“Living” free radical polymerization process

Details “Living” free radical polymerization process “Living” free radical polymerization process

2002-05-30

2003-02-04

Pezzuto, Helen L (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S195000, C526S184000, C526S189000, C526S197000, C526S198000, C526S217000, C526S242000, C526S303100, C526S314000, C526S328000, C526S341000, C526S346000, C568S001000, C568S006000, C568S558000

Reexamination Certificate

active

06515088

ABSTRACT:

FIELD OF INVENTION
The invention relates to a new class of living free radical initiators that are based on alkylperoxydiarylborane derivatives with the general formula of R—[O—O—B—&phgr;
1
(—&phgr;
2
)]
n
. The initiators exhibit living polymerization at ambient temperature to produce white solid vinyl polymers with pre-determined molecular weight and narrow molecular weight distribution. By sequential monomer addition, the initiators also produce block copolymers with controlled copolymer composition and narrow molecular weight distribution.
BACKGROUND OF THE INVENTION
The control of polymer structure has been an important facet in polymer synthesis, both for academic interests and industrial applications. A living polymerization mechanism provides an optimal means for preparing polymers having well-defined molecular structures, i.e. molecular weight, narrow molecular weight distribution, polymer chain end, as well as for preparing block and star polymers. In the past, the most viable techniques in living polymerization reactions were mediated by anionic, cationic, and recently metathesis initiators [for anionic living polymerization, see Holden, et al, U.S. Pat. No. 3,265,765; for cationic living polymerization, see Kennedy, et al, U.S. Pat. No. 4,946,899; and for metathesis living polymerization, see R. H. Grubbs, et al,
Macromolecules,
21, 1961 (1988)]. However, these polymerization processes are very limited to a narrow range of monomers, due to the sensitivity of active sites to functional (polar) groups.
In many respects, free radical polymerization is the opposite of living ionic and metathesis polymerizations since it is compatible with a wide range of functional groups, but offers little or no control over polymer structure. Despite this drawback, free radical polymerization is the preferred industrial choice in the commercial production of vinyl polymers, especially those containing functional groups.
Early attempts to realize a living free radical polymerization involved the concept of reversible termination of the growing polymer chains by iniferters, such as N,N-diethyldithiocarbamate derivatives [Otsu, et.al,
J. Macromol.Sci., Chem.,
A21, 961 (1984);
Macromolecules,
19, 287 (1986);
Eur. Polym. J.,
25, 643 (1989); Turner, et.al,
Macromolecules,
23, 1856 (1990)]. However, this strategy suffered from poor control of polymerization reaction and polymer formed having high polydispersity.
The first living radical polymerization was observed in the reactions involving a stable nitroxyl radical, such as 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO), that does not react with monomers but forms a reversible end-capped propagating chain end [see, Moad, et.al,
Polymer Bull.,
6, 589 (1082); Georges, et.al,
Macromolecules,
26, 2987 (1993); Georges, et.al, U.S. Pat. Nos. 5,322,912 and 5,401,804; Hawker, et.al,
J. Am. Chem. Soc.,
116, 11185 (1994); and Koster, et.al, U.S. Pat. No. 5,627,248]. The formed covalent bonds reduce the overall concentration of free radical chain ends, which leads to a lower occurrence of unwanted termination reactions, such as coupling and disproportionation reactions. For an effective polymerization, the reaction has to be carried out at an elevated temperature (>100° C.). Relatively high energy is needed in the cleavage of the covalence bond, which maintains a sufficient concentration of propagating radicals for monomer insertion. Furthermore, this living radical polymerization seems effective only with styrenic monomers.
Subsequently, several research groups have replaced the stable nitroxyl radical with transition metal species as the capping agents to obtain a variety of copper, nickel, iron, cobalt, or ruthenium-mediated living free radical systems, so-called atom transfer radical polymerization (ATRP) [see, Matyjaszewski, et.al,
