Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating
Reexamination Certificate
2000-06-13
2002-07-16
Seidleck, James J. (Department: 1711)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
C264S001320, C264S029300, C264S029300, C264S175000, C264S299000, C264S319000, C428S411100, C428S412000, C428S480000, C428S492000, C428S500000, C522S116000, C522S113000, C522S119000, C522S114000, C522S120000, C522S121000
Reexamination Certificate
active
06419858
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the fields of polymerization, polymer phase morphology, and molding. More particularly, it is related to a process for locking in the morphological structure of single-phase or multi-phase polymeric systems. This process enables the production of objects that possess a resistance to further changes in their phase morphology in later processing steps or during use.
BACKGROUND OF THE INVENTION
Phase-separated systems are ubiquitous in the polymer world, primarily because few polymer blends are truly compatible. Fortunately, multi-phase morphologies have proven useful in polymer systems more often than not. One reason is that phase-separated materials provide a higher performance through synergism, as evidenced by multi-phase systems exhibiting important properties such as: impact resistance, toughness, high temperature performance, high modulus, tensile strength, lower expansion coefficients, dimensional stability, high strength-to-weight ratio for plastics, improved elasticity or damping for elastomers, flammability resistance, elongation, gloss, and/or better adhesion. Polymer blends may also enable one to achieve desired physical properties such as melt viscosity, higher or lower softening point, easier processability, and solvent resistance. Finally, the use of polymer mixtures or blends may be simply dictated by economics, using dilution of a more expensive material by a cheaper material for reduced cost.
The benefits of polymer blends are not without their drawbacks, however. For instance, some desirable phase morphologies may be difficult to achieve, requiring high processing temperatures or intensive mixing. Other morphologies, once attained, may be sensitive to external stimuli, being easily destroyed or altered by induced stress, high-temperature excursions or exposure to solvents. For example, certain material systems containing one or more polymers exhibit Critical Solution Temperature (CST) phase transitions during processing, whereby the system phase separates upon crossing a phase boundary. When phase separation is seen upon heating, the system exhibits a Lower Critical Solution Temperature (LCST). When phase separation is seen upon cooling, the system exhibits an Upper Critical Solution Temperature (UCST). The temperature at which the LCST or UCST transition takes place depends on the composition of the system, as well as other physical conditions such as pressure, pH, etc. Such phase transitions, however, dramatically alter the phase morphology of a given polymer blend and are often undesirable. An optically clear polymer blend that turns cloudy upon cooling due to a phase separation is one example of a material system that exhibits an unstable phase morphology.
Polymer morphology may also be important in single-component or homogeneous multi-component systems when the molecular-level orientation of polymer chains produces either a desired, or unwanted, effect. One such case is seen in polycarbonate systems that undergo “solvent induced” crazing when exposed to various solvents. The crazing event is characterized by a chain re-orientation process (microcrystallization in this case) that leads to a brittle and/or opaque material and is therefore undesirable. Alternatively, molecular level orientation is sometimes beneficial, such as in drawn polymer films or fibers in which the obtained molecular orientation provides for improved properties such as tensile strength or puncture or tear resistance. Additionally, oriented films find use in optical applications due to their inherent optical anisotropy. Oriented films and fibers are often attained by stretching at elevated temperatures, which in and of itself is a time- and energy-consuming process. In addition, the molecular level orientation achieved by such techniques is susceptible to chain re-randomization upon later exposure to high temperatures, leading to recoil, shrinkage, and degradation of properties. Thus, it would be desirable to have material systems that possess a resistance to such morphology-altering crazing and/or re-randomization processes upon being exposed to adverse environments.
Whether during processing or in-use, adverse conditions often lead to the undesirable alteration or destruction of a given material morphology. The problems associated with the instability of the morphologies present in polymeric systems, either in part or in whole, are subsequently addressed by the invention disclosed herein.
SUMMARY OF THE INVENTION
The present invention is directed to a method for manipulating and controlling the phase-separation behavior, morphology, and molecular orientation in a wide variety of materials containing at least one polymeric component. It can be an extremely economical process suitable for mass manufacture. The invention is further directed to the formulation of a new class of polymeric materials that exhibit trapping of the phase morphology or molecular level orientation, resulting in stabilization of the optimized engineering properties of the final object. A unique feature of this invention is that the phase morphology and molecular orientation present just prior to cure of a polymerizable composition is subsequently trapped or locked in place by a curing step so that further changes in morphology are hindered or prevented. Such morphology trapping may be directed to macrophase-, microphase-, and nanophase-separated systems, or to systems that are homogeneous down to the molecular level. The resulting polymeric materials may comprise one or more polymeric components, and said polymeric molecules may be randomly coiled or oriented with respect to each other. Single-phase, binary-phase, and multi-phase systems all fall within the scope of this invention.
More particularly, this invention is directed to a process for the rapid in-situ polymerization of materials to provide polymeric macromolecular networks and articles of manufacture that are “morphology-trapped”; that is, they exhibit a fixed phase morphology and/or molecular orientation that is locked in by the polymerization step. The process includes the steps of mixing together a dead polymer, a reactive plasticizer and an initiator to give a polymerizable composition; further processing the mixture in order to achieve a desired phase morphology and/or molecular orientation of the polymeric constituents; shaping the polymerizable composition into a desired geometry; and exposing the polymerizable composition to a source of polymerizing energy, without mixing, to give a final product with dimensional stability and the desired phase morphology and/or molecular orientation locked in place. In a presently preferred embodiment, the polymerizable composition is a semi-solid.
In this method, both the desired material morphology (phase morphology as well as molecular orientation) and the desired overall shape or configuration of the part are set prior to material cure. The morphology-trapped article so produced can optionally be transparent and/or have resistance to impact (resilient). The resulting morphology-trapped macromolecular network is characterized as having either i) a semi-interpenetrating crosslinked polymer network of reactive plasticizer wrapped around and within an entangled dead polymer (semi-IPN); ii) an interpenetrating crosslinked polymer network of reactive plasticizer within an entangled dead polymer, the reactive plasticizer polymer network being further crosslinked to the dead polymer; or iii) interpenetrating reactive plasticizer polymer chains (uncrosslinked), which may be linear, branched, etc., within an entangled dead polymer. Thus, curing of the polymerizable composition leads to a final composite polymeric material in which the phase morphology and/or molecular orientation present just prior to the initiation of curing is preserved by the formation of the reactive plasticizer polymeric chains and/or network. Such phase morphology trapping is made possible in accordance with the present invention by physically or chemically locking in the molecular structure
Hino Toshiaki
Houston Michael R.
Soane David S.
Larson Jacqueline S.
McClendon Sanza L
Seidleck James J.
ZMS LLC
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