AbstractThe network structure evolution of a hexamethylenetetramine (HMTA)-cured novolac-type phenolic resin over a curing temperature range of 135–155 °C was investigated using 1H-pulse nuclear magnetic resonance spectroscopy and small-angle and wide-angle X-ray scattering techniques. The aim was to elucidate the mechanism responsible for the apparent absence of inhomogeneity after curing at 175 °C, in which the inhomogeneity was first observed at the gel point below 130 °C. The HMTA-cured phenolic resin exhibited high-cross-link and low-cross-link density domains (denoted as HXD and LXD, respectively). The LXD was a minor structure having a cross-link fraction of 0.2, which was 5–6 nm in size and comprised a few meshes. As curing proceeded, intradomain reactions in the LXD occurred, and the electron density in the domain increased, decreasing the electron density difference between the HXD and LXD. This reduction in the electron density difference decreased the cross-link inhomogeneity in the phenolic resins in terms of electron density fluctuations. This structural evolution caused the apparent absence of inhomogeneity in the fully HMTA-cured phenolic resins.The network structure evolution of a hexamethylenetetramine-cured novolac-type phenolic resin was investigated using 1H-pulse NMR spectroscopy, SAXS and WAXS to elucidate the mechanism responsible for the apparent absence of inhomogeneity after curing, in which the inhomogeneity was first observed at the gel point.

中文翻译：

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六亚甲基四胺固化酚醛树脂的网络结构演变

摘要使用 1H 脉冲核磁共振光谱和小角和广角 X 射线散射研究了六亚甲基四胺 (HMTA) 固化的酚醛清漆型酚醛树脂在 135-155 °C 的固化温度范围内的网络结构演变。技术。目的是阐明导致在 175 °C 固化后明显不存在不均匀性的机制，其中首先在低于 130 °C 的凝胶点观察到不均匀性。HMTA 固化的酚醛树脂表现出高交联和低交联密度域（分别表示为 HXD 和 LXD）。LXD 是交联分数为 0.2 的次要结构，其尺寸为 5-6 nm，包含几个网格。随着固化的进行，LXD 发生域内反应，域中的电子密度增加，减小 HXD 和 LXD 之间的电子密度差异。就电子密度波动而言，电子密度差的这种减小降低了酚醛树脂中的交联不均匀性。这种结构演变导致完全 HMTA 固化的酚醛树脂明显不存在不均匀性。使用 1 H 脉冲 NMR 光谱、SAXS 和 WAXS 研究了六亚甲基四胺固化酚醛型酚醛树脂的网络结构演变，以阐明负责的机制固化后明显不存在不均匀性，其中首先在凝胶点观察到不均匀性。