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
2001-07-26
2003-03-25
Boykin, Terressa 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...
C428S423700, C525S133000, C525S191000, C528S176000, C528S196000, C528S198000
Reexamination Certificate
active
06538065
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for preparation of thermally stable copolyestercarbonates comprising polyester chain members derived from at least one 1,3-dihydroxybenzene and at least one aromatic dicarboxylic acid. The invention also relates to articles made from thermally stable copolyestercarbonates.
Various resinous articles comprising polymers have a problem of long term color instability. In many cases this instability is seen as yellowing of the polymer, detracting from the article's attractiveness and also transparency when the polymer was initially transparent. Loss of gloss can also be an undesirable long term phenomenon in a resinous article.
Yellowing of polymers is often caused by the action of ultraviolet radiation, and such yellowing is frequently designated “photoyellowing”. Numerous means for suppressing photoyellowing have been employed and proposed. Many of these involve incorporation in the polymer of ultraviolet absorbing compounds (UVA's). For the most part, UVA's are low molecular weight compounds, which must be employed at relatively low levels, typically up to 1% by weight, to avoid degradation of the physical properties of the polymer such as impact strength and high temperature properties as reflected in heat distortion temperature.
One way of protecting a resinous article against photoyellowing and loss of gloss is to apply a coating of a weatherable second polymer, the term “weatherable” as used herein signifying resistance to such phenomena. Coatings made from polyesters containing chain members derived from at least one 1,3-dihydroxybenzene derivative and at least one aromatic dicarboxylic acid (sometimes referred to hereinafter as resorcinol arylate polyesters) often possess good weatherability properties. The arylate moieties typically comprise isophthalate, terephthalate, or especially mixtures of iso- and terephthalate units. Resorcinol arylate polyesters comprising mixtures of isophthalate and terephthalate chain members typically have good weatherability properties and may provide protection against photoyellowing when coated over a resinous substrate.
The good weatherability properties of polyesters comprising resorcinol arylate units is believed to arise in large part from the screening effect said polymers may provide to ultraviolet (UV) light. On exposure to UV light polymers comprising resorcinol arylate chain members may undergo photochemical Fries rearrangement converting at least a portion of the polymer from polyester chain members to o-hydroxybenzophenone-type chain members. The o-hydroxybenzophenone-type chain members act to screen further UV light and protect UV-sensitive components in a resorcinol arylate-containing composition. The good weatherability properties of polymers comprising resorcinol arylate chain members make them especially useful in blends and also in multilayer articles in which said polymers may act as a protecting layer for more sensitive substrate components.
Polyesters containing resorcinol arylate chain members have been prepared by an interfacial method. The interfacial method comprises a solvent mixture containing water and at least one organic solvent substantially immiscible with water. According to U.S. Pat. No. 3,460,961 and Eareckson, Journal of Polymer Science, vol. XL, pp. 399-406 (1959), preparation of resorcinol arylate polyesters with a mixture of iso- and terephthalate chain members is performed by an interfacial method in water and a water-immiscible solvent such as chloroform or methylene chloride using 1:1 stoichiometric ratio of resorcinol to either iso- or terephthaloyl dichloride, or a mixture thereof, in the presence of aqueous sodium hydroxide. The resorcinol is combined with the aqueous sodium hydroxide before addition of acid chlorides, and the reaction is run at pH which is initially high but which decreases as the reaction proceeds. The molecular weight of the polymers is not controlled. The method provides polymer with very high weight average molecular weight (Mw) and low hydroxy end-group concentration, making the polymer unsuitable for some applications. Furthermore, the polymer has poor thermal stability and loses molecular weight upon thermal treatment.
Block copolyestercarbonates comprising resorcinol arylate chain members in combination with carbonate chain members are disclosed in commonly owned, co-pending application Ser. No. 09/416,529, filed Oct. 12, 1999. These copolymers have excellent weatherability and are compatible with polycarbonates in blends. In one embodiment these block copolyestercarbonates are prepared by a method which comprises the steps of: (A) preparing a hydroxy-terminated polyester intermediate having a degree of polymerization of at least 4 by the reaction of at least one 1,3-dihydroxybenzene moiety with at least one aromatic dicarboxylic acid dichloride under alkaline conditions; and (B) conducting a reaction of said polyester intermediate with a carbonate precursor. The polyester intermediate is synthesized by an interfacial method employing in one embodiment resorcinol, isophthaloyl dichloride, terephthaloyl dichloride, water and methylene chloride, which is often the organic solvent of choice.
The polyester intermediate comprises hydroxy end-groups suitable for growing polycarbonate chains in a subsequent reaction step with a carbonate precursor, and optional second dihydroxy compound. However, formation of hydroxy terminated, low molecular weight resorcinol arylate polyester oligomers (for example, with degree of polymerization of about 5-20) is quite difficult when typical procedures are followed. This is believed to be due to high water solubility and very low methylene chloride solubility of resorcinol as compared to other dihydric phenol monomers. Conventional methods of producing resorcinol arylate polyester oligomers lead to very high molecular weight polyesters, even when a large excess of resorcinol is employed. In addition such polyesters typically exhibit thermal instability, which is believed to be due to the presence of anhydride linkages in the polyester chains. Control of oligomer molecular weight and polymer terminal groups in resorcinol arylate polyester oligomers can be achieved to some extent by the use of phase transfer catalysts, as disclosed in commonly owned, copending application Ser. No. 09/368,706, filed Aug. 5, 1999. Unfortunately, several issues with the use of phase transfer catalysts in large scale operations exist. Emulsions can be encountered during work-up and washing steps using centrifugal separators, and the presence of phase transfer catalysts can accelerate polymer hydrolysis during work-up or cause problems with recycle brine streams. Thus, it would be desirable to obtain hydroxy-terminated, thermally stable, low molecular weight polyester oligomers comprising 1,3-dihydroxybenzene moieties via an alternative process.
A method previously disclosed for the formation of high molecular weight (as opposed to low molecular weight) polyesters comprising arylate structural units is a melt process wherein the polymerization reaction is a transesterification or redistribution reaction of diphenylphthalates and a dihydric phenol, such as is described in GB 924,607. In order to shift the reaction equilibrium to the product polyester and thus increase molecular weight, the phenol by-product is continuously removed from the reaction mixture, typically under reduced pressure. The molecular weight build in the melt process typically takes place in two or more steps in a cascade of reactors with subsequently higher temperatures and higher vacuum to remove the phenol from an increasingly more viscous polymer.
Japanese Kokai 56/133,332 describes copolyestercarbonates “having a highly alternating orientation” rather than a block structure. They are prepared by a 2-step process in which the first step is preparation of a hydroxy-terminated polyester oligomer having a degree of polymerization of only 1-2 and made by an interfacial process in the presence of methylene chloride. The
Brunelle Daniel Joseph
O'Neil Gregory Allen
Siclovan Tiberiu Mircea
Suriano Joseph Anthony
Webb Jimmy Lynn
Boykin Terressa M.
Brown S. Bruce
Johnson Noreen C.
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