Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-06-08
2001-09-18
Nutter, Nathan M. (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...
C525S194000, C525S250000, C525S271000
Reexamination Certificate
active
06291584
ABSTRACT:
BACKGROUND TO THE INVENTION
The present invention relates to the production of haze-free block copolymers, in particular block copolymers of at least one hydrocarbon conjugated diene, such as butadiene, and at least one monovinylarene, such as styrene, prepared via anionic polymerisation using an alkali metal initiator.
DESCRIPTION OF THE PRIOR ART
It is well known in the art to decolorise polymers of the vinyl aromatic-conjugated diene block copolymer type by using a mineral acid or a mono- or polycarboxylic acid to avoid the deep yellowish colour generated during polymerisation and processing. This treatment results in transparent but yellowish polymers. It is important for the polymer appearance, and particularly for the use of the polymers with foodstuffs, to make this yellowish coloration disappear and to obtain totally transparent, haze-free and colourless copolymers. A number of methods are known for obtaining such transparent, haze-free colourless copolymers by treating solutions of such copolymers with a decolorising agent.
It is known in the art that vinyl aromatic-conjugated diene block copolymers, such as styrene-butadiene-styrene (SBS) block copolymers, may be prepared by anionic polymerisation employing an alkali metal initiator. In such a process, alkali metal derivatives, primarily alkali metal alcoholates, are required to be neutralised prior to recovery of the polymer with an acid capable of converting those derivatives into neutral and inert alkali metal salts of the corresponding acids. Typically the alkali metal employed is lithium and a typical reaction scheme is as follows:
R—OLi+R′—COOH→R—O—H+R′−COOLi
where R is a polymer, typically an SBS block copolymer, a styrene butadiene rubber, a butadiene rubber or a polybutadiene, and R′ is a saturated aliphatic group.
If such an acidification step is not carried out, the alkali metal species may generate, among others, the following disadvantageous reactions, producing highly adverse properties in the resultant block copolymer:
reaction with phenolic moieties present in an antioxidant system provided for protecting the block copolymers against thermoxidative attack, which would otherwise promote the formation of strongly coloured by-products. Such reactions by such alkali metal species therefore would decrease or suppress the resistance to thermoxidative attack of the transparent colourless block copolymers;
reaction with ester (R—O—COR′) groups of some antioxidants, leading to chain cleavage and producing volatile residues;
reaction with the functional groups of fillers, pigments, colorants, and ultraviolet-protecting additives, thereby reducing their efficiency.
EP-A-0084795 and its corresponding U.S. Pat. No. 4,403,074 disclose the production of clear, haze-free, colourless impact-resistant resinous copolymers, in particular SBS block copolymers, in which alkaline lithium derivatives comprising the coupled polymer-lithium entity, are terminated with water and linear saturated aliphatic dicarboxylic acids selected from C
2
, C
3
and C
5
-C
16
acids. While it is disclosed in those documents that the use of such a wide range of linear saturated aliphatic dicarboxylic acids produces haze-free polymers, the process disclosed in those prior specifications can produce polymers which suffer significant reduction in transparency and significant increase in haze when the polymer is subjected to a humid environment.
U.S. Pat. No. 4,877,863 discloses the production of vinyl aromatic-conjugated diene copolymers in which the copolymers are decolorised by treating the copolymer with a thiocarboxylic acid which may be a monoacid or a diacid. The use of such thiocarboxylic acids as disclosed in that document can also lead to degradation in the transparency and haze of the polymer when the polymer is subjected to a high humidity environment
It is also known to employ carbon dioxide or propionic acid as a decolorising agent to neutralise the alkaline lithium residues. The use of carbon dioxide or propionic acid also leads to such polymers degrading with regard to their transparency and haze-free properties when the polymers are required to withstand a highly humid environment.
SUMMARY OF THE INVENTION
It is an aim of the present invention to provide for the production of transparent, haze-free, colourless block copolymers having an enhanced resistance to degradation of the optical properties, in particular the transparency and haze-free properties, when the polymers are subjected to a highly humid environment.
Accordingly, the present invention provides the use of an alkyl dicarboxylic acid having C
9
to C
16
in the neutralisation of alkali metal derivatives of a vinyl aromatic-conjugated diene polymer for reducing the water take up of the polymer when subjected to a humid environment.
The present invention further provides a process for producing a vinyl aromatic-conjugated diene block copolymer, the process comprising solution polymerising at least one vinyl aromatic hydrocarbon and a conjugated diene in the presence of a catalyst based on an alkali metal to produce copolymer chains and treating the copolymer chains in solution with an alkyl dicarboxylic acid, whereby for enhancing the resistance of the copolymers to degradation in transparency and haze in a humid environment, the dicarboxylic acid has from 9 to 16 carbon atoms.
The dicarboxylic acid is preferably a C
9
to C
12
linear dicarboxylic acid and more preferably comprises azelaic acid, sebacic acid or dodecanoic acid.
The present invention is predicated on the surprising finding by the present inventors that although for obtaining decolorisation of polymers of the vinyl aromatic-conjugated diene type, many acidification techniques have been described and employed commercially, and most of then essentially permit or disclose the manufacture of transparent, haze-free and colour-free block copolymers, when such polymers are required to withstand a highly humid environment, and even when required to be immersed in cold water or hot water, the initial transparency and haze-free property may be rapidly lost. The degradation of these optical properties is generally a function of the treatment time. The degradation phenomenon, which has not been recognised in EP-A-0084975, U.S. Pat. No. 4,403,074 or U.S. Pat. No. 4,877,863, accordingly destroys the technical advantage of such block copolymers, particularly SBS block copolymers, with respect to high transparency and low haze. Such SBS block copolymers have at least some transparency and a haze-free property for styrene contents of from 15 to 95 wt %, and are regarded as fully transparent at styrene contents of at least 70 wt %. Such optical properties are required when such polymers are for use in applications such as blister-packaging, the manufacture of food-contacting containers, toys, trays, cups, etc.
Without being bound by theory, it is believed by the inventors that the increase in haze of the copolymer as a result of being subjected to a highly humid environment, leading to an increase in opacity and a decrease in transparency, develops within the polymer matrix because of water migration into the material. In addition, high levels of absorbed and occluded water in the polymer leads to surface and appearance defects of extruded or moulded items formed from the block copolymers, which requires costly and time-consuming polymer drying operations in the manufacturing process.
The prior art referred to hereinabove does not recognise the technical problem of a reduction in transparency and an increase in haze as a result of the block copolymers being subjected to particular environments, in particularly highly humid environments. The present inventors have discovered surprisingly that the selection of a particular class of decolorising agents permits not only transparent haze-free vinyl aromatic-conjugated diene block copolymers to be produced, but also the properties of those polymers to be maintained even in highly humid environments. These decolourising agents compri
Asinovsky Olga
Fina Research S.A.
Nutter Nathan M.
Wheelington Jim D.
LandOfFree
Production of haze-free block copolymers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Production of haze-free block copolymers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production of haze-free block copolymers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2444474