The chemistry of novolac resins - VI. Reactions between benzoxazine intermediates and model phenols
Section snippets
INTRODUCTION
Substituted benzoxazines and benzylamines are the major first-formed intermediates produced in the curing of novolac resins with hexamethylenetetramine (HMTA), and further reaction of these intermediates leads to a highly cross-linked network1, 2, 3, 4, 5, 6. The thermal decomposition of 3-(3,5-dimethyl-2-hydroxybenzyl)-6,8-dimethyl-3,-4-dihydro-(2H)-1,3-benzoxazine, as a model of benzoxazine intermediates, has been reported in the previous paper[7], providing reaction pathways from benzoxazine
Samples
3-(3,5-Dimethyl-2-hydroxybenzyl)-6,8-dimethyl-3,4-dihydro-(2H)-1,3-benzoxazine was prepared by the method reported previously4, 6. The compound was heated with 2,4- or 2,6-xylenol, respectively, in a ratio of 1:1 by wt% in a Eurotherm 902 oven under the same conditions used to cure novolac resins with HMTA[6]and the benzoxazine model system[7]. The samples were heated at 90°C for 6 h, then the temperature was increased at a rate of 3.7°C h−1 until 135°C, thereafter, 12°C h−1 until 205°C, and
Reactions between benzoxazine and 2,4-xylenol
13C spectra of 3-(3,5-dimethyl-2-hydroxybenzyl)-6,8-dimethyl-3,4-dihydro-(2H)-1,3-benzoxazine (1) heated with 2,4-xylenol to various temperatures are shown in Fig. 1Fig. 2. In the 13C spectra of low chemical shift range (10–100 ppm), the peaks with open circles are either CH or CH3, while the rest are CH2 carbons. In the high chemical shift range (100–200 ppm) the peaks marked by open circles are due to CH and the rest are quaternary carbons, as detected by the DEPT technique. The three strong
CONCLUSION
The 13C n.m.r. study provides direct evidence about the formation of methylene linkages between phenol rings from reactions of 3-(3,5-dimethyl-2-hydroxybenzyl)-6,8-dimethyl-3,4-dihydro-(2H)-1,3-benzoxazine and 2,4- or 2,6-xylenols. Various amines, amides and imines were also obtained during the reaction process, but the diphenylmethanes (dimers) are the predominant products in both systems. However, the reaction pathways of the two systems are different. The benzoxazine can react with
Acknowledgements
The work was supported by the Australian Industry Research and Development Board (Grant no. 15068), Australian Research Council, and Comalco Aluminium Limited. We also thank Dr. M.G. Looney and Mr. A.C. Potter for their helpful discussion.
References (10)
- et al.
Polymer
(1998) - et al.
Journal of Polymer Science and Polymer Chemistry
(1973) - et al.
Macromolecules
(1981) Kauchuk i Rezina
(1984)- et al.
Macromolecules
(1987)
Cited by (32)
4-Hydroxybenzenesulfonic acid triggers rapid preparation of phenolic aerogel composites by ambient pressure drying
2024, Chemical Engineering JournalThe study on curing and weight-loss mechanisms of benzoxazine during thermal curing process
2020, Polymer Degradation and StabilityCharacterization of the crosslinking reaction in high performance adhesives
2017, International Journal of Adhesion and AdhesivesToughening and reinforcing of benzoxazine resins using a new hyperbranched polyether epoxy as a non-phase-separation modifier
2017, PolymerCitation Excerpt :The etherification reaction between oxirane rings and phenolic hydroxyl groups formed from the oxazine ring-opening; 2. The ortho-position of phenolic hydroxyl group is connected to benzoxazine [47,48]. The catalytic reactions are listed in Scheme 3.
Structure-mechanical property relationships in crosslinked phenolic resin investigated by molecular dynamics simulation
2017, PolymerCitation Excerpt :In this study, the conversion α is defined as the degree of crosslinking given by α = (2NCH2)/(3NPhOH), where NCH2 and NPhOH are the number of reacted methylene units and the number of total phenolic rings in the system, respectively. The value of α corresponds to a branching coefficient of three-functional monomer system in gelation theory [1,3] and can be estimated experimentally by 13C NMR spectroscopy [27–29]. In this simulation, two types of crosslinked phenolic resins, RN and HO, were used as structure models with various reaction conversions after gelation (αgel = 0.57).