May 7, 2009  9  US 2009/0117314 Al  sents, for example, n-pentyl, 1-methylbutyl, 2-methylbutyl,  3-methylbutyl, neopentyl, 1-ethylpropyl, cyclohexyl, cyclo› pentyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,  1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-me› thylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethyl› butyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethyl› butyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2- trimethylpropyl,  1,2,2-trimethylpropyl,  l-ethyl-1- methylpropyl,  l-ethyl-2-methylpropyl  or  l-ethyl-2- methylpropyl;  C$_{1 }$-C$_{10}$ -alkyl additionally represents, for  example, n-heptyl and n-octyl, pinacyl, adamantyl the iso› meric menthyls, n-nonyl or n-decyl; C$_{1}$-C$_{34}$-alkyl addition› ally represents, for example, n-dodecyl, n-tridecyl, n-tetrade› cyl, n-hexadecyl or n-octadecyl. The same applies to the  corresponding alkyl radical, for example, in aralkyl or alky› laryl, alkylphenyl or alkylcarbonyl radicals. Alkylene radi› cals in the corresponding hydroxyalkyl or aralkyl or alkylaryl  radical represent for example, the alkylene radicals corre› sponding to the preceding alkyl radicals.  [0142]  Ary! represents a carbocyclic aromatic radical hav› ing 6 to 34 skeletal carbon atoms. The same applies to the  aromatic moiety of an arylalkyl radical, also referred to as  aralkyl radical, and to aryl constituents of more complex  groups, such as, for example, arylcarbonyl radicals.  [0143]  Examples of  CcC$_{34}$ -aryl are phenyl, o-, p- and  m-tolyl, naphthyl, phenanthrenyl, anthracenyl or fluorenyl.  [0144]  Arylalkyl or aralkyl denotes, in each case indepen› dently, a straight-chain, cyclic, branched orunbranched alkyl  radical according to the above definition, which may be  monosubstituted, polysubstituted or completely substituted  by aryl radicals according to the above definition.  [0145]  The preceding lists are to be understood as being by  way of example and not as limiting.  [0146]  There is in principle no limitation and restriction  with regard to the manner and plant in which and the proce› dure according to which the process is carried out. The pro› cess can preferably be carried out as described below.  [0147]  Furthermore, there is no special limitation and  restriction with regard to the temperatures and the pressures  for the process according to the invention. Any condition is  possible as long as the chosen temperatures, pressures and  catalysts permit a melt transesterification with appropriately  rapid removal of the monohydroxyaryl compound elimi› nated.  [0148]  The temperatures over the entire process are in gen› eral between 180 and 330°  C. and the pressures between 15  bar absolute and 0.01 mbar absolute.  [0149]  A continuous procedure is preferably chosen  because this may be advantageous for the product quality.  [0150]  Such a continuous process according to the inven› tion is preferably carried out in such a way that one or more  dihydroxyaryl compounds are subjected to precondensation  with one or more diary! carbonate(s) and optionally further  reactants with the use of at least one catalyst and the molecu› lar weight of the end product is increased to the desired level  after this precondensation without separating off the resulting  monohydroxyaryl compound(s) in a plurality of subsequent  reaction-evaporator stages with temperatures increasing step› wise and pressures decreasing stepwise.  [0151]  The devices, apparatuses and reactors suitable for  the individual reaction-evaporator stages are, corresponding  to the course of the process, heat exchangers, flash appara› tuses, separators, colunms, evaporators, stirred containers  and reactors and other commercial apparatuses which pro- vide the required residence time at selected temperatures and  pressures. The chosen devices must permit the necessary  introduction of heat and be designed so that they are suitable  for the continuously increasing melt viscosities.  [0152]  All devices are connected to one another via pumps,  pipelines and valves. The pipelines between all facilities  should of course be as short as possible and the number of  bends in the pipes should be kept as small as possible in order  to avoid unnecessarily lengthened residence times. The exter› nal, i.e. technical boundary conditions and requirements for  assemblies of chemical plants should be taken into account.  [0153]  For carrying out the process according to a preferred  continuous procedure, the reactants can be melted together or  the solid dihydroxyaryl compound(s) in the diarylcarbonate  melt or the solid diary! carbonate or carbonates in the melt of  the dihydroxyaryl compound(s) can be dissolved or both raw  materials are combined as a melt, preferably directly from the  preparation. The residence times of the separate melts of the  raw materials, in particular those of the melt of the dihy› droxyaryl compound, are set as short as possible. The melt  mixture can on the other hand have a longer residence time  without losses of quality owing to the lower melting point of  the raw material mixture in comparison with the individual  raw materials at correspondingly lower temperatures.  [0154]  The catalyst or catalysts, preferably dissolved in a  suitable solvent, such as, for example, phenol, is or are then  admixed and the melt is heated to the reaction temperature.  [0155]  In preferred embodiments of the process according  to the invention, a part-stream, into which at least one inhibi› tor is metered, is taken off from the melt stream between the  penultimate reactor and the finish reactor by means of a gear  pump. Directly thereafter, the mixture is pumped back into  the main stream for thorough mixing via a static mixer. Fol› lowing the entry point in the direction of flow is a further static  mixer which ensures the homogeneous distribution in the  main melt stream, which is then passed into the final reactor.  In the final reactor, which is used for reducing residual mono› mers, the residual monomers are then reduced at temperatures  of260to 310°  C. preferably at 265 to 300°  C. and particularly  preferably at 270 to 290°  C. and at pressures of0.01 to 3 mbar,  preferably of 0.2 to 2.5 mbar and particularly preferably of  0  .4  to 2 mbar. The levels of fill are set in the final reactor so as  to be as low as permitted by the process engineering. The  residence time in the final reactor-also referred to as finish  reactor-is of the order of magnitude of a few minutes to  hours, preferably 5 to 180 minutes, particularly preferably 10  to 150 minutes and very particularly preferably 15 to 120  minutes. A possible slight increase in molecular weight in the  final reactor, in which predominantly the expulsion of the  residual monomers in vapour form is to take place, can be  compensated by reducing the entry molecular weight to such  an extent that, after the expulsion of the residual monomers in  vapour form, the desired final molecular weight is exactly  achieved. The finished polycarbonate is discharged from the  final reactor by means of the pump device, if required pro› vided with additives for improving the properties by known  methods, extruded, cooled and granulated. The pump device  used is as a rule a gear pump. Alternatively, screws having a  very wide range of designs or positive displacement pumps of  special design can also be used.  [0156]  The particularly preferred embodiment of the pro› cess according to the invention in which, for example, 2,2- bis( 4-hydroxyphenyl)propane (bispheno!A, BPA) and diphe-