Reoplex(R) 346, a low number-average molecular weight ((M) over bar(n)) poly 1,3-butylene adipate-frequently used as plasticizer in PVC-based cling-films-was studied by H-1 and quantitative C-13 NMR. It was found that Reoplex(R) results from the linear polyesterification of adipic acid (A) by an excess of butane 1,3-diol (B) with a (A/B) molar ratio of 0.88 giving a polyester having a number-average degree of polymerization (<(DP)over bar>n) and an absolute (M) over bar(n) of 15.7 and 1600 g/mol, respectively. As primary alcohol function is more reactive than secondary alcohol, Reoplex(R) chain-ends are made up of 28.6% of primary alcohol and 71.4% of secondary alcohol. (C) 2000 Elsevier Science Ltd. All rights reserved.