WO2021097557A1

WO2021097557A1 - Initiator system for cationic polymerization of olefins

Info

Publication number: WO2021097557A1
Application number: PCT/CA2020/051526
Authority: WO
Inventors: Gilles Arsenault; Khatera Hazin; Derek Gates; Anna Bennett
Original assignee: ARLANXEO Canada Inc.; The University Of British Columbia
Priority date: 2019-11-19
Filing date: 2020-11-12
Publication date: 2021-05-27

Abstract

A Brønsted-Lowry acid initiator system for cationic polymerization of an ethylenically unsaturated monomer involves an initiator having a structure of Formula (I) in an anhydrous polymerization medium: (I) where: M is tantalum (Ta) or niobium (Nb); R₁ and R₂ are the same or different and are H, unsubstituted C_1-3 alkyl, C_1-3 alkyl substituted with one or more F atoms, unsubstituted phenyl or phenyl substituted by one or more halogen atoms, C_1-4 alkyl moieties or halogenated C_1-4 alkyl moieties; L is a molecule that coordinates to H+; and, x is 0.125 or more.

Description

INITIATOR SYSTEM FOR CATIONIC POLYMERIZATION OF OLEFINS

Field

This application relates to a process for producing a polymer from one or more ethylenically unsaturated monomers. The application further relates to an initiator system for the process, and to compounds in the initiator system.

Background

Various types of initiator systems for cationic polymerization of ethylenically unsaturated monomers are known in the art, including systems based on protonic or Bransted-Lowry acids, Lewis acids (e.g. Friedel-Crafts catalysts), carbenium ion salts and ionizing radiation. Common protonic acids include phosphoric, sulfuric, fluoro-, and triflic acids, which tend to produce only low molecular weight polymers.

Lewis acids are the most common compounds used for initiation of cationic polymerization, and include, for example, SnCI , AICI₃, BF₃ and TiCI₄. Although Lewis acids alone may be able to induce polymerization, the reaction occurs much faster with a co-initiator that acts as a suitable cation source (e.g. water, alcohols, HCI). However, such cationic polymerization reactions generally require very low temperature (about -100°C to about -90°C) to produce polymers of suitable molecular weight. Further, polymerization processes performed at such low temperatures are energy intensive; therefore, a process that can produce polymers with similar molecular weights at higher temperatures would significantly reduce the energy consumption and manufacturing cost of the process.

An initiator system for cationic polymerization has been developed based on a pentavalent phosphorus (V) complex with a dihydroxy compound (United States Patent Publication US 2012/0208971 published August 16, 2012). However, this initiator system produces low molecular weight products at higher temperatures, requiring lower temperatures to produce polymers of desirably high molecular weight. For example, the polymerization of a-methyl styrene at -50°C produces poly(a-methylstyrene) having M_n of less than about 7000 g/mol, Further, in order to produce polystyrene having M_n of greater than 100,000 g/mol, the polymerization must be done at temperatures lower than -80°C. The phosphorus complex can also be difficult to handle due to lack of stability.

Initiator systems based on metal complexes with catechol compounds have been recently developed (WO 2018/107295 published June 21 , 2018 and WO 2019/113674 published June 20, 2019). Planar catechol ligands used to make such initiators have aromatic rings that both stabilize negative charge on the oxygen atoms and offer less steric hindrance to reaction at the oxygen atoms, facilitating reaction of the catechol ligands with the metal halide to form the initiator molecule.

There remains a need for initiator systems for cationic polymerization, which can produce suitably high molecular weight polymer at higher temperatures.

Summary

A strong Bransted-Lowry acid based on complexes of tantalum (V) ions or other isoelectronic metal ions (e.g. vanadium (V) or niobium (V) ions) provides an efficient initiator system for cationic polymerization of ethylenically unsaturated monomers at higher temperatures. High molecular weight polymers may be formed with the use of the present initiator system at higher temperatures.

In one aspect, there is provided a process for producing a polymer, the process comprising polymerizing one or more ethylenically unsaturated monomers under anhydrous conditions in presence of a Bransted-Lowry acid polymerization initiator, the Bransted-Lowry acid polymerization initiator having a structure of Formula (I):

where:

M is tantalum (Ta) or niobium (Nb);

Ri and R₂ are the same or different and are H, unsubstituted Ci-₃ alkyl, Ci-₃ alkyl substituted with one or more F atoms, unsubstituted phenyl or phenyl substituted by one or more halogen atoms, C-M alkyl moieties or halogenated CM alkyl moieties;

L is a molecule that coordinates to H⁺; and, x is 0.125 or more.

