Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-02-08
2002-09-10
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S263000, C526S328500, C526S329100, C526S329200
Reexamination Certificate
active
06448353
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a continuous process for the production of anionically-polymerizable polymers in a plug-flow, temperature-controlled reactor.
BACKGROUND INFORMATION
Various types of polymers can be prepared from different monomeric materials, the particular type formed being generally dependent upon the procedures followed in contacting the materials during polymerization. For example, random copolymers can be prepared by the simultaneous reaction of the copolymerizable monomers. Block copolymers are formed by sequentially polymerizing different monomers.
Useful classes of polymers are synthesized via anionic methods. During anionic polymerization, at least one end of the growing polymer is “living,” i.e., provides a site for additional monomers to add onto the polymer.
SUMMARY OF THE INVENTION
An ongoing need exists for a controlled process that allows continuously making controlled architecture polymers via anionic polymerization. Controlled architecture refers to a polymer with a designed topology (linear, branched, star, combination network), composition (block copolymer, random copolymer, homopolymer, graft copolymer, tapered or gradient copolymer), and/or functionality (end, site specific, telechelic, multifunctional, macromonomers). The present invention addresses that need.
Briefly, one aspect of the present invention provides a continuous method of producing anionically-polymerized organic material having controlled architecture, including, for example, homopolymers, random copolymers, block copolymers, and starbranched polymers, and end-functionalized polymers.
One embodiment of the present invention provides a continuous process for making an anionically-polymerized organic material having a targeted architecture comprising
a) introducing into a reactor having one or more temperature controlled sections at least one anionically-polymerizable monomer, at least one initiator, and a solvent such that the monomer concentration is 10 to 50 weight %;
b) allowing the monomer to polymerize as the reaction mixture travels in an essentially plug flow manner through the reactor; and
c) discharging the polymerized organic material.
In other embodiments, the process may further include adding one or more steps between b) and c) above wherein one or more polymerizable monomers are sequentially added to the reaction mixture such that a block copolymer is formed as the reaction mixture continues to travel in an essentially plug flow manner through the stirred tube reactor. Embodiments of the process may also include simultaneously introducing two anionically-polymerizable monomers into the reactor such that a random copolymer is formed. The process may also be used to form star-branched polymers and end-functionalized polymers.
In still other embodiments, the process may further include quenching the polymerized organic material and removing solvent from the polymerized organic material.
This invention is particularly useful when at least one anionically-polymerized monomer is temperature sensitive.
The present invention allows the architecture of the produced organic material produced to be controlled by a number of factors including temperature or temperature profile in the reactor, the molar ratio of monomers to initiators, and monomer addition sequence. These factors affect the molecular weight, polydispersity and structure of the final polymerized organic material.
The average molecular weight of the resultant polymeric material is established by controlling the monomer to initiator ratio. This ratio is established by controlling the respective monomer and initiator flow rates. Narrow molecular weight distributions can be obtained by controlling the temperature of the reaction mixture. Avoiding high temperatures minimizes unwanted side reactions that can result in polymer chains having differing molecular weight averages.
Polydispersity can be influenced by the reaction kinetics of the reaction mixture and the minimization of side reactions, especially when temperature sensitive monomers are present. Maintaining optimum temperatures: in each zone of the reactor can positively influence reaction kinetics. Maintaining optimum temperatures can also advantageously affect the solution viscosity and the solubility of the reactants.
The structure of the polymerized organic material is determined by the sequence of monomer addition(s). Homopolymers are formed when only one monomer type is used, random copolymers when more that one monomer type is introduced simultaneously, and segmented block copolymers when more than one monomer type is introduced sequentially.
For the process of the present invention it is preferable that the temperature profile of the reactor be controllable over time and that the reaction mixture be impelled in a relatively plug flow manner through the reactor. This allows the reaction mixture in the reactor at a given location to be subjected to the same reaction conditions as those encountered by previous and subsequent reaction mixture portions as they pass by the same location.
Maintaining temperature control and movement of the reaction mixture in an essentially plug flow manner are complicated by the exothermic nature of the type of reaction being performed, i.e., anionic polymerizations. The use of anionic polymerization methods for the production of block copolymers containing polar monomers (e.g., vinyl pyridine, and alkyl methacrylates) is complicated by side reactions and solution phenomena associated with the aggregation of these materials in solution as micelles. Adequate mixing and temperature control promote the ability to reproduce the same materials, e.g., having a similar average molecular weight and having a narrower polydispersity index (PDI) than obtained without temperature control. Preferably the PDI of the polymers of this invention is less than 3, more preferably less than 2, and most preferably less than 1.5.
One suitable plug-flow, temperature-controlled reactor is a stirred tubular reactor (STR). Any type of reactor, or combination of reactors, in which a reaction mixture can move through in an essentially plug flow manner is also suitable. Combinations of STRs, including combinations with extruders, are also suitable. Regardless of the type of reactor chosen, the temperature or temperature profile of the reactor is preferably controllable to the extent that a plug of the reaction mixture in a particular location within the reaction zone (i.e., the portion of the reaction system where the bulk of polymerization occurs) at time t
1
will have essentially the same temperature or temperature profile as another plug of the reaction mixture at that same location at some other time t
2
. The reaction zone can include more than one temperature-controlled zone of the reactor. STRs may provide for essentially plug flow of the reaction mixture and can be configured such that good temperature control can be attained, and are therefore useful in getting the average molecular weight of the polymer product to remain close to a target value, i.e., have a narrow polydispersity range.
As used herein:
“continuous” means that reactants enter a reactor at the same time (and, generally, at the same rate) that polymer product is exiting the same reactor;
“polydispersity” means the weight average cell diameter divided by the number average cell diameter; polydispersity is reported on a polydispersity index (PDI);
“living anionic polymerization” means, in general, a chain polymerization that proceeds via an anionic mechanism without chain termination or chain transfer. (For a more complete discussion of this topic, see
Anionic Polymerization Principles and Applications.
H. L. Hsieh, R. P. Quirk, Marcel Dekker, NY, N.Y. 1996. Pg 72-127);
“living end” means an anionically-polymerizable reactive site;
“temperature-sensitive monomer” means a monomer susceptible to significant side reactions of the living ends with reactive sites, such as carbonyl groups, on the same, or a different, polymer chain as the reaction temperatu
Annen Michael J.
Cernohous Jeffrey J.
Ferguson Robert Wade
Heldman Barry Eugene
Higgins James Alan
Gover Melanie
Pezzuto Helen L.
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