Polymerization method

Details Polymerization method Polymerization method

2001-02-21

2002-10-01

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S086000, C526S090000, C526S135000, C526S171000, C526S204000, C526S217000, C526S220000, C526S317100, C526S319000, C526S346000

Reexamination Certificate

active

06458903

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of controlling atom transfer radical polymerizations.
BACKGROUND ART
Various living polymerization techniques have so far been developed and it has become possible to produce polymers controlled in molecular weight, molecular weight distribution and terminal structure. As examples, there may be mentioned the anionic coordination polymerization of polypropylene glycol and the living cationic polymerization using an iniferter and a Lewis acid catalyst. In addition, in recent years, the technique of living radical polymerization has been developed, which makes it possible to control the radical polymerization, which has so far been regarded as very difficult to control.
Living radical polymerization is a radical polymerization in which the activity of the polymerization terminus is not lost but is maintained. While, in its narrow sense, the term “living polymerization” means the polymerization which proceeds while the terminal activity is maintained, it generally includes the so-called pseudo-living polymerization in which terminally inactivated species and terminally active species are in equilibrium. It is the latter definition that applies in the present invention. In recent years, living polymerization has been energetically studied by a number of groups. As examples, there may be mentioned a technique using such a radical scavenger as a cobalt-porphyrin complex (J. Am. Chem. Soc., 1994, 116, 7943) or a nitroxide compound (Macromolecules, 1994, 27, 7228) and the atom transfer radical polymerization (ATRP) technique using an organic halide as an initiator and a transition metal complex as a catalyst, among others. Atom transfer radical polymerization is generally carried out using an organic halide or sulfonyl halide compound as an initiator and, as a catalyst, a metal complex containing a central metal atom selected from among elements of the groups 7, 8, 9, 10 and 11 of the Periodic Table (see e.g. Matyjaszewski et al., J. Am. Chem. Soc., 1995, 117, 5614; Macromolecules, 1995, 28, 7901; Science, 1996, 272, 866; or Sawamoto et al., Macromolecules, 1995, 28, 1721). According to these techniques, the rate of polymerization is generally very high, and, in spite of the fact that they involve radical polymerization in which such a termination reaction as coupling of radicals readily occurs, the polymerization proceeds in a living manner to give a polymer with a narrow molecular weight distribution (Mw/Mn=1.1 to 1.5), and the molecular weight can be arbitrarily controlled by selecting the monomer/initiator charge ratio. In the present specification, the term “molecular weight distribution” means the weight average molecular weight
umber average molecular weight ratio as determined by gel permeation chromatography.
As the term “atom transfer radical polymerization” indicates, an initiator-derived halogen atom generally occurs at the growing polymer terminus. In actuality, however, it is a problem that such atom may disappear owing to various side reactions.
Of the catalysts useful in atom transfer radical polymerization, some are completely soluble in the polymerization system and give homogeneous systems but most of them are not completely soluble, hence are used in heterogeneous systems. For example, when 2,2′-bipyridyl, one of the ligands in most frequent use, is used in the polymerization using CuCl or CuBr, the polymerization systems generally become heterogeneous. As a measure for obtaining a homogeneous system, there is a technique involving substitution of an alkyl group on the pyridine rings of bipyridyl and it is reported that substitution of 1-butylpentyl or the like results in formation of a homogeneous system. Further, it is reported that the use of a highly polar solvent such as ethylene carbonate results in an increased solubility of the complex to give a system more close to a homogeneous one (Macromolecules, 1998, 31, 1535). However, it is also mentioned that, even in that case, a reduction in solvent amount leads to a decreased solubility and a reduced rate, for instance.
It has recently been reported that aliphatic polyamines (e.g. pentamethyldiethylenetriamine), which are inexpensive and commercially available, are also effective ligands and can be used in lieu of bipyridyl ligands and the like. However, even the use of such ligands cannot render the polymerization system completely homogeneous.
If the polymerization system is heterogeneous, the catalyst may precipitate and/or stick to the vessel wall, so that it is not easy to stabilize the rate of polymerization and it is difficult to control the rate of polymerization because of the changing catalyst concentration.
On the other hand, the use of acetonitrile as a solvent is mentioned as an example in a patent specification (WO 97/18247), without mentioning any particular effect thereof. There is no description of the appropriateness of this for use in combination with aliphatic polyamine ligands. Furthermore, the relevant descriptions made therein are all concerned with the use thereof as a solvent. There is no description at all of the addition of acetonitrile or a nitrile compound in small amounts as an additive.
The initiation of atom transfer radical polymerization is generally effected by preparing a monomer/catalyst/solvent mixture and finally adding an initiator. When a liquid initiator is used, it can be added with ease using a syringe or the like. When it is a solid, it also can be added in the form of a solution in a solvent. Upon addition of the initiator, the polymerization begins to proceed immediately. Therefore, for obtaining a polymer with a narrow molecular weight distribution, it is necessary to add the initiator all at once. However, if the initiator is added all at once and the polymerization begins to take place immediately, a considerable heat liberation will be encountered. In large-scale production, this heat liberation is very dangerous. For avoiding this problem, a method is conceivable which would comprise adding the catalyst last after preparing a monomer/initiator/solvent mixture. In this case, catalyst addition can be made while watching the state of polymerization initiation, whereby the danger in question may be avoided. As far as the catalyst is concerned, unlike the case of the initiator mentioned above, adding the same over a certain time period theoretically does not give a remarkable influence on the molecular weight distribution and the like. However, the technique of atom transfer radical polymerization most often uses a metal complex, which is a solid, as the catalyst. Moreover, many a catalyst gives a heterogeneous polymerization system as mentioned above, and it is not easy to dissolve it in a solvent. It is, therefore, not easy to initiate the polymerization by addition of catalyst. In fact, no report has been made so far concerning such a process involving the addition of a catalyst in this manner.
In living polymerization, a growing terminus retains the polymerizing activity from the initial to terminal stage of polymerization and, as a result, the rate of polymerization shows an approximately linear relation with the monomer concentration. When living polymerization is carried out batchwise by charging the reaction apparatus with the whole amount of the monomer to be used in polymerization from the beginning, the amount of the monomer polymerized per unit time is greatest at the early stage and then gradually decreases as the monomer is consumed. Similar problems are encountered even in semi-batchwise polymerization, which is conducted by supplementing the monomer batchwose or continuously after initiation to avoid the risk of uncontrolled progress of polymerization, which is a matter of particular concern in radical polymerization. In this case, even if the amount of the monomer remaining in the polymerization system is maintained at a constant amount, the growing terminus concentration and catalyst concentration are highest at the early stage and then diluted with the accumulation of the poly

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