Polyesters prepared from adipic acid (AA), phthalic anhydride (PA), isophthalic acid (IPA), terephthalic acid (TPA), and 2-butyl-2-ethyl-1,3-propanediol (BEPD) were investigated by gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOFMS). All polyesters were found to contain a fraction of low molecular weight molecules that were identified as cyclic ester oligomers. The most abundant cyclic oligomer varied with the diacid used in the synthesis but, in every case, it was either a dimer or a trimer. In addition, the relative amounts of the polyester starting materials influenced the amount of cyclic oligomers formed in the polyesterification reaction. Copyright # 2001 John Wiley & Sons, Ltd.Cyclic ester oligomers have already been known as common by-products of the polyesterification reactions for many years.1±3 Recently, they have been synthesized also on purpose to be used as feedstocks for environmentally friendly ring-opening polymerizations and as building blocks for novel polymeric structures. 4±6 Nevertheless, cyclic oligomers are undesirable in polyester coatings because they are mobile and tend to migrate to the surface of the coating where they are responsible for hazy surface deposits. Studies on the polyester of terephthalic acid (TPA) and 2,2-dimethyl-1,3-propanediol (NPG) have shown that cyclic ester dimers can turn the surface of the polyester whitish when the polyester is stored at temperatures above its glass transition temperature T g .
16±20We were interested in the cyclic oligomers found in polyesters prepared from phthalic acids and diols such as 2-butyl-2-ethyl-1,3-propanediol (BEPD). These polyesters are used in industrially produced coating materials. They exhibit good mechanical properties and are chemically resistant. Commercial polyesters used in coatings often contain as many as four to eight different monomers. The polyesters of our study were prepared from two components, one of four different diacids and one diol at a time. The starting materials of the polyesters were adipic acid (AA), phthalic anhydride (PA), isophthalic acid (IPA), or terephthalic acid (TPA) as diacid and BEPD as diol.We applied GPC and matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOFMS) for the characterization of our polyester samples. GPC was used to monitor the polyesterification reactions, while only the final products were analyzed by mass spectrometry. The influence of the diacid used and the diacid/diol ratio on the formation of cyclic oligomers was investigated.
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