GB2442952A

GB2442952A - Alkoxyamines and nitroxide free radical mediators for polymerisation of vinyl monomers

Info

Publication number: GB2442952A
Application number: GB0620973A
Authority: GB
Inventors: Neil Cameron; Olivier Lagrille
Original assignee: University of Durham
Current assignee: University of Durham
Priority date: 2006-10-21
Filing date: 2006-10-21
Publication date: 2008-04-23
Also published as: GB0620973D0

Abstract

Nitroxides of formula II, and the corresponding alkoxyanuines of formula I (from which these nitroxides are produced) can be used as mediators for the controlled radical polymerisation or copolymerisation of one or more vinyl monomers at temperatures less than 100 {C. The nitroxides are produced from the corresponding alkoxyamines during the (co)polymerisation reaction. <EMI ID=1.1 HE=38 WI=86 LX=596 LY=1104 TI=CF> wherein: <DL TSIZE=14> <DT>R<1><DD>is C1-30 optionally unsaturated alkyl or cycloalkyl; <DT>R<2> and R<3><DD>are H, C1-10 optionally unsaturated alkyl or cycloalkyl, C1-10 aryl or aralkyl; or <DT>R<2> and R<3><DD>, together with the carbon to which they are attached, form a cyclic structure having 3-8 atoms; <DT>R<4><DD>is H, C1-10 optionally unsaturated alkyl or cycloalkyl, or C1-10 aryl or aralkyl; <DT>R<5><DD>is C3-12 cycloalkyl or -CR<6>R<7>R<8>; and <DT>R<6>, R<7> and R<8><DD>are H, C1-10 optionally unsaturated alkyl or cycloalkyl, optionally substituted aryl or -CN. </DL>

Description

I

NITROXIDE MEDIATORS FOR POLYMERISATION

Background

Nitroxide stable free radicals of general formula R2N-0 can be used to control radical polymerisations, which results in a number of desireable features of the polyrnerisation reaction including control over the final polymer molecular weight achieved, a narrow polydispersity and the ability to form block copolymers. In such nitroxide-mediated polymerisations, the nitroxide moiety is commonly employed in the form of an alkoxyamine of general formula R2N-O-R'. The alkoxyamine is the initiator of the radical polymerisation, and the nitroxide forms in situ through cleavage of the NO-R' bond during the polymerisation reaction. The prior art describes the use of alkoxyamines derived from cyclic nitroxides such as 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) for this process, however these cyclic nitroxides possess several limitations. Polymerisation is slow and only occurs at elevated temperatures, such as at 125 C. In addition, these nitroxides do not give efficient polymerisation of monomers such as acrylates and acrylamides. Other prior art describes the use of alkoxyamines derived from open chain nitroxide species which show some advantages compared to the cyclic species described above. These nitroxides, which include tert-butyl-1-phenyl-2-methylpropyt nitroxide (known as TIPNO) and tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide (known as OEPN or SGI), have been shown to mediate radical polymensations at lower temperatures, typically C but occasionally at 90 C, and can also control the polymerisations of acrylates and acrylamides. However, efficient control over the polymerisation of acrylates and acrylamides is only achieved when a small extra portion of free nitroxide is used in combination with the alkoxyamine. Furthermore, the polymerisation proceeds very slowly at temperatures of less than 100 C. Free radical polymerisations are typically conducted at temperatures of 50-80 C over 8 hours, thus these acyclic nitroxides are not directly usable in existing chemical processes employed in industry. A further disadvantage of the nitroxides described in the prior art is that the required high temperatures make heterogeneous polymerisations, in which monomer is dispersed in an aqueous medium, difficult to conduct. Typically, pressure vessels are required in order to conduct these polymerisations at temperatures greater than 100 C. Heterogeneous polymerisations such as emulsion polymerisation are very commonly employed in industry to manufacture polymers by free radical methods. The requirements of high temperatures and pressure vessels represent a severe drawback for industrial implementation of nitroxides in heterogeneous polymerisations.

Statement of invention

The invention relates to the use of nitroxide stable free radicals and the alkoxyamines from which they are derived in the polymerisation or copolymensation of at least one monomer which is polymerisable by radical methods. We have surprisingly found that nitroxides of the general formula described herein allow the rapid and controlled polymerisation of vinyl monomers at temperatures below 100 C and even as low as C.

