Thermoset foams are often produced by chemical foaming with control of both curing degree and foaming gas generation rate in a heating process. In this study, to analyze the effect of the degree of curing on bubble nucleation independently from the effect of the gas generation rate, batch physical foaming was conducted with a thermoset polymer with controlled crosslinking degree using supercritical carbon dioxide. A styrene/divinylbenzene (DVB) mixture was polymerized with various copolymer ratios and used as model thermoset polymer with different crosslinking degrees. The foaming experiments clearly showed that not the viscosity of the polymer but the distance between crosslinking points was the key factor in determining the bubble nucleation in the physical foaming process. When the distance between the crosslinking points was shorter than the critical diameter of a bubble calculated from classical nucleation theory, bubbles could not be nucleated, i.e., the distance between the crosslinking points determined the foamability of the thermoset polymer.

热固性泡沫通常是在加热过程中通过控制固化度和发泡气体产生速率的化学发泡来生产的。在这项研究中，为了独立于气体产生速率的影响来分析固化程度对气泡成核的影响，使用具有超临界二氧化碳的交联度可控的热固性聚合物进行间歇物理发泡。苯乙烯/二乙烯基苯（DVB）混合物以各种共聚物比例聚合，并用作具有不同交联度的模型热固性聚合物。发泡实验清楚地表明，在物理发泡过程中，不是聚合物的粘度而是交联点之间的距离是决定气泡成核的关键因素。