Characterization of the crosslinking reaction in high performance adhesives

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multiple components Using a combination of infrared spectroscopy, thermal analysis, and low field NMR, we have elucidated the role of a new class of nonreactive plasticizers on the crosslinking reaction between hexamethylenetetramine (HMTA) and phenol formaldehyde resin These two seemingly dissimilar reactants are responsible for the exceptionally high mechanical strength in a number of organic–inorganic composites The efficiency of the curing reaction is characterized by the changing functionality of HMTA Infrared active vibrations are used to characterize the changing molecular structures as a function of temperature The T1 spin-lattice relaxation time is used for the characterization of segmental dynamics of the chains in the formation of the crosslinked product The segmental mobility depends on the amount of crosslinking and the stiffness of the chain This study shows that this new class of nonreactive plasticizer can induce highly crosslinked structures without any of the environmental impact of the current technology An efficient crosslinking reaction in phenolic resin can be achieved by using methyl benzoate as a nonreacting plasticizer Low field NMR, in conjunction with infrared spectroscopy (mid and near) and DSC, clarified the crosslinking reaction mechanism and the ensuing structure © 2016 Wiley Periodicals, Inc J Polym Sci, Part B: Polym Phys 2016

An analysis of the role of nonreactive plasticizers in the crosslinking reactions of a rigid resin

Circular of the Bureau of Standards no. 498:: bibliography of recent research in the field of high polymers

Molecular dynamics simulations and experimental measurements were used to investigate the thermal and mechanical properties of cross-linked phenolic resins as a function of the degree of cross-linking, the chain motif (ortho–ortho versus ortho–para), and the chain length. The chain motif influenced the type (interchain or intrachain) as well as the amount of hydrogen bonding. Ortho–ortho chains favored internal hydrogen bonding whereas ortho–para favored hydrogen bonding between chains. Un-cross-linked ortho–para systems formed percolating 3D networks of hydrogen bonds, behaving effectively as “hydrogen gels”. This resulted in differing thermal and mechanical properties for these systems. As cross-linking increased, the chain motif, chain length, and hydrogen bonding networks became less important. Elastic moduli, thermal conductivity, and glass transition temperatures were characterized as a function of cross-linking and temperature. Both our own experimental data and literature values were used to valid...

Computational and Experimental Study of Phenolic Resins: Thermal–Mechanical Properties and the Role of Hydrogen Bonding

Molecular dynamics simulations of phenolic resin: Construction of atomistic models

From a consideration of molecular dimensions and bond angles, it is deduced that a Novolak resin must consist of highly kinked, asymmetrical molecules. As a result, it is concluded that such a resin, when hardened with “hexa, “ will contain much less than the theoretically possible number of methylene cross-links. A hardened resin will have a sponge-like structure which can explain, partially, certain physical and chemical properties. Phenol-methylene resins derived from formaldehyde are contrasted with phenol-ethylene resins, which can have a symmetrical structure. An explanation is given of the good “tack” producing properties of Koresine, based on this symmetry. It is advocated that attention should be given to the synthetic method, as opposed to the analytical procedure hitherto used in investigating Novolaks. The importance of the synthetic approach is stressed, because of the comparative lack of information on crystalline intermediates. Finally, other methods of attack are outlined, including the desirability of determining the fine structure of simple phenol-formaldehyde condensation products.

Molecular structure and its influence on the properties of phenolic resins

The structure of the monoalcohol of 3 : 5-dimethylphenol, first made by von Auwers and believed to be a para-substituted derivative, has now been confirmed. The synthesis of a new dialcohol, which has been characterized as an ortho-ortho compound, is described. The effect of reaction conditions on the position of methylol substitution is discussed. It has been shown that during characterization of the monoalcohol, by pyrolysis with lime, methyl migration may occur.

N. J. L. Megson

Papers

Molecular structure and its influence on the properties of phenolic resins

Formaldehyde condensations with phenol and its homologues. V. The methylol compounds of 3 : 5‐dimethylphenol

Plastics and coal