Advantages The invention overcomes the disadvantages described above of nitroxide stable free radicals employed in free radical polymerisations. The nitroxides described in the present invention allow excellent control of polymerisation while still ensuring a much faster rate of polymerisation compared to the nitroxides described in the prior art.

Another advantage of the present invention is that an additional quantity of nitroxide need not be used in conjunction with the alkoxyamine to ensure good control over the polymerisation of vinyl monomers. A further advantage of the present invention is that polymerisations can be conducted at temperatures below 100 C and even as low as 60 C..

Introduction to Drawings

Figure 1 shows the synthetic scheme for the nitroxide TITNO and its alkoxyamine St-TITNO.

Figure 2 shows the kinetic plot for the bulk polymerisation of styrene (100 equivalents) with St-TITNO (1 equivalent) at 70 C.

Figure 3 shows the time dependence of ln([M]0ILMI) for the bulk polymerisation of styrene (100 equivalents) with St-TITNO (1 equivalent) at 70 C1 indicating agreement with the Persistent Radical Effect theory of Fischer et al. (ref) Figure 4 shows evolution of M and polydispersity index (P01) with conversion for the bulk polymerisation of styrene (100 equivalents) with St-TITNO (1 equivalent) at 70 DC.

Figure 5 shows gel permeation chromatography (GPC) traces for the polymers described in Examples 7 and 9.

Figure 6 shows an Arrhenius plot for the decomposition of the alkoxyamine St-TITNO.

Figure 7 shows the values for activation energy (Es) and dissociation rate constant at 120 C (kd'20) for St-TITNO and St-TIPNO.

Detailed Description

The invention concerns nitroxides that are efficient mediators for free radical polymerisations, the corresponding alkoxyamines that produce these nitroxides during the polymerisation reaction and their subsequent use in the polymerisation of vinyl monomers in a controfled fashion at temperatures below 100 C.

One aspect of the present invention concerns nitroxides of the general formula R1__ in which R1 represents a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, bearing from I to 30 carbon atoms; R2 and R3, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, an aryl or aralkyl fragment containing from I to 10 carbon atoms, or are part of a cyclic structure that also includes the carbon to which R2 and R3 are attached, said cyclic structure containing between 3 and 8 atoms; and R4 represents a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from 1 to 10 carbon atoms, or an aryl or aralkyl fragment containing from 1 to 10 carbon atoms.

Of the compounds represented by general formula I the preferred embodiment is when R' = (CH3)3C-, R2 = (CH3)2CH-, R3 (CH3)3C-and R4 = H. The nitroxides represented by general formula I can be prepared by methods described in the literature. A commonly employed method involves the addition of fragment R3 as a nucleophile to an electrophilic compound that already bears fragments R', R2 and R4. Examples of nucleophilic reagents suitable for adding R3 in this manner include organomagnesium reagents of the general formula RMgX (X = a halogen atom) and organolithium reagents of the general formula RLi. One example of an electrophihc molecule that can couple with said nucleophilic reagents is a nitrone, as described by Hawker et al. (Journal of the American Chemical Society, 1999, 121, 3904). The product of this coupling reaction is a hydroxylamine, which is converted into a nitroxide by treatment with an oxidant such as Pb02. A further example of an electrophilic molecule that can couple with said nucleophilic reagents is an imine, as described by Grimaldi et al. (WO 96/24620, 1996). The product of this coupling reaction is an amine which is converted into a nitroxide by treatment with an oxidant such as meta-chloroperbenzoic acid (mCPBA).

The preferred method of those described above for the preparation of compounds of general formula I is the addition of an organolithium species R3-Li to an imine bearing R', R2 and R4, followed by oxidation of the resulting amine with mCPBA. The procedure employed usually consists of adding a solution of R3-Li in an organic solvent dropwise to a solution of the imine in an organic solvent, previously cooled to below room temperature. The resulting mixture is warmed to occ over 2h, then quenched with concentrated NH4CI aqueous solution and pure water to dissolve any solids. The organic phase is extracted at room temperature in a suitable organic solvent and the aqueous phase is washed twice with that organic solvent. The fractions are combined and the solvent is then gently removed under reduced pressure at room temperature. The resulting crude intermediate product is dissolved in dichioromethane and added dropwise to a solution of mCPBA in dichioromethane at 15-17 C in a water bath for 2h. The mixture is then quenched by a concentrated aqueous solution of sodium hydrogenocarbonate, and the organic layer is extracted and rinsed twice with water. The solvent is then removed under reduced pressure at room temperature and the product is purified by flash chromatography with an eluent of ethyl acetate/hexane.