In another aspect, there is provided a Bransted-Lowry acid initiator system for cationic polymerization of an ethylenically unsaturated monomer, the Bransted-Lowry acid initiator system comprising an initiator having a structure of Formula (I) as defined above in an anhydrous polymerization medium.

In another aspect, there is provided a compound of Formula (I), where M, R, L and x are as defined above.

Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art.

Detailed Description

The strong Bransted-Lowry acid comprises a metal complex of organic ligands as described above for Formula (I).

Ri and R2 are preferably H, fully fluorinated C1-3 alkyl groups (e.g. CF3, CF3CF2), CH₃, phenyl, 4-methylphenyl, 4-trifluoromethyphenyl or phenyl substituted by one or more F or Cl atoms (e.g. 4-fluorophenyl). Ri and R₂ are more preferably CF₃. Ri and R₂ are preferably the same.

The Bransted-Lowry acid polymerization initiator is particularly useful for initiating the polymerization or copolymerization of ethylenically unsaturated monomers. Ethylenically unsaturated monomers are compounds having at least one olefin bond therein. The monomers preferably comprise from 2 to 20 carbon atoms. Some examples of ethylenically unsaturated monomers include alkyl vinyl compounds (e.g. alkyl vinyl ethers and the like), aryl vinyl compounds (e.g. styrene, a-methylstyrene, p- methylstyrene, p-methoxystyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 4-vinyltoluene and the like) and isoprene. Of particular note are n-butyl vinyl ether, styrene, a- methylstyrene, isobutlylene and isoprene. Polymers formed from the polymerization of the monomers may be homopolymers, copolymers, terpolymers or other forms of polymers. The polymers may be linear, branched or star branched. Mixtures of two or more monomers may be polymerized into copolymers or terpolymers. Some examples of polymers include polystyrene, poly(a-methylstyrene), poly(N-vinylcarbazole), polyterpenes, polyisoprenes, polyisobutylenes and the like. Of particular note are copolymers of isobutylene and isoprene (e.g. butyl rubber), polyisobutylene, polyisoprene, polystyrenes (e.g. polystyrene and poly(a-methylstyrene) and poly(n-butyl vinyl ether).

Polymers produced in the polymerization of ethylenically unsaturated monomers may have number average molecular weights (M_n) of at least about 2,000 g/mol, or at least about 5,000 g/mol, or at least about 10,000 g/mol, or at least about 20,000 g/mol, or at least about 30,000 g/mol, or at least about 50,000 g/mol, or at least about 100,000 g/mol, depending on the monomer or momomers undergoing polymerization, the relative amounts of monomer and initiator, the temperature at which the polymerization is conducted and other process conditions. The polymer may have number average molecular weights (M_n) up to about 1,000,000 g/mol, or up to about 500,000 g/mol, or up to about 250,000 g/mol.

