Synthesis and characterization of bio-based alkyl terminal hyperbranched polyglycerols: a detailed study of their plasticization effect and migration resistance

We develop a plasticizer composed of alkyl terminal hyperbranched polyglycerol (alkyl-HPG) for the production of non-toxic, phthalate-free flexible poly(vinyl chloride) (PVC). The synthesized alkyl-HPGs are transparent liquids at room temperature and exhibit considerably lower volatility than di(2-ethylhexyl) phthalate (DEHP). The miscibility analyses reveal that the alkyl termination and the hyperbranched architecture of alkyl-HPG are the key factors for improving its miscibility with PVC, and butyl-terminated HPGs (