Controlled free radical polymerization process

A polymerization process for the preparation of (meth)acrylate containing homopolymers or block copolymers comprises heating a mixture of a free radical initiator, a stable free radical agent, and a polymerizable monomer compound to form a thermoplastic resin or resins with a narrow polydispersity. The stable free radical agent is a piperazinone or morpholone based nitroxide or any adducts thereof.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to the application of new nitroxides in the
 controlled free radical polymerization of a thermoplastic resin or resins.
 More particularly, the invention relates to a controlled free radical
 polymerization process wherein piperazinone and morpholone based
 nitroxides as well as their adducts are used to provide styrene and
 (meth)acrylate homopolymers and block copolymer resin products
 characterized by high monomer to polymer conversion and possessing narrow
 polydispersity properties.
 2. Description of the Prior Art
 Stable Free Radical Polymerization (SFRP) refers to a free radical
 polymerization in the presence of a stable free radical such as a
 nitroxide. The nitroxide traps carbon-centered radicals to form adducts.
 The trapping is reversible but the equilibrium is such that most (99%)
 polymer chains are dormant and only a very small fraction is dissociated.
 Thus, the concentration of free radicals is effectively lowered at all
 times in the polymerization as shown below, wherein P.cndot. represents
 the growing polymer radical, .cndot.ON represents the nitroxide, and M
 represents a monomer.
 ##STR1##
 This in turn affects propagation and transfer rates but has an even greater
 effect on termination, since the latter is second order in radical
 concentration.
 Thus, stable free radical polymerization minimizes chain termination
 reactions, while improving molecular weight and polymer architecture
 control. On the other hand, the SFRP technology slows down the
 polymerization process.
 In U.S. Pat. No. 5,412,047, issued May 2, 1995 to Georges, et al.,
 processes for the preparation of homopolymers of (meth)acrylic monomers
 and copolymers containing (meth)acrylate segments by nitroxide mediated
 polymerization are shown. The polymerization process comprises heating a
 mixture of a free radical initiator and an oxo-nitroxide, specifically
 4-oxo-TEMPO (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy), as a stable free
 radical agent, at least one polymerizable (meth)acrylate monomer compound,
 and optionally a solvent, to form a homopolymeric (meth)acrylate
 containing thermoplastic resin or resins with a high monomer to polymer
 conversion and a narrow polydispersity.
 Examples of other stable free radical compounds said to be suitable for use
 in the '047 Patent include: 2,2,6,6-tetramethyl-1-piperidinyloxy free
 radical (TEMPO); 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy free
 radical; 2,2,5,5-tetramethyl-1-pyrrolidinyloxy;
 3-carboxy-2,2,5,5-tetramethyl-1 pyrrolidinyloxy; and ditert-butyl
 nitroxide. As noted in the '047 Patent, though, surprisingly and
 unexpectedly, the aforementioned stable free radical compounds, and
 related derivatives, while said to be quite satisfactory for the purpose
 of moderating the polymerization of a wide variety of different monomer
 types and comonomers, are completely ineffective when used in
 homopolymerizations of (meth)acrylate monomers. That is to say, no
 homopolymeric product formation could be detected by GPC when a mixture of
 n-butyl acrylate, a free radical initiator such as benzoyl peroxide or
 AIBN, and a stable free radical compound of the type listed in the '047
 Patent were heated for about 10 hours at about 140.degree. C.
 A solution to the problem of forming (meth)acrylate copolymers and
 copolymers was said to be achieved in the '047 Patent by substituting, for
 example, the carbonyl containing stable free radical
 4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy (4-oxo-TEMPO) in place of the
 aforementioned ineffective stable free radical compounds. However,
 4-oxo-TEMPO is not a stable free radical when heated above 100.degree. C.
 in the presence of carbon radicals. Under these conditions it is known by
 those skilled in the art that 4-oxo-TEMPO decomposes rapidly to phorone
 and other non-radical compounds as set out in Volodarsky, L. B. et al.,
 "Synthetic Chemistry of Stable Nitroxides", p. 50 (CRC Press 1993) and
 Yoshioka, T., Higa Shida, S., Morimura, S., and Murayama, K., 44 Bull.
 Chem. Soc. Jpn., Volume 44, pp. 2207-2210 (1971).
 All nitroxides based on TEMPO and its derivatives and used by the inventors
 of the '047 Patent, including 4-oxo-TEMPO, are problematic, particularly
 when used in the synthesis of (meth)acrylate homopolymers, styrene-n-butyl
 acrylate block copolymers, and n-butyl acrylate-styrene block copolymers,
 in that the polymers can not be synthesized in a controlled fashion with
 high yields. Further, these nitroxides are undesirable for various
 practical reasons--that is, the nitroxides cannot be synthetically
 modified easily. Nor do the nitroxides have a long shelf-life.
 Thus, there remains a need for a controlled free radical polymerization
 process, which can be used to simply and economically synthesize high
 yields of (meth)acrylate homopolymers as well as styrene-n-butyl acrylate
 or n-butylacrylate-styrene block copolymers. In this regard, a need also
 exists for a stable free radical nitroxide for use in the polymerization
 process, which can be easily synthesized and stored over long periods of
 time.
 INCORPORATION BY REFERENCE
 U.S. Pat. Nos. 5,412,047, 4,914,232, 4,466,915, 5,401,804, and 4,581,429
 are incorporated by reference herein as background information with
 respect to the present invention.
 BRIEF SUMMARY OF THE INVENTION
 We have discovered that piperazinone and morpholone based nitroxides as
 well as their adducts can be used in the (meth)acrylate polymerization
 processes of the '047 Patent with unexpectedly high efficiencies. These
 nitroxides are advantageous in that they are easily synthesized,
 particularly with regard to tailoring the nitroxide structure to improve
 reaction rates, introduce functionality, and tailor solubility. Further,
 these nitroxides have an improved shelf-life stability, since they are
 highly crystalline and can be stored indefinitely at room temperature or
 higher.
