Dynamic light scattering study of the curing mechanisms of novolac-type phenolic resins

Abstract

The curing behavior of a novolac resin (NV) cured with hexamethylenetetramine (HMTA), as well as the influence of an excess amount of HMTA on the curing reaction, were investigated by dynamic light scattering and gel permeation chromatography. A two-roll mixing mill process was applied to control the curing reaction degree. The dependence of the number of mixing times on the weight-average molecular weight (M w ) and hydrodynamic radius (R h ) of NV differed significantly with the HMTA amount. A larger quantity of HMTA resulted in faster growth and larger R h and M w values. The relationship between M w and R h for NV in tetrahydrofuran indicates two different polymer-growth mechanisms irrespective of the excess amount of HMTA (that is, powerlaw and subsequent deviation corresponding to the chain extension and intermolecular reactions between larger molecules, respectively). These results suggest that structural differences governing the mechanical properties of phenolic resins are initiated in the pregel stage, followed by noticeable differences in the mechanical properties during the subsequent curing process.

Microstructural properties, thermal insulation and thermal degradation behavior of boron‐containingmonolithic novolac xerogels

“…As mentioned previously, the microgels grow without restraint at the beginning of the curing process until the impingement, reaching a maximum. Shudo et al 18 investigated the influence of an excess amount of HMTA on the curing behavior of novolac resin by dynamic light scattering and gel permeation chromatography. The results of this study indicated that a larger quantity of HMTA resulted in faster growth of novolac network, larger hydrodynamic radius, and higher weight‐average molecular weight values.…”

“…To the best our knowledge, no studies have been conducted on the effect of HMTA on the microstructural properties of sol–gel derived novolac monoliths. But, the mechanism of novolac gelation has been deeply characterized in bulk state 17–20 . The results of these studies suggest that the microstructural properties govern the mechanical and thermal behavior of cured novolac.…”

Phenolic Resins – Recent Progress of Structure and Properties Investigations

“…In order to understand the structure‐property relationship and to improve the mechanical properties of phenolic resin, we carried out a systematic studies on phenolic resins by experiments, such as NMR and small‐angle X‐ray scattering (SAXS), dynamic light scattering (DLS), and by large‐scale atomistic molecular dynamics (MD) simulations . After examining the validity of simulated structure of cross‐linked phenolic resin by comparing experimental results, we successfully reproduced the experimental scattering functions from MD, and discussed the relationship between the inhomogeneity and the molecular interactions as a function of the conversion, α .…”

Preparation of Lignin-Based High-Ortho Thermoplastic Phenolic Resins and Fibers

“…When more ortho connections occur than para connections (i.e., the O/P value is higher than 1), a high-ortho phenolic resin is formed [ 22 , 23 ]. The high-ortho phenolic resin structure is more ordered, while the highly reactive para-position group is retained, which results in faster curing [ 24 , 25 , 26 , 27 , 28 , 29 ]. Therefore, the special structure of high-ortho resin is more conducive to phenolic fiber preparation.…”