A further aspect of the present invention concerns alkoxyamines of the general formula R2 in which R1 represents a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, bearing from I to 30 carbon atoms; R2 and R3, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, an aryl or aralkyl fragment containing from I to 10 carbon atoms, or are part of a cyclic structure that also includes the carbon to which R2 and R3 are attached, said cyclic structure containing between 3 and 8 atoms; R4 represents a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, or an aryl or aralkyl fragment containing from I to 10 carbon atoms; and R5 represents a cyclic alkyl fragment of between 3 and 12 atoms or a fragment of the general formula in which R6, R' and R8, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from 1 to 10 carbon atoms, a phenyl group, a substituted phenyl group with between I and 5 substituents, an aryl group, a substituted aryl group with between I and 9 substituents, or a cyano group.

Of the compounds represented by general formula 2 the preferred embodiment is when R1 = (CH3)3C-, R2 = (CH3)2CH-, R3 = (CH3)3C-, R4 = H and R5 = (CH3)(Ph)CH- (R6=CH3, R7 Ph, R8=H).

The alkoxyamines represented by general formula 2 can be prepared by methods described in the literature. A commonly employed method involves generating an alkyl radical corresponding to fragment R5 which couples to the nitroxide molecule of general formula 1, forming the alkoxyamine. Methods for generating the alkyl radicals equivalent to R5 include the decomposition of peroxy compounds of general formula RO-OR (Cameron et al., Macromolecular Chemistry and Physics, 2000, 201, 2510), abstraction of hydrogen by peroxy radicals from hydrocarbons of the general formula R5-H (Drockenmuller et al., Macromolecules, 2004, 37, 2076) and treatment of halo compounds of the type R5-X with a transition metal catalyst-ligand system such as CuBr/bipyridine (Matyjaszewski et al., Macromolecules, 1998, 31, 5955). A further commonly employed method of preparing alkoxyamines of general formula 2 from nitroxides of general formula I involves reaction of the nitroxide with a vinyl monomer such as styrene, catalysed by [N, N9-bis(3,5-di-teilbutylsalicylidene)-1 2-cyclohexanediaminato]-manganese (Ill) chloride (Jacobsen's catalyst) in the presence of NaBH4 and air at room temperature (Hawker et al., Journal of the American Chemical Society, 1999. 121, 3904). A yet further commonly employed method of preparing alkoxyamines of general formula 2 from nitroxides of general formula I involves the oxidation of alkyl hydrazines of general formula R5-NHNH2 with Pb02 in the presence of nitroxide I (Hawker et al., Journal of the American Chemical Society, 1999, 121, 3904).

The preferred method of those described above for the preparation of compounds of general formula 2 is the reaction involving Jacobsen's catalyst. The procedure involves bubbling air through a mixture of toluene and ethanol (111) for 1 h before adding styrene, nitroxide, [N, N9-bis(3,5-di-tertbutylsalicylidene)-1,2-cyclohexanediaminato]-manganese (Ill) chloride and sodium borohydride, in that order. Air is bubbled through the resulting mixture for 13 h while stirring is continued.

The resulting solution is then filtered twice through a layer of silica on sand to remove the solids. The solvent is removed on a rotary evaporator and the crude product is purified by flash chromatography.

