Addition-Fragmentation Crosslinking Agents for Polymer Stress Relief
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Solution Overview
Problem
Free-radical polymerization in materials like dental restoratives and adhesives often results in volumetric shrinkage, leading to stress and microcracks that can cause adhesion failure and reduce durability due to the inability of existing technologies to effectively manage polymerization-induced stress.
Innovation Solution
The introduction of addition-fragmentation crosslinking agents that provide labile crosslinks, allowing for stress relief by cleaving and reforming during polymerization, thereby delaying the gel point and reducing shrinkage and stress in the cured polymers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If free-radical polymerization is used to convert monomers to polymer, then polymerization occurs and material is formed, but volumetric shrinkage produces stress leading to microcracks and adhesion failure
Solution Approach 1:
The patent changes the chemical parameters of the polymerization system by introducing addition-fragmentation crosslinking agents with labile crosslinks. These crosslinks dynamically adjust the network structure during polymerization, changing the physical state from rigid to flexible, thereby reducing polymerization stress while maintaining high conversion rates and adhesion durability
Solution Approach 2:
The patent introduces dynamic labile crosslinks that can continuously cleave and reform during the polymerization process. This dynamic behavior allows the crosslinking network to adapt and reorganize, relieving build-up stress in real-time while maintaining the integrity of the cured composition, thus resolving the contradiction between productivity and reliability
2Strength
If crosslinking agents are used to strengthen the polymer network, then strength increases, but polymerization stress also increases leading to microcracks
Solution Approach 1:
The patent changes the nature of crosslinks from permanent to dynamic by using addition-fragmentation agents. The labile crosslinks provide a different physical state that allows stress relaxation while maintaining network strength, thus improving strength without increasing harmful polymerization stress
Solution Approach 2:
The labile crosslinks act as intermediaries between the polymerizing monomers and the final cured network. They temporarily hold the network together during polymerization, allowing stress relief through cleavage and reforming, while still providing the necessary strength in the final cured composition
3Stability of the object's composition
If the gel point is reached early in polymerization, then the material transitions to elastic solid, but stress relief through material flow is reduced
Solution Approach 1:
The patent introduces dynamic labile crosslinks that delay the effective gel point by allowing continuous cleavage and reforming. This dynamic behavior maintains a more viscous state for longer during polymerization, enabling stress relief through material flow while still achieving stable crosslinked composition at the end
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 use of addition-fragmentation crosslinking agents effectively reduces polymerization-induced stress, enhancing the durability and adhesion properties of cured materials by allowing for network reorganization and delayed gelation, thus improving the mechanical properties of polymers.
Implementation Method 1
The addition-fragmentation process of crosslinking results in a chain-transfer event that provides novel polymers that may be further functionalized
Implementation Method 2
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: wherein R4 is hydrogen, a C1 to C4 alkyl group, x is 1 or 2, R5 is a di- or trivalent (hetero)hydrocarbyl linking group, -A*-X2*- is a group formed between A and X2, wherein X2 comprises an electrophilic or nucleophilic functional group and A is a functional group that is co-reactive with functional group X2, and n is 0 or 1.