Addition-Fragmentation Agents for Polymerization Stress Relief
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Solution Overview
Problem
Free-radical polymerization in materials like dental compositions and thin films often results in volumetric shrinkage, leading to stress that can cause microcracks, deformation, and failure in adhesion due to the transfer of stress at the interface between the cured composition and a substrate, affecting the durability of the cured material.
Innovation Solution
The introduction of addition-fragmentation agents with labile linkages that can cleave and reform during polymerization, providing stress relief by delaying the gel point and allowing material flow, thereby reducing polymerization-induced stresses and enabling self-bonding or self-priming capabilities through surface-binding functional groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If free-radical polymerization is used to cure polymerizable compositions, then the composition transforms from a viscous material to an elastic or viscoelastic solid, but volumetric shrinkage occurs leading to polymerization stress
Solution Approach 1:
The patent introduces addition-fragmentation agents that change the polymerization parameters by providing labile linkages which cleave and reform during the process. This dynamic parameter change allows the system to adjust its stress state during curing, reducing polymerization-induced stress while maintaining adhesion. The labile linkages create a time-dependent mechanical property evolution that mitigates stress accumulation.
Solution Approach 2:
The addition-fragmentation agents act as intermediaries between the crosslinking network and the stress field. The labile linkages in these agents serve as stress-absorbing intermediaries that can reversibly break and reform, thereby mediating the stress transfer and preventing stress concentration at the substrate interface.
2Productivity
If crosslinking proceeds rapidly to achieve quick curing, then productivity increases, but stress concentration increases leading to microcracks and deformation
Solution Approach 1:
The addition-fragmentation process introduces a periodic or cyclic mechanism where labile linkages continuously cleave and reform during polymerization. This periodic bond breaking and forming allows the network to dynamically reorganize, relieving stress accumulations that would otherwise lead to deformation while maintaining overall curing progress.
Solution Approach 2:
The patent employs dynamic covalent chemistry through addition-fragmentation agents, where bonds are not static but can reversibly break and reform. This dynamic character allows the crosslinking network to adapt its structure during curing, accommodating volumetric changes and reducing stress concentration even as crosslinking progresses rapidly.
3Stability of the object's composition
If the gel point is reached early in polymerization, then the material transitions to an elastic solid early, but stress relief through material flow is reduced
Solution Approach 1:
The addition-fragmentation agents provide self-service stress relief by containing labile linkages that automatically cleave and reform in response to stress accumulation. This self-regulating mechanism allows the network to autonomously relieve stress without requiring external intervention, maintaining stability while accommodating volumetric changes.
Solution Approach 2:
The labile linkages are pre-installed in the addition-fragmentation agents before polymerization begins. These pre-positioned stress-relief mechanisms are ready to activate when stress accumulates, providing preliminary preparedness for stress management throughout the curing process.
4Ease of manufacture
If conventional polymerizable compositions are used without surface treatment, then the process is simple, but adhesion to substrates is poor requiring separate primer applications
Solution Approach 1:
The addition-fragmentation agents serve multiple functions simultaneously: they reduce polymerization stress through labile linkage cleavage and reforming, and they provide surface binding capability through functional groups that interact with substrates. This multi-functionality eliminates the need for separate primer applications while maintaining process simplicity.
Solution Approach 2:
The patent merges the stress-relief function and the adhesion-promotion function into a single additive component. The addition-fragmentation agent combines the labile linkage structure for stress relief with surface-binding functional groups, consolidating multiple requirements into one material solution.
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 addition-fragmentation agents effectively reduce polymerization-induced stresses, enhance adhesion, and improve the durability of cured materials by allowing for network reorganization and delayed gel point transition, leading to reduced microcracks and improved bonding properties.
Implementation Method 1
a labile addition-fragmentation group that can cleave and reform to relieve strain
Implementation Method 2
at least two surface-binding functional groups that associates with the surface of a substrate, such as by forming a covalent or ionic bond
Implementation Method 3
at least two surface-binding functional groups that associates with the surface of a substrate, such as by forming a covalent or ionic bond
Implementation Method 4
Free-radical polymerization is typically accompanied by a reduction in volume as monomers are converted to polymer
Data Source
AI summary
Addition-fragmentation agents of the formula are disclosed having the following functional groups: 1) a labile addition-fragmentation group that can cleave and reform to relieve strain, 2) at least two surface-binding functional groups that associate with the surface of a substrate.