Silicone Emulsion Polymerization Low Temperature
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Solution Overview
Problem
Existing methods for producing silicone in water emulsions, particularly for high viscosity silicones, face challenges in minimizing residual cyclosiloxanes, cyclic polymerization by-products, and particle size, which are critical for stability and regulatory compliance in applications like cosmetics and personal care.
Innovation Solution
A method involving the combination of silanol end-blocked organosiloxane, water, and surfactants, followed by emulsification and polymerization at controlled temperatures, specifically below 16 °C, using high-shear mixing to maintain particle sizes under 1 micron and reduce cyclic formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If emulsion polymerization is used to prepare high viscosity silicone emulsions, then the viscosity requirement is met, but residual cyclosiloxanes (D4, D5) remain at high levels (2-10%)
Solution Approach 1:
The patent applies parameter changes by conducting polymerization at controlled low temperatures (0-25°C, preferably 5-15°C) and adjusting pH to specific ranges (2-4 or 7-9) to minimize cyclic by-product formation while achieving high viscosity. This temperature and pH control transforms the reaction conditions to favor linear polymer growth over cyclic formation.
Solution Approach 2:
The patent uses preliminary action by pre-forming silanol-terminated polydiorganosiloxane with controlled molecular weight and viscosity before emulsion polymerization. This starting material is carefully selected to have specific properties (viscosity 1-1000 Pa.s, SiOH content 0.1-5%) that predispose the reaction toward linear chain growth and reduce cyclic by-product formation from the outset.
2Device complexity
If conventional mixers are used for mechanical emulsification, then the process is simple, but particle size becomes too high above 600 Pa.s viscosity
Solution Approach 1:
The patent replaces mechanical emulsification with chemical emulsion polymerization. Instead of relying on mechanical shear forces to break down high viscosity silicone into small particles, the process uses in-situ polymerization where monomers polymerize within emulsion droplets, naturally forming small particles (0.1-10 μm) without requiring intensive mechanical mixing.
Solution Approach 2:
The patent changes the physical state and properties of the starting materials by using low molecular weight cyclosiloxane monomers (D4, D5, D6) that are easily emulsifiable, and controlling the polymerization temperature and pH to maintain small particle sizes throughout the reaction, achieving high viscosity through molecular weight increase rather than particle aggregation.
3Temperature
If condensation reaction is used with short hydroxyl terminated siloxanes, then high internal phase viscosity is achieved, but cyclic by-products (D4, D5) are generated at around 1%
Solution Approach 1:
The patent substitutes condensation reaction with addition polymerization of siloxane monomers. This chemical mechanism replacement eliminates the cyclic by-product formation inherent in condensation reactions, as the addition polymerization of D4, D5, or D6 monomers to silanol-terminated chains does not generate cyclic structures as by-products.
Solution Approach 2:
The patent changes the reaction mechanism and conditions by using addition polymerization catalyzed by platinum or other catalysts at controlled temperatures and pH, rather than acid or base-catalyzed condensation. This parameter change fundamentally alters the reaction pathway to avoid cyclic by-product formation while achieving the desired viscosity increase.
4Productivity
If polymerization is performed at higher temperatures for faster reaction, then productivity increases, but cyclic formation increases
Solution Approach 1:
The patent changes the temperature parameter to low ranges (0-25°C, preferably 5-15°C) and adjusts pH to specific ranges (2-4 or 7-9) to achieve a unique kinetic regime where polymerization proceeds at acceptable rates while cyclic by-product formation is minimized. This parameter optimization balances reaction rate and selectivity.
Solution Approach 2:
The patent uses catalysts (platinum, organometallic catalysts, or acid/base catalysts depending on the pathway) as intermediaries to facilitate polymerization at low temperatures. These catalysts lower the activation energy barrier, enabling reasonable polymerization rates at temperatures that suppress cyclic formation, thus mediating between productivity and purity requirements.
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 effectively reduces the levels of residual cyclosiloxanes and cyclics to less than 0.1%, achieving stable emulsions with smaller particle sizes, thereby enhancing stability and compliance with regulatory requirements.
Implementation Method 1
polymerizing the starting polymer to form a longer chain silanol end-blocked organopolysiloxane polymer
Implementation Method 2
combining a silanol endblocked organosiloxane starting polymer, water, and a surfactant
Implementation Method 3
emulsifying the starting polymer by agitating or shearing the ingredients
Data Source
AI summary
The invention relates to a method for the production of silicone in water emulsions by emulsion polymerisation. The emulsion contains particles of an organopolysiloxane polymer having an average particle diameter of less than 1µm. The method comprises: - combining a silanol end-blocked organosiloxane starting polymer, water, and a surfactant; said starting polymer having a viscosity of at least 2 Pa.s preferably at least 2.5 Pa.s preferably at least 3.5 Pa.s preferably at least 4 Pa.s and up to 150 Pa.s; - emulsifying the starting polymer by agitating or shearing the ingredients; - polymerizing the starting polymer to form a longer chain silanol end-blocked organopolysiloxane polymer; wherein at least a portion of said polymerising step is performed at a temperature of less than or equal to 16 ºC preferably less than or equal to 15 ºC.