[0001] The present application claims the benefit of priority from copending U.S. provisional patent application number 61/303,349, filed on February 11 , 2010, the contents of which are incorporated herein by reference in their entirety for all purposes.

Field of the Application

[0002] The present application is in the field of radical polymerization, in particular the controlled radical polymerization of functionalized vinyl monomers using a vanadium-based catalyst.

Background of the Application

[0003] Significant progress in the development of controlled radical polymerization (CRP) has resulted in extraordinary control over polymer molecular weight and molecular weight distributions. ¹ Several of these processes exploit transition metal based catalysts to control the radical concentrations, minimize bimolecular termination reactions and exchange growing and dormant polymer chains. These include atom transfer radical polymerization (ATRP), ² where a halogen capped polymer chain and a transition metal catalyst are in reversible equilibrium with a polymeric radical and the corresponding higher oxidation state metal halide. Organometallic mediated radical polymerization (OMRP) is based upon the lability of metal- carbon bonds under thermal or photolytic treatment, where the reversible formation of an organometallic dormant chain is in equilibrium with a lower oxidation state metal complex and a polymeric radical. The OMRP process has been most thoroughly studied for cobalt-mediated radical polymerization, ³ and has also been implicated in molybdenum ⁴ and iron systems, ⁵ including significant study into the interplay between ATRP and OMRP in these systems. ⁶ [0004] For these CRP processes, vinyl acetate has proven to be a particularly challenging monomer to control ⁷ due to an imbalance between metal-halogen and carbon-halogen bond strengths in ATRP and strong metal- carbon bonds in OMRP. Jerome et al. reported an intriguing cobalt system that can efficiently control the polymerization of vinyl acetate, albeit with an extremely long initiation time (>10h) and a radical initiator, 2,2'-azo-bis(4- methoxy-2,4-dimethyl valeronitrile), which must be stored at -20°C and requires reaction temperatures to remain at 30°C. ^3,8

Summary of the Application

[0005] A controlled radical polymerization mediated by a vanadium catalyst has been achieved. Specifically, a novel OMRP of vinyl acetate (VAc) using a standard 2,2'-azo-bis(isobutyronitrile) (AIBN) initiator and the bis(iminopyridine) complex [BIMPY]VCI ₃ ([BIMPY] =

Ar = 2,6-(iPr) ₂ C ₆ H ₃ )) at 120°C was achieved. BIMPY is an example of a class of ligands known as non-innocent ligands.

[0006] Accordingly, the present application relates to a process for the controlled radical polymerization of a suitable monomer comprising contacting the monomer with an effective amount of a vanadium catalyst comprising a non-innocent ligand in the presence of an initiator under conditions for the controlled polymerization of the monomer.

[0007] In an embodiment of the application, the monomer is a compound of the formula (I):

CH ₂ =CR ¹ R ^1' (I)

[0008] wherein R and R ^r are independently selected from the group H, Ci. ₂₀ alkyl, C _6- i ₈ aryl, OC(O)Ci _-20 alkyl, OC(O)C ₆ -i ₈ aryl, C(O)Ci _-20 alkyl and C(O)C _6- i8aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, Ci-ealkyl, OCi _-6 alkyl, fluoro-substituted Ci _-6 alkyl and fluoro-substituted OCi _-6 alkyl, provided that at least one R ¹ and R is not H. [0009] In another embodiment, more than one monomer is present and block co-polymers are prepared.

[0010] In another embodiment of the application, the non-innocent ligand is a bis(imino)pyridine of the formula (II):

[0011] wherein

[0012] R ² and R ² are independently selected from the group H, Ci. ₆ alkyl and C _6- i ₄ aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, C-i. ₄ alkyl, OCi _-4 alkyl, fluoro-substituted C-i _-4 alkyl and fluoro-substituted OC-i _-4 alkyl;

[0013] R ³ and R ³ are independently selected from the group H, C-i. ealkyl and C _6- i ₄ aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, Ci_ ₄ alkyl, OCi _-4 alkyl, fluoro-substituted C _1-4 alkyl and fluoro-substituted OC-i _-4 alkyl; and

