Polymerization process

Details Polymerization process Polymerization process

1999-11-18

2001-10-23

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...

C526S171000, C526S173000, C526S147000, C526S161000

Reexamination Certificate

active

06306995

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to novel “living” polymerization process, particularly to a “living” polymerization process under phase transfer conditions.
BACKGROUND OF THE INVENTION
Conventional chain polymerization of vinyl monomers usually consists of three main elemental reaction steps: initiation, propagation, and termination. Initiation stage involves creation of an active center from an initiator. Propagation involves growth of the polymer chain by sequential addition of monomer to the active center. Termination (including irreversible chain transfer) refers to termination of the growth of the polymer chain. Owing to the presence of termination and poorly controlled transfer reactions, conventional chain polymerization typically yields a poorly controlled polymer in terms of predicted polymer properties. Moreover, conventional chain polymerization processes mostly result in polymers with simple architectures such as linear homopolymer and linear random copolymer.
In 1950s, a so-called living polymerization was discovered by Szwarc (Szwarc, et al. J. Am. Chem. Soc. 78,2656 (1956)). Living polymerization was characterized by the absence of any kinds of termination or side reactions which might break propagation reactions. The most important feature of living polymerization is that one may control the polymerization process to design the molecular structural parameters of the polymer. Additional polymerization systems where the termination reactions are, while still present, negligible compared to propagation reaction have also been disclosed. As structural control can generally still be well achieved with such processes, they are thus often termed “living” or controlled polymerization (Wang, Macromolecules, 28, 7901 (1995)). In living and “living” (or controlled) polymerization, as only initiation and propagation mainly contribute to the formation of polymer, molecular weight can be predetermined by means of the ratio of consumed monomer to the concentration of the initiator used. The ratio of weight average molecular weight to number average molecular weight, i.e., molecular weight distribution (Mw/Mn), may accordingly be as low as 1.0. Moreover, polymers with the specifically desired structures and architectures can be purposely produced. In terms of topology, such structures and architectures may include: linear, star, comb, hyperbranched, dendritic, cyclic, network, and the like. In terms of sequence/composition distribution such structures and architectures may include: homopolymer, random copolymer, block copolymer, graft copolymer, gradient copolymer, tapered copolymer, periodic copolymer, alternating copolymer, and the like. In terms of functionalization, such structures and architectures may include: telechlics, macromonomer, labeled polymer, and the like.
Over the past 40 years, a number of living/“living” polymerization processes have been developed. Examples of these polymerization processes include: anionic polymerization (Szwarc, J. Am. Chem. Soc. 78, 2656 (1956)), cationic polymerization (Sawamoto, Trends Polym. Sci. 1,111 (1993)), ring opening methathesis polymerization (Gillium and Grubbs, J. Am. Chem. Soc. 108, 733 (1986)), nitroxides-mediated stable radical polymerization (Solomon, U.S. Pat. No. 4,581,429 (1986), Georges, Macromolecules, 26,2987 (1993)), Cobalt complexes-mediated radical polymerization (Wayland, J. Am. Chem. Soc. 116, 7943 (1994)), and transition metal catalyzed atom transfer radical polymerization (Wang, U.S. Pat. No. 5,763,548 (1998)).
Living/“living” polymerization processes have been successfully used to produce numerous specialty polymeric materials which have been found to be very useful in many applications. One example is the commercialization of styrenic thermoplastic elastomers such as styrene-b-butadiene-b-styrene triblock copolymers (SBS) by Shell chemicals and others. SBS is made by sequential anionic living polymerization of styrene and butadiene. However, except for living anionic polymerization of non-polar monomers such as styrene and dienes using alkyl lithium as an initiator, almost all of other living/“living” systems mentioned-above currently showed little promise for wide industrial commercialization, mainly due to high cost to industrially implement these processes. Thus, searching for practical living/“living” polymerization processes is a major challenge in the field of polymer chemistry and materials.
Alkyl halides have been used as initiator in several “living” polymerization systems. Sawamoto et al used a series of mixtures of alkyl halide and Lewis acid as initiating system in “living” cationic polymerization of vinyl ether, isobutylene, and styrene (Sawamoto, Trends Polym. Sci. 1,111 (1993)). However, these cationic polymerizations required very restricted conditions such as moisture and impurities free reaction systems. Ganyor et al disclosed that combination of certain alkyl iodide with conventional radical initiator such as AIBN induced a “living” polymerization of styrene, methyl methacrylate, and methyl acrylate (Gaynor et al. Macromolecules 28, 8051 (1995)). The discovery of transition metal catalyzed atom transfer radical polymerization (ATRP) by Wang represents a very important step towards practical “living” polymerization (Wang, J. Am. Chem. Soc., 117, 5614 (1995)). Using alkyl halide as an initiator and transition metal species as a catalyst, ATRP not only works well with a very broad variety of important vinyl monomers but also provides much easier pathway towards a variety of polymers with various structure and architectures. However, the use of heavy transition metal salts or complexes requires multi-step purification of the resultant polymers. Moreover, heavy transition metal salts or complexes are often toxic and not environmentally friendly. These drawbacks limit the wide implementation of current version ATRP process in industrial production.
An initiating system comprising an alkyl halide and an onium salt has been also found to be effective in promoting “living” polymerization. Reetz (Reetz et al. Macromol. Rapid Commun. 17, 383 (1996)) disclosed that while neither diethyl or dimethyl iodomethylmalonate nor tetra-n-butylammonium iodide alone initiated the polymerization of methyl methacrylate (MMA), a “living” polymerization of MMA was achieved by using diethyl or dimethyl iodomethylmalonate/tetra-n-butylammonium iodide (1/1) as an initiating system in polar solvents. The controlled poly (methyl methacrylate) was obtained in the number-average molecular weight range of 2000 to 8000, with molecular weight distribution being fairly narrow (ratio of weight- to number-average molecular weights Mw/Mn 1.2-1.3). Although the underlying mechanism is still unclear, the onium salt used acts as a catalyst in this homogenous polymerization system. In comparison with other “living” systems, the alkyl iodide/ammonium salt combined catalyst system disclosed by Reetz represents a simpler and cleaner one towards “living” polymerization. Due to the instability of iodide containing organic compounds, however, such process may not be commercially feasible, and it has been found that more stable alkyl chlorides or bromides alone are not reactive enough to react with onium salt to generate initiating species in chain polymerization.
Phase-transfer catalysis, PTC, was first coined by Starks in 1971 (J. Am. Chem. Soc., 93, 195 (1971)). It has been widely and practically used in various preparative organic, organometallic and polymer chemistry. PTC is a technique for conducting reactions between two or more reagents in one or two or more phases, when reaction is inhibited because the reactants cannot easily come together and one reagent is not reactive enough towards another one. A “phase-transfer agent” is added to transfer one of the reagents to a location where it can conveniently and rapidly react with another reagent. Two types of phase transfer agents are found efficient: quaternary salts and certain chelating reagents such as crown ethers, cryptands, poly(ethylene glycol) and their

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