 In addition, these nitroxides, quite unexpectedly, can be used to
 efficiently make high yields of styrene-n-butyl acrylate or n-butyl
 acrylate-styrene block copolymers with narrow polydispersities (1.0-3.0)
 simply and economically, while controlling both molecular weight and
 composition. Indeed, when used in the preparation of these
 styrene-block-acrylate copolymers, high yields of styrene or
 (meth)acrylate prepolymer are obtained in the first step of the
 polymerization process, thus enabling high yields of the
 styrene-block-(meth)acrylate copolymers in the second step of the
 polymerization process.
 Block copolymers made in the presence of stable free radicals have been
 claimed in U.S. Pat. Nos. 5,322,912, 5,401,804, 5,449,998 and 5,545,504
 but have only been reduced to practice for a styrene-styrene sulfonate
 diblock copolymer. We have found that (meth)acrylate containing block
 copolymers cannot be made using the nitroxides claimed in the
 aforementioned patents.
 In addition, use of our nitroxides for styrene or (meth)acrylate
 homopolymerization showed a distinct rate advantage over TEMPO and its
 derivatives.
 The present invention, then, provides an improvement in the process for the
 stable free radical polymerization by using new nitroxides to make
 homopolymers of (meth)acrylate monomers and copolymers containing
 (meth)acrylate segments by nitroxide mediated polymerization.
 According to a first aspect of the invention, a free radical polymerization
 process for the preparation of a thermoplastic resin or resins is
 disclosed, which comprises heating from about 80.degree. C. to about
 160.degree. C. a mixture of a free radical initiator, at least one
 polymerizable monomer compound, and a stable free radical agent comprising
 a nitroxyl radical to form the thermoplastic resin or resins having a
 polydispersity from about 1.0 to about 3.0. The nitroxyl radical has the
 following formula:
 ##STR2##
 wherein X is CH.sub.2 or C.dbd.O, Y is O or N--R, R, R.sub.1, R.sub.2,
 R.sub.3, and R.sub.4 are independently selected from the group consisting
 of aryl, alkyl having from 1 to about 24 carbon atoms, cycloalkyl having
 from 5 to about 7 carbon atoms, aralkyl having from 7 to about 20 carbon
 atoms, cyanoalkyl having from 2 to about 12 carbon atoms, ether having
 from 4 to about 18 carbon atoms, and hydroxyalkyl having from 1 to about
 18 carbon atoms; and
 R.sub.1 and R.sub.2 together, or R.sub.3 and R.sub.4 together, or each
 pair, may be cyclized forming a ring having from about 5 to about 14
 carbon atoms.
 According to a second aspect of the present invention, a free radical
 polymerization process for the preparation of a thermoplastic resin or
 resins is disclosed, which comprises heating from about 80.degree. C. to
 about 160.degree. C. a mixture of at least one polymerizable monomer
 compound, and a preformed nitroxide adduct to form the thermoplastic resin
 or resins. The preformed nitroxide adduct has the following formula:
 ##STR3##
 wherein X is CH.sub.2 or C.dbd.O, Y is O or N--R, R, R.sub.1, R.sub.2,
 R.sub.3, R.sub.4, and R.sub.5 are independently selected from the group
 consisting of aryl, alkyl having from 1 to about 24 carbon atoms,
 cycloalkyl having from 5 to about 7 carbon atoms, aralkyl having from 7 to
 about 20 carbon atoms, cyanoalkyl having from 2 to about 12 carbon atoms,
 ether having from 4 to about 18 carbon atoms, and hydroxyalkyl having from
 1 to about 18 carbon atoms; and
 R.sub.1 and R.sub.2 together, or R.sub.3 and R.sub.4 together, or each
 pair, may be cyclized forming a ring having from about 5 to about 14
 carbon atoms.
 According to a third aspect of the invention, a free radical polymerization
 process for the preparation of a (meth)acrylate containing block copolymer
 is closed. In the first step, a first mixture of either (1) a free radical
 initiator; a first polymerizable monomer compound; and a stable free
 radical agent comprising the nitroxide radical having the formula
 disclosed above; or (2) a first polymerizable monomer compound and a
 preformed nitroxide adduct having the formula disclosed above is heated
 from about 80.degree. C. to about 160.degree. C. to form a prepolymer. In
 the second step, a second mixture containing the prepolymer and the second
 polymerizable compound is heated from about 80.degree. C. to about
 60.degree. C., the second polymerizable monomer compound being different
 than the first polymerizable monomer compound.
 One advantage of the present invention is that a new nitroxide useful in
 the controlled free radical polymerization of a thermoplastic resin or
 resins can be easily synthesized, particularly with regard to tailoring
 the nitroxide structure to improve reaction rates, introduce
 functionality, tailor solubility, etc.
 Another advantage of the present invention is that a new nitroxide useful
 in the controlled radical polymerization of a thermoplastic resin or
 resins has an improved shelf-life stability. The new nitroxides are highly
 crystalline and can be stored indefinitely at room temperature (or
 higher), which cannot be said for TEMPO and its derivatives.
 Still another advantage of the present invention is that a controlled
 radical polymerization process is disclosed wherein styrene can be
 polymerized at a faster rate.
 Still another advantage of the present invention is that a controlled free
 radical polymerization process is disclosed wherein higher conversions in
 styrene and (meth)acrylate are achieved.
 Still another advantage of the present invention is that
 styrene-block-acrylate copolymers can be synthesized using a controlled
 free radical polymerization process wherein high yields of a styrene or
 (meth)acrylate prepolymer are obtained in the first step of the
 polymerization process, thus enabling high yields of the
 styrene-block-(meth)acrylate copolymers in the second step of the
 polymerization process.
 Still another advantage of the present invention is that a controlled
 radical polymerization process is disclosed wherein styrene-nBA block
 copolymers can be simply and economically synthesized.
 Still another advantage of the present invention is that a controlled
 radical polymerization process is disclosed wherein nBA-styrene block
 copolymers can be simply and economically synthesized.
 Still other benefits and advantages of the invention will become apparent
 to those skilled in the art upon a reading and understanding of the
 following detailed specification.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention provides (meth)acrylate polymerization processes for
 preparing (meth)acrylate containing polymeric resins with well-defined
 molecular weight properties and narrow polydispersities.
