Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-04-13
2001-04-10
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S192000, C526S193000, C526S204000, C526S216000, C526S217000, C526S220000, C526S222000, C526S224000, C526S225000, C526S236000, C526S346000
Reexamination Certificate
active
06214945
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing high molecular weight monovinylidene aromatic polymers and polymodal molecular weight monovinylidene aromatic polymer compositions.
High weight average molecular weight (Mw) monovinylidene aromatic polymers have been previously produced by free radical polymerization in the presence of a vinyl acid have a pKa of less than 2 as disclosed in U.S. Pat. No. 5,145,924, which is incorporated herein by reference and in U.S. Pat. Nos. 5,962,605 and 5,948,874. The free radical polymerization is typically conducted in the presence of an initiator. However, it is well known in the art that at some point during the polymerization, the initiator is expended and thermal polymerization occurs unless additional initiator is added. During thermal polymerization of vinyl aromatic monomer, conversion becomes difficult due to the presence of the acid and low Mw fractions are produced, as taught in
J. Phys. Org. Chem
(1995) 8, p. 301. Additionally, the presence of acid during thermal polymerization catalyzes the formation of 1-phenyltetralin, a by-product, as described in Polymer (1992) 33, p. 3055. At the high temperatures used to increase conversion in the absence of initiator, 1-phenyltetralin forms rapidly in the presence of acid and must be removed from the polymer composition.
Polymodal molecular weight monovinylidene aromatic polymer compositions, wherein the polymer composition comprises more than one distinct weight average molecular weight, have previously been produced in a number of ways including blending and in situ polymerization. Blending two polymers having different molecular weights offers a high degree of control, but is inefficient due to the addition of the compounding step. U.S. Pat. No. 4,585,825 discloses a bimodal composition, however, the high molecular weight polymer is produced at low temperatures and low conversion rates which require very long reaction times. U.S. Pat. Nos. 5,962,605, and 5,948,874, herein incorporated by reference, disclose bimodal compositions produced using free radical polymerization, characterized in that high molecular weight polymer is produced in the presence of a vinyl acid having a pKa of less than 2.0, and low molecular weight polymer is produced by adding initiator and chain transfer agent to the reaction mixture containing high molecular weight polymer. However, the presence of the vinyl acid retards the polymerization rate and continues to encourage high molecular weight polymer production, thus requiring large amounts of chain transfer agent in order to produce the low molecular weight polymer.
Therefore, it remains highly desirable to provide an improved process to produce high molecular weight monovinylidene aromatic polymers, which does not require additional initiators, and reduces by-product formation; and to provide an improved process to produce polymodal compositions comprising such high molecular weight polymers which does not require large amounts of chain transfer agent in order to make a low molecular weight polymer.
SUMMARY OF THE INVENTION
The present invention is an improved process for producing a high molecular weight monovinylidene aromatic polymer, wherein a vinyl aromatic monomer is free radically polymerized in the presence of a vinyl acid having a pKa at 25° C. of less than 2.0, wherein the improvement comprises:
neutralizing the vinyl acid, after the production of the desired amount of high molecular weight polymer, with a sufficient amount of base such that substantially all of the acid is neutralized, and continuing the free radical polymerization in the absence of the vinyl acid, under conditions such that additional high molecular weight monovinylidene aromatic polymer is produced.
In another embodiment, the present invention is an improved process for producing polymodal molecular weight monovinylidene aromatic polymer compositions, wherein a vinyl aromatic monomer is free radically polymerized in the presence of a vinyl acid having a pKa at 25° C. of less than 2.0, to produce a high molecular weight monovinylidene aromatic polymer and low molecular weight monovinylidene aromatic polymer is produced in a subsequent step, wherein the improvement comprises:
neutralizing the vinyl acid, after the production of the desired amount of high molecular weight polymer, with a sufficient amount of base such that substantially all of the acid is neutralized, and continuing the free radical polymerization in the absence of the vinyl acid, under conditions such that a monovinylidene aromatic polymer having a low molecular weight is produced.
This process can produce high molecular weight monovinylidene polymers with increased conversion without by-product formation or significant low molecular weight fractions. It also offers better control of the polymer molecular weights within the polymodal composition and does not have the disadvantages of the prior art.
DETAILED DESCRIPTION OF THE INVENTION
Monovinylidene aromatic polymers can be produced by free radical polymerization of vinyl aromatic monomers. Vinyl aromatic monomers for use according to the present invention include, but are not limited to, those vinyl aromatic monomers previously known for use in polymerization processes, such as those exemplified in U.S. Pat. Nos. 4,666,987, 4,572,819 and 4,585,825. Preferably, the monomer is of the formula:
wherein R is hydrogen or methyl, Ar is phenyl, halophenyl, alkylphenyl or alkylhalophenyl, wherein any alkyl group contains 1 to 6 carbon atoms. The term halophenyl refers to a phenyl substituted with one or two halogen atoms, the term alkylphenyl refers to a phenyl substituted with one or two alkyl groups, and the term alkylhalophenyl refers to phenyl substituted with one or two alkyl groups which contain a halogen substituent or to a phenyl substituted with a halogen and an alkyl substituent. More preferably Ar is phenyl or alkylphenyl with phenyl being most preferred. In addition, the polymerization may be conducted in the presence of predissolved elastomer to prepare impact modified, or grafted rubber containing products, examples of which are described in U.S. Pat. Nos. 3,123,655, 3,346,520, 3,639,522, and 4,409,369.
The acid catalyst used in the process of the present invention may be any acid having a pKa at 25° C. of less than 2. The pKa is used to express the extent of dissociation of acids in water, and is the negative logarithm (to the base 10) of the equilibrium constant, Ka. Such acid catalysts include, but are not limited to, 2-sulfoethylmethacrylate (SEM), acrylamidopropane sulfonic acid (AMPS), 2-sulfopropylmethacrylate, methanesulfonic acid, camphorsulfonic acid, p-toluenesulfonic acid, phosphoric acid, sulfuric acid, or mixtures thereof. Preferably the acid catalyst is a vinyl functional sulfonic or vinyl functional phosphonic acid of the formulas:
wherein X is O and n is either 0 or 1; Y is H, methyl or phenyl; Z is C
1
-C
6
alkyl, aryl or O—Y; and R is —C(═O)CH
2
CH(Y)—, —C(═O)NHCH
2
CH(Y)—, phenyl or a direct bond. Examples of such acids include 2-sulfoethylmethacrylate (SEM), vinylphosphonic acid (VPA), 2-sulfopropyl-methacrylate (SPM), styrenesulfonic acid (SSA), styrene-phosphonic acid (SPA), 4-vinylbenzylphoshonic acid (VBPA), 2-sulfoethylacrylate (SEA), &agr;-phenylvinylphosphonic acid (PVPA), or mixtures thereof, with the most preferred vinyl acid being SEM. These acids are known and are commercially available or can be made by processes as described in U.S. Pat. No. 4,529,559, which is incorporated herein by reference.
The acid catalyst can be dispersed in a (meth)acrylic acid or ester thereof, before combining with the vinyl aromatic monomer. The term (meth)acrylic acid refers to either a methacrylic acid or an acrylic acid. A (meth) acrylic acid ester would be any C
1
-C
8
ester of methacrylic acid or acrylic acid. Accordingly, throughout the application, any teachings referring to (meth)acrylic acid can also be applied to an ester thereof. The (meth)acrylic acid acts as a reactive dispersant,
Pike William C.
Priddy Duane B.
Rego Jose M.
Roe James M.
Teskin Fred
The Dow Chemical Company
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