Aqueous Polymer Dispersion Stabilization Without Emulsifiers
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Solution Overview
Problem
Existing methods for producing aqueous secondary dispersions of water-insoluble polymers require the use of surface-active substances like emulsifiers, which are undesirable in applications such as cosmetics and pharmaceuticals, and fail to produce stable dispersions when polyvinylpyrrolidone is used during or after polymerization of hydrophobic monomers.
Innovation Solution
The method involves free-radical solution polymerization of ethylenically unsaturated monomers, including a hydrophobic monomer with limited water solubility and a hydrophilic, nonionic comonomer, with the addition of a monomer composition comprising mainly the hydrophilic monomer towards the end of polymerization, allowing for solvent replacement with water without the need for emulsifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If surface-active substances like emulsifiers are added to stabilize aqueous secondary dispersions, then the dispersion stability is improved, but the suitability for cosmetic and pharmaceutical applications deteriorates due to undesirable interface-active substances
Solution Approach 1:
The patent applies self-service by utilizing the polymerization process itself to generate stabilizing structures. The copolymer formed during polymerization automatically provides steric stabilization through its hydrophilic-composable structure, eliminating the need for external emulsifiers. The system serves its own stabilization need through the inherent properties of the polymerizing components.
Solution Approach 2:
The patent changes the chemical composition parameters by using specific copolymer structures with controlled hydrophilic and hydrophobic segments. By adjusting the ratio and type of monomers (e.g., vinylpyrrolidone to acrylate ratio), the polymer achieves optimal stabilization properties without requiring emulsifiers, thus resolving the contradiction between stability and purity.
2Ease of manufacture
If polyvinylpyrrolidone is added during or after polymerization to stabilize polymer particles, then the stabilization function is improved, but the dispersion stability deteriorates due to coagulation and sedimentation
Solution Approach 1:
The patent applies preliminary action by incorporating hydrophilic monomers into the polymerization process before the polymer particles are formed. This pre-inclusion of hydrophilic segments (vinylpyrrolidone, N-vinylacetamide, etc.) during the polymerization stage ensures that the polymer structure is built with inherent stabilization capabilities, preventing later coagulation and sedimentation issues.
Solution Approach 2:
The patent uses composite materials by creating copolymers that combine hydrophobic monomers (for polymer structure) with hydrophilic monomers (for stabilization). This composite copolymer structure simultaneously provides mechanical integrity and colloidal stability, eliminating the need for separate stabilizing agents that would cause coagulation.
3Quantity of substance
If hydrophilic monomers with high water solubility are used in aqueous emulsion polymerization, then the monomer solubility is improved, but the polymerization quality deteriorates due to homopolymerization of hydrophilic monomers
Solution Approach 1:
The patent applies local quality by creating regions of different hydrophilicity within the polymer structure. The copolymer contains localized hydrophobic segments (from monomers like acrylate, methacrylate) that drive polymerization and form the polymer matrix, while localized hydrophilic segments (from vinylpyrrolidone, N-vinylacetamide) that provide stabilization. This spatial differentiation of properties allows both high solubility and good polymerization quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in stable aqueous secondary dispersions that resist coagulation and sedimentation over prolonged storage, eliminating the need for emulsifiers and making the dispersions suitable for cosmetic and pharmaceutical applications.
Implementation Method 1
free-radical solution polymerization of ethylenically unsaturated monomers M
Implementation Method 2
subsequent replacement of the organic solvent by water
Data Source
AI summary
The present invention relates to a method of producing aqueous secondary dispersions of water-insoluble copolymers by free-radical solution polymerization of ethylenically unsaturated monomers M comprising:i) at least one hydrophobic, monoethylenically unsaturated monomer M1 with a solubility in water of not more than 30 g/l at 25° C. and 1 bar andii) at least one hydrophilic, monoethylenically unsaturated, nonionic comonomer M2 with a solubility in water of at least 80 g/l at 25° C. and 1 bar,in an organic, water-miscible solvent or a mixture of water with an organic, water-miscible solvent as polymerization medium and subsequent replacement of the organic solvent by water in which, toward the end of the polymerization, some of the monomers M are added in the form of a monomer composition M′ which comprises essentially only monomers M2 as monomers. The present invention also relates to the aqueous polymer dispersions obtainable by the method according to the invention and to their use, particularly in pharmacy and cosmetics.