Many photocrosslinked polymers and composites start with a mixture of low molecular mass / viscosity resins containing one or more reactive functionalities. The polymerization process leads to drastic changes in the material properties of the final products, many of which are dictated by the reaction rate and the degree of polymerization conversion when crucial transitions occur.
Polymerization shrinkage is one general outcome of the chemical reaction. Large shrinkage may lead to accumulation of internal residual stress in freestanding materials. Polymerization shrinkage can also lead to larger interfacial stress when used as a filled material or coating. In both cases, premature failure may occur. Efforts are underway to develop new chemistries and processing parameters to reduce the stress build up in polymerized materials. Measurements that provide holistic views of the evolution of multiple properties during polymerization can provide datasets to underpin the design and optimization of materials and processes.
We have developed techniques that use simultaneous measurements of evolution of multiple polymerization properties combined with computational approaches. In-situ measurements including stress evolution, chemical evolution, and temperature changes during polymerization and computation approaches can be used to determine changes in the relaxation time and final structure of the polymerized materials. As an example of a specific usecase, we can evaluate the effect of curing protocols on kinetics of material evolution and structure and properties of the polymerized materials. We demonstrate the use of percolation theory in conjunction with experimental data to understand network microscopic structural heterogeneity from the macroscopic measurements.
Sarkar, S., Baker, P. J., Chan, E., Lin-Gibson, S., & Chiang, M. (2017). Quantifying the sensitivity of network structure and properties from simultaneous measurements during photopolymerization. Soft Matter.
Software to analyze simultaneous multiparametric measurements from NIST Stress Tensometer (SRI 6005) is available: