Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1994-04-05
2002-01-01
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S271000
Reexamination Certificate
active
06335404
ABSTRACT:
FIELD OF INVENTION
This invention relates to an efficient aqueous free radical addition polymerization process for preparing novel water soluble polymer products having a weight average molecular weight less than 30,000. These polymer products are formed from about 3 to about 50 weight percent of at least one monoethylenically unsaturated dicarboxylic acid monomer, and from about 50 to about 97 weight percent of at least one water soluble monoethylenically unsaturated monocarboxylic acid monomer, and from 0 to about 40 weight percent of one or more carboxyl-free monoethylenically unsaturated monomers, based on the total weight of monomers. More specifically, the process of the present invention provides an efficient method of controlling the molecular weight of the polymer product through the use of at least one chain transfer agent and through maintaining the polymerization at an aqueous solution pH of 3 or less. The chain transfer agent has the added benefit, in certain applications, of enhancing the performance of the polymer product.
BACKGROUND OF THE INVENTION
Polymers of monoethylenically unsaturated dicarboxylic acids, monoethylenically unsaturated monocarboxylic acids, and carboxyl-free monoethylenically unsaturated monomers having weight average molecular weights (Mw) less than 30,000 are useful as scale inhibitors, deflocculants, dispersants, in water circulating systems and as encrustation inhibitors, builders, anti-filming agents, sequestering agents, and dispersants in detergents and cleaning formulations.
A well known problem in preparing these polymers is that it is difficult to control the molecular weight and degree of branching during the preparation of these polymers. The control of molecular weight is especially difficult when preparing polymers containing low levels of monoethylenically unsaturated dicarboxylic acids of from about 3 to about 50 weight percent. Another problem associated with preparing these polymers is that it is difficult to achieve low residual levels of monomer in the polymer product, preferably less than 3.0 weight percent based on the weight of the polymer product.
One solution to controlling the molecular weight of the polymer is disclosed in U.S. Pat. No. 5,100,980 to Hughes et al., hereinafter referred to as “'980 patent.” The '980 patent discloses a process for preparing copolymers containing from about 3 to about 25 weight percent monoethylenically unsaturated dicarboxylic acids and 75 to about 97 weight percent monoethylenically unsaturated monocarboxylic acids having a Mw less than 25,000. The process described in the '980 patent requires the monomers to be polymerized in the presence of a polymerization initiator, copper salt polymerization moderator, and neutralizer. The presence of the copper salt moderator in the '980 patent is believed to promote high conversion of the monomers and control the molecular weight of the resulting copolymers.
U.S. Pat. No. 5,244,988 also to Hughes, et al., hereinafter referred to as the “'988 Patent,” discloses another process for making low molecular weight copolymers of ethylenically unsaturated dicarboxylic acid monomers. The copolymers in the '988 patent are produced by cofeeding the monomers and a neutralizer in the presence of a metal salt activator. The copolymers produced have molecular weights ranging from about 1000 to about 100,000 and the cofeeding of the monomers is believed to produce a copolymer of more uniform composition.
However, the processes disclosed in the '980 and '988 patents produce a copolymer which is completely or partially neutralized. It may be desirable in some applications for performance or cost reasons to directly produce a polymer product which is not neutralized. Additionally, the '988 and '980 patents produce a polymer product which is colored dark yellow to brown due to the processing conditions.
Therefore, it is an aim of this invention to produce polymers formed from 3 to 50 weight percent monoethylenically unsaturated dicarboxylic acids, and 50 to 97 weight percent monoethylenically unsaturated monocarboxylic acids having weight average molecular weights less than 30,000 without using a neutralizer.
It is also an aim of this invention to provide a process for making polymers formed from monoethylenically unsaturated dicarboxylic acids and monoethylenically unsaturated monocarboxylic acids where the resulting polymer product has low color.
It is also an aim of this invention to produce polymers formed from monoethylenically unsaturated dicarboxylic acids and monoethylenically unsaturated monocarboxylic acids having comparable or improved performance over polymers currently in use.
SUMMARY OF THE INVENTION
We have discovered an aqueous free radical addition polymerization process comprising:
a) establishing an initial charge of water in a reactor;
b) adding into the reactor to form a reaction mixture
i) at least one water soluble chain transfer agent,
ii) at least one water soluble initiator,
iii) at least one metal promoter,
iv) from about 50 to about 97 weight percent, based on the total weight of the monomer added to the reactor, of at least one water soluble monoethylenically unsaturated monocarboxylic acid monomer,
v) from about 3 to about 50 weight percent, based on the total weight of the monomer added to the reactor, of at least one monoethylenically unsaturated dicarboxylic acid monomer,
vi) from 0 to about 40 weight percent, based on the total weight of the monomer added to the reactor, of one or more water soluble carboxyl-free monoethylenically unsaturated monomers;
c) maintaining the reaction mixture at a temperature of from about 60° C. to about 120° C. over a reaction time;
d) maintaining the reaction mixture at a pH of 3 or less over the reaction time; and
e) recovering a water soluble polymer product; wherein the chain transfer agent, initiator, and monoethylenically unsaturated monocarboxylic acid monomer are added to the reactor over at least 25 percent of the reaction time.
DETAILED DESCRIPTION OF THE INVENTION
We have discovered an efficient, cost effective aqueous free radical polymerization process for making a water soluble polymer product formed from a) at least one monoethylenically unsaturated dicarboxylic acid, hereinafter called “dicarboxylic acid monomer”, b) at least one monoethylenically unsaturated monocarboxylic acid, hereinafter called “monocarboxylic acid monomer,” and optionally c) one or more carboxyl-free monoethylenically unsaturated monomers, hereinafter called “carboxyl-free monomers”. This process provides a route for making a polymer product containing from about 3 to about 50 weight percent of at least one dicarboxylic acid monomer, from about 50 to about 97 percent of at least one monocarboxylic acid monomer, and from 0 to 40 weight percent of one or more carboxyl-free monomers. The polymer product made by the process of the present invention has a molecular weight less than 30,000. To achieve molecular weights less than 30,000, the process of the present invention uses at least one chain transfer agent and at least one metal promoter in combination with at least one initiator. Additionally, the process of the present invention is conducted at an aqueous solution pH of about 3 or less. Conducting the polymerization at a pH of about 3 or less allows the dicarboxylic acid monomer to react with the other monomers rather than react only with the chain transfer agent.
The process of the present invention has the added advantage of producing a polymer product which has comparable or improved performance properties over polymers currently in use. The resulting polymer product is also low in color which may be desirable to the end user of the polymer product.
In the process of the present invention first an initial charge of water is placed in a reactor. The following ingredients are added to the reactor: i) at least one water soluble chain transfer agent, ii) at least one water soluble initiator, iii) at least one metal promoter, iv) at least one monocarboxylic acid
Kirk Thomas Cleveland
Witiak David
Henderson Christopher
Rohm and Haas Company
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