[0014] R ⁴ , R ⁵ and R ⁶ are independently selected from the group H, halo, Ci _-6 alkyl and Ce-uaryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, C-i. alkyl, OCi _-4 alkyl, fluoro-substituted Ci _-4 alkyl and fluoro-substituted OCi _-4 alkyl, or R ⁴ and R ⁵ or R ⁵ and R ⁶ are linked together with the atoms to which they are bonded to form a 5- to 10-membered mono- or bicyclic, saturated, unsaturated or aromatic carbocyclic ring system and the ring system is unsubstituted or substituted with one or more substituents selected from the group halo, Ci- alkyl, OCi _-4 alkyl, fluoro-substituted Ci _-4 alkyl and fluoro- substituted OCi _-4 alkyl. [0015] The initiator is suitably any known compound that is effective to initiate a radical polymerization reaction, including, for example, halogen molecules, azo compounds, organic peroxides and metal alkyls.

[0016] In a further embodiment of the application the process further comprises treating the resulting polymer under conditions to remove the vanadium catalysts. For example, by treatment with an alkylthiol, such as 1- propanethiol, in a suitable solvent, such as methanol, at a temperature of about 20°C to 100°C until the catalyst has been removed.

[0017] Other features and advantages of the present application will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description.

Brief description of the drawings

[0018] The embodiments of the application will now be described in greater detail with reference to the attached drawings in which:

[0019] Figure 1 shows the dependence of PVAc M _n on monomer conversion for the bulk polymerization of vinyl acetate at 120°C. [BIMPY]VCI ₃ :AIBN:VAc is 1 :0.6:100.

[0020] Figure 2 shows the time dependence of ln([M]o/[M _n ]) for the bulk polymerization of vinyl acetate at various temperatures. [BIMPY]VCI ₃ :AIBN:VAc is 1 :0.6:100 and [M] ₀ and [M) _n are the [VAc] at times 0 and t respectively.

[0021] Figure 3 shows the start-stop experiment for the bulk polymerization of vinyl acetate. [BIMPY]VCI ₃ :AIBN:VAc 1 :0.6:100. T = 120°C /-30°C.

Detailed description of the Application

I. Definitions [0022] Unless otherwise indicated, the definitions and embodiments described in this and other sections are intended to be applicable to all embodiments and aspects of the disclosure herein described for which they are suitable as would be understood by a person skilled in the art.

[0023] The term "non-innocent ligand" as used herein means a ligand in a metal complex where the oxidation state is unclear. Ligands with extended pi-delocalization are often non-innocent.

[0024] The term "alkyl" as used herein means straight and/or branched chain, saturated alkyl groups containing the specified number of carbon atoms. For example, contains from 1 to 20 carbon atoms and d. ₆ alkyl contains from 1 to 6 carbon atoms. Alkyl groups include, for example, methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl, isobutyl, t-butyl, 2,2- dimethylbutyl, n-pentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, n- hexyl and the like.

[0025] The term "aryl" as used herein means a monocyclic or polycyclic carbocyclic ring system containing at least one aromatic ring and the specified number of carbon atoms. For example, C6-isaryl contains from 6 to 18 carbon atoms and C6-ioaryl contains from 6 to 10 carbon atoms. Aryl groups include, for example, phenyl, naphthyl, anthracenyl, 1 ,2-dihydronaphthyl, 1 ,2,3,4- tetrahydronaphthyl, fluorenyl, indanyl and indenyl, and the like.

[0026] The term "halo" as used herein means a halogen atom, such as fluorine, chlorine, bromine or iodine.

[0027] The term "fluoro-substituted" with respect to any specified group as used herein means that one or more, including all, of the available hydrogen atoms in the group have been replaced with a fluorine, and includes trifluoromethyl, pentafluoroethyl, fluoromethyl, pentafluorophenyl and the like.

[0028] The term "ring system" as used herein refers to a carbon- containing ring system containing the specified number of carbon atoms and includes monocyclic and polycyclic rings. Ring systems include saturated, unsaturated or aromatic rings, or mixtures thereof. Where specified the ring system is optionally substituted.

[0029] The term "polycyclic" as used herein means groups that contain more than one ring linked together and includes, for example, groups that contain two (bicyclic), three (tricyclic) or four (quadracyclic) rings. The rings may be linked through a single bond, a single atom (spirocyclic) or through two atoms (fused and bridged).

