Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-07-11
2003-09-09
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S329100, C525S329200, C525S329900, C525S351000, C525S354000, C525S369000
Reexamination Certificate
active
06617390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to hydrophilic polymers and their preparation. More specifically, the present invention relates to improved methods of making synthetic hydrophilic polymers in a controlled fashion to reduce or eliminate short block formation and ensuing difficulties, by specified multistep reaction sequences.
2. Information Disclosure Statement
Hydrophilic polymers are useful for a large number of applications in medicine, agriculture, pharmacy, the food industry, cosmetics, construction, and other fields. Many hydrophilic polymers are water soluble in a large range of temperatures and pH. Some such polymers are derived from natural sources. Examples of these are agar, gelatin, carboxymethylcellulose, hyaluronic acid, alginic acid, and many others. In many applications, the disadvantage of natural polymers is their capacity for hydrolytic and biological degradation, often along with low availability and a high price.
For that reason a whole variety of synthetic polymers were developed, whether entirely water soluble ones or ones gelling under certain conditions. An example of these are polyvinyl alcohol, polyethylene oxide, polyvinyl ether, polyvinyl pyrrolidone, polyacrylic acid, or poly-2-hydroxyethylmethacrylate prepared by polymerizing appropriate monomers. Hydrophilic polymers are described in a number of publications, such as:
Philip Molyneux: Water-soluble Synthetic Polymers, Vol. I and II, CRC Press, Inc., Boca Raton, Fla. (1987)
Nikoloas A. Peppas (Ed.): Hydrogels in medicine and pharmacy, Vol. I to III, CRC Press, Inc.,
Joseph D. Andrade (Ed.): Hydrogels for medical and related applications, American Chemical Society, Washington, D.C. (1976)
Hydrophilic derivatives of polyacrylic and polymethacrylic acids are also sometimes prepared using hydrolysis or aminolysis of polyacrylonitrile (PAN) or polymethacrylonitrile (PMAN). The hydrolysis of PAN is described in a number of patents, such as the U.S. Pat. No. 3,926,930 (Ohfuka et al) and the U.S. Pat. No. 3,200,102 (H. Kleiner).
Of special value are the products of partial hydrolysis or aminolysis, which have a character of block copolymers. In these, blocks of hydrophilic acrylic groups alternate with blocks of hydrophobic acrylonitrile units. These so-called “multiblock copolymers” form hydrogels or viscous aqueous solutions under certain gelling conditions. Such polymers are described in a number of patents, such as the U.S. Pat. Nos. 4,337,327; 4,379,874; 4,420,589; 3,897,382.
An alkali-catalyzed PAN hydrolysis can be performed in an aqueous NaSCN solution, as described for example in the U.S. Pat. No. 4,107,121 (Stoy). The nitrile group in PAN can also react with alcohols, hydrazine, hydroxylamine, etc. and form subsequent derivatives of acrylic acid. This non-hydrolytic reaction of PAN solutions result in randomly arranged rather than multiblock copolymers, however. Multiblock copolymers can be prepared using these reactions in a so-called “aquagel state”, as described in the U.S. Pat. No. 4,943,618 (V. Stoy, G. Stoy and Lovy).
Multiblock copolymers of acrylonitrile with various annexed groups can also be prepared by PAN aminolysis, as described in the U.S. Pat. No. 5,252,692 (Lovy and Stoy). As apparent from the above list, these copolymers can be created under various conditions: partial hydrolysis in the solutions of strong acids, acid or alkaline heterogeneous hydrolysis, solution-based alkaline hydrolysis, solution-based or heterogeneous aminolysis, hydrazinolysis, and other reactions.
Methods used to date have a number of limitations. One of these is the necessity of interrupting the reaction during a certain, but incomplete, reaction conversion in order to retain remnant nitrile group sequences. If one of the co-reagents is water, which is usually present in these reactions in a significant molar excess, these reactions must be terminated by the washing out or neutralization of the acidic or alkaline catalyst as soon as the desired reaction conversion is attained. Accurate reaction termination requires meticulous observation of its progress and a rapid interruption at a certain point in time; otherwise the product could be worthless.
The washing out of the catalyst requires a certain period of time, during which the reaction continues in those places where the catalyst concentration remains high. This increases the heterogeneity and decreases the quality of the product. The heterogeneity is especially high in reactions where PAN is in a solid state, whether in the form of suspended particles, fibers, or an aquagel. The kinetics of the reaction in these cases is also complicated by the diffusion of the reagent and the catalyst into the polymer.
A better homogeneity of the product is generally achieved using a solution-based reaction, where the resulting polymer is dissolved in a suitable solvent, such as a concentrated inorganic acid (nitric or phosphoric acid), a concentrated zinc chloride solution, or a concentrated sodium thiocyanate solution. Even in these cases the product is somewhat heterogeneous, however, especially in terms of the distribution of the block lengths. The distribution of the block length approximates the 1. Markovian distribution, which in practical terms means that short group sequences are over-represented. The kinetics and statistical distribution of groups were described in a number of papers, such as the following:
Stoy, V. A., Journal of Polymer Science, Chemistry Edition, 15: 1029 (1977)
The presence of short sequences (short blocks) negatively affects the quality of phase separation and thus also the quality of crystalline domains and the resulting mechanical properties (especially shape and thermal stability).
When using a solution-based reaction, the solvent as well as the catalyst needs to be removed from the product. The catalyst and solvent removal using water extraction does not generally present significant problems as long as the resulting product is entirely insoluble in water and forms a low-swelling hydrogel. When the resulting product strongly swells in water or is partially or entirely water soluble, however, it's isolation from the reaction mixture is difficult. It is usually difficult or even impossible to coagulate it using water because of strong swelling or even dissolution of a certain fraction of the product, which results in low yields. In these cases, it is practically impossible to isolate the whole product with its original length and distribution of polymer chains. This decreases the quality control of the end product and often negatively affects it's properties.
A disadvantage in such cases is the necessity of isolation and purification of the product using precipitation in organic solvents, dialysis, and other techniques, which significantly increase the production cost and affect the product quality.
Another disadvantage of present production technologies is the limitation to products, which contain at most two types of blocks: one hydrophobic (remnant continuous sequences of units with pendant nitrile groups in 1,3 positions) and one hydrophilic (continuous sequence of groups formed by a particular reaction of the nitrile group, such as for example the acrylamide created by an acid-catalyzed addition of water to form a nitrile). For a number of applications it is advantageous that the polymer contains two or more types of hydrophilic blocks (such as one with neutral and one with negatively charged groups). Such polymers were not described to date and for the above stated reasons, the present invention methods and resulting products are neither anticipated nor rendered obvious thereby.
SUMMARY OF THE INVENTION
The present invention involves a method of making a multiblock copolymer containing two or more types of sequences of derivatives of acrylic acid with at least one derivative being acrylic acid salt and at least one being acrylamide. The method includes:
(a) in sequence, a first step being a catalytic reaction of nitrile groups in polyacrylonitrile dissolved in an ino
Drunecky Tomas
Kozlova Zdena
Stehlicek Petr
Stoy Vladimer A.
Carter DeLuca Farrell & Schmidt LLP
Lipman Bernard
Replication Medical Inc.
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