cr-Cr bond is 63% dissociated at 300K (Kiss, G.; Zhang, K.; Mukerjee, S. L.; Hoff, C. D. J. Am. Chem. Soc. 1990, 112, 5657-5658). A Mayo plot of lb at 70 °C is shown below; its slope Cs is 6300, which is approximately six times greater than that with la.

Mayo plot for MMA with (C5Me5) Cr (CO) 3 (1b) at 70°C.

[00084] A derivative of lb, the compound Cp*Cr (CO) 2 (PMe3)#, has also proven active as a chain transfer catalyst. The slope Cs of its Mayo plot at 70 °C is 4200, or about four times as large as that with la. A Mayo plot of Cp*Cr (CO) 2 (PMe3) is shown below.

Mayo plot for MMA with (C5Me5) Cr (CO) 2 (PMe3)# at 70°C.

[00085] (C5H5) Cr (CO) 3 has been reported to have a chain transfer constant of 100 for the radical polymerization of MMA [Janowicz, A. H. (Dupont) U. S. Patent No. 4,746, 713; Janowicz, A. H. (E. I. DuPont de Nemours and Co. , USA) EP 222619]. Surprisingly, however, applicants have found that (C5H5) Cr (CO) 3 is a very active chain transfer catalyst when used in an AIBN-initiated radical polymerization of neat MMA. Under these conditions, the Cs for (C5H5) Cr (CO) 3 was found to be 25,000 (see Mayo plot below), which is much larger than that of (C5Me5) Cr (CO) 3*. Given the high air sensitivity of (CsHs) Cr (CO) 3, and without wishing to be bound by theory, applicants believe that the much lower Cs value previously reported by Janowicz was caused by the decomposition of the Cr metalloradical, while in applicants'experiments the reaction of (C5Mes) Cr (CO) 3-with air was prevented by using Schlenk, high-vacuum, or inert-atmosphere-box techniques.

Mayo plot for MMA with (C5H5) Cr (CO) 3' at 70°C.

[00086] (C5H5) Cr (CO) 2 (PPh3)#, the PPh3 substituted derivative of (C5H5) Cr (CO) 3 was also found to be an effective chain transfer catalyst in the radical polymerization of MMA, with a Cs value of 1,200.

Mayo plot for MMA with (C5H5) Cr (CO) 2 (PPh3)# at 70°C.

[00087] The chain transfer constants of these Cr metalloradicals are summarized below in Table 4.

Table 4. Chain Transfer Constants of Cr Metalloradicals in Radical Polymerization of MMA at 70°Ca Cr Metalloradical Chain Transfer Constant (CS) (C5Ph5) Cr (CO) 3# 1,000 (CPhs) Cr (CO) 2 (PMe3)# 4 (CsPh5) Cr (CO) 2P (OMe) 3 40 (C5Me5) Cr (CO) 3# 6, 300 (C5Me5) Cr (CO) 2 (PMe3)'4, 200 (CsH5) Cr (CO) 3# 25, 000 (C5Hs) Cr (CO) 2 (PPh3) 1, 200 a All polymerizations were performed with 0. 1% (w/v) of AIBN in neat MMA [00088] Comparing the reported Cs value (100) of (C5H5) Cr (CO) 3-with the value of (C5Phs) Cr (CO) 3# (CS=1000), Gridnev concluded that the greater steric bulk of the phenyl- substituted metalloradical (CPhs) Cr (CO) 3 increases the dissociation, thereby making the active paramagnetic components more available for the catalytic process than in a catalytic chain transfer polymerization with (C5H5) Cr (CO) 3* (Gridnev, A. A.; Ittel, S. D. Allem. Rev.

2001, 101, 3611-3659). However, the Cr-Crbond in the dimer of [(C5H5)Cr(CO)3]2 is very weak, with a bond strength of only 15.8 kcal/mol (McLain, S. J. J. Am. Chem. Soc. 1988,110, 643-644). With such a weak bond, the Cr dimer would fully dissociate at the high temperatures and low catalyst concentrations that are typically required in a polymerization reaction. In fact, the activation parameters reported by McLain show that only 0.7% of [ (CsHg) Cr (CO) 3] 2 exists as a dimer for the dissociation equilibrium at 70°C, when the initial dimer concentration is le M. This calculation indicates that the steric bulk of the phenyl- substituted metalloradical is not as important as Gridnev thought in preventing dimerization of Cr metalloradicals.

[00089] For further comparison, known cobalt metalloradicals have been demonstrated to have the activities shown in Table 5.

