Miniemulsion copolymerization of polymerizable fatty acid-derived monomers and crosslinking of derived films via autoxidation.

摘要

The incorporation of fatty chains, from fatty acids or their alcohol derivatives, into a latex polymer via copolymerization of a free-radical polymerizable fatty acid-derived monomer (FAM) to achieve crosslinking at room temperature was investigated. The following FAMs were synthesized: 2-methacryloxyethyl linoleate (MAOEL), allyl linoleate (AL), oleyl methacrylate (OM), and a mixture of linoleyl and oleyl methacrylates (LOM). All of the FAMS were synthesized via esterification reactions. MAOEL and AL were synthesized by reacting linoleic acid with 2-hydroxyl ethyl methacrylate (HEMA) or allyl alcohol, respectively. The OM and LOM were synthesized by reacting their corresponding alcohol, instead of the acid, with methacrylic anhydride. OM was also synthesized using oleyl alcohol and methylacryloyl chloride (MACl).;All the FAMs were miniemulsion copolymerized with 2-ethylhexyl methacrylate (EHMA) using a thermal initiator. The conversion for the copolymerization of MAOEL with EHMA decreased with increasing amounts of MAOEL due to chain transfer of the free radical on the growing polymer chain to the fatty chain in the MAOEL. The copolymer produced was highly crosslinked, and since it was unclear whether the crosslinking was caused by the MAOEL or the ethylene glycol dimethacrylate, a side-product from the MAOEL synthesis, the FAM was switched to AL. Allyl linoleate was chosen because it can be made directly from a fatty acid, without any side-products being formed. However, when the AL was copolymerized with EHMA, the conversion of the EHMA was found to decrease with increasing amounts of AL. Reduced conversion was observed with the MAOEL copolymerization, but the conversion was still higher than that in the AL system. Although an increase in reaction time increased the conversion, a more reactive monomer, such as a methacrylate monomer, was deemed necessary.;To synthesize a methacrylate PAM the starting material for the FAM synthesis was switched from a fatty acid to a fatty alcohol. The subsequent monomers synthesized from the fatty alcohols, OM and LOM, were then miniemulsion copolymerized with EHMA using a thermal initiator. The resulting polymer was found to be highly crosslinked. Moreover, the conversion of EHMA dramatically decreased with increasing LOM content. Both of these phenomena were caused by chain transfer near the double bond on the fatty chain. To reduce chain transfer and the activity of the radical formed on the fatty chain, the reaction temperature was decreased. Lowering the temperature required a switch from a thermal initiator system to a redox initiator system. The reduction in temperature effectively lowered the amount of crosslinking and increased the conversion of the monomers. Although the amount of crosslinking was lowered the p(EHMA-co-LOM) still had at least 40% of the polymer crosslinked.;The p(EHMA-co-OM) and p(EHMA-co-LOM) latexes were then tested for crosslinking both at room temperature and 100°C. At 100°C, an increase in the double bond concentration led to an increase in crosslink density, although there appear to be an optimum value of double bonds, beyond which the value the crosslink density no longer increased. At room temperature, the p(EHMA-co-OM) samples crosslinked, but the p(EHMA-co-LOM) samples containing large amounts of LOM did not to a large extent if at all. Since the crosslinking reaction did occur at room temperature for the p(EHMA-co-OM), it was hypothesized that diffusion of the polymer chains for the p(EHMA-co-LOM) containing high amounts of LOM was limited due to crosslinking that occurred during the polymerization reaction. Thus the reactive sites on polymer chains could not diffuse together to undergo the crosslinking reaction. The ratio of crosslink density for a given time to the final crosslink density scales linear with time to the ½ power. Thus the data supports that polymer chain diffusion is important in the crosslinking reaction for the p(EHMA-co-FAM).