[0030] The term "suitable" as used herein means that the selection of the particular compound or conditions would depend on the specific synthetic manipulation to be performed, and the identity of the molecule(s) to be transformed, but the selection would be well within the skill of a person trained in the art. All process steps described herein are to be conducted under conditions sufficient to provide the product shown. A person skilled in the art would understand that all reaction conditions, including, for example, reaction solvent, reaction time, reaction temperature, reaction pressure, reactant ratio and whether or not the reaction should be performed under an anhydrous or inert atmosphere, can be varied to optimize the yield of the desired product and it is within their skill to do so.

[0031] The terms "a," "an," or "the" as used herein not only include aspects with one member, but also includes aspects with more than one member. For example, an embodiment including "a monomer" should be understood to present certain aspects with one monomer or two or more additional monomers.

[0032] In understanding the scope of the present disclosure, the term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives. Finally, terms of degree such as "substantially", "about" and "approximately" as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. These terms of degree should be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies.

II. Process of the Application

[0033] The present application relates to a process for the controlled radical polymerization of a suitable monomer comprising contacting the monomer with an effective amount of a vanadium catalyst comprising a non- innocent ligand in the presence of an initiator under conditions for the controlled polymerization of the monomer.

[0034] The suitable monomer is any monomer that is polymerizable through radical polymerization. In an embodiment of the application, the monomer is a functionalized monomer, for example, but not limited to styrene- type monomers, acrylates, methacrylates, acrylonitrile and isobutylene. In another embodiment, the monomer is a compound of the formula (I):

CH ₂ =CR ¹ R (I)

[0035] wherein R ¹ and R ^r are independently selected from the group H, Ci _-20 alkyl, C _{6- 8} aryl, OC(O)Ci _-20 alkyl, OC(0)C _6- i8aryl, C(O)Ci _-20 alkyl and C(0)C6-i8aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, Ci-6alkyl, OCi-6alkyl, fluoro-substituted Ci-6alkyl and fluoro-substituted OCi-6alkyl, provided that at least one R ¹ and R ^r is not H.

[0036] In an embodiment of the application R and R are independently H, C _1-6 alkyl, OC(0)d _-6 alkyl or OC(0)C ₆ -i ₄ aryl, provided that at least one R ¹ and R ¹ is not H. In another embodiment, R is OC(0)Me, OC(0)Et or OC(0)Ph and R ^r is H. In a further embodiment R ¹ is OC(0)Me and R ¹ is H. In another embodiment, R ¹ and R ¹ are each, independently, Ci_ ₆ alkyl.

[0037] In a further embodiment, more than one different monomer is present in the process such that block co-polymers are obtained. [0038] The non-innocent ligands are bi- tri- or tetra-dentate ligand frameworks, and include, but are not limited to alpha-diimine ligands, 1 ,2- dithiolate ligands, 2,2'-bipyridine ligands, porphyrins, phthalocyanines, dioxalenes, dithiolenes and bis(imino)pyridines.

[0039] In an embodiment of the application, the non-innocent ligand is a bis(imino)pyridine of the formula (II):

[0040] wherein

[0041] R ² and R ² are independently selected from the group H, Ci. ₆ alkyl and C _6- i4aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, C-i. ₄ alkyl, OCi _-4 alkyl, fluoro-substituted Ci _-4 alkyl and fluoro-substituted OCi _-4 alkyl;

[0042] R ³ and R ^3' are independently selected from the group H, Ci_ ₆ alkyl and C _6- i ₄ aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, Ci. ₄ alkyl, OCi _-4 alkyl, fluoro-substituted Ci _-4 alkyl and fluoro-substituted OCi _-4 alkyl; and

[0043] R ⁴ , R ⁵ and R ⁶ are independently selected from the group H, halo, Ci-6alkyl and C6-i ₄ aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, d. alkyl, OCi _-4 alkyl, fluoro-substituted Ci _-4 alkyl and fluoro-substituted OC-i- alkyl, or R ⁴ and R ⁵ or R ⁵ and R ⁶ are linked together with the atoms to which they are bonded to form a 5- to 10-membered mono- or bicyclic, saturated, unsaturated or aromatic carbocyclic ring system and the ring system is unsubstituted or substituted with one or more substituents selected from the group halo, Ci- alkyl, OCi- alkyl, fluoro-substituted Ci _-4 alkyl and fluoro- substituted OCi _-4 alkyl. [0044] In an embodiment of the application, R ² and R ² are the same. In another embodiment of the application, R ² and R ² are both phenyl or naphthyl, and each phenyl or naphthyl is unsubstituted or substituted with one to five substituents selected from the group halo, Ci _-4 alkyl and fluoro- substituted C _1-4 alkyl. In a further embodiment of the application, R ² and R ² are both phenyl, and each phenyl is unsubstituted or substituted with one or two substituents selected from the group halo and Ci _-4 alkyl. In a further embodiment, R ² and R ² are both phenyl, and each phenyl substituted with one or two Ci _-4 alkyl.