The initiator is a cationic initiator because the initiator is a Bransted-Lowry acid, thereby further comprising a hydrogen ion (H⁺) as counterion to an anionic metal complex. To stabilize the hydrogen ion, the initiator may further comprise a stabilizing molecule (L) for the hydrogen ion. The stabilizing molecule is a molecule that is able to stabilize the hydrogen ion without making the hydrogen ion unavailable for catalyzing the polymerization. The value of x may be an integer or a fractional number depending on whether H⁺ ions associated with neighboring complexes in a bulk material of the polymerization initiator share a molecule, L. When a molecule L is shared between neighboring H⁺ ions, the value of x may be fractional. The value of x is preferably 0.5 or more, more preferably 0.5, 1 , 1.5, 2, 2.5 or 3. In one embodiment, there are two stabilizing molecules for each H⁺ ion (i.e. x = 2). The stabilizing molecule may be a molecule that can form hydrogen bonds with the hydrogen ion. The stabilizing molecule may therefore contain one or more atoms that have lone pairs of electrons, for example O or N atoms. Sterically-hindered stabilizing molecules having one or more lone pairs of electrons are particularly useful as they sufficiently stabilize the hydrogen ion while permitting the hydrogen ion to initiate carbocationic polymerization. Some examples of stabilizing molecules include ethers and the like. Aprotic stabilizing molecules are preferred. Alkyl and cycloalkyl ethers are particularly preferred. Some examples of suitable stabilizing molecules are tetrahydrofuran, tetrahydropyran, dioxane, dimethyl ether, diethyl ether, bis(2-chloroethyl) ether, dipropyl ether, diisopropyl ether, methyl ethyl ether, methyl n-propyl ether, methyl isopropyl ether, bis(2-chloroisopropyl) ether, methyl tert-butyl ether, ethyl tert-butyl ether, diisobutyl ether, dihexyl ether, 2,5- dimethyltetrahydrofuran, 2-chloro ethyl ether, 2-methyltetrahydrofuran, cyclopentyl methyl ether, diethylene glycol dimethyl ether (diglyme), tetraethylene glycol dimethyl ether, diphenyl ether, 2,6-di-tert-butyl pyridine, crown ethers and the like. In one embodiment, the stabilizing molecule is diethyl ether. Where the stabilizing molecule is a solvent, the stabilizing molecule may form a solvate with the hydrogen ion. The compound of Formula (I) may be synthesized by contacting a metal ion precursor compound in a reaction mixture with an organic diol ligand compound of Formula (II):

where Ri and R₂ are as defined above. Mixtures of different organic diol ligand compounds may be used. Some examples of organic diol ligand compounds are: hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol; 1 ,1 ,1 ,2,2,5,5,6,6,6-decafluoro-3,4- bis(trifluoromethyl)-3,4-hexanediol; 1 ,1 ,1 ,4,4,4-hexafluoro-2,3-butanediol; 1 ,1 ,1 ,4,4,4- hexafluoro-2,3-dimethyl-2,3-butanediol; 1 ,1,1 ,4,4,4-hexafluoro-2-methyl-3-phenyl-2,3- butanediol; 1 ,1 ,1 ,4,4,4-hexafluoro-2,3-diphenyl-2,3-butanediol; 1 ,1 ,1 ,4,4,4-hexafluoro-2,3- bis(4-methylphenyl)-2,3-butanediol; and, stereoisomers thereof.

The metal ion precursor compound and organic diol ligand compounds may be present in the reaction mixture in amounts to provide a molar ratio that results in the metal complex having sufficient ligands to provide a negative charge to the metal complex. To provide metal complexes of the Formula (I), about 4 molar equivalents of the organic diol ligand compound of Formula (II) is suitable to result in the metal complex having three bidentate ligands.

Compounds of the Formula (II) are aliphatic diols as opposed to aromatic diols such as catechols. Aromatic diols are planar offering less steric hindrance to reactions at the diol oxygen atoms, and also stabilize the negative charge on the diol oxygen atoms through delocalization of electron density. In contrast, the oxygen atoms of the aliphatic diols of Formula (II) are more sterically hindered and do not benefit from stabilization due to resonance delocalization. Therefore, it is unexpected that the aliphatic diols of Formula (II) can react with the metal precursor to produce compounds of the Formula (I) in yields that are at least comparable to the yields found with catechol ligands.

The metal ion precursor compound may be a compound of a metal ion with leaving groups as ligands. Suitable leaving groups include, for example, halogen (Cl, Br), CO, CN and the like. The metal ion precursor compound and organic ligand compounds are preferably dry and high purity. Contacting the metal ion precursor compound with the organic ligand compounds may be performed in the presence or absence of a solvent, preferably in the presence of a solvent. The solvent may comprise an aprotic organic solvent, preferably a non-coordinating solvent. Some examples of suitable solvents include alkyl halides (e.g. dichloromethane), aliphatic hydrocarbons (e.g. hexanes) and aromatic hydrocarbons (e.g. toluene). A stabilizing molecule for hydrogen ions is included in the reaction mixture, preferably after the metal complex is formed, to solvate the hydrogen ion. The reaction is preferably conducted under anhydrous conditions. The reaction may be conducted at elevated temperature, for example by refluxing the solvent. The reaction may be conducted for an amount of time sufficient to maximize the yield of the initiator, for example for a time up to about 3 hours. The reaction is preferably conducted by slowly adding the ligand compound to a reaction mixture containing the metal ion precursor compound, although other addition schemes may be used. The initiator may be recovered from the reaction mixture by standard techniques, for example filtration, washing, recrystallization and drying.