 The processes can be run as batch, semi-continuous or continuous processes.
 The polymerization process for the preparation of (meth)acrylate
 containing resins is initiated using a classical free radical initiator in
 the presence of a slight excess of free nitroxide and comprises heating a
 mixture comprised of a free radical initiator, a stable free radical
 agent, at least one polymerizable (meth)acrylate monomer compound, and
 optionally a solvent, to form a (meth)acrylate containing resin with a
 high monomer to polymer conversion and a narrow polydispersity. As used in
 the present specification, the terminology "(meth)acrylate containing"
 means that about 5 to 100 wt. % of the total monomer polymerized is a
 (meth)acrylate type monomer and that the (meth)acrylate monomer is
 polymerized in the presence of the stable free radical compound or
 nitroxide containing prepolymers.
 Suitable for use as free radical initiators in the processes of the present
 invention include any conventional free radical initiators known in the
 art. These initiators can include oxygen, hydroperoxides, peresters,
 percarbonates, peroxides, persulfates and azo initiators. Specific
 examples of some suitable initiators include hydrogen peroxide, t-butyl
 hydroperoxide, ditertiary butyl peroxide, tertiary-amyl hydroperoxide,
 dibenzoyl peroxide (AIBN), potassium persulfate, and methylethyl ketone
 peroxide. The initiators are normally used in amounts of from about 0.01%
 to about 4% based on the weight of total polymerizable monomer. A
 preferred range is from about 0.05% to about 2% by weight of the total
 polymerizable monomer.
 Redox initiators may also be used in the practice of the present invention
 and include sodium bisulfite, sodium sulfite, isoascorbic acid, sodium
 formaldehyde-sulfoxylate, and the like, used with suitable oxidizing
 agents, such as the thermal initiators noted above. If used, the redox
 initiators may be used in amounts of 0.001% to 5%, based on the weight of
 total monomer. A preferred range is from about 0.01 to about 3% by weight
 of total polymerizable monomer.
 The stable free radical selected for use in the present invention are
 piperazinone and morpholone based nitroxides and their adducts. These
 nitroxides are critical to the success of the stable free radical
 polymerization process disclosed in the present invention. For example,
 controlled nitroxide mediated polymerization of n-butyl acrylate has not
 been reported in the prior art. The process described in the '047 Patent,
 wherein TEMPO and its derivatives are used as the nitroxide stable free
 radical agent, can only be controlled at very low conversions--that is,
 less than 15%.
 In particular, the piperazinonyl nitroxides compare favorably to
 4-oxo-TEMPO in the homopolymerization of n-butyl acrylate. Indeed, a
 comparison of our iBu nitroxide (TABLE I) and our C7 nitroxide (TABLE I)
 versus 4-oxo-TEMPO in a high temperature polymerization demonstrates large
 differences in the obtained yields and molecular weights as shown in
 Examples 13 and 14 and Comparative Example 2.
 The synthesis of the piperazinone based nitroxides is shown below in
 Equation (1). An alternative morpholone based nitroxide, is shown in
 reaction (2), which uses a much more readily available amino alcohol
 starting material. The nitroxides are obtained in high yields by either
 method.
 ##STR4##
 Certain piperazinone based nitroxides and morpholone based nitroxides
 obtained and used in the practice of the present invention, including
 their abbreviations, are listed below in TABLE I. The nomenclature adopted
 reflects the nature of the substituents introduced via the ketone.
 TABLE I
 NITROXIDE NITROXIDE
 STRUCTURE ABBREVIATION STRUCTURE
 ABBREVIATION
 ##STR5## Dimethyl (1-tertbutyl- 3,3,5,5- tetramethyl-2-
 piperazinone- oxide) ##STR6## iBu (3-isobutyl-1-
 isopropyl-3,5,5- trimethyl-2- piperazinone- oxide)
 ##STR7## Phenyl (1-isopropyl-3- phenyl-3,5,5- trimethyl-2-
 piperazinone- oxide) ##STR8## C5 (3,3- tetramethylene-
 5,5-dimethyl-1- isopropyl-2- piperazinone- oxide)
 ##STR9## C6 (3,3- pentamethylene- 5,5-dimethyl-1-
 isopropyl-2- piperazinone- oxide) ##STR10## C7 (3,3-
 hexamethylene- 5,5-dimethyl-1- isopropyl-2- piperazinone- oxide)
 ##STR11## diMe Morpholone (3,3,5,5- tetramethyl-2-
 morpholone- oxide) ##STR12## C6 Morpholone (3,3-
 pentamethylene- 5,5-dimethyl-2- morpholone- oxide)
 ##STR13## C7 Morpholone (3,3- hexamethylene- 5,5-dimethyl-2-
 morpholone oxide) ##STR14## Dicyclohexyl (bis-3,3,5,5-
 pentamethylene- 2,6- piperazinone- dione-oxide)
 One class of carboxylic acid or acrylic monomers suitable for use in the
 present invention are C.sub.3 -C.sub.6 monoethylenically unsaturated
 monocarboxylic acids, and the alkaline metal and ammonium salts thereof.
 The C.sub.3 -C.sub.6 monoethylenically unsaturated monocarboxylic acids
 include acrylic acid, methacrylic acid, crotonic acid, vinyl acedic acid,
 and acryloxypropionic acid. Acrylic acid and methacrylic acid are the
 preferred monoethylenically unsaturated monocarboxylic acid monomers.
 Another class of carboxylic acid monomers suitable for use in the present
 invention are C.sub.4 -C.sub.6 monoethylenically unsaturated dicarboxylic
 acids and the alkaline metal and ammonium salts thereof, and the
 anhydrides of the cis dicarboxylic acids. Suitable examples include maleic
 acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, and
 citraconic acid. Maleic anhydride and itaconic acid are preferred
 monoethylenically unsaturated dicarboxylic acid monomers.