Alkoxyamines of general formula 2 according to the present invention may be used in the polymerisation and copolymerisation of vinyl monomers possessing a carbon-carbon double bond, by free radical polymerisation methods. The polymerisation procedure is familiar to those skilled in the art and involves dissolving the alkoxyamine in the monomer, either alone or in the presence of an additional solvent such as an organic solvent, water or an aqueous solution. The resulting mixture is deoxygenated then heated at a temperature between 0 and 150 C for a given period of time. Suitable monomers include vinyl aromatics such as styrene, substituted styrenes and divinylbenzene, dienes including butadiene and isoprene, acrylate esters including methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl acrylate, hexyl acrylate, 2-ethyihexyl acrylate, dodecyl acrylate, N,N-dimethylaminoethyl acrylate, glyceryl acrylate, oligo(oxyethylene) acrylate and poly(oxyethylene) acrylate, acrylic acid, acrylic anhydride, acrylamide and N-substituted acrylamide derivatives including N,N-dimethyl acrylamide, N-isopropyl acrylamide and methacrylamide derivatives such as 2-hydroxypropyl methacrylamide. Other suitable monomers include vinyl compounds such as vinyl chloride, vinylidene dichioride, vinylidene difluoride, acrylonitrile and N-vinyl pyrrolidone. The alkoxyamine may be used at concentrations from 0.02 to 5% by moles relative to the monomer content. Unlike related work described in the prior art (Hawker et al, Journal of the American Chemical Society, 1999, 121, 3904), an additional quantity of free nitroxide of general formula I need not be used in conjunction with the alkoxyamine of general formula 2 to ensure control over the polymerisation.

Polymers prepared from alkoxyamines of general formula 2 as described in the preceding section may then be used to prepare block copolymers. The procedure is familiar to those skilled in the art and involves dissolving the polymer prepared as described in the preceding section in a monomer, which may be identical to the first monomer or different, either alone or in the presence of an additional solvent such as an organic solvent, water or an aqueous solution. The resulting mixture is deoxygenated then heated at a temperature between 0 and 150 C for a given period of time. Suitable second monomers include vinyl aromatics such as styrene, substituted styrenes and divinylbenzene, dienes including butadiene and isoprene, acrylate esters including methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl acrylate, hexyl acrylate, 2-ethyihexyl acrylate, dodecyl acrylate, N,N-dimethylaminoethyl acrytate, glyceryl acryf ate, oligo(oxyethylene) acrylate and poly(oxyethylene) acrylate, acrylic acid, acrylic anhydride, acrylamide and N-substituted acrylamide derivatives including N,N-dimethyl acrylamide, N-isopropyl acrylamide and methacrylamide derivatives such as 2-hydroxypropyl methacrylamide.

Other suitable monomers include vinyl compounds such as vinyl chloride, vinylidene dichioride, vinylidene difluoride, acrylonitrile and N-vinyl pyrrolidone. The polymer prepared as described in the preceding section may be used at concentrations from 0.02 to 5% by moles relative to the monomer content. I0

Example I

Synthesis of feit-butyl-iso-propyl-tett-butyl amine.

In a Schlenk tube containing isobutyraldehyde 98% (1g. 13.59mmoI) gently degassed by nitrogen at 0 C during 10mm., tert-butylamine 98% (1.6mL 1.1 equiv.) was slowly added dropwise by syringe at 0 C. The Schtenk tube was then sealed (with a Rotaflo tap) under nitrogen and the mixture was warmed up to 35 C and stirred for 2h. Conversion checked by H NMR: 97-98%. 1H NMR (500MHz, CDCI3): 6ppm = 7.32 (IH, d, N=CH-CH(CH3)2, J=7.OHz), 2.34 (IH, m, Qj(CH3)2), 1.10 (3H, d, CH(Qj)2, J=7.OHz), 1.09 (9H, S, NC(.j)3), 0.97 (3H, d, CH()2, J=7.OHz). After the mixture was cooled down at room temperature, lOmL of hexane was poured and MgSO4 was added, filtered out and rinsed with I OmL of hexane. The filtrate was then cooled to -78 C and fert-butyl lithium (12.OmL, 1.5 equiv.) was added dropwise by syringe. The mixture was warmed up to 0 C during 2h, quenched by lOmL of concentrated NH4CI and 5mL of pure water was added to dissolve any solIds. The organic phase was extracted at room temperature and the aqueous phase was washed twice by lOmL of hexane. The solvent was then gently removed under reduced pressure at room temperature to give 2.17g of pure compound (yield= 86%).