The initiator is preferably used in amount to provide a monomer to initiator mole ratio ([M]:[l]) of at least about 20:1. A higher [M]:[l] may be preferred in some embodiments to produce high yields of high molecular weight polymer. In some embodiments, the [M]:[l] may be at least about 100:1. In some embodiments, the [M]:[l] may be in a range of about 100:1 to about 1000:1 , or about 200:1 to about 800:1, or about 300:1 to about 500:1 .

The polymerization is generally conducted in a polymerization medium. The polymerization medium may be provided, for example, by a solvent or diluent. Solvents or diluents for the polymerization may include, for example a halogenated organic liquid, a non-halogenated organic liquid or mixtures thereof. Halogenated organic liquids include, for example, chlorinated or fluorinated organic compounds. Chlorinated organic compounds include, for example C1-C4 alkyl chlorides (e.g. dichloromethane (DCM) and methyl chloride (MeCI)). DCM is generally useful as a solvent for solution polymerization, while MeCI is generally useful as a diluent for slurry polymerization. Fluorinated organic compounds include, for example, hydrofluorocarbons (HFC) such as 1 , 1 ,1 ,2- tetrafluoroethane and the like, and hydrofluorinated olefins (HFO) such as 2, 3,3,3- tetrafluoro-1-propene and the like. Fluorinated organic compounds are generally useful as diluents for slurry polymerization. Non-halogenated organic liquids include, for example, aliphatic hydrocarbons (e.g. cyclohexane, cyclopentane, 2,2-dimethylbutane, 2,3- dimethylbutane, 2-methylpentane, 3-methylpentane, n- hexane, methylcyclopentane and 2,2-dimethylpentane). Halogenated organic solvents, in particular C1-C4 alkyl chlorides are preferred. Dichloromethane (CH2CI2) or methyl chloride (MeCI) are particularly preferred.

The solvent or diluent is preferably present in the polymerization medium in an amount of about 10-80 vol%, based on volume of the polymerization medium. In preferred embodiments, the medium may comprise a diluent in an amount of about 50-85 vol%, or a solvent in an amount of about 10-50 vol%.

The polymerization is conducted under anhydrous conditions. Preferably, water is present in an amount less than about 1 ppm, more preferably less than about 0.5 ppm, yet more preferably less than about 0.1 ppm. It is preferable to eliminate water from the polymerization medium altogether. Reducing or eliminating moisture in the polymerization medium helps to produce polymers having higher molecular weights at higher yields.

It is an advantage of the present initiator system that the polymerization may be conducted at a higher temperature than with other Bransted-Lowry acid or Lewis acid initiator systems, while being able to produce suitably high molecular weight polymers at good yield. The temperature at which the polymerization is conducted may be -90°C or higher, or -85°C or higher, or -80°C or higher, or -70°C or higher, or -60°C or higher, or -50°C, or -40°C or higher. The temperature may be as high as 30°C or lower, or 20°C or lower, or 10°C or lower, or 0°C or lower, or -10°C or lower, or -15°C or lower, or -20°C or lower, or -25°C or lower, -30°C or lower, or -35°C or lower.

EXAMPLES:

General Materials and Procedures·.

All experiments were performed using standard Schlenk or glove box techniques under nitrogen atmosphere.

Dichloromethane (CH₂CI₂) and diethyl ether (Et₂0) were deoxygenated with nitrogen and dried by passing through a column containing activated alumina. CH₂CI₂ (Sigma Aldrich), Et₂0 (Fisher Scientific), styrene (Sigma Aldrich) and n-butyl vinyl ether (Sigma Aldrich) were dried over calcium hydride, distilled and freeze-pump-thaw (x3) degassed prior to use. CH₂CI₂ and Et₂0 were stored over molecular sieves prior to use.

Tantalum pentachloride (Aldrich) and niobium pentachloride (Aldrich) were used without further purification. Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (Matrix Scientific) was used without further purification.

