Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-10-25
2003-01-28
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S271000
Reexamination Certificate
active
06512078
ABSTRACT:
The present invention refers to the production of a polyester-type polymer and particularly to the solid phase condensation of a polyester.
The main method to obtain polyester-type polymers consists in a high-temperature condensation either of the esterification product of a carboxylic diacid and a diol or the transesterification product of a diester and a diol. This condensation is effected in molten state. For the obtention of poly(ethylene terephthalate) (PET), the product of the transesterification of methyl terephthalate (DMT) and ethylene glycol (EG) or the esterification product of purified terephthalic acid (PTA) and ethylene glycol. The condensation is carried out until the obtention of a compound having the desired molecular weight. This condensation cannot lead to polymers having a very high viscosity index, specifically above 85 ml/g. Above such a viscosity, the type of technology presently employed does not permit the continuation of the reaction. If the obtention of a high molecular weight is desired, it is however necessary to carry out a solid state post-condensation at temperatures around 200° C. This consists in heating a load of polymer granules. This solid state low temperature procedure permits especially the obtention of polymers at low degradation levels.
Du Pont de Nemours company, especially in U.S. Pat. No. 5,548,868 and U.S. Pat. No. 5,510,454 describes another method for obtaining polyesters. This method consists in producing prepolymer tablets presenting low degrees of polymerization, ranging between 2 and 40. The tablets are subsequently condensed to solid state according to the procedure previously described for post-condensation. It is possible through this method to obtain polymers of any molecular weight, having viscosity indexes under or over about 85 ml/g, according to the post-condensation operational conditions.
The previously described solid state condensation and post-condensation procedures present considerably low kinetics and constitute a limiting step in the manufacture of polyesters. Notwithstanding the progresses attained, constant efforts are being made in order to improve the performance of the solid phase condensation or post-condensation step.
The object of the present invention is to overcome the problems inherent to solid phase condensation by proposing a process which permits increasing the kinetics of solid phase condensations. It proposes an alternative to known processes through effecting a solid phase condensation dispersed in a liquid. This permits overcoming the difficulties encountered in the usual processes, increasing the condensation kinetics and hence attaining faster the desired degrees of polymerization. The accomplishment of the solid phase condensation in a liquid medium must be effected on a solid prepolymer having particular properties, necessary for the good conduction of the process and speeding up of the kinetics. The object of the invention however is also a process for obtaining the prepolymer in solid phase dispersed to be condensed, as well as the characteristics, particularly the crystalline characteristics which permit making it sufficiently reactive.
The invention presents a process for manufacturing polyester which comprises at least the steps described above. It may comprise other upstream, downstream or intermediate steps. The process steps may be effected continuously or discontinuously in separate devices, or in the same devices. The essential steps are the following:
a) esterifying or transesterifying a carboxylic diacid or a carboxylic acid diester with a diol,
b) prepolymerizing the esterification or transesterification product in liquid phase until an average degree of polymerization between 10 and 50, preferably between 20 and 45,
c) preparing a dispersion of the prepolymer in a non-solvent of diol and non-swelling of the prepolymer liquid, the prepolymer being present in the dispersion in the form of solid particles having diameters under 2 mm and crystallized, with a crystalline lamella thickness under 17 nm,
d) polymerizing in dispersed solid phase,
e) recovering solid particles.
The process may be applied to the polymerization of any carboxylic diacid with any diol. It may be particularly applied with the following diacids: terephthalic acid, isophthalic acid, naphthalenedioic acid, sulfo-5-isophthalic acid and mixtures thereof. It may be applied particularly with the following diols: ethylene glycol, butane diol, neopentyl glycol, diethylene glycol, bisphenols, 1-2 propane diol, cyclohexyldimethanol, and mixtures thereof.
The process may be applied particularly to the synthesis of poly(ethylene terephthalate), from terephthalic acid or methyl terephthalate and diethylene glycol monomers.
Esterification or transesterification step a) is a step commonly carried out in the polyester manufacturing industrial processes. Two routes for example are mainly employed to manufacture poly(ethylene terephthalate).
The first route of obtention is via said “methyl terephthalate” (DMT). It comprises a transesterification reaction. Molten DMT is solubilized in ethylene glycol (EG) present in excess, the molar ratio EG/DMT being about 1.9 to 2.2, and the reaction is carried out under atmospheric pressure and at temperatures around 130° C. to 250° C. A catalyst such as for example manganese acetate must be present. The methanol during the reaction is eliminated through destilation. The ethylene glycol present in excess is eliminated by evaporation after the transesterification reaction. The catalyst which is also a degradation catalyst of the polyester is blocked with the aid of phosphorous compounds after the reaction. The product resulting from the transesterification is a blend of bis-hydroxyethyl-terephthalate (BHET) oligomers.
The second route is the route called “direct esterification”. It refers to an esterification reaction of terephthalic acid with ethylene glycol. It is carried out at temperatures between 130° C. and 280° C. Terephthalic acid, molten at such temperatures, is not soluble in the ethylene glycol but is so in the ester product of the reaction. However the solubilization of the reagent in the medium is progressive. The ethylene glycol is present in a molar ratio EG/terephthalic acid around 1 to 3. From this reaction results a mixture of oligomers having end functions in the form of terephthalic acid or of hydroxyethyl terephthalate.
The utilization of such processes are the object of several studies described in literature. The above-indicated conditions do not constitute a limitation to the scope of the present invention.
The subsequent solid phase prepolymerization and polymerization steps are condensation polymerization steps. They are generally catalyzed with the aid of metal compounds, for example antimony, titanium or germanium compounds. They may be catalyzed by any polycondensation catalyst of the prior art.
Liquid phase prepolymerization step b) may be accomplished preferably by two modes. The first mode for carrying out this step is to carry out the prepolymerization in molten phase. The second mode therefor consists in effecting the prepolymerization of the molten phase dispersed in a liquid medium. The way for accomplishing these two embodiments will be described subsequently. The prepolymer obtained presents an average degree of polymerization between 10 and 50, preferably between 20 and 45.
By “average degree of polymerization” it is to be understood the absolute average polymerization degree defined by the following formula:
DP
n
=
1
M
o
*
∑
i
n
i
M
i
∑
i
n
i
=
M
n
M
o
where M
0
is the molecular weight of the repetitive portion of the polymer, M
i
is the molecular weight of the referenced chain length i, and n
i
is the number of referenced chain lengths. The molecular weights are absolute molecular weights.
The average degree of polymerization is related to the absolute number average molecular weight M
n
, according to the formula above. The latter is is evaluated by Gel Permeation Chromatography (GPC) with viscosimetrical coupling.
The
Gantillon Barbara
Lepage Jean-Luc
McKenna Timothy
Pasquet Veronique
Spitz Roger
Boykin Terressa M.
Darby & Darby
Rhodia Ster S.A.
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