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
2000-09-29
2002-03-26
Seidleck, James J. (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...
C525S250000, C525S319000, C526S087000, C526S136000
Reexamination Certificate
active
06362282
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to polymer compositions with high vinyl end segments and methods for their preparation.
BACKGROUND
Polymers and copolymers of conjugated dienes such as polybutadiene, polyisoprene, and styrene-butadiene rubbers possess physical properties which make them suitable for many important applications such as synthetic rubbers and as additives to other polymeric systems such as, for example, high impact polystyrene (HIPS). Moreover, HIPS can be manufactured by polymerization of styrene in the presence of 5-10% dissolved polybutadiene or butadiene copolymer rubber. Early in the polymerization, phase separation begins because of the immiscibility of the rubber within the polystyrene being formed and the depletion of the styrene phase. Grafting of polybutadiene with the polystyrene then takes place. Toughness, as well as other mechanical and rheological properties of HIPS, is strongly affected by the nature of the rubber phase. In this regard, some of the characteristics of the rubber which may be modified to control the overall HIPS performance include concentration, volume, particle size, grafting and crosslinking ability, molecular weight, viscosity, and vinyl content. More particularly, it is often desirable to have high vinyl content in the end segments. High vinyl polymers contain alkenyl groups pendant to the polymer backbone as opposed to a cis/trans configuration of alkenyl groups within the polymer backbone. High vinyl end segments are often desirable in a polymer because high vinyl configurations have a higher grafting efficiency than cis/trans configurations.
Polymers with high vinyl end segments have been produced by initiating polymerization and allowing the reaction to proceed to near completion. As the polymerization reaction approaches completion, additional monomer and a vinyl modifier are added. The final segment of the polymer thus has a higher vinyl content than the beginning segment. The vinyl concentration of the end segment can be controlled to levels as high as about 70%. However, if one wishes both ends of the polymer, or the ends of a star branched polymer, to have high vinyl content with the remaining segments having low vinyl content, this method will not work because coupling reactions result in high vinyl in the center of the polymer chain or star branched polymer. Making polymers with high vinyl end segments on all or some of the polymer chains and low vinyl content throughout the remainder of the polymer structure remains desirable.
SUMMARY OF THE INVENTION
In an exemplary embodiment of this invention, a polymer composition including at least two end segments which include less than 15% of the total polymer composition is provided. Each of the end segments has a vinyl content greater than about 45%, more preferably greater than about 50%. In contrast, the remainder of the polymer has a vinyl content of less than about 35%. This polymer composition is formed by producing, via living anionic polymerization in the presence of a vinyl modifier, a living prepolymer high vinyl initiator having a relatively low molecular weight (less than about 2500) and a high vinyl content (greater than about 45%, more preferably greater than about 50%). The living prepolymer high vinyl initiator is subsequently used to initiate a second living polymer chain containing less vinyl modifier than the living prepolymer high vinyl initiator. The second living polymer chain with a high vinyl content in the beginning segment is then coupled to at least one other living polymer chain with a high vinyl content in the beginning segment. This coupling results in a polymer chain with two or more ends having high vinyl content. Typically, the high vinyl ends will make up less than about 5% of the coupled polymers total weight.
In a further exemplary embodiment, a polymer with end segments of high vinyl concentration greater than about 45%, more preferably greater than about 50%, is provided with a linear, branched, or star-shape. The use of di- and multi-functional coupling agents can produce these alternate shapes.
In yet another exemplary embodiment, a polybutadiene polymer is made having end groups of greater than about 45% vinyl concentration, more preferably greater than about 50%, and a vinyl concentration less than about 35% throughout the remainder of the polymer.
In another exemplary embodiment, a styrene-butadiene block copolymer is formed with end segments having a vinyl content greater than about 45%, more preferably greater than about 50%.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a coupled polymer composition including at least two end segments of high vinyl content prepared by living anionic polymerization, via batch or continuous polymerization. The polymer composition is provided with more than one high vinyl end segment by coupling two or more different polymer chains to each other. The polymer composition includes polymers which are linear, branched, or star-shaped, depending on the coupling agent used.
The polymer compositions of the present invention are formed by living anionic polymerization. Living polymerizations are polymerizations in which propagating centers do not undergo either termination or transfer. After 100% conversion is reached, additional polymerization takes place by adding more monomer to the reaction system. The added monomer is also polymerized quantitatively. Such polymerizations offer the potential for producing structures with defined end groups and block copolymers.
Three steps may be employed in the process of forming the present polymer compositions:
1. Preparation of a living prepolymer initiator having a high concentration of vinyl-configured butadiene units,
2. Preparation of polymers with high vinyl end segments utilizing the living prepolymer initiator, and
3. Coupling of the high vinyl end segment polymers.
To make this product in a continuous mode, the living prepolymer high vinyl initiator is made continuously in one reactor and fed to a second reactor where the bulk of the polymer is made. This continuous product can then be sent to a third device such as a reactor or mixer, preferably a reactor, where a coupling agent is introduced to react with the live polymer end. The coupling agent can be difunctional or higher.
Preparation of the living prepolymer high vinyl initiator is carried out by adding an initiator to a mixture of monomers in the presence of a vinyl modifier. Any initiator known in the art as suitable for the polymerization of conjugated dienes may be used. Preferred initiators include anionic initiators, and the most preferred are organo-lithium initiators. Preferred organo-lithium compounds have the formula RLi
x
, wherein R represents a hydrocarbyl radical of about 1 to about 20, preferably about 2 to about 8 carbon atoms per R group and x is an integer from 1 to about 4. Typical R groups include aliphatic and cycloaliphatic groups. Specific examples of R groups for substitution in the above formulas include primary, secondary, and tertiary groups, such as n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, etc., and mixtures thereof A preferred initiator for the present invention is n-butyl lithium.
Specific examples of other suitable lithium initiators include p-tolyllithium, 4-phenylbutyl lithium, 4-butylcyclohexyl lithium, lithium dialkyl amines, lithium dialkyl phosphines, lithiumalkyl aryl phosphine, lithium diaryl phosphines and mixtures thereof
The amount of initiator used depends on the amount of monomer used and the molecular weights desired in the respective products. Under ideal conditions, where the polymerization system is free of impurities that can deactivate a portion of the initiator, the amount of initiator is determined by the amount of monomer being used for the initial block and the molecular weight desired in that block. Generally, in such polymerizations, each initiator molecule is responsible for the initiation of one polymer chain. Then for subsequent blocks, sufficient monomer is added in each case to form the desired m
Asinovsky Olga
Burleson David G.
Firestone Polymers LLC
McCollister Scott A.
Seidleck James J.
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