Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-09-24
2003-06-17
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S310000, C528S315000, C528S312000, C528S324000, C528S326000, C264S143000, C264S144000
Reexamination Certificate
active
06579965
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the anionic polymerization of lactams. The production of polyamide by the anionic route consists in adding a catalytic system to a lactam and in then heating in order to obtain the polyamide in a few minutes. The catalytic system is composed of a catalyst, consisting of a strong base capable of forming a lactamate, and of an activator (sometimes referred to as a regulator), such as a bisamide. Mention may be made, as examples of strong bases, of sodium and sodium hydride and mention may be made, as examples of regulators, of ethylenebisstearamide (EBS) and ethylenebisoleamide. A filler, such as glass fibres, can also be added to the lactam, before its polymerization and in addition to the catalytic system. A reinforced material is thus obtained directly. The present invention relates to the catalytic system and more particularly the way of preparing it, of storing it and of using it to bring about the polymerization of the lactam.
THE PRIOR ART AND THE TECHNICAL PROBLEM
Application FR 2 291 231 discloses the polymerization of lactams in the presence of a catalytic system composed (i) of a product chosen from sodium, potassium, alkali metal hydrides and alkali metal hydroxides and (ii) of a product chosen from organic isocyanates, from ureas, from amides and from acid chlorides. The example describes only the use of sodium hydride and of a promoter, without specifying the name thereof. The extruder is fed with the blend of lactam, of hydride and of promoter at 170° C., the extruder being at 250° C. There is nothing written or suggested regarding storage of this blend of unknown composition and even less regarding its stability. According to this technique, it is necessary to add the catalytic system to the lactam immediately before the polymerization.
The work Book of Abstracts 212 ACS Meeting (1996) in chapter 19, pages 255 to 266, published in 1998 by the American Chemical Society describes the polymerization of caprolactam in the presence of lactamate and of N-acyllactams. The two components of the catalytic system are mixed with a lactam stream and these streams are brought into contact in the polymerization reactor, either batchwise or continuously. This process is theoretically more flexible than the preceding process since each of the lactam solutions, not comprising a complete catalytic system, cannot polymerize as long as they are not mixed. On the other hand, this process has the disadvantage that it is necessary to accurately meter these two streams of the reaction mixture in order to obtain the correct proportions of catalyst and of activator and thus to obtain a polyamide with the desired characteristics. It is necessary to thoroughly mix the two streams in order for the catalyst and the activator to be properly distributed in the lactam but the polymerization begins before the reactor.
Patent EP 231381 discloses the preparation of polyamide items reinforced by carbon fibres, in which the carbon fibres are placed in a mould and then two lactam streams are introduced into this mould. One of the streams comprises a catalyst and the other comprises the regulator. Patent EP 491043 discloses a similar technique. These two European patents disclose techniques similar to what is described in the abovementioned work published by the ACS.
Patent EP 786 482 discloses the polymerization of lactams using a liquid catalytic system which is added in a proportion of 3 to 10 parts to 100 parts of lactam to be polymerized. This catalytic system is composed of an N-alkyl-2-pyrrolidone, of caprolactam, of a sodium lactamate and of a diisocyanate blocked by a lactam. The temperature of this catalytic system must not exceed 70° C., then it is added to the lactam and heating is carried out. For example, it results in the polymerization of lactam 12 from 175° C.
Patent EP 786485 discloses a similar process but the N-alkyl-2-pyrrolidone can be entirely or partially replaced by a substituted urea, such as N,N′-dimethylpropyleneurea.
Patent EP 872508 discloses the polymerization of lactams using a liquid catalytic system which is added in a proportion of 3 to 7 parts to 100 parts of lactam to be polymerized. This catalytic system is composed of a solvent, such as dimethylpropyleneurea, of caprolactam, of sodium methoxide and either of a diisocyanate blocked by a lactam or of cyclohexylcarbodiimide. This catalytic solution must subsequently be cooled to ambient temperature, then it is added to the lactam and heating is carried out in order to bring about the polymerization of the lactam.
The processes disclosed in these three preceding European patents have the disadvantage of introducing impurities into the lactam and thus into the polyamide. The catalytic systems disclosed bring about the polymerization of lactam 12 from 175° C., which does not make possible good impregnation of the fibres when the polymerization is carried out in the presence of glass fibres since the viscosity increases too quickly. Furthermore, the solutions of the catalytic system which are disclosed are not completely stable.
A catalytic system has now been found which is a mixture of a strong base capable of giving a lactamate and of an amide or a bisamide in solution in the lactam. As regards, for example, lactam 12, this solution is stable for 24 hours at 160° C. This solution can comprise the amounts of catalyst and of activator which are sufficient to bring about its polymerization as soon as it is heated to a sufficient temperature; for example, for lactam 12, it is sufficient to heat to between 200 and 350° C., preferably between 230 and 300° C., in order for polymerization to take place in a few minutes. The polymerization of lactam 12 only significantly begins starting from 230° C. which, when polymerization is carried out in the presence of glass fibres, gives the lactam the time to thoroughly impregnate the glass fibres. This solution can also comprise much more catalyst and activator than is necessary to polymerize the lactam in which they are dissolved; it is thus a masterbatch which is added to lactam in an amount such that there are sufficient proportions of catalyst and of activator to bring about the polymerization of the whole of the lactam. It has thus been found that this solution could be cooled to ambient temperature and thus become solid and could then subsequently be reheated without any loss in activity. This solution can be cooled in a device such that it is converted into granules, into powder, into chips or into pellets. This conversion is particularly useful when it is a masterbatch. This form of the invention is particularly easy to implement; complicated preparations no longer have to be carried out. It is sufficient to take lactam of commercial quality and to add thereto the granules, the powder, the chips or the pellets, which may be available in bags or in containers. It is also possible, depending upon the circumstances of the polyamide production, such as the availability of the moulds or mould-release time, to reheat these granules and thus to have available a stable solution ready to be added to the lactam to be polymerized.
BRIEF DESCRIPTION OF THE INVENTION
There is now provided, according to a first embodiment, a novel process for the anionic polymerization of lactams, in which:
(a) (i) a catalyst capable of creating a lactamate and (ii) a regulator chosen from amides of formula R1-NH—CO—R2, in which R1 can be substituted by an R3-CO—NH— or R3-O— radical and in which R1, R2 and R3 denote an aryl, alkyl or cycloalkyl radical, are dissolved in the molten lactam,
(a1) the solution from stage (a) is cooled, optionally to the solid state preferably in particulate form,
(a2) the product from stage (a1) is optionally reheated to a temperature below the polymerization temperature of the lactam,
(a3) optionally, the product from stage (a1) is reheated and is maintained at a temperature between the melting temperature of the lactam and 15° C. above,
(b) the product from any one of stages (a1), (a2) or (a3) is in
Faulhammer Heike
Hoogen Nicola
Muelhaupt Rolf
Wollny Andreas
Atofina
Hampton-Hightower P.
Millen White Zelano & Branigan P.C.
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