Process for increasing the molecular weight of polycondensates

Details Process for increasing the molecular weight of polycondensates Process for increasing the molecular weight of polycondensates

2000-11-01

2004-03-16

Sergent, Rabon (Department: 1711)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S146000, C525S165000, C525S178000, C525S340000, C525S341000, C525S377000, C525S420000, C525S423000, C525S438000, C525S449000, C525S462000, C525S463000, C525S467000

Reexamination Certificate

active

06706824

ABSTRACT:

The invention relates to a process for increasing the molecular weight and/or viscosity of polycondensates which remain thermoformable after the process.
Polycondensates, such as polyamides, polyesters and polycarbonates, are important engineering plastics with a wide variety of potential uses, for example in the form of films, bottles, fibers and injection mouldings. It is common to these polymers that they are prepared by polycondensation reactions.
Damage to such polycondensates through processing and use leads, owing to chain cleavage, to polymer fragments containing functional end groups.
The mechanical and physical properties of polymers are crucially dependent on the molecular weight of the polymer. High-grade recycling of used polyesters, polyamides and polycarbonates from production wastes, for example from fiber production and injection moulding, is only possible to a restricted extent without aftertreatment, owing to the reduced molecular weight. For certain applications there is also a demand for high molecular mass virgin polycondensates, the synthesis of which is difficult.
Increasing the molecular weight of polycondensates such as polyamides or polyesters, for example, is known in principle. One possibility, for example, is post-condensation in the solid state (“solid state polycondensation”) as is described in “Ullmann's Encyclopedia of Industrial Chemistry Vol. A 21, 5th Edition”, page 188 [polyamides] and page 236 [polyesters] (1992) and is also practised industrially. An alternative method is the build-up of molecular weight by means of reactive additives, such as epoxides, tetracarboxylic dianhydrides, diisocyanates, bisoxazolines or dicarboxylic bisimides, which is referred to in general as chain extension and is disclosed, for example, in EP-A-0 074 337.
EP-A-0 604 367 discloses a process for increasing the molecular weight of polyamides which comprises heating a polyamide, with the addition of a polyfunctional epoxy resin and of a sterically hindered hydroxyphenyl-alkyl-phosphonic ester or monoester, at above the melting point or glass transition point of the polyamide.
U.S. Pat. No. 5,496,920 likewise discloses a process for increasing the molecular weight of polyamides, which comprises heating a polyamide, with the addition of a bismaleimide and of a sterically hindered hydroxyphenyl-alkyl-phosphonic ester or monoester, at above the melting point and/or glass transition point of the polyamide.
The use of reactive additives, for example epoxides, for building up the molecular weight of polycondensates has the disadvantage that relatively long reaction times are quite often necessary. Under such conditions, it is not possible to rule out follow-on reactions, such as discoloration, increased oxidation or uncontrolled crosslinking of the polycondensate, for example. Moreover, commercially available epoxides are often liquid products, especially if a high content of functional groups is necessary, whose addition to the polycondensate employed causes difficulties.
The object of the present invention, therefore, was to provide a system for building up the molecular weight of polycondensates which is highly effective in a relatively short reaction time and which lacks the disadvantages set out above.
WO-A-90/00574 discloses the preparation of polyiminocarbonates starting from bisphenols and dicyanates.
JP-A-04 202 316 discloses a resin composition comprising two polyesters with different glass transition temperatures and a polycyanate. This resin composition is suitable, in contact with sheet steel, for reducing the vibration of the sheet steel (“damping sheet steel”) in a relatively large temperature range, and can also be used as a bonding coat between two steel sheets. In that publication there is no indication that polycyanates are suitable for inducing an increase in the molecular weight of the polyester in the melt.
It has now surprisingly been found that aromatic dicyanates are suitable for increasing the molecular weight and/or viscosity of virgin polycondensate or polycondensate recyclate (i.e. recycled polycondensate) or of a mixture thereof.
The present invention therefore provides a process for increasing the molecular weight and or viscosity of polycondensates which remain thermoformable after the process, which comprises heating a polycondensate, with addition of at least one aromatic dicyanate, at above the melting point or glass transition point of the polycondensate.
A thermoformable polymer is a polymer which is neither crosslinked nor cured in the manner of a thermoset resin. The build-up of molecular weight according to the present invention is referred to in general as chain extension and is disclosed, for example, in EP-A-0 074 337.
The invention also provides a process for increasing the molecular weight and/or viscosity of polycondensates which remain thermoformable after the process, which comprises heating a polycondensate, with the addition of at least one aromatic dicyanate and at least one polyfunctional compound selected from the group consisting of the sterically hindered hydroxyphenyl-alkyl-phosphonic esters and monoesters, diphosphonites or secondary aromatic amines, at above the melting point or glass transition point of the polycondensate.
The present invention also provides a process for increasing the molecular weight and/or viscosity of polycondensates which remain thermoformable after the process, which comprises heating a polycondensate, with the addition (i) of at least one aromatic dicyanate; (ii) of at least one polyfunctional compound selected from the group consisting of the sterically hindered hydroxyphenyl-alkyl-phosphonic esters and monoesters, diphosphonites or secondary aromatic amines; and (iii) of a difunctional epoxide, at above the melting point or glass transition point of the polycondensate.
The increase in molecular weight brings about improvement in the properties of the polycondensates, which becomes evident, for example, in the injection-moulding sector, in the extrusion sector and, in particular, in connection with recyclates. With the aid of the novel process it is possible, in particular, to achieve an increase in molecular weight in polycondensate recyclates from production wastes, as are obtained, for example, during the manufacture of fibers, or from the collection of used industrial components, for example from automotive and electrical applications. This allows recyclates to be passed on for high-grade re-use, for example as high-performance fibers, injection mouldings, extrusion applications or foams. Such recyclates also originate, for example, from industrial or domestic collections of recyclable materials, from production waste, for example from fiber production and trimmings, or from obligatory takeback schemes, for example collections of PET drinks bottles.
A preferred polycondensate is a polycondensate recyclate.
The novel process is of particular interest if the polycondensate is a polyamide, a polyester, a polycarbonate or a copolymer of these polymers.
In addition to polyester, polyamide or polycarbonate, the present invention also embraces the corresponding copolymers and blends, for example PBT/PS, PBT/ASA, PBT/ABS, PBT/PC, PET/ABS, PET/PC, PBT/PET/PC, PBT/PET, PA/PP, PA/PE and PA/ABS. However, in this context it must be borne in mind that the novel process, like all methods which permit substitution reactions, for example transesterification or transamidation, between the blend components, may result in the blend being influenced, i.e. may lead to the formation of copolymeric structures.
Of particular interest is a process wherein the polycondensate is a PBT/PC blend or a blend comprising predominantly PBT/PC or a corresponding recyclate or a blend of a recyclate and a virgin polymer component.
The term polyamides, i.e. both virgin polyamides and polyamide recycdates, refers to aliphatic and aromatic polyamides or copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or their corresponding lactams. Examples of suitabl

Affiliated with

Also associated with

Rating

Process for increasing the molecular weight of polycondensates does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for increasing the molecular weight of polycondensates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for increasing the molecular weight of polycondensates will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3256326