Development of VOC-free, high-Tg latex binders by a high-temperature water-extended latex technology
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- Lee, D.I. & Chen, F.B. J Coat Technol Res (2007) 4: 161. doi:10.1007/s11998-007-9016-1
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The potentiometric titration of carboxylated methyl methacrylate latexes prepared with varying amounts of methacrylic acid showed that only very small amounts of their total acids copolymerized were neutralized at room temperature until the acid level was well above 10%. However, it was found that all the acids copolymerized were completely titrated either in a 50/50 water/ethanol mixture at room temperature or in water at high temperatures near their backbone polymer Tgs, regardless of their acid contents, as predicted from the existing theories on the alkali-swelling of carboxylated latexes. It was also found that these high-temperature alkali-swollen latex particles remained in the swollen state even after they were cooled down to room temperature and became film-forming at much lower temperatures. This discovery led to a new technology coined as a high-temperature water-extended latex technology. This new technology enabled us to develop VOC-free water-extended latexes of high-Tg polymers that would exhibit good film formation at ambient temperature and turn into hard and non-blocking latex films and latex-bound pigmented coatings upon drying. Particularly, when fugitive bases were used for neutralization at high temperatures, the resulting water-extended latexes became hard, non-blocking, and water-resistant binders upon drying.