Table 5. Comparative Chain Transfer Constants of Co Metalloradicals Complex Temp (°C) ktr/kp Co (II) Hematoporphysina 60 2, 400 Co (In meso TPPa 60 4, 100 Co (II)Me2glyoxime(OH)2PPh3b 60 100, 000 Co (InMe2glyoxime (BF) 2 C 60 40, 000 aSmironv, B. R. et al. Dokl. Chers., 1980, 254, 426 b Gridnev, A. , J. Polym. Chem., 2000, 38, 1753 ° Heuts, J. P. A. et al., Macromolecules, 1998, 31, 2894 [00090] Hydrides should have the same activity in chain transfer catalysis as their corresponding metalloradicals. From the slope of Mayo plot, the Cs of (C5Ph5) Cr (CO) 3H is found to be 1370, which is approximately the same as the value for (CsPhs) Cr (CO) 35.

Mayo plot for MMA with (C5Ph5) Cr (CO) 3H at 70 °C [00091] Besides MMA, these metalloradicals and hydrides are expected to be active in a large number of monomers that used in free radical polymerization. (C5Ph5) Cr (CO) 3 was found to be an active chain transfer catalyst in free radical polymerization of styrene, although it's less active in styrene than in MMA. With 0. 1% (w/v) AIBN in neat MMA, the Cs value at 70°C is 15.

Mayo plot for styrene with (C5Phs) Cr (CO) 3-at 70°C Example 3 Chain Transfer Catalysis by Molybdenum Metalloradicals [00092] Other chromium metalloradicals include the Cr tris (pyrazolyl) borate complex, TpCr (CO) 3, and its derivatives. Tris (pyrazolyl) borate ligands resemble cyclopentadienyl ligands structurally and in terms of electron count, although their steric and electronic properties, and their reactivity, often differ (Trofimenko, S. Progr. Inorg. Chem. 1986, 34, 115, and other references collected as reference 2 in part b). After comparing their IR spectra and electrochemical behavior under identical conditions Tilset has concluded that TpM (CO) 3- are more electron-rich than their Cp analogues (Skagestad, V.; Tilset, M. J. Am. Chem. Soc.

1993, 115, 5077-5083).

[00093] Unfortunately, Tp-chromium compounds are unstable at elevated temperatures, and both TpCr (CO) 3 and Tp*Cr (CO) 3 decompose rapidly at 70°C. However, the Tp complexes of molybdenum are more stable, and the air-and heat-stable compound Tp*Mo (CO) 3 (Shiu, K. -B. ; Lee, L.-Y. J. Organomet. Chenu. 1988,348, 357-360) was investigated in the radical polymerization of MMA according to the methodology of Example 2. The Mayo plot for Tp*Mo (CO) 3 (see below) gave a Cs value of 22 at 70°C.

Mayo plot for MMA with Tp*Mo (CO) 3 at 70°C [00094] The chain transfer constant of Tp*Mo (CO) 3 is small, given the steric bulk of the metal center (caused by the methyl groups on the pyrazolyl ring) (Shiu, K.-B. ; Lee, L.-Y. J. organoHzet. Chem. 1988, 348, 357-360).

[00095] Certain features are needed for Tp complexes of molybdenum to be effective as chain transfer catalysts. Substituents are needed on the 4 or 5 positions of the pyrazolyl ring, or on boron, to stabilize the compound towards heat (see below). On the other hand, a substituent on the 3 position of the pyrazolyl ring will not be helpful, since even a methyl there will bring steric hindrance to the Mo center and will decease chain transfer efficiency.

Example 4 Chain Transfer Catalysis by Seventeen-Electron Vanadium Metalloradicals [00096] Vanadium radicals have been shown to exhibit fast metal-to-carbon H-transfer.

For example, kH is about 2 x 107 M-ls-l, which is an order of magnitude larger than that for Bu3SnH, as reported for [CpV (CO) 3H]- (Kinney, R. J.; Jones, W. D.; Bergman, R. G. J. Arn.

Chem. Soc. 1978, 100, 635-637 and 7902-7915). The reaction of [CpV (CO) 3H]- with MMA is examined. Sufficiently fast H transfer in the presence of a radical initiator will allow the evaluation of [CpV (CO) 3H]-l [CpV (CO) 3-]- as a chain transfer catalyst. [CpV (CO) 3H]- is stable in the presence of H20, although its solubility is not clear from the literature (Kinney, R. J.; Jones, W. D.; Bergman, R. G. J. Am. Chem. Soc. 1978, 100, 635-637 and 7902-7915).

Such a catalyst can be useful in extending chain transfer catalysis to new environments, i. e., to aqueous solution, and perhaps to acrylamides as substrates.

[00097] V (CO) 4 (PPh3) 2 (Werner, R. P. M. Z. Naturforschung., B 1961, 16, 477), V (CO) 4 (dppe) (Davison, A.; Ellis, J. E. J. Organomet. Chenu. 1972,36, 131-136), and trans- V (CO) 2 (dppe) 2 (Rehder, D.; Süssmilch, F. ; Priebsch, W.; Fornalczyk, M. J. Organomet.