Macromolecules,
28, 7901 (1995);
J. Am. Chem. Soc.,
117, 5614 (1995); Mardare, et.al, U.S. Pat. No. 5,312,871; Sawamoto, et.al,
Macromolecules,
28, 1721 (1995); Percec, et.al,
Macromolecules,
28, 7970 (1995); Teyssie, et.al,
Macromolecules,
29, 8576 (1996); and Fryd, et.al, U.S. Pat. No. 5,708,102]. Overall, all of these systems have a central theme, i.e., reversible termination via equilibrium between active and dormant chain end at an elevated temperature, which is regulated by a redox reaction involving metal ions. The main advantage of this reaction is that, through a proper choice of the metal compound, it is possible to operate with a broad spectrum of monomers. However, a major drawback is the formation of a deep colored reaction mixture that requires extensive purification procedures to obtain the desired final product.
It has also been known that trialkyborane in an oxidized state becomes an initiator for the polymerization of a number of vinyl monomers [see Furukawa, et al,
J. Polymer Sci.,
26, 234, 1957;
J. Polymer Sci.
28, 227, 1958;
Makromol. Chem.,
40, 13, 1961; Welch, et.al,
J. Polymer Sci.
61, 243, 1962 and Lo Monaco, et. al. U.S. Pat. No. 3,476,727]. The polymerization mechanism involves free radical addition reactions. The initiating radicals may be formed from homolysis of peroxyborane or by the redox reaction of the peroxyborane with unoxidized trialkylborane. A major advantage of borane initiators is the ability to initiate the polymerization at low temperature. Peroxides and azo initiators, when used alone, usually require considerable heat input to decompose and thereby to generate free radicals. Elevation of the temperature often causes significant reduction in molecular weight of the polymer accompanied by the loss of important properties of the polymer.
U.S. Pat. No. 3,141,862 discloses conducting a trialkylborane-initiated free radical polymerization in the presence of an alpha-olefin hydrocarbon polymer. Apparently, the graft-onto reaction by this route was very difficult. The inert nature and insolubility of polyolefin (due to crystallinity) also seems to have hindered the process and resulted in very poor graft efficiency. The reactions shown in the examples of this patent also seem to require a very high concentration of organoborane initiator and monomers and to require elevated temperature. The majority products are homopolymers or insoluble gel. No information about the molecular structure of copolymers is provided in this patent.
Despite the advantage of borane initiators, organoborane-initiated polymerizations tend to be unduly sensitive to the concentration of oxygen in the polymerization system. Too little or too much oxygen results in little or no polymerization. High oxygen concentration causes organoborane to be transfered rapidly to borinates, boronates and borates that are poor initiators at low temperature. Moreover, polymerization is often inhibited by oxygen. To facilitate the formation of free radicals, some borane-containing oligomers and polymers [see Bollinger, et.al. U.S. Pat. No. 4,167,616 and Ritter, et.al. U.S. Pat. No. 4,638,092] were used as initiators in the free radical polymerizations. These organoboranes are prepared by the hydroboration of diene monomerss or polymers or copolymers. Similar polymeric organoborane adducts, prepared by the hydroboration of 1,4-polybutadiene and 9-borabicyclo(3,3,1)-nonane (9-BBN), have also been reported in
Macromol. Chem.,
178, 2837, (1977).
In the past decade, we have been focussing on the selective oxidation of trialkylborane and studying the mono-oxidative adducts as a new free radical initiation system. The research objective was centered around the functionalization of polyolefins by first incorporating borane groups into a polymer chain, which was then selectively oxidized by oxygen to form the mono-oxidized borane moieties that initiate free radical graft-from polymerization at ambient temperature to form polyolefin graft and block copolymers [Chung, et.al, U.S. Pat. Nos. 5,286,800 and 5,401,805;
Macromolecules,
26, 3467 (1993);
Polymer,
38, 1495 (1997);
Macromolecules,
31, 5943(1998);
J. Am. Chem. Soc

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