Molecular weight of polymers was determined by triple detection gel permeation chromatography (GPC-LLS) utilizing an Agilent 1260 Series standard auto sampler, an Agilent 1260 series isocratic pump, Phenomenex Phenogel™ 5 pm narrowbore columns (4.6 x 300 mm) 10⁴ A (5000-500,000), 500 A (1 ,000-15,000), and 10³ A (1 ,000-75,000), a Wyatt Optilab™ rEx differential refractometer (l = 658 nm, 25 °C), as well as a Wyatt tristar miniDAWN (laser light scattering detector (l = 690 nm)) and a Wyatt ViscoStar viscometer. Samples were dissolved in THF (ca. 2 mg mL^-1) and a flow rate of 0.5 mL min^-1 was applied. The differential refractive index (dn/dc) of poly(n-butyl vinyl ether) (dn/dc = 0.068 mL g^_1) in THF was calculated by using Wyatt ASTRA software 6.1. The differential refractive index (dn/dc) of poly(styrene) ( dn/dc = 0.185 mL g^_1) and of poly(a- methylstyrene) (dn/dc = 0.204 mL g^_1) has been reported in McManus NT, Penlidis A. J. Appl. Polym. Sci. 1998, 70, 1253-1254. The differential refractive index (dn/dc) of poly(isoprene) (dn/dc = 0.129 mL g^_1) (Jackson C, Chen YJ, Mays JW. J. Appl. Polym. Sci. 1996, 61 , 865) has been reported. Initiator (III)

Synthesis of H(0Et2)2[Ta(1,2-C₂02(CF₃)4)3] (III)

TaCI₅ (0.242 g, 0.895 mmol) was stirred in anhydrous CH₂CI₂ (8 mL) and the white suspension was slowly heated to reflux under N₂ atmosphere. In a separate Schlenk flask, perfluoropinacol (1.312 g, 3.927 mmol) was dissolved in warm anhydrous CH₂CI₂ (10 mL) and the solution was added via cannula to the refluxing TaCIs solution to afford a brown mixture. The reaction mixture was refluxed for 100 min and cooled to ambient temperature. Upon addition of Et₂0 (20 mL), a brown clear solution formed. The solution was cooled in an ice bath to afford an off-white precipitate within 30 min. The solid was collected by filtration, washed with CH₂CI₂ (2 mL) and dried in vacuo. Yield = (0.553 g, 0.447 mmol, 50%).

Ή NMR spectrum at -90°C: H⁺ at 16.72 ppm. ESI-MS(-ve): 1176.6 m/z.

The position in the ¹H NMR spectrum for the H⁺ peak demonstrates that the proton is highly acidic.

Polymerization of monomers using Initiator (III)

Polymerization of monomers with Initiator (III) was performed by the following general procedure.

Initiator and monomer are initially stored at -30°C inside a freezer in a glovebox under a positive atmosphere of dry N2 gas. The initiator (0.010 g, 0.010 mmol) is transferred to a 25 mL Schlenk flask, which is sealed with a rubber septum and then brought outside the glovebox maintaining isolation from the outside atmosphere to be connected to a dry N2 gas line. The initiator in the flask is cooled to -78°C with an acetone/dry ice bath. Anhydrous, degassed CH₂CI₂ (2.0 mL) stored over activated molecular sieves is added via syringe to the initiator under a flow of dry N₂ gas and stirred to guarantee a homogenous solution at -78°C. The mixture is kept at -78°C for 10 minutes, or warmed or cooled to a different desired temperature and held at that temperature for 10 minutes, before addition of the monomer.

Freshly prepared and degassed monomer in an amount to achieve a desired monomer to initiator ratio ([M]:[l]) is collected in a 1 ml single-use plastic syringe inside the glovebox. The monomer is then injected rapidly through the rubber septum on the Schlenk flask into the initiator solution at the desired temperature under a constant flow of dry N₂ gas, and the reaction mixture is continuously stirred for 15 minutes while polymerization occurs. After the 15 minutes, the reaction is quenched with 0.2 mL of a solution of NH4OH in MeOH (10 vol%), the Schlenk flask is removed from the cooling bath and all volatiles are removed in vacuo. The crude product is dissolved in 2 mL CH₂CI₂ and added one drop at a time via syringe to vigorously stirred MeOH (40 mL) to precipitate an oily residue. The polymer is collected by centrifugation and dried in vacuo. Absolute molecular weight (M_n) is determined using triple-detection GPC. n-butyl vinyl ether polymerization

Table 1 shows data for the polymerization of n-butyl vinyl ether using Initiator (III). The data for each example represents the average of at least three separate polymerization reactions. Table 1 shows that significant yield of poly(n-butyl vinyl ether) having a good molecular weight (M_n) can be achieved at a temperature well above -90°C, and even at room temperature.

