Hider, Jennifer Agnes (2003) Analysis of a thermosetting polyester resin with novel crosslinking agent. (PhD thesis), Kingston University, .
Abstract
A novel crosslinking agent, 2,4-diallyloxy-6-diethylaminotriazine, was used for the cure of unsaturated polyester resins based on maleic anhydride. The aim of this investigation was to analyse the chemical structure of these cured resins. The analysis of thermosets is difficult because once cured the resin is both insoluble and infusible. An analytical strategy was devised to overcome these difficulties by using several different approaches. Spectroscopy formed an important part of this investigation. Both NMR and FT-IR were used to characterise the precursor materials and FT-IR spectroscopy for the final products. This technique was also used to monitor the curing reaction in conjunction with DSC studies. These studies showed that other chemical changes were taking place as well as the expected loss of the carbon double bonds. The extent of cure of these resins is usually determined by a solvent extraction method and this was followed by C,H,N analysis of both the soluble and insoluble (gel) fraction. An HPLC method was developed to measure the amount of unreacted monomer in the extract. Further information on the cured structure could only be obtained by destructive methods and both chemical and thermal degradation methods were examined. The attempt to release the crosslinking chain from the cured polyester by alkaline hydrolysis was unsuccessful because the cyanurate links were found to be more susceptible to hydrolysis than the phthalate and maleate links. Pyrolysis of the resins gave an extremely complex mixture of products. Many of the products identified for the resins were also identified when a homopolymer of 2,4- diallyloxy-o-diethylaminotriazine was pyrolysed. These included aromatic and other ring structures. This evidence in conjunction with the spectroscopic studies suggested that the monomer did not produce linear crosslinking chains but that several monomer units were linked together to form a three-dimensional structure which acted as a crosslinking junction for the linear polyester chains and that this structure was likely to involve some fused rings. A further aim of this research was to review the methods currently available for the analysis of thermosets and make recommendations based on this study and the literature search to other analysts dealing with this class of materials. There have been major developments in spectroscopic techniques which mean that far more data can now be obtained on these systems than previously. FT-IR spectroscopy is probably the most applicable method. There are also major developments in the use of pyrolysis with GC and/or MS, but interpretation of these results with respect to the original structure requires care. Development of chemical modification methods are continuing, particularly on the small scale for identification of components by GC. In the case of structural analysis, once an appropriate method for cleaving the structure has been obtained, then spectroscopic analysis of the products can provide a great deal of information, particularly NMR spectroscopy.
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