[0045] In an embodiment of the application, R ³ and R ³ are the same. In another embodiment of the application, R ³ and R ³ are both unsubstituted Ci- ₆ alkyl. In a further embodiment of the application, R ³ and R ³ are both methyl or ethyl.

[0046] In embodiment of the application, R ⁴ , R ⁵ and R ⁶ are independently selected from the group H, halo, Ci _-4 alkyl and C6-ioaryl, and each alkyl or aryl group is unsubstituted, or R ⁴ and R ⁵ or R ⁵ and R ⁶ are linked together with the atoms to which they are bonded to form a 5- to 6-membered monocylic saturated, unsaturated or aromatic carbocyclic ring and the ring is unsubstituted. In another embodiment of the application, R ⁴ , R ⁵ and R ⁶ are each H.

[0047] In an embodiment of the application the non-innocent ligand is a compound of the formula D-CR ⁷ =CR ^7' -D' (III) or D=CR ⁷ -CR ^7' =D' (IV), wherein D and D' are independently selected from the group O, S and NR ⁸ and R ⁷ , R ⁷ and R ⁸ are independently selected from Ci _-6 alkyl and C _6- i ₄ aryl, and each alkyl or aryl group is unsubstituted or substituted with one or more substituents selected from the group halo, Ci _-4 alkyl, OCi- alkyl, fluoro-substituted Ci _-4 alkyl and fluoro-substituted OCi _-4 alkyl.

[0048] In an embodiment of the application, in addition to the non- innocent ligand, the vanadium catalyst further comprises one or more anionic ligands. The number of anionic ligands will depend on the valency requirements of the vanadium in view of the number of donor atoms in the non-innocent ligand. For example, if the non-innocent ligand is tridentate, the catalyst would further comprise, for example, three anionic ligands. If more than one anionic ligands is required, these ligands may be the same or different and are selected from any of the well known anionic ligands known for use in these catalysts as would be known to a person skilled in the art. For example, the anionic ligands are any ancillary ligand, including phosphine, amine, alkene, diamine, diphosphine, aminophosphine, halo (for example, fluoro, chloro, bromo or iodo, specifically chloro), HO ^" , R ⁹ O ^" and R ⁹ C(O)O ^" , wherein R ⁹ is H or C _h alky!. The anionic ligand can also be a multidentate ligand.

[0049] The initiator is suitably any known compound that is effective to initiate a radical polymerization reaction, including, for example, halogen molecules, azo compounds and organic peroxides. In an embodiments of the application, the initiator is 2,2'-azobis(isobutyronitrile) (AIBN) or 1 ,1 '- azobis(cyclohexanecarbonitrile) (ABCN).

[0050] The conditions for the controlled radical polymerization of the monomer comprise concentrations, solvents, temperature and time that is sufficient to initiate and effect the polymerization of the monomer and will vary depending on the identity of the monomer, catalyst and initiator as would be known to a person skilled in the art. For example, for vinyl acetate, the conditions for the controlled radical polymerization of the monomer comprise combining vinyl acetate, the initiator and catalyst in mole ratio of about 20:1 :1 to about 1000:1 :1 , at a reaction temperature of about 100°C to about 140°C, suitably about 120°.

[0051] In a further embodiment of the application the process further comprises treating the resulting polymer under conditions to remove the vanadium catalysts. For example, by treatment with an alkylthiol, such as 1 - propanethiol, in a suitable solvent, such as methanol, at a temperature of about 20°C to 100°C until the catalyst has been removed.

[0052] The following non-limiting examples are illustrative of the present application: V. Examples

Materials and Methods

[0053] All experiments involving moisture and air sensitive compounds were performed under a nitrogen atmosphere using a Mbraun LABmaster sp glovebox system equipped with a -33°C freezer, a built in Siemens Simantic Touch Panel and [H ₂ 0] and [0 ₂ ] analyzers.