 The acid monomers useful in this invention may be in their acid forms or in
 the form of the alkaline metal or ammonium salts of the acid. Suitable
 bases useful for neutralizing the monomer acids includes sodium hydroxide,
 ammonium hydroxide, potassium hydroxide, and the like. The acid monomers
 may be neutralized to a level of from 0 to 50% and preferably from 0 to
 about 20%. More preferably, the carboxylic acid monomers are used in the
 completely neutralized form.
 In addition, up to 100% by weight of the total polymerizable monomers may
 be monoethylenically unsaturated carboxylic acid-free monomers. Typical
 monoethylenically unsaturated carboxylic acid-free monomers suitable for
 use in the invention include alkyl esters of acrylic or methacrylic acids
 such as methyl acrylate, ethyl acrylate, butyl acrylate; hydroxyalkyl
 esters of acrylic or methacrylic acid such as hydroxyethyl acrylate,
 hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl
 methacrylate; acrylamide, methacrylamide, N-tertiary butylacrylamide,
 N-methylacrylamide, N,N-dimethyl acrylamide; acrylonitrile,
 methacrylonitrile, dimethylaminoethyl acrylate, dimethylaminoethyl
 methacrylate, phosphoethyl methacrylate, N vinyl pyrrolidone,
 N-vinylformamide, N-vinylimidazole, vinyl acetate, styrene, hydroxylated
 styrene, styrenesulfonic acid and salts thereof, vinylsulfonic acid and
 salts thereof, and 2-acrylamido-2-methylpropanesulfonic acid and salts
 thereof.
 Other suitable comonomers include acrylamides, alkyl and aryl amide
 derivatives thereof, and quaternized alkyl and aryl acrylamide
 derivatives.
 Monomers, polymers and copolymers of the present invention can, in
 embodiments, be separated from one another or from the polymerization
 reaction mixture by, for example, changing the pH of the reaction media
 and other well-known conventional separation techniques.
 In the (meth)acrylate polymerization of the present invention, reactions
 can be supplemented with a solvent or co-solvent to help insure that the
 reaction mixture remains a homogeneous single phase throughout the monomer
 conversion. However, in the preferred embodiment, the (meth)acrylate
 polymerization reactions are carried out in the absence of a solvent.
 Exemplary solvent or co-solvents useful in the present invention include
 compatible aliphatic alcohols, glycols, ethers, glycol ethers,
 pyrrolidones, N-alkyl pyrrolidones, N-alkyl pyrrolidones, polyethylene
 glycols, polypropylene glycols, amides, carboxylic acids and salts
 thereof, esters, organosulfides, sulfoxides, sulfones, alcohol
 derivatives, hydroxyether derivatives such as CARBITOL.RTM. or
 CELLOSOLVE.RTM., amino alcohols, ketones, and the like, derivative
 thereof, and mixtures thereof. Specific examples include ethylene glycol,
 propylene glycol, diethylene glycol, glycerine, dipropylene glycol,
 tetrahydrofuran, and the like, and mixtures thereof. When mixtures of
 water and water soluble or miscible organic liquids are selected as the
 reaction media, the water to co-solvent weight ratio typically ranges from
 about 100:0 to about 10:90, and preferably from about 97:3 to about 25:75.
 Temperature of the polymerization may range from about 80.degree. C. to
 about 160.degree. C., preferably from about 110.degree. C. to about
 130.degree. C. At temperatures above about 180.degree. C., conversion of
 the monomer into polymer decreases and uncertain and undesirable
 by-products are formed. Frequently, these by-products discolor the polymer
 mixture and may necessitate a purification step to remove them or they may
 be intractable.
 Since solvent and co-solvent admixtures can be used as the reaction media,
 the elevated temperatures of the polymerization require that the
 polymerization reactor be equipped to operate at elevated pressure. In
 general it is preferred to conduct the polymerization at from about 10 to
 about 2000 lbs. per square inch (psi), and more preferably at from about
 50 to about 1000 (psi).
 Additives such as (a) camphorsulphonic acid (CSA), or (b) 2-fluoro-1-methyl
 pyridinium p-toluene sulfonate (FMPTS) having the chemical formulations
 shown below, can be added to the polymerization mixture to significantly
 increase the rate of polymerization. These additives and their usefulness
 in a stable free radical polymerization process are discussed in detail in
 E.P. 735,052, the disclosure of which is incorporated herein by reference.
 ##STR15##
 Batch or metered addition of CSA to (meth)acrylate polymerizations with our
 nitroxides further enhances the monomer conversion. The polymers obtained
 from these acid accelerated polymerizations can be chain-extended with
 styrene to form block copolymers.
 The molar ratio of nitroxide agent to free radical initiator is from about
 1:1 to 10:1. The molar ratio of nitroxide agent to free radical initiator
 is preferably from about 1.3:1 to 1.7:1.
 The influence of the ratio of initiator to stable free radical is
 significant in the polymerization of n-butyl acrylate when AIBN is used as
 the initiator. First-order plots of polymerization conducted in the
 presence of AIBN and the C7 nitroxide at 130.degree. C. show that at a
 1:1.6 ratio, the first-order plot becomes more linear. Below this ratio,
 an exotherm is often observed, the molecular weight does not increase with
 conversion, and the polydispersity is broad. Above this ratio molecular
 weight increases with increasing conversion. The exact stoichiometry is
 extremely important: 1:1.60 often gives an exotherm, whereas 1:1.70 gives
 a slow but controlled polymerization. The slightest experimental error or
 the presence of small amounts of impurities, then, can give widely varying
 results.
 When benzoyl peroxide (BPO) is used as the initiator as opposed to AIBN,
 the polymerizations are insensitive toward the ratio of initiator to
 stable free radical. In general, broader polydispersities (&gt;2) are also
 observed.
 The processes of the present invention provide, in embodiments, a
 conversion rate or degree of polymerization as high as 95% by weight.
 The processes of the present invention weight average molecular weights
 ranging from about 500 to about 200,000 and more preferably from about
 2000 to about 100,000 while maintaining narrow polydispersity.
 Applications of (meth)acrylate block copolymers or styrene block copolymers
 or styrene or (meth)acrylate homopolymers can include toner compositions,
 adhesives, cellulosic fiber binders, compatibilizers for thermoplastic
 blends, emulsifiers, thickeners, processing aids for thermoplastic resins,
 pigment dispersants, coatings, asphalt modifiers, molded articles, sheet
 molding compounds, and impact modifiers.
 The present invention will now be described in greater detail in the
 following examples.
 The styrene and n-butyl acrylate used in each of the foregoing examples
 were obtained from Aldrich. The inhibitors were removed using t-butyl
 catechol and hydroquinone inhibitor remover (Aldrich). Reaction samples
 were diluted with either THF or CH.sub.2 Cl.sub.2 for GC analysis, which
 was done on a HP5890 GC with a HP-1 column and thermal conductivity
 detector running at a constant 150.degree. C. oven temperature. The
 internal reference used was ortho-dichlorobenzene. GPC samples were
 evaporated by air drying and dried overnight at 60.degree. C. in a vacuum
 oven. Molecular weights reported in the examples were determined by GPC in
 THF versus polystyrene standards.
 As used in the examples, M.sub.n refers to the number average molecular
 weight, M.sub.w refers to the weight average molecular weight, M.sub.p
 refers to peak molecular weight, and PDI, the polydispersity ratio, is the
 ratio of the weight average molecular weight to the number average
 molecular weight.

EXAMPLE 1
 N-tertbutyl-2-methyl-1,2-propanediamine (0.1 mol), chloroform (0.15 mol),
 acetone (0.2 mol), Aliquat 336 tricaprylylmethylammonium chloride (0.003
 mol), and 100 mL toluene were mixed and cooled to 10.degree. C. under
 nitrogen atmosphere. Solid sodium hydroxide beads (0.5 mol) were added in
 30 minutes to keep the temperature below 20.degree. C. After the addition
 and three hours stirring at 15-20.degree. C., the reaction was filtered,
 dried over sodium sulfate and concentrated to afford greater than 90%
 yield of product, which was about 95% pure by gas chromatograph. The
 solidified product was recrystallized from hexanes to afford an
 analytically pure sample.
 The amine was oxidized in the conventional manner to the corresponding
 dimethyl nitroxide by following procedures known by those skilled in the
 art and described in the reference Rozantzev, E. G., "Free Nitroxyl
 Radicals" (Plenum Press 1970).
 EXAMPLE 2
 Example 1 was repeated under identical conditions, with the exception that
 4-methyl-2-pentanone was substituted for the acetone to give the iBu
 nitroxide.
 EXAMPLE 3
 Example 1 was repeated under identical conditions, with the exception that
 acetophenone was substituted for the acetone to give the phenyl nitroxide.
 EXAMPLE 4
 Example 1 was repeated under identical conditions with the exception that
 cyclopentanone was substituted for the acetone to give the C5 nitroxide.
 EXAMPLE 5
 Example 1 was repeated under identical conditions with the exception that
 cyclohexanone was substituted for the acetone to give the C6 nitroxide.
 EXAMPLE 6
 Example 1 was repeated under identical conditions with the exception that
 cycloheptanone was substituted for the acetone to give the C7 nitroxide.
 EXAMPLE 7
 2-Amino-2-methyl-1-propanol (17.8 g, 0.2 mol), chloroform (35.8 g, 0.3
 mol), cycloheptanone (45.1 g, 0.4 mol), Aliquat 336 (3.23 g, 0.008 mol),
 and 120 mL toluene were mixed under nitrogen at 10.degree. C. Sodium
 hydroxide beads (40.0 g, 0.5 mol) were added in 30 minutes to keep the
 temperature below 20.degree. C. After stirring at 15-20.degree. C. for
 another 2 hours and 45 minutes, the reaction was filtered and rinsed with
 a small amount of toluene. The solid was extracted with 2.times.100 mL
 methanol. The combined methanol solutions were concentrated to afford 61 g
 of the carboxylate intermediate. The white solid was refluxed with 80 mL
 concentrated hydrochloric acid in air for 10 hours. It was then cooled to
 about 75.degree. C. and 150 mL toluene was then added. The excess acid and
 water were removed with a Dean-Stark trap. The toluene solution was
 concentrated and distilled to 185-195.degree. C. at 14 mmHg to afford 35 g
 3,3-hexamethylene-5,5-dimethyl-2-oxomorpholine as a clear yellow oil,
 which was used to make the nitroxide.
 The amine was oxidized in the conventional manner referenced in Example 1
 to give the C7 morpholone nitroxide.
 EXAMPLE 8
 Example 7 was repeated under identical conditions with the exception that
 the cycloheptanone was replaced with acetone to give the diMe morpholone.
 EXAMPLE 9
 Example 7 was repeated under identical conditions with the exception that
 cyclohexanone was substituted for the cycloheptanone to give the C6
 morpholone.
 EXAMPLE 10
 Styrene (15 g ), benzoyl peroxide (0.62 mmol, 0.150 g ), and the C6
 nitroxide (0.8 mmol, 0.125 g ) of Example 5 were charged to a 150 mL
 cylindrical flask with a 4-head Teflon coated head equipped with
 condenser, bubbler, magnetic stir bar and two septa ports. The solution
 was purged thoroughly with argon for 15 minutes and then lowered into an
 oil bath preheated to 140.degree. C. The polymerization was carried out
 for 6 hours. The polymer solution was diluted in 10 mL THF and
 precipitated into a ten times excess of methanol. The polymer was filtered
 and dried under vacuum overnight. A conversion of 67% (determined
 gravimetrically) and a yield of 9.9 g rams of polystyrene was obtained
 with M.sub.n equal to 12, 678, M.sub.p equal to 20, 044, M.sub.w equal to
 18, 100 and PDI is 1.42.
 EXAMPLE 11
 Example 10 was repeated under identical conditions, with the exception that
 the dimethyl nitroxide of Example 1 was substituted for the C6 nitroxide.
