Addition-Fragmentation Agents for Polymerization Stress Relief
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Solution Overview
Problem
Free-radical polymerization in polymerizable compositions often results in volumetric shrinkage, leading to stress and microcracks, which can cause adhesion failure and affect durability due to the transfer of stress to the interface between the cured composition and a substrate.
Innovation Solution
The use of addition-fragmentation agents with labile crosslinks that can cleave and reform during polymerization, delaying the gel point and allowing for stress relief by maintaining the polymerizable mixture in a viscous state longer, thereby reducing polymerization-induced stresses and promoting self-bonding or self-priming properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If free-radical polymerization is performed to convert monomers to polymer, then polymerization is achieved, but volumetric shrinkage occurs leading to stress and microcracks
Solution Approach 1:
The patent changes the chemical parameters of the polymerization system by introducing addition-fragmentation agents with labile crosslinks. These agents modify the polymerization kinetics and network formation process, allowing the system to achieve high conversion while managing stress through controlled bond cleavage and reforming events
Solution Approach 2:
The addition-fragmentation agents act as intermediaries in the polymerization process. The labile crosslinks serve as temporary mediators that can cleave and reform, facilitating stress relief while maintaining network integrity. This intermediary mechanism allows the system to tolerate volumetric shrinkage without developing critical stress concentrations
2Strength
If crosslinking is performed to strengthen the polymer network, then strength is improved, but stress concentration increases leading to adhesion failure
Solution Approach 1:
The patent introduces dynamic, reversible crosslinks through addition-fragmentation agents. These labile crosslinks can continuously cleave and reform during and after polymerization, allowing the network to dynamically relax stress concentrations that would otherwise lead to adhesion failure. The crosslinking density and strength are maintained while the system gains stress-relief capability
Solution Approach 2:
The labile crosslinks provide beforehand cushioning by serving as pre-positioned stress-relief mechanisms within the polymer network. Before stress can accumulate to failure levels, the labile bonds cleave to absorb excess stress, preventing catastrophic adhesion failure at the substrate interface
3Strength
If the polymerizable mixture gels quickly to form an elastic solid, then structural integrity is achieved, but stress relief time is reduced
Solution Approach 1:
The addition-fragmentation process creates a periodic action within the polymer network through continuous cleavage and reforming of labile crosslinks. This periodic bond breaking and forming allows the network to progressively relieve stress over an extended time period rather than requiring all stress relief to occur simultaneously during the gelation window
Solution Approach 2:
The labile crosslinks provide preliminary stress-relief capability before the network fully gels. By having stress-relief mechanisms in place during the viscous stage, the system can begin stress relaxation earlier in the polymerization process, extending the effective stress-relief window before final structural integrity is achieved
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, prevent microcrack formation, and enhance the durability of the cured composition by allowing for stress relief and delayed gelation, resulting in improved adhesion and reduced deformation.
Implementation Method 1
addition-fragmentation agents that can cleave and reform to relieve strain
Implementation Method 2
the addition-fragmentation process results in a chain-transfer event that provides novel polymers
Implementation Method 3
a surface-modifying functional group that associates with the surface of a substrate
Implementation Method 4
curable compositions of this disclosure are self-bonding or self-priming
Data Source
Figure 1
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) a free-radically polymerizable group, and 3) a surface-modifying functional group that associates with the surface of a substrate.