Synthesis of polymers with combined flame retardance and low shrinkage properties

Identifier:  TDX:794

Handle: https://hdl.handle.net/20.500.11797/TDX794

Authors:  Canadell Ayats, Judit

Abstract:
Over the last few decades, the polymeric materials has been replaced the conventional materials due to the versatility, low density, and their interesting properties. However, they present as an important limitation, their high flammability and in presence of heat and oxygen, they burn easily and rapidly. The problem is not only the destruction of the material but the smoke and toxic gases which are the main causes of hazards in a fire.<br/>In the last years different strategies have been developed to minimize the flammability of polymeric materials, such as the use of additives, the modification of commercial polymers or through the synthesis of specific polymers. The first strategy is the most widely use in the industry because is the most economic way to achieve flame retardancy. Nevertheless, this method has several disadvantages, because the additives have to be used in relatively high concentrations and this may affect the physical and mechanical properties of the material. Also, additives may be leached, or may volatilize from the polymer during service. The alternative strategy is to use reactive flame retardants, where the flame retardant is covalently bonded to the polymer chains.<br/>Although in the last few years there has been an increase of heteroelements used as flame retardants, the commercial market is still dominated by compounds based on halogens. These compounds present exceptional efficiency, interfering with the reactions responsible of flame propagation. However, during the combustion they release toxic and corrosive gases. Because of that, in the last few years has increased the interest in the research of halogen-free based flame retardants, such as phosphorus or silicon based flame retardants, which are more environmentally friendly and less aggressive in a fire. <br/>Another problem of polymeric materials is the shrinkage during polymerization and polymer curing, and the consequences can be presented in many different forms. For example, in polymeric coatings poor adhesion of the substrate can be observed. In cast electrical insulators, polymerization shrinkage can produce internal stress in the polymer, which can reduce the durability of the material as a consequence of the appearance of microvoids and microcracks. The most common way to solve this problem is through the use of fillers, however this method present several problems, such as an increase of the viscosity which make difficult to fill molds. Another more advisable strategy is through the use of 'expanding monomers', thus means, that during the polymerization and curing they don't shrink or even can produce some expansion. The spiroorthoesters are one kind of expanding monomers. <br/>The main purpose of this thesis is the obtention of new environmentally flame retardant materials that present low shrinkage during polymerization and polymer curing. Several approaches have been developed to achieve these desired properties:<br/>1. Synthesis of new monomers based on spiroorthoesters that contains phosphorus or silicon in their structure. It has been synthesized two spiroorthoesters with phosphorus, (1,4,6-trioxaspiro-[4.4] nonan-2-yl)-methyl 3-[10-(9,10-dihydro-9-oxa-9-phosphaphenanthrene-10-oxide-10-yl)] propanoate and bis[(1,4,6-trioxaspiro-[4.4] nonan-2-yl)-methyl 2-[10-(9,10-dihydro-9-oxa-9-phosphaphenanthrene-10-oxide-10-yl)] maleate and one with silicon in its structure, the 1,4,6-trioxaspiro [4.4]-2-nonylmethyl 3-trimethylsilyl propanoate. These new spiroorthoesters were synthesized with good yields through the modification of previously synthesized spiroorthoesters by a Michael addition or esterification reaction. The spiroorthoester moiety was obtained from &#61543;-butirolactone and an epoxide. <br/>These spiroorthoesters were polymerized and copolymerized with epoxy resins with ytterbium triflate as a cationic initiator.<br/>Also, with the aim to investigate the possible synergistic effect between phosphorus and silicon were both combined into the same material.<br/>2. Synthesis of linear polymers which contains phosphorus and spiroorthoester moieties in the side chain. They were obtained by radical polymerization from an acrylate-containing spiroorthoesters and different radically polymerizable phosphorus-containing comonomers. The polymers were crosslinked by a cationic double ring-opening of the spiroorthoester moieties with ytterbium triflate as an initiator.<br/>Also, it was studied the cationic copolymerization of a linear polymer which contains a spiroorthoester moiety in the side chain with different epoxy resins. Through the use of phosphorus-containing glycidyl derivatives it was introduced phosphorus into the material. <br/>3. It was studied a new method of copolymerization of spiroorthoesters with epoxy resins using microwave irradiation with the purpose to minimize the curing time. The results were compared with conventional heating conditions.