[0054] Vinyl acetate (99% Aldrich) and styrene (>99% Aldrich) were dried over calcium hydride overnight, degassed by four freeze-thawing cycles after being distilled under reduced pressure and stored under nitrogen. Anhydrous THF, pentane and diethyl ether were obtained from an Innovative Technologies glove box with an inline Solvent Purification System, consisting of alumina and a copper catalyst. 2,6-Diisopropylaniline (90%, Aldrich) was purchased at technical grade and was distilled under vacuum. 2,6- Diacetylpyridine (99%, Aldrich), azobisisobutyronitrile (AIBN, 98%, Aldrich), propanethiol (99%, Aldrich), potassium hydroxide (KOH, Analar), vanadium(lll) chloride (97% Aldrich), chloroform (HPLC grade, Fisher), methanol (MeOH, HPCL grade, Caledon) were used as received.

Characterization

[0055] Gel permeation chromatography (GPC) was carried out in THF (flow rate: 1 mL min ^" ) at 50 °C with PL-GPC 50 Plus integrated GPC system which includes three 300x7.5 mm Resipore columns. Polystyrene and/or poly(methyl methacrylate) standards were used for calibration. ¹ H-NMR and 2-D spectra were recorded with a Bruker Avance Spectrometer (300 MHz) in CDCI ₃ or D ₂ 0. Elemental analyses were conducted by Guelph Analytical Laboratories.

Example 1 : General Polymerization Procedure

[0056] [BIMPY]VCI ₃ (3.130 x 10 ^'4 mol), AIBN (1.879 x 10 ^"4 mol) and vinyl acetate (0.031 mol) were placed into a 50 mL ampoule under an inert atmosphere. The ampoue was sealed and placed in a pre-heated oil bath at 120°C for a defined period of time. At the end of the reaction, the ampoule was cooled to room temperature. Addition of 10 mL pentane induced the precipitation of the polymer that was collected by filtration. The polymer was then dissolved in 5 mL THF and precipitated with 10 mL pentane and then repeated. The deep red polymer sample was then dried under vacuum for 12h and weighed to gravimetrically determine % conversion, and characterized by GPC and NMR. For kinetic experiments, ampoules were loaded in parallel and removed at defined intervals to track polymerization progress over time.

Example 2: Further Purification of the PVAc Polymer

[0057] A 10 cm silica gel column was used (100 - 200 mesh). 0.200 g of polymer was dissolved in THF and loaded onto the column using 50 mL of hexanes. After the polymer was fully loaded onto the column, the column was eluted with 50 mL CHCI ₃ to remove impurities. The remaining red fragment was eluted with 20 mL of THF. Solvent was evaporated under vacuum until approx. 5 mL and polymer precipitated by addition of 10 mL of pentane. The polymer was collected via filtration and dried under vacuum for 12h to isolate 0.122 g of purified PVAc.

Example 3: General Procedure of Stop - Start Experiment

[0058] For this experiment three different ampoules were used. All three ampoules with same amount of AIBN-VCI3BIMPY and VAc were heated and stirred in an oil-bath at 120°C for 3 hours. After 3 hours one of the ampoules was taken out and the molecular weight was determined by GPC. The remaining two ampoules were stored in the freezer (-35°C) for 24 hours. After 24 hours another ampoule was taken out and its molecular weight was determined by GPC. The last ampoule was put into an oil bath at 120°C and heated for more 3 hours.

Example 4: Preparation of Proton Terminated Polyvinyl acetate)

[0059] 0.200g (Run No: 5) PVAc polymer was added to a flask under an inert atmosphere in 10mL of degassed methanol. Then degassed 1- propanethiol was added with a syringe under an inert atmosphere. The mixture was heated to 50°C for 24h. The polymer was precipitated in heptane before being dried under vacuum before analysis by GPC and NMR. Resulting polymer: M _n = 3077, color = off-white, weight = 0.122g. H NMR (CDC ): 4.86 ppm (CH2CHOCOCH3, polymer chain); 3.87 (CH2CH2OCOCH3, proton terminated polymer chain); 2.04 (CH ₂ CHOCOCH ₃ , polymer chain); 1.7- 1 .9 (CH ₂ CHOCOCH ₃ , polymer chain); 1.4-1.5 (AIBN, partially obscured).