Table 1

styrene polymerization

Table 2 shows data for the polymerization of styrene using Initiator (III). The data for each example represents the average of at least three separate polymerization reactions. Table 2 shows that very good yield of polystyrene can be achieved at a temperature well above -90°C, and that the yield is even much better at room temperature than at -78°C.

Table 2

a-methylstyrene polymerization

Table 3 shows data for the polymerization of a-methylstyrene using Initiator (III). The data for each example represents the average of at least three separate polymerization reactions. Table 3 shows that poly(a-methylstyrene) having a high molecular weight (M_n) can be achieved at lower temperature.

Table 3

isoprene polymerization

Table 4 shows data for the polymerization of isoprene using Initiator (III). The data for each example represents the average of at least three separate polymerization reactions. Table 4 shows that very high yields of polyisoprene can be achieved at room temperature. While the molecular weight is low, such polyisoprene would be well suited for adhesive applications. Table 4

isobutylene polymerization

Isobutylene polymers (PIB) and isobutylene-isoprene copolymers (MR - butyl rubber) were prepared using Initiator (III) by a different procedure as follows.

Initiator (III) (100 mg) was stirred in anhydrous CH₂CI₂ (25 mL) for 30 minutes at -30°C. In another reaction flask, 6 mL of dry isobutylene (or 6 mL of dry isobutylene and 0.25 mL of isoprene when producing MR) and 50 mL CH₂CI₂ was stirred at -30°C, then 7 mL of the initiator solution was added. The reaction mixture was stirred for 17 minutes at -30°C. Afterwards, the polymerization was stopped by adding 0.1 mL alcohol containing 1

Molar tetrakis-[methylene-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)] methane (CAS# 6683-19-8). The solvent was evaporated from the reaction mixture. The polymer residue was dissolved in hexane, filtered, and then the hexane removed to provide a polymer. Table 5 shows data for the preparation of PIB (Ex. 16 and 17) and NR (Ex. 18). The data for each example represents one polymerization reaction. Table 5 shows that good yields of polyisobutylene and butyl rubber can be achieved.

Table 5

Initiator (IV)

Synthesis ofH(OB^JNb(1,2-C₂02(CF^4)^ (IV)

Initiator (IV) in 50% yield was synthesized by the process described above for Initiator (III), except that NbCI₅ was used as the metal precursor.

Ή NMR spectrum at -90°C: H⁺ at 16.68 ppm. ESI-MS(-ve): 1088.6 m/z.

The position in the ¹H NMR spectrum for the H⁺ peak demonstrates that that the proton is highly acidic.

Polymerization of monomers using Initiator (IV) Polymerization of monomers with Initiator (IV) was performed by the same procedure as described above for Initiator (III). n-butyl vinyl ether polymerization

Table 6 shows data for the polymerization of n-butyl vinyl ether using Initiator (IV). The data for each example represents the average of at least three separate polymerization reactions. Table 6 shows that significant yield of poly(n-butyl vinyl ether) having a good molecular weight (M_n) can be achieved at a temperature well above -90°C, and even at room temperature. Table 6

styrene polymerization

Table 7 shows data for the polymerization of styrene using Initiator (IV). The data for each example represents the average of at least three separate polymerization reactions. Table 7 shows that very good yield of polystyrene can be achieved at a temperature well above -90°C, and that the yield is even much better at room temperature than at -78°C.

Table 7

a-methylstyrene polymerization

Table 8 shows data for the polymerization of a- methyl styrene using initiator (IV). The data for each example represents the average of at least three separate polymerization reactions. Table 8 shows that poly(a-methylstyrene) having a high molecular weight (M_n) can be achieved at lower temperature.

Table 8

isoprene polymerization

Table 9 shows data for the polymerization of isoprene using initiator (IV). The data for each example represents the average of at least three separate polymerization reactions. Table 9 shows that very high yields of polyisoprene can be achieved at room temperature. While the molecular weight is low, such polyisoprene would be well suited for adhesive applications.

