Figure 3.
Representative schematic illustrating the effects of network constitutional isomerization in high nx BBEs with (a) nx < M/I and (b) nx = M/I. While network constitutional isomers (NCIs) with nx < M/I have larger numbers of cross-links for each backbone which comprise the network, NCIs where nx → M/I have so few cross-links that a proportion of backbone chains will have only one or two cross-links per backbone, with the low polymerization concentration resulting in an increased probability for intramolecular cyclization. Samples with nx → M/I will thus contain dangling fractals which contribute highly to the viscous component of samples, while also containing the same number of stress-supporting strands as their isomeric counterparts. The backbones here are depicted as straight “rods” solely for ease of presentation of concepts—they are Rouse-like chains. (c) Plot of Tan(δ) for high nx samples with nx = M/I (red data) and nx < M/I (black data), as determined via dynamic mechanical analysis (DMA). The viscous component of the nx = M/I NCI is considerably larger than that of the nx < M/I NCI. (d) Plot of the storage (E′) and loss moduli (E″) for the nx = 1000, M/I NCI. Note the similarities between this profile and that of gels near the criticality point.