Example 5: Base-catalyzed Methanolysis to Produce Polyvinyl alcohol)

[0060] 0.200g VAc polymer (Run No: 6) was dissolved in 5 mL THF and 0.05g KOH was dissolved in 10 mL MeOH. The polymer solution was added slowly to KOH solution and this mixture stirred for 48h at room temperature. After removing all solvent under vacuum, the remaining residue was dissolved in 3mL distilled water and the polymer precipitated with 10ml_ of cold acetone. The product was collected by filtration and dried under vacuum before analysis by GPC and NMR. Resulting polymer, color = white, weight = 0,097g. ¹ H NMR (D ₂ 0): 4.14 (CH ₂ CHOH, polymer chain); 3.45 (CH ₂ CH ₂ OH, end group); 1.5-1.8 (CH ₂ CHOH, polymer chain); AIBN end groups partially obscured.

Discussion

[0061] The bis(iminopyridine) complex [BIMPY]VCI ₃ ([BIMPY] = 2,6- (ArN=CMe) ₂ C ₅ H ₃ N, Ar = 2,6-( ⁱ Pr)2C ₆ H ₃ )) ¹⁰ was screened for the CRP of styrene and vinyl acetate (VAc) initiated by AIBN at 120°C. While not wishing to be limited by theory, under these conditions, two potential equilibria could be established; an ATRP equilibrium, where the starting V(lll) complex provides the halogen to cap growing polymer chains or an OMRP equilibrium, where the V(lll) complex could trap growing polymer chains to form a dormant organometallic complex. Additionally, these two reactions could both be at work, where radicals extract halogens from V(lll) complexes to form V(ll) species in situ. These V(ll) species can then reversibly trap growing polymer chains. This potential interplay is shown in Scheme 1 .

[0062] For VAc, a controlled process is observed, as assessed by the linear increase of the molar mass with monomer conversion, while styrene polymerizations under the present conditions were uncontrolled. For VAc, polymer molecular weights accurately matched the chain length expected from monomer conversion in addition to the molecular weight of the vanadium complex (Figure 1). Significant deviations are noted at high conversions, and correlate with a change in solution color signifying the decomposition of the catalyst. Polydispersities (M Mn) are relatively low (-1.3) compared to styrene polymerizations (-1 .6-1 .8), but non-ideal. The distributions remain constant throughout the polymerization, suggesting inefficient initiation of AIBN.

[0063] Polymeric material isolated by repeated precipitation in pentane or purification by silica-gel column chromatography retained a strong red colour reminiscent of the catalyst, and ¹ H NMR characterization of the polymer showed no halogen terminated polymer chains. Discerning the end- groups through 2-D NMR was inconclusive, potentially due to the proximity of the paramagnetic vanadium catalyst. The kinetics of this process are first order in monomer, as exhibited by the linear dependence of ln([M] ₀ /[M _n ]) versus time, supporting a constant radical concentration (Figure 2). A short burst of uncontrolled polymerization as the reaction reaches equilbrium supports an inefficient initiation process. However, no long initiation period is observed and productive polymerization begins immediately, but the rate and level of control in the reaction varies based upon reaction temperature. Higher than expected molecular weights that are independent of conversion and broadened polydispersities are noted when polymerizations are conducted at 70°C and 90°C suggesting inferior initiation and chain exchange at these temperatures. These results suggest a vanadium-mediated radical polymerization, where polymer chains are reversibly trapped by vanadium complexes. While the [BIMPYJVC catalyst is sensitive to oxygen and moisture, the resultant red polymers are stable. Polymerizations can be stopped by simply lowering the temperature, and restarted by raising the temperature to 120°C, reinitiating the polymerization at the same rate to generate polymers which continue to match monomer conversion (Figure 3). Similarly, polymers can be isolated, purified by precipitation with pentane or silica-gel column chromatography, and used as macroinitiators with the addition of a new aliquot of vinyl acetate.

[0064] While the vanadium-capped polymer chains are robust, the catalyst can be readily removed. The thermal hemolytic cleavage of the V-C bond at 50°C in the presence of propane thiol afford the desired proton terminated polymer chains and the corresponding disulphide, ¹⁰ as confirmed by H and COSY NMR spectroscopy, generating nearly colorless polymer when recovered. Polymer chains can also be readily converted to polyvinyl alcohol) by a base-catalyzed methanolysis, ¹¹ removing the vanadium end-cap in the process. These reactions are shown in Scheme 2. Scheme 2

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