Functionalized alkoxyamine initiators

Details Functionalized alkoxyamine initiators Functionalized alkoxyamine initiators

2000-08-31

2003-10-14

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S205000, C526S217000, C526S220000, C526S318000, C526S319000, C526S341000, C564S001000, C564S300000, C564S301000

Reexamination Certificate

active

06632895

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a new process for the preparation of functionalized alkoxyamine initiators, new alkoxyamine initiators based on (meth)acrylate which are prepared by this process, and their use for the preparation of polymers.
2. Description of the Prior Art
Living free radical polymerization is a relatively young method of controlled free radical polymerization. It combines the advantages of a conventional free radical polymerization (simple synthesis process, broad monomer base) with those of a living polymerization (polymers of defined structure, molecular weight and distribution and end group functionality). The aim of precise control of free radical polymerization is achieved here by a reversible chain termination or blocking (“end-capping”) after each growth step. The equilibrium concentration of the polymerization-active (“living”) chain ends in this case is so low compared with the equilibrium concentration of the blocked (“dormant”) chain ends that termination and transfer reactions are severely suppressed compared with the growth reaction. Since the end-capping proceeds reversibly, all the chain ends remain “living” if no termination reagent is present. This allows control of the molecular weight, a low polydispersity and controlled functionalization of the chain ends by termination reagents.
Controlled free radical polymerization using tetraalkythiuram disulfides is described by Otsu et al. (Makromol. Chem.,
Rapid Commun
. 1982, 3, 127-132).
U.S. Pat. No. 4,581,429 discloses alkoxyamines which are formed by reaction of linear or cyclic nitroxides, such as 2,2,6,6-tetra-methylpiperidin-1-oxyl (TEMPO) with organic carbon-based free radicals, and a process for the preparation of vinyl polymers using these compounds as initiators. At temperatures >100° C., the C—ON bond can be cleaved reversibly to re-form the C radical (“active species”) and the stable nitroxide radical. The equilibrium lies far on the side of the alkoxyamine (“dormant species”).
The result of this reaction is a low, stationary, concentration of free radicals which, in the free radical polymerization of vinyl monomers, means that bimolecular termination reactions are disadvantaged kinetically compared with the unimolecular growth reaction. Side reactions are thus largely suppressed and a “living” reaction procedure is possible for the free-radical polymerization. The use of alkoxyamine initiators which additionally carry functional groups is not described.
The preparation of vinyl polymers by living free radical polymerization (“Stable Free Radical Polymerization”, SFRP) on the basis of alkoxyamines is described by Hawker et al. (
J. Am. chem. Soc
. 1994, 116, 11185
; Macromolecules
1995, 28, 1993) and Georges et al. (Xerox Comp., U.S. Pat. No. 5,322,912, U.S. Pat. No. 5,401,804, U.S. Pat. No. 5,412,047, U.S. Pat. No. 5,449,724, WO 94/11412, WO 95/26987 and WO 95/31484). The carbon radicals are prepared by addition of free radical initiators (peroxides or azo initiators) on to monomers which can be polymerized by free radicals; these free radicals are then captured in situ by TEMPO to give alkoxyamines. These alkoxyamines are the actual initiators, since they are cleaved reversibly at temperatures >100° C. into free radicals and can thus initiate polymerization of the monomers metered in. The use of functionalized alkoxyamine initiators would thus allow the synthesis of polymers of controlled end group functionality in a simple manner if the functional groups of the alkoxyamine initiators remain in the terminal position in the polymer.
Various working groups have concerned themselves with the synthesis of alkoxyamine initiators, and specifically those functional alkoxyamine initiators for SFRP of vinyl monomers. The following partly functionalized alkoxyamine initiators I-IV have been prepared by this synthesis by reaction of a free radical species with a stable nitroxide radical, by nucleophilic substitution reactions or oxidative addition.
Hawker el al. (
Macromolecules
1996, 29, 5245-5254) developed a synthesis route for species I in which dibenzoyl peroxide free radical initiator initially introduced into the reaction vessel is captured by a stable nitroxide radical after addition on to a styrene monomer. Subsequent hydrolysis of the ester function gives a mono- or difunctional alkoxyamine initiator, depending on the substitution of the nitroxide radical. This process shows a low selectivity and gives only yields of <<40% of functionalized products.
The synthesis of alkoxyamine initiators of type II by the method of Hawker et al. (
Macromolecules
1996, 29, 5245-5254), Yozo Miura et al. (
Macromolecules
1998, 31, 4659-4661) and Braslau et al. (
Macromolecules
1997, 30, 6445-6450) takes place with free radical initiators which, after their dissociation, can abstract activated hydrogen atoms from suitable substrates. Typical initiators are di-tert-butyl peroxide, di-tert-butyl hyponitrite and di-tert-butyl diperoxalate. Yields of these reactions are in the range from 40 to 90%. By using substituted aromatics (Br, COOEt, OMe), the synthesis of hydroxy-functional alkoxyamine initiators is possible in further reaction steps (Yozo Miura et al.
Macromolecules
1998, 31, 4659-4661). The expensive multi-stage reaction procedure via organometallic intermediate stages makes this process scarcely realizable industrially and economically uninteresting.
Compounds of type III were obtained by Hawker et al. (
Macromolecules
1996, 29, 5245-5254) by capturing the carbon radicals formed on dissociation of azo free radical initiators. By using expensive functionalized azo free radical initiators, synthesis of functionalized alkoxyamine initiators is thus possible. The yields of this reaction are <30%.
Alkoxyamine initiators of type I and IV were prepared by Matyjaszewski et al. (
Macromolecules
1998, 31, 5955-5957) by reaction of benzylic or otherwise activated bromine compounds with a system, similar to ATRP (Atom Transfer Radical Polymerisation), of Cu
0
/Cu
2+
and a substituted bipyridine in the presence of a stable nitroxide radical. A carbon radical is generated here by an ATRA reaction (Atom Transfer Radical Addition) with abstraction of the bromine atom, and is captured immediately by the nitroxide radical. The yields for this reaction are between 76 and 92%; functionalized alkoxyamine initiators were not prepared.
Braslai el al. (
Macromolecules
1997, 30, 6445-6450) report on the synthesis of alkoxyamine initiators of type II and IV by various demanding multi-stage nucleophilic and oxidative or photooxidative addition routes with yields of 30-78%. Functionalized alkoxyamine initiators were not prepared.
Another route to alkoxyamine initiators according to Bergbreiter et al. (
Macromolecules
1998, 31, 6380-6382) leads to N-allyloxyamines in yields of 10 to 74% starting from allylic amines. Functional alkoxyamine initiators were not prepared.
With none of the methods described can functionalized alkoxyamines with 1 or 2 functional groups which are capable of a further reaction or crosslinking with the known functional groups in coatings chemistry be prepared in an industrially simple manner and in high yields.
The object of the present invention was therefore to provide a process for the preparation of functional initiators of the type In—OH and/or Y—In—OH which does not have the abovementioned disadvantages of the prior art, wherein “In” represents a substituted hydrocarbon radical which is capable of initiating an SFRP and Y represents a functional group which is capable of a further reaction or crosslinking with the known functional groups in coatings chemistry.
SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of alkoxyamine initiators of the formula (I)
wherein
R
1
, R
2
and R
3
are the same or different and represent H, C
1
-C
20
-(cyclo)alkyl, C
6
-C
24
-aryl, halogen, CN, C
1
-C
20
-(cyclo)alkyl ester or -amide or C
6
-C
24
-aryl ester or -amide, and
R
4
and R
5

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