 A conversion of 50% (determined gravimetrically) and a yield of 7.5 g rams
 of polystyrene were obtained with M.sub.n equal to 12,312, M.sub.p equal
 to 15,661, M.sub.w equal to 14,989, and PDI equal to 1.2.
 EXAMPLE 12
 Example 11 was repeated under identical conditions, with the exception that
 the phenyl nitroxide of Example 3 was substituted for the dimethyl
 nitroxide. A conversion of 54% (determined gravimetrically) and a yield of
 8.1 g rams of polystyrene were obtained with M.sub.n equal to 13,306,
 M.sub.p equal to 16,624, M.sub.w equal to 15,919, and PDI equal to 1.19.
 COMATIVE EXAMPLE 1
 Example 10 was repeated under identical conditions, with the exception that
 TEMPO was substituted for the C6 nitroxide. A conversion of 35%
 (determined gravimetrically) and a yield of 5.2 g rams of polystyrene were
 obtained with M.sub.n equal to 8,174, M.sub.p equal to 11,130, M.sub.w
 equal to 10,406, and PDI equal to 1.27.
 EXAMPLE 13
 7 mL of n-butyl acrylate, 0.12 g of the isobutyl nitroxide of Example 2,
 and 0.074 g of BPO were heated at 130.degree. C. for 24 hours. A polymer
 having M.sub.n equal to 6800 and PDI equal to 1.32 was isolated in a 40%
 yield.
 EXAMPLE 14
 7 mL of n-butyl acrylate, 74 mg of BPO and 0.130 g of the C7 morpholone
 nitroxide of Example 7 were heated at 130.degree. C. for 28 hours. A
 polymer having M.sub.n equal to 27,000 and PDI equal to 1.71 was isolated
 in a 50% yield.
 COMATIVE EXAMPLE 2
 Example 14 was repeated under identical conditions with the exception that
 4-oxo TEMPO was substituted for the C7 morpholone nitroxide. A polymer
 having bimodal distribution was obtained in a 15% yield with M.sub.n equal
 to 3000, PDI equal to 2.06.
 EXAMPLE 15
 Tetramethyl morpholone (141.3 g, 0.90 mole), molybdenum oxide (3.0 g ) and
 ethylbenzene (720 mL) were mixed and heated to 110.degree. C. under
 N.sub.2 atmosphere. t-Butyl hydroperoxide (70% aq. solution, 249.1 g, 2.49
 mole) was added dropwise in 1 hour. The addition funnel was replaced with
 a distillation column and t-butyl alcohol-water was distilled over slowly
 in 15 hours. The reaction content was dried over sodium sulfate and
 concentrated to a dark oil, which solidified on standing. The solid was
 recrystallized from hexanes to obtain beige-colored crystals (155 g ).
 EXAMPLE 16
 The styrene prepolymer end-capped with the C6 nitroxide formed in Example
 10 (2 g ), n-butyl acrylate (5 g ), and DMSO (5 mL) were charged into a
 glass reactor of the type described in Example I, purged thoroughly with
 argon for 15 minutes, and then lowered into an oil bath preheated to
 80.degree. C. The prepolymer had a M.sub.n equal to 12,678, M.sub.w equal
 to 18,100 and a molecular weight distribution of 1.4. The polymerization
 was carried out for 6 hours. Samples were withdrawn with time to monitor
 the progress of the reaction. The polymer solution was diluted with THF
 and precipitated into a ten times excess of methanol. The polymer was
 filtered and dried under vacuum overnight.
 The molecular weight data for the final polymer obtained after
 precipitation into methanol was M.sub.n equal to 18,524, M.sub.w equal to
 51,899, with a molecular weight distribution of 1.4. An increased
 .DELTA.M.sub.w of 33,799 was obtained on formation of the block copolymer.
 Analysis of GC and NMR results indicated between 70-72% conversion of
 n-butyl acrylate. The molar incorporation of n-butyl acrylate in the
 diblock copolymer was found to be approximately 46%.
 EXAMPLE 17
 Example 16 was repeated under identical conditions, with the exception that
 after the low temperature initiation of 80.degree. C. was used for 1 hour,
 the polymerization temperature was increased to 100.degree. C. The
 polymerization temperature in the flask, however, did not increase beyond
 90.degree. C. A yield of 6 grams of diblock copolymer was obtained
 corresponding to approximately 90% conversion of n-butyl acrylate. The
 molecular weight data for the diblock copolymer was M.sub.n equal to
 35,353, M.sub.w equal to 90,288, with a molecular weight distribution of
 2.55. An increase in .DELTA.M.sub.w of 72,188 was obtained on formation of
 the block copolymer. NMR analysis indicated approximately 63% molar
 incorporation of n-butyl acrylate, corresponding to approximately 100%
 conversion of n-butyl acrylate.
 EXAMPLE 18
 Example 16 was repeated under identical conditions with the exception that
 after the low polymerization temperature of 80.degree. C. was used for 1
 hour, the polymerization temperature was increased to 150.degree. C. The
 actual reaction temperature was between 135-140.degree. C. for 6 hours. A
 yield of 4.3 g rams was obtained, corresponding to approximately 61%
 conversion of n-butyl acrylate. The molecular weight data for the diblock
 copolymer was M.sub.n equal to 16,525, M.sub.w equal to 40,251, and PDI
 equal to 2.4. NMR indicated approximately 53% molar incorporation of
 n-butyl acrylate into the block copolymer. An increase in M.sub.w of
 22,151 was obtained for the polymer after chain extension with n-butyl
 acrylate.
 EXAMPLE 19
 Example 10 was repeated under identical conditions with the exception that
 the C6 nitroxide was replaced with the C7 nitroxide of Example 6. The
 reaction was stopped at 52% conversion, the resultant prepolymer having
 M.sub.n equal to 10,735, M.sub.w equal to 13,221, and PDI equal to 1.23.