Chem. 1991, 411, 357-367) are also seventeen-electron vanadium complexes sufficiently stable that they may be able to function as chain-transfer catalysts. Vanadium hydrides have been reported in some cases (e. g., HV (CO) 5 (PPh3) (Hieber, W.; Winter, E.; Schubert, E.

Chem. Ber. 1962, 95, 3070-3077) and HV (CO) 4 (dppe) (Davison, A.; Ellis, J. E. J.

Organomet. Chem. 1972, 36, 131-136) ), but to our knowledge no V-H bond strengths have been determined.

[00098] Electrochemical (i. e. , the potential of metalloradical reduction, in CH3CN if possible) and quantitative pKa measurements can be evaluated to determine V-H bond strengths. The only V-H pKa of which applicants are aware, with a value of 6.8 for HV (CO) 5 (PPh3), was carried out potentiometrically by Hieber in 1962 (Hieber, W.; Winter, E.; Schubert, E. Chem. Ber. 1962, 95, 3070-3077). Qualitative reports on the acidity of vanadium hydrides are summarized in a review (Kristjansdottir, S. S.; Norton, J. R. In Transition Metal Hydrides ; Dedieu, A. , Ed.; VCH: New York, 1992, Chapter 9).

[00099] Facile H transfer for vanadium hydride complexes is also suggested by their reactions with dienes, as shown in equation 16 (Franke, U.; Weiss, E. J. Organomet. Chem.

1980, 193, 329-337). H transfer mechanisms have been established for the reaction of acyclic and exo-methylene cyclic dienes with HFe (CO) 4SiCl3 (Connolly, J. W.

Organometallics 1984,3, 1333-1337), and for the reaction of acyclic and cyclic dienes with CpFe (CO) 2H (Shackleton, T. A.; Baird, M. C. Organometallics 1989, 8, 2225-2232).

[000100] The V-H bond strength data allows selection of appropriate systems (metalloradicals or the corresponding hydrides), determination of the rates of isotope exchange between the hydrides and MMA-d5, and determination of the chain transfer constants (for the metalloradicals) according to the methodology of Examples 1 and 2.

Example 5 Chain Transfer Catalysis by Iron Metalloradicals and Hydrides [000101] Of the known seventeen-electron metalloradicals surveyed in a book by Astruc (Electron TransferAnd Radical Processes In Transition-Metal Chemistry ; Astruc, D. ; VCH Publishers, Inc.: New York, 1995; Chapter 3), many contain iron. Although [(C5Phs) Fe (CO) 2] 2 exists largely as a dimer (Kuksis, I.; Kovacs, I.; Baird, M. C.; Preston, K.

F. Organometallics 1996, 15, 4991-5002, and references therein), the pentaisopropyl derivative does not dimerize at all in solution (Sitzmann, H.; Dezember, T.; Kaim, W.; Baumann, F. ; Stalke, D.; Kacher, J.; Dormann, E.; Winter, H.; Wachter, C.; Kelemen, M.

Angew. Chem. Int. Ed. Engl. 1996, 35, 2872-75). The metalloradical Cp*Fe (dppe) is not only monomeric but thermally stable (Hamon, P.; Toupet, L.; Hamon, J. -R. ; Lapinte, C.

Organometallics 1996, 15, 10-12), and CpFe (cod) and Cp*Fe (cod) have been reported (Jonas, K.; Klusmann, P.; Goddard, R. Z. Naturforsch. 1995, 50b, 394-404, and references therein). Many iron metalloradicals are not only monomeric but thermally stable.

[000102] (C5Ph5) Fe (CO) 2* was synthesized, but found be insoluble in most solvents.

However, (C5Ph5) Fe (CO) 2H (McVey, S.; Pauson, P. L. J. Chem. Soc. 1965,4312-18) was found to be an active chain transfer catalysts in MMA polymerization, with a Cs value of 1400.

Mayo plot of MMA with (C5Ph5) Fe (CO) 2H at 70 °C [000103] Similarly, Cp*Fe (dppe) H (Roger, C.; Hamon, P.; Toupet, L.; Rabaa, H.; Saillard, J. -Y. ; Hamon, J. -R. ; Lapinte, C. Orgarzometallics 1991, 10, 1045-54) is also active in chain transfer catalysis during MMA polymerization. The Cs value is 5.3.

Mayo plot of MMA with (C5Me5) Fe (dppe) H at 70 °C [000104] CpFe (cod) and Cp*Fe (cod) have also been reported (Jonas, K. ; Klusmann, P.; Goddard, R. Z. Naturforsch. 1995, 50b, 394-404, and references therein). Again, analysis of Fe-H bond strengths, determination of the rates of isotope exchange of these hydrides with MMA-d5, as well as determination of the chain transfer constants (for the metalloradicals) can be performed according to the methodology of Examples 1 and 2.

[000105] While the invention has been described in detail with reference to certain embodiments thereof, it will be understood that the invention is not limited to these embodiments. Indeed, modifications and variations are within the spirit and scope of that which is described and claimed.