Waterborne Dispersion Process Using Cobalt Chelate Catalyst
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Solution Overview
Problem
Existing processes for preparing amphiphilic block copolymers using reversible addition-fragmentation chain transfer (RAFT) polymerization require organic solvents, result in low monomer conversion, and produce products with unpleasant odors and colors due to sulfur-based control agents, while also involving complex and time-consuming steps.
Innovation Solution
A process for preparing a waterborne dispersion of amphiphilic block copolymers in a one-pot procedure in water, using a cobalt chelate complex for free-radical polymerization, which eliminates the need for organic solvents, increases monomer conversion to near quantitative yields, and reduces color and odor issues by avoiding sulfur-based agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RAFT polymerization is used to prepare amphiphilic block copolymers, then colloidal stability of waterborne polymer dispersions is improved, but unpleasant odor and color are generated due to sulfur-based control agents
Solution Approach 1:
The patent removes the sulfur-based control agent from the polymerization system and replaces it with a cobalt chelate complex as catalyst. This extraction of the harmful sulfur component while maintaining the controlled polymerization functionality resolves the contradiction between achieving colloidal stability and avoiding unpleasant odor and color in the final product.
Solution Approach 2:
The patent changes the chemical parameters of the polymerization system by switching from RAFT mechanism with sulfur-based agents to cobalt-catalyzed controlled radical polymerization. This parameter change eliminates the source of unpleasant odor and color (thiocarbonylthio moiety decomposition) while maintaining the ability to produce stable waterborne dispersions.
2Ease of manufacture
If organic solvents are used in RAFT polymerization, then amphiphilic block copolymers can be prepared, but extra process steps are required for solvent removal
Solution Approach 1:
The patent changes the reaction medium parameter from organic solvent to water, enabling the polymerization to proceed directly in the final dispersion medium. This eliminates the need for separate solvent removal steps and simplifies the overall process while maintaining the ability to prepare amphiphilic block copolymers with desired properties.
Solution Approach 2:
Water serves multiple functions in the patent: it is both the reaction medium for polymerization and the final dispersion medium for the waterborne coating composition. This multi-functionality eliminates the need for separate solvent removal and dispersion steps, reducing process complexity.
3Ease of manufacture
If RAFT polymerization is used, then block copolymer can be prepared, but reaction time is long and monomer conversion remains low
Solution Approach 1:
The patent changes the mechanism parameter from RAFT polymerization to cobalt-catalyzed controlled radical polymerization. This mechanism change significantly improves polymerization kinetics, reducing reaction time from many hours to shorter durations while achieving near-quantitative monomer conversion, thus improving productivity.
Solution Approach 2:
The patent substitutes the RAFT mechanism (which relies on sulfur-based control agents and equilibrium processes) with a cobalt-catalyzed mechanism that operates through different chemical pathways. This substitution enables faster reaction rates and higher conversion efficiency while maintaining control over polymer architecture.
4Manufacturing precision
If sulfur-based control agents are used in RAFT polymerization, then controlled polymer chain composition is achieved, but low molecular weight sulfur compounds cause odor and color issues
Solution Approach 1:
The patent extracts and removes the sulfur-based control agent from the system, replacing it with a cobalt chelate complex. This eliminates the source of low molecular weight sulfur compounds that cause odor and color problems while maintaining the ability to control polymer chain composition through catalytic mechanisms.
Solution Approach 2:
The cobalt chelate complex acts as an intermediary catalyst that enables controlled radical polymerization without requiring sulfur-based control agents. It mediates the polymerization process to achieve controlled chain composition while avoiding the formation of harmful sulfur-containing byproducts.
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
The process achieves high monomer conversion, reduces reaction time, and maintains desirable coating performance such as water resistance, while eliminating the use of organic solvents and sulfur-based agents, resulting in a more efficient and environmentally friendly production method.
Implementation Method 1
subjecting at least ethylenically unsaturated monomer(s) (i) bearing acid-functional groups to a free-radical polymerization process in an aqueous medium in the presence of a free radical initiator and a cobalt chelate complex
Implementation Method 2
amphiphilic block copolymers prepared using RAFT are able to provide excellent colloidal stability of waterborne polymer dispersions
Implementation Method 3
the polymer P is obtained in the presence of the block copolymer by an emulsion polymerization process
Data Source
AI summary
The present invention relates to a process for preparing a waterborne dispersion comprising amphiphilic block copolymer comprising at least blocks [A] and [B], and polymer P comprising ethylenically unsaturated monomer(s) different from monomer(s) (i) (monomer(s) (iii)), whereby the amount of block copolymer is higher than 0.5 and lower than 50 wt. %, based on the total weight of monomers used to prepare the block copolymer and polymer P, wherein the process comprises at least the following steps: (I) subjecting at least ethylenically unsaturated monomer(s) (i) bearing acid-functional groups to a free-radical polymerization process in an aqueous medium in the presence of a free radical initiator and a cobalt chelate complex to obtain block [A], (II) subjecting at least ethylenically unsaturated monomer(s) (ii) different from monomer(s) (i) to an emulsion polymerization process in aqueous medium in the presence of block [A] and a free radical initiator, whereby the amount of ethylenically unsaturated monomer(s) (ii) in block [B] is at least 70 wt. %, relative to the total weight amount of monomers used to prepare block [B] and whereby the ethylenically unsaturated monomer(s) (ii) is (are) selected from the group consisting of methacrylic acid esters, dialkyl esters of itaconic acid, methacrylonitrile, α-methyl styrene and any mixture thereof, (III) subjecting at least ethylenically unsaturated monomer(s) (iii) different from monomer(s) (i) to an emulsion polymerization process in aqueous medium at a pH in the range of from 5 to 10 in the presence of the amphiphilic block copolymer to obtain the block copolymer-polymer P, and the process further comprises deactivating the cobalt chelate complex, which remains from step (I), prior to and/or during step (II).