 The prepolymer (2 g ) and n-butyl acrylate (10 mL) were charged into a
 glass reactor of the type described in Example 10, purged thoroughly with
 argon for 15 minutes, and then lowered into an oil bath preheated to
 140.degree. C. The prepolymer had an M.sub.n equal to 10,735, M.sub.w
 equal to 13,221, and a molecular weight distribution of 1.23. The
 temperature inside the flask was at 130.degree. C. The polymerization was
 carried out for approximately 23 hours. The polymer solution was diluted
 with THF and precipitated into a ten times excess of methanol. The polymer
 was filtered and dried under vacuum overnight.
 The molecular weight data for the final polymer obtained after
 precipitation into methanol was M.sub.n equal to 20,720 and M.sub.w equal
 to 27,881, with a PDI equal to 1.34. Samples withdrawn from the reaction
 mixture indicated that the conversion increased with time.
 EXAMPLE 20
 Example 19 was repeated under identical conditions. Samples were withdrawn
 over time and are characterized in TABLE II.
 TABLE II
 SAMPLE 1 SAMPLE 2 SAMPLE 3
 M.sub.n 17,534 19,555 21,881
 M.sub.w 21,192 24,534 28,006
 PDI 1.29 1.255 1.28
 Percentage 29% 48% 50%
 Conversion
 EXAMPLE 21
 Example 10 was repeated under identical conditions with the exception that
 45 mL styrene, 0.19 g of the dimethyl morpholone nitroxide of Example 8
 and 0.206 g BPO were used. The reaction was stopped at 47% conversion, the
 resultant prepolymer having M.sub.n =18,500 M.sub.w equal to 26,800 and
 PDI equal to 1.45.
 The styrene prepolymer end capped with the DiMe morpholone nitroxide
 (M.sub.n =18,500, M.sub.w =26,800, PDI=1.45) (5 g ) and n-butyl acrylate
 (10 mL) were charged into a glass reactor of the type described in Example
 10, purged thoroughly with argon for 15 minutes and then lowered into an
 oil bath preheated to 140.degree. C. The polymerization was carried out
 for approximately 22 hours. The polymer solution was diluted with THF and
 precipitated into a ten times excess of methanol. The polymer was filtered
 and dried under vacuum overnight. The molecular weight data for the final
 polymer obtained after precipitation into methanol is set out in TABLE
 III.
 EXAMPLE 22
 Example 10 was repeated under identical conditions with the exception that
 30 mL styrene, 0.36 g of the C7 morpholone nitroxide of Example 7 and 0.3
 g of BPO were used. The reaction was stopped at 70% conversion, the
 resultant prepolymer having M.sub.n equal to 14,800, M.sub.w =18,300, and
 PDI=1.24.
 Example 21 was then repeated under identical conditions, except that the
 styrene prepolymer end capped with the C7 morpholone nitroxide (M.sub.n
 =14,800, M.sub.w =18,300, PDI=1.24) was substituted for the prepolymer of
 Example 21 and an additional 10 mL of n-butyl acrylate was used. The
 molecular weight data for the final polymer obtained after precipitation
 into methanol is set out in TABLE III, below. FIG. 1, a plot of molecular
 weight of the styrene-n-butyl acrylate block copolymer versus percent
 conversion, shows that molecular weight evolution with regard to
 conversion occurred in a linear fashion indicating a controlled free
 radical polymerization and a clean formation of the block copolymer.
 Molecular weights were determined by GPC in THF versus polystyrene
 standards. Data points were taken at 0, 3, 6, 9 and 23 hours.
 ##STR16##
 EXAMPLE 23
 Example 10 was repeated under identical conditions with the exception that
 the C6 nitroxide was replaced with the diMe morpholone nitroxide of
 Example 8. The reaction was stopped at 80% conversion, the resultant
 prepolymer having M.sub.n equal to 12,900, M.sub.w =19,100, and PDI equal
 to 1.24.
 Example 22 was then repeated under identical conditions, except that the
 styrene prepolymer end capped with the diMe morpholone nitroxide (M.sub.n
 =14,800, M.sub.w =18,000, PDI=1.47) was substituted for the prepolymer of
 Example 10 and an additional 10 mL of n-butyl acrylate was used. The
 molecular weight data for the final polymer obtained after precipitation
 into methanol is set out in TABLE III, below.
 TABLE III
 Polystyren
 Example e-nitroxide n-butylacrylate M.sub.n (diblock) M.sub.n (diblock)
 No. (g, Mn,) (mL) Exptal Targeted Conversion PDI
 23 C- 20 22,400 36,000 65 1.54
 dimethyl
 (10 g,
 12K)
 21 C- 10 36,900 51,600 80 1.7
 dimethyl
 5 g, 18K)
 22 C-7 20 34,500 41,000 85 1.68
 10 g, 15K)
 EXAMPLE 24
 5 mL styrene, 116 mg BPO, and 174 mg of the dicyclohexyl nitroxide were
 heated at 130.degree. C. for 4 hours. A polymer was obtained in 66% yield
 with M.sub.n =6200, PDI=1.40. The synthesis procedure used for the
 dicyclohexyl nitroxide is known and is described with particularity in
 Yoshioka, T., Mori, E., and Murayama, K., "Synthesis and ESR Spectral
 properties of Hindered Piperazine N-Oxyls", Bulletin of the Chemical
 Society of Japan, Vol. 45, pp. 1855-1860 (1972).
 The styrene prepolymer end-capped with the dicyclohexyl nitroxide (M.sub.n
 =6200, PDI=1.40) (0.5 g ) was dissolved in 3 mL of n-butyl acrylate and
 heated at 130.degree. C. for 20 hours. A block copolymer having M.sub.n
 equal to 8400 and PDI equal to 1.34 was obtained after 10% of the monomer
 was converted.
 EXAMPLE 25
 A three neck, 25 mL roundbottom flask equipped with a mechanical stirrer,
 temperature probe, argon inlet and condenser was charged with 5 mL
 styrene, 1 mL ortho-dichlorobenzene and 0.36 g of the n-butyl acrylate
 prepolymer obtained in Example 8 having an isobutyl nitroxide endgroup
 (M.sub.n =6800, PDI=1.32). Argon was bubbled through the solution while
 stirring for 1 hour and the reaction mixture was lowered into a preheated
 oil bath at 130.degree. C. The reaction was carried out overnight and was
 too viscous to sample for GC conversion. GPC analysis in THF showed a
 molecular weight increase to a M.sub.n equal to 53,000, and PDI equal to
 2.2. GPC analysis in trichlorobenzene showed only a very small amount of
 n-butyl acrylate prepolymer remaining, indicating that the prepolymer
 contained virtually no dead chains.
