Isocyanate Prepolymer Synthesis via Segmented Reactivity and Distillation
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Solution Overview
Problem
Existing methods for producing isocyanate prepolymers often result in high viscosity and broad molecular weight distribution due to uncontrolled polymerization and the presence of highly branched products, along with health hazards from monomeric isocyanates, which limits their suitability for applications like adhesives and coatings.
Innovation Solution
A two-stage process where a polyol with multiple hydroxyl groups is first reacted with a diisocyanate having different reactivity groups, followed by reaction with an excess of a more reactive di- or triisocyanate, with subsequent distillation to remove unreacted isocyanates, resulting in a prepolymer with terminal NCO groups of varying reactivity and minimal by-products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If polyols are reacted with polyisocyanates to synthesize prepolymers, then reactive NCO groups are formed for further synthesis or application, but uncontrolled polymerization occurs forming highly functional NCO oligomers and branched polymers with high viscosity and broad molecular weight distribution
Solution Approach 1:
The patent segments the isocyanate reactant into two distinct components: a polyisocyanate providing the polyol reaction framework and a monomeric isocyanate providing controlled NCO group addition. This segmentation prevents uncontrolled polymerization while maintaining versatility for further synthesis.
Solution Approach 2:
The patent changes the reactivity parameter by using a monomeric isocyanate with specifically controlled NCO group reactivity that is lower than typical polyisocyanate NCO groups. This parameter change allows controlled reaction with polyols while preventing runaway polymerization and maintaining narrow molecular weight distribution.
2Manufacturing precision
If excess isocyanate is used in the reaction, then complete conversion of polyol is achieved, but monomeric isocyanates remain as harmful by-products
Solution Approach 1:
The patent extracts and removes monomeric isocyanate by-products through vacuum distillation after the reaction. This extraction step achieves complete polyol conversion while eliminating harmful monomeric isocyanate residues from the final prepolymer product.
Solution Approach 2:
The patent discards monomeric isocyanate by-products through vacuum distillation, separating them from the desired prepolymer product. This recovery process ensures high conversion completeness while removing harmful substances from the final product.
3Adaptability or versatility
If polyisocyanates are reacted with diols or higher-hydric alcohols, then prepolymers are formed, but highly branched products are generated with increased viscosity
Solution Approach 1:
The patent segments the reaction system into polyol + polyisocyanate (for backbone formation) and monomeric isocyanate (for controlled end-group modification). This segmentation prevents the formation of highly branched structures that would increase viscosity, while still achieving complete polyol conversion.
Solution Approach 2:
The patent uses partial action by employing monomeric isocyanate in controlled excess rather than polyisocyanate. This partial excessive action ensures complete polyol conversion without creating the highly branched structures that would result from using polyisocyanate in excess, thereby controlling viscosity.
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 yields prepolymers with an ideal structure, reduced polymeric by-products, and low monomeric isocyanate content, enhancing their suitability for applications by improving viscosity and molecular weight distribution, while minimizing health risks.
Implementation Method 1
The excess of NCO groups in the second reaction stage is at most 2:1. A distillation step for the reduction of monomeric diisocyanates is not described.
Data Source
AI summary
A description is given of a process in which a polyol having from 2 to 10 OH groups is reacted with a diisocyanate having NCO groups of differing reactivity and in which the ratio of equivalents of OH:mole of diisocyanate is integral and less than 1, an intermediate having NCO and OH groups is obtained, this is reacted with an excess of an isocyanate having more reactive groups in an amount of at least 4:1 and the monomeric, unreacted isocyanates are distilled off. Furthermore, a prepolymer which has a predominantly ideal structure and bears at least two NCO groups of differing reactivity is described.