H NMR (500MHz, CDCI3): Sppm = 2.01 (IH, d, !jNH, J=2.OHz), 1.85 (1H, m, CH(CH3)2), 0.98 (9H, s, NC(j)3), 0.92 (3H, d, CH(Qj)2, J=7.OHz), 0.78 (9H, S. CH(f)3), 0.75 (3H, d, CHC(Q!)2, J=7.OHz). 13C NMR (100MHz, CDCI3): Sppm = 64.08 (Q!NH), 49.51 (NHC(CH3)3), 36.72 (CHC(CH3)3), 31.49 (NHC()3), 28.03 (f(CH3)2), 27.34 (CHC(c!)3), 24.28 (CH(Q)2), 19.28 (CH(j)2).

Example 2

Synthesis of tert-butyl-iso-propyl-tert-butylamine N-oxyl (TITNO).

feit-butyl-iso-propyl-teif-butyl amine, previously described, in 5mL of dichloromethane was added dropwise (by syringe) to a mixture of mCPBA (previously dissolved in a minimum of dichloromethane, dried over magnesium sulfate and filtered) in 3OmL of dichioromethane at 15-17 C in a water bath for 2h.

The mixture was quenched by a concentrated solution of sodium hydrogen carbonate (25mL), the organic layer was extracted and rinsed twice by water (25mL). The solvent was removed under reduced pressure at room temperature. The product was purified by flash chromatography with an eluent ethyl acetate/hexane 1/1 00 (Rf 0.3, in ethyl acetate/hexane: 1/40) to give I.07g of pure compound (yield 49%). H NMR of the raw material in the presence of mCBA (500MHz, CDCI3): 6ppm = 3.12 (1H, s, CHNH), 2.73 (1H, m, CH(CH3)2), 1.44 (911, S. NC(f)3), 1.26 (3H, d, CH(Qj)2, J=7.OHz), 1.24 (9H, s, CH(jj)3), 1.20 (311, d, CHC(Q!)2, J=7.OHz). 13C NMR of the raw material in the presence of mCBA (100MHz, CDCI3): ppm = 76.06 (jNH), 69. 07 (NHC(CH3)3), 36.67 (CHC(CH3)3), 29.26 (NHC(j)3), 28.93 ((CH3)2), 25.23 (CHC(Qj)3), 23.33 (CH(Q)2), 20.57 (CH(j)2). MS (ES, MeOH): 144.1 [M+H-tBu=57]; 201.0 [M+HJ; 202.2 [M+2HJ. C20H35N0 (FW 200.341): CaIc. C 71.94, H 13.08, N 6.99; Found C 71.10, H 13.09, N 6.64.

Example 3

Synthesis of N-tert-butyl-N-(1 -iso-propyl-2,2-dimethyl-propyl)-O-(1 -phenyl-ethyl)-hydroxylamine (St-TITNO).

Procedure. H NMR (500MHz, CDCI3, both diastereoisomers 1.25/1: a/b): Sppm = 7.40-7.17 (IOH, m, H, a and b), 5.01 (111, q, CHO, J7.OHz, a), 4.95 (111, q, jO, J=7.OHz, b), 2.76 (211, s, JjNH, a and b), 2.66 (2H, m, j(CH3)2, a and b), 1.57 (3H, d, CH3CHO, J7.OHz, a), 1.51 (3H, d, CH3CHO, J7.OHz, b), 1.20(1811, s, NC(fj,)3, a and b), 1.11 (6H, d, CH(Qj)2, J=7.OHz, a and b), 1.08 (18H, s, CH(W3, a and b), 1.01 (611, d, CHC(Ctj)2, J7.OHz, a and b). 3C NMR (100MHz, CDCI3): Sppm = 144.72, 128.38, 128.16, 127.20, 126.76, 126.64 (cw, a and b), 83.34 (jO, b), 77. 58 (ijO, a), 72.57 (jNHI a and b), 61.50 (NHC(CH3)3, a and b), 36.67 (CHC(CH3)3, a and b), 31.03 (NHC(Qj)3, a and b), 29.48 (f(CH3)2, a and b), 28.64 (CHC(Q)3, a and b), 26.00 (CH(f)2 a and b), 25.24 ( =jCHO, b), 22. 43 (.Q!jCHO, a), 20.19 (CH(Q)2, a and b). MS (ES, MeOH): 144.1 (M+H-tBu=57-Styryl=1051; 186.3 [M+2H-StyrylO= 121]; 202.1 [M+2H-Styty!= I 05]; 306.2 (M+HJ; 307.2 [M+2HJ.