 EXAMPLE 26
 A 100 mL reaction flask with a 45/50 joint was equipped with a reactor head
 and a stirbar. Through the center joint of the reactor head a
 near-infrared probe was fitted with teflon tape (UPO instruments, model
 Insight IV fiber optic spectrometer). The other joints were used for a
 condenser with bubbler, Argon inlet, temperature probe and sample port.
 The flask was charged with 54 g n-butyl acrylate, 0.95 g of the C7
 morpholone nitroxide of Example 7, 0.34 g AIBN and 7.5 mL
 ortho-dichlorobenzene as the internal standard. A 25 mL syringe was filled
 with a 0.233 M solution of triflic acid in diethyl carbonate and fitted on
 a syringe pump. Through the sample port of the reactor, a syringe filled
 with 0.20 M.sub.n C7 morpholone nitroxide in diethyl carbonate was fitted.
 The mixture was heated at 130.degree. C. and the reaction conversion was
 followed by GC and near infrared. Acid was metered in slowly until a rise
 in the reaction temperature, or increase in conversion was noted. At this
 point 0.1 mL of the nitroxide solution was injected which slowed the
 polymerization instantaneously. Addition of acid and nitroxide was
 continued while keeping the temperature of the reactor below 135.degree.
 C. At the end of the polymerization, a polymer was obtained in 91% yield
 with M.sub.n equal to 6300, PDI equal to 4.3. This polymer was purified by
 precipitation from methanol to remove any impurities.
 EXAMPLE 27
 Example 26 was repeated under identical conditions with the exception that
 198 mg of the isobutyl nitroxide of Example 2 was substituted for the C7
 morpholone nitroxide. A polymer having M.sub.n equal to 81,900 and PDI
 equal to 2.07 was obtained in 82% yield.
 EXAMPLE 28
 The prepolymer of Example 27 (1 g ) was heated in 5 mL of styrene with 0.5
 mL of ortho-dichlorobenzene as an internal standard. After 16 hours at
 130.degree. C. a polymer having M.sub.n equal to 164,000 and PDI equal to
 2.50 was isolated. GPC analysis in trichlorobenzene showed no trace of the
 starting prepolymer indicating that the acrylate-styrene block copolymer
 had formed completely.
 EXAMPLE 29
 5 mL of n-butyl acrylate and 48 mg of the adduct of ethylbenzene and
 dimethyl morpholone nitroxide formed in Example 15 were heated at
 130.degree. C. for 40 hours. A polymer having M.sub.n equal to 13,900 and
 PDI equal to 1.8 was obtained in 77% yield.
 EXAMPLE 30
 Styrene (2.5 g ), AIBN (0.11 g ) and the C7 morpholone of Example 7 (0.24 g
 ) were heated at 130.degree. C. for 4 hours. The prepolymer obtained in a
 40% yield by precipitating the reaction in methanol had M.sub.n equal to
 940 and a PDI equal to 1.12.
 The prepolymer (1 g ) was then heated in t-butyl acrylate at 130.degree. C.
 for 6 hours. The conversion by GC of t-butyl acrylated was 44%. The
 resultant block copolymer had M.sub.n equal to 1600 and a PDI equal to
 1.46.
 COMATIVE EXAMPLE 3
 A polystyrene prepolymer with a TEMPO endgroup (2 g ) having M.sub.n equal
 to 20,500 and PDI equal to 1.28 was heated with 5 mL of t-butyl acrylate
 and 2 mL of DMSO at 128.degree. C. After 5 hours, the polymer obtained
 contained no acrylate as determined by NMR.
 EXAMPLE 31
 The prepolymer of Example 22 (0.5 9) was heated in 2 mL dimethyl aminoethyl
 acrylate at 130.degree. C. for 24 hours. The conversion of the acrylate
 monomer by GC was determined to be 37%. The polymer obtained was
 completely soluble in methanol and the molecular weight was determined by
 NMR to be 29,500, showing that a clean block copolymer was obtained.
 EXAMPLE 32
 The block copolymer of Example 22 (7 g ) was heated in styrene at
 140.degree. C. for 17 hours. A triblock copolymer (18 g ) was obtained
 having M.sub.n equal to 72,600 and PDI equal to 2.7.
 The stable free radical mediated polymerization process claimed in a number
 of patents results in narrow polydispersity resins and linear molecular
 weight growth with conversion. This opens the possibility to synthesize
 block copolymers. The SFRP process depends uniquely on the stable free
 radical mediator used. The patents cited above use TEMPO and TEMPO
 derivatives and show examples of polymerization of styrene and styrene
 derivatives. However, as shown in the comparative Examples, these
 nitroxides do not enable efficient polymerization of acrylates either as
 homopolymers or in combination with other monomers to form block
 copolymers.
 We have found, unexpectedly, that by altering the nitroxide structure to a
 highly hindered piperazone or morpholone nitroxide, acrylate
 polymerization mediated by these stable free radicals is feasible with
 high efficiency. Specifically, we have shown improved homopolymerization
 of acrylates using these nitroxides. We have also shown that block
 copolymers can be formed in very high yields starting with either styrene
 prepolymers endcapped with the new nitroxides or acrylate prepolymers
 endcapped with the new nitroxides. Indeed, the block copolymer formation
 occurs in a controlled fashion with formation of narrow polydispersity
 resins. These significant improvements are due to the structural
 differences between piperazone and morpholone nitroxides, on the one hand,
 and TEMPO and its derivatives, on the other.
 The invention has been described with reference to preferred and alternate
 embodiments. Obviously, modifications and alterations will occur to others
 upon the reading and understanding of this specification. It is intended
 to include all such modifications and alterations insofar as they come
 within the scope of the appended claims or the equivalents thereof.