Table 9

Initiator (V) Synthesis of non-fluorinated intiiator from TaCI5 and 2,3-bis(methyl)-2,3-butanediol

Initiator (V) was synthesized in the same manner as Initiator (III) described above using 3 molar equivalents of 2,3-bis(methyl)-2,3-butanediol as the ligand instead of 4 molar equivalents of 2,3-bis(trifluoromethyl)-2,3-butanediol. 2,3-bis(methyl)-2,3-butanediol is a non-halogenated analogue of 2,3-bis(trifluoromethyl)-2,3-butanediol. 1H NMR spectrum at -90°C: several H⁺ signals between 8 and 16 ppm. H⁺ signals below 16 ppm indicate a weakly acidic proton. Multiple proton resonances indicate multiple types of acidic protons, which suggests a mixture of products. ¹³C{¹H} NMR spectrum: pinacol signals at 24.7 ppm. 25.2 ppm and 75.1 ppm. n-butyl vinyl ether polymerization Table 10 shows data for the polymerization of n-butyl vinyl ether using Initiator (V).

The data for each example represents the average of at least three separate polymerization reactions. Table 10 shows that significant yield of poly(n-butyl vinyl ether) can be achieved at a temperature well above -90°C, but that no polymer is formed at low temperatures. Table 10

styrene and a-methylstyrene polymerization

Attempts to polymerize styrene and a-methylstyrene using Initiator (V) all failed to produce polymer. It is apparent from these polymerization attempts and the Example 31 that Initiator (V) possessing non-halogenated pinacol ligands has a less reactive proton than the initiators having halogenated pinacol ligands.

Compared to initiators comprising non-halogenated pinacol ligands, the initiators comprising halogenated pinacol ligands are superior at initiating polymerization across a broader selection of monomers.

The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.

Claims

Claims:

1. A Bransted-Lowry acid initiator system for cationic polymerization of an ethylenically unsaturated monomer, the Bransted-Lowry acid initiator system comprising an initiator having a structure of Formula (I) in an anhydrous polymerization medium:

where:

M is tantalum (Ta) or niobium (Nb);

Ri and R₂ are the same or different and are H, unsubstituted Ci-₃ alkyl, Ci-₃ alkyl substituted with one or more F atoms, unsubstituted phenyl or phenyl substituted by one or more halogen atoms, Ci_ alkyl moieties or halogenated Ci_ alkyl moieties;

L is a molecule that coordinates to H⁺; and, x is 0.125 or more.

2. The system according to claim 1, wherein M is Ta.

3. The system according to claim 1 or 2, wherein L is an alkyl ether or a cycloalkyl ether.

4. The system according to claim 1 or 2, wherein L is diethyl ether.

5. The system according to any one of claims 1 to 4, wherein Ri and R₂ are the same and is CF₃.

6. The system according to any one of claims 1 to 5, wherein L is Et₂0 and x is 2.

7. The system according to any one of claims 1 to 6, wherein the polymerization medium comprises dichloromethane or methyl chloride.

8. The system according to any one of claims 1 to 7, containing substantially no water.

9. A process for producing a polymer, the process comprising polymerizing one or more ethylenically unsaturated monomers with the initiator system as defined in any one of claims 1 to 8.

10. The process according to claim 9, wherein the polymerization is performed at a temperature of -85°C or higher.

11. A compound of Formula (I):

where:

M is tantalum (Ta) or niobium (Nb);

Ri and F¾ are the same or different and are H, unsubstituted C1-3 alkyl, C1-3 alkyl substituted with one or more F atoms, unsubstituted phenyl or phenyl substituted by one or more halogen atoms, Ci_ alkyl moieties or halogenated Ci_ alkyl moieties;

L is a molecule that coordinates to H⁺; and, x is 0.125 or more.

12. The compound according to claim 11, wherein M is Ta.

13. The compound according to claim 11 or 12, wherein L is an alkyl ether or a cycloalkyl ether.

14. The compound according to any one of claims 11 to 13, wherein Ri and R₂ are the same and are CF3.

15. The compound according to claim 11, wherein L is Et₂0 and x is 2.