Example 4

Kinetics of C-O bond homolysis of alkoxyamine prepared in Example 3.

The activation energy of the C-O bond homolysis Ea was determined by EPR spectroscopy. The decomposition of alkoxyamines was conducted in anhydrous p-xylene at temperatures between 320 and 370K in the presence of air1. The nitroxide concentration was determined by double integration of the EPR signal calibrated with standard solutions of TITNO in anhydrous p-xylene.

Examples 5-10

Polymerisation of styrene and n-butyl acrylate using N-tert-butyl-N-(1-iso-propyl-2,2-dimethyl-propyl)-O-( 1 -phenyl-ethyl)-hydroxylamine (St-TITNO) synthesised according

to Example 3.

A mother solution of the system alkoxyamine/styrene or alkoxyamine/n-butyl acrylate (1:100) was divided into several batches separately degassed (by three freeze-pump-thaw cycles) and sealed under gaseous nitrogen. Separate experiments were conducted at a series of temperatures ranging from 60 to 125 C and in each case the polymerization was stopped upon cooling to room temperature. The conversion was determined gravimetrically (samples recovered by THF (for polystyrene) or dichloromethane (for poly(n-butyl acrylate)), poured into a Petri dish and dried at 40 C in vacuo to constant mass). The molecular weight and polydispersity index were determined by size exclusion chromatography (SEC) calibrated with polystyrene standards. Exam

pie monomer temp ( C) time (h) cony (%) Mn' Mn' PDI styrene 125 1.4 74.7 8116 13441 2.384 6 styrene 90 4.5 73.8 8025 9111 1170 7 styrene 60 14.6 36.5 4127 4139 1.186 8 styrene 60 47.3 64.6 7030 6024 1.113 9 n-butylacrylate 90 2.6 81.9 8829 11151 1.103 n-butyl acrylate 60 51.0 65. 1 7130 8722 1.113

Claims

Claims 1. A compound of formula R2 R1NCR3 5 in which R1 represents a

linear, branched or cyclic alkyl fragment, either saturated or unsaturated, bearing from 1 to 30 carbon atoms; R2 and R3, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, an aryl or aralkyl fragment containing from 1 to 10 carbon atoms, or are part of a cyclic structure that also includes the carbon to which R2 and R3 are attached, said cyclic structure containing between 3 and 8 atoms; R4 represents a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from 1 to 10 carbon atoms, or an aryl or aralkyl fragment containing from I to 10 carbon atoms; and R5 represents a cyclic alkyl fragment of between 3 and 12 atoms or a fragment of the general formula 5 in which R6, R7 and R8, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from 1 to 10 carbon atoms, a phenyt group, a substituted phenyl group with between 1 and 5 substituents, an aryl group, a substituted aryl group with between 1 and 9 substituents, or a cyano group. )
2. A compound of claim I in which R1 is a branched alkyl group of less than 10 carbon atoms.
3. A compound of claim I in which R1 is a te,t-butyl group.
4. A compound of claim I in which R2 is a branched alkyl group of less than 10 carbon atoms.
5. A compound of claim I in which R2 is an iso-propyl group.
6. A compound of claim I in which R3 is a branched alkyl group of less than 10 carbon atoms.
7. A compound of claim I in which R3 is a tert-butyt group.
8. A compound of claim I in which R4 is hydrogen.
9. A compound of any of the preceding claims in which R8 is an aromatic group.
10. A compound of claim 9 in which R6 is a phenyl group.
11. A compound of any of the claims 1-9 in which R7 is a linear alkyl group.
12. A compound of claim 11 in which R7 is a methyl group.
13. A compound of any of the claims 1-9 in which R8 is a hydrogen.
14. A compound according to any of the preceding claims, being N-terl-butyl-N-(1-iso-propyl-2,2-dimethyl-propyl)-O-(l -phenyl-ethyl)-hydroxylamine: cc (F-C)3C-N--C-c(cH3)3 o i-i Cl-kCPh
15. A compound of the formula in which R' represents a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, bearing from I to 30 carbon atoms; R2 and R3, which can be either identical or different, represent a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, an aryl or aralkyl fragment containing from 1 to 10 carbon atoms, or are part of a cyclic structure that also includes the carbon to which R2 and R3 are attached, said cyclic structure containing between 3 and 8 atoms; and R4 represents a hydrogen atom, a linear, branched or cyclic alkyl fragment, either saturated or unsaturated, containing from I to 10 carbon atoms, or an aryl or aratkyl fragment containing from I to 10 carbon atoms.
16. A compound of claim 15 in which R1 is a branched alkyl group of less than 10 carbon atoms.
17. A compound of claim 15 in which R1 is a tert-butyl group.
18. A compound of claim 15 in which R2 is a branched alkyl group of less than 10 carbon atoms.
19. A compound of claim 15 in which R2 is an isa-propyl group.
20. A compound of claim 15 in which R3 is a branched alkyl group of 4 carbon atoms.
21. A compound of claim 15 in which R3 is a tert-butyl group.
22. A compound of claim 15 in which R4 is hydrogen.
23. A compound of any of the claims 15-22, being N-teif-butyl-N-(1 -iso-propyl-2,2-dimethyl-propyl)amine N-oxyl: (-C-N---C-c(a-hJ3 0 H
24. A process whereby at least one vinyl monomer is polymerised or copolymerised in the presence of any of the compounds described in claims 1-14. Suitable monomers include vinyl aromatics such as styrene, substituted styrenes and

J

divinylbenzene, dienes including butadiene and isoprene, acrylate esters including methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, glycidyl acrylate, n-hexyl acrylate, 2-ethyihexyl acrylate, n-dodecyl acrylate, N,N-dimethylaminoethyl acrylate, glyceryl acrylate, oligo(oxyethylene) acrylate and poty(oxyethylene) acrylate, acrylic acid, acrylic anhydride, acrylamide and N-substituted acrylamide derivatives including N,N-dimethyl acrytamide, N-isopropyl acrylamide, methacrylamide derivatives such as 2-hydroxypropyl methacrylamide and vinyl compounds such as vinylidene dichioride, vinylidene difluoride, acrylonitrile, 2-vinyl pyridine, 4-vinyl pyridine and N-vinyl pyrrolidone.
25. A process according to claim 24 in which the vinyl monomer is preferably a vinyl aromatic, most preferably styrene.
26. A process according to claim 24 in which the vinyl monomer is preferably an acrylate ester, most preferably n-butyl acrylate.
27. A process according to claim 24 in which the polymerisation temperature is between 0 and 150 C, preferably between 20 and 90 C and most preferably 70 C.
28. A process according to claim 24 in which the concentration of the compound described in claims 1-14 is between 0.02 and 5 mole % of the monomer concentration, preferably between 0.1 and 2 mole % and most preferably 1 mole %.
29. A process whereby a polymer prepared as described in claims 24-28 is then used to initiate a second monomer, thus forming a block copolymer. Suitable monomers include vinyl aromatics such as styrene, substituted styrenes and divinylbenzene, dienes including butadiene and isoprene, acrylate esters including methyl acrylate, ethyl acrylate, n-butyl acrylate, t-butyl acrylate, glycidyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-dodecyl acrylate, N,N-dimethylaminoethyl acrylate, glyceryl acrylate, oligo(oxyethylene) acrylate and poly(oxyethylene) acrylate, acrylic acid, acrylic anhydride, acrylamide and N-substituted acrylamide derivatives including N,N- dimethyl acrylamide, N-isopropyl acrylamide, methacrylamide derivatives such as 2-hydroxypropyl methacrylamide and vinyl compounds such as vinylidene dichloride, vinylidene difluoride, acrylonitrile, 2-vinyl pyridine, 4-vinyl pyridine and N-vinyl pyrrolidone.
30. A process according to claim 29 in which the polymer is preferably derived from a vinyl aromatic, most preferably styrene, and the monomer is preferably an acrylate ester, most preferably n-butyl acrylate.
31. A process according to claim 29 in which the polymer is preferably derived from an acrylate ester, most preferably n-butyl acrylate, and the monomer is preferably a vinyl aromatic compound, most preferably styrene.
32. A process according to claim 29 in which the polymerisation temperature is between 0 and 150 C, preferably between 20 and 90 C and most preferably 70 C.
33. A process according to dalm 29 in which the concentration of the polymer prepared as described in claims 24-28 is between 0.02 and 5 mole % of the monomer concentration, preferably between 0.1 and 2 mole % and most preferably 1 mole%.