XDI-Terminated Polyurethane Viscosity Stability

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Solution Overview

Problem

Existing polyurethane compositions with low residual MDI monomer content are highly viscous and unstable over time, making them unsuitable for use as adhesives or surface coatings at low temperatures, and require large quantities of diluents for viscosity reduction, which is not desirable.

Innovation Solution

A polyurethane prepolymer with meta-xylylene diisocyanate (XDI) terminations is developed, achieved through a specific molar ratio of XDI to diphenylmethylene diisocyanate (MDI) and polyol reactions, resulting in a composition with reduced residual monomers and improved viscosity stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the residual MDI monomer content is reduced to less than or equal to 1% by weight, then the toxicity problems are reduced, but the viscosity increases rapidly over time and stability problems occur

Engineering Contradiction:

ImprovetoxicityVSAvoidviscosity stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent changes the chemical composition parameters by introducing XDI isocyanate groups to terminate the polyurethane chains instead of using excess MDI. This parameter change (switching from MDI-based termination to XDI-based termination) reduces toxicity while maintaining viscosity stability through the specific chemical properties of XDI groups

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite polyurethane system combining polyol, MDI, and XDI components. The specific composition ratio (0.5-10% XDI, 95-90% MDI, and polyol in 80-150 parts by weight) creates a composite material that achieves both low toxicity and viscosity stability through synergistic interaction of components

Inventive Principle:

Principle #40Composite materials

2Ease of operation

If diluents such as hydrocarbon organic solvents or plasticizers are used to decrease viscosity, then the viscosity is reduced, but large quantities are required and viscosity stability is not effectively maintained

Engineering Contradiction:

ImproveviscosityVSAvoiddiluent quantity

Core Design Contradiction:

Ease of operationVSQuantity of substance

Solution Approach 1:

The patent extracts and eliminates the need for diluents by using XDI-terminated polyurethane composition. The chemical structure and composition of the polyurethane itself provide appropriate viscosity characteristics without requiring additional diluent substances, thus removing the harmful dependency on large quantities of diluents

Inventive Principle:

Principle #2Taking out (Extraction)

3Ease of manufacture

If a stoichiometric excess of MDI (NCO/OH ratio > 1) is used to obtain terminal isocyanate groups, then the polyurethane with NCO terminations is obtained, but significant residual levels of MDI monomer remain

Engineering Contradiction:

Improvepolyurethane synthesisVSAvoidresidual MDI monomer

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent applies partial excess action by using a controlled, limited amount of XDI (0.5-10% of total isocyanate content) instead of a large stoichiometric excess of MDI. This partial excess is sufficient to terminate the polyurethane chains and provide NCO groups while minimizing residual monomer content through the specific reactivity and properties of XDI

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent uses XDI as a temporary terminating agent that reacts completely to form stable end groups. The XDI serves its purpose of creating NCO-terminated polyurethane and then effectively disappears from the system as unreacted monomer, leaving minimal residual content compared to traditional MDI excess methods

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 XDI-terminated polyurethane composition maintains satisfactory viscosity and mechanical properties, is stable over long storage periods, and complies with regulatory limits for residual monomer content, allowing for effective use as adhesives or surface coatings at low temperatures.

Implementation Method 1

The invention relates to a process for the preparation of a polyurethane with XDI terminations and based on diphenylmethylene diisocyanate or based on a mixture of meta-xylylene diisocyanate and diphenylmethylene diisocyanate, said polyurethane being non-solid at a temperature ranging from 5 to 35°C

Methodology Applied

Scientific EffectPolyaddition reaction: Chemical Bonding

Data Source

PatentEP3394141B1Xdi-terminated polyurethane, and composition comprising said polyurethane

Publication Date: 2022.11.09 BOSTIK SA(FR)

AI summary

The invention relates to a new XDI-terminated polyurethane. The invention also relates to the use of said polyurethane for manufacturing an adhesive, mastic and/or surface coating composition, in particular for the construction industry, said composition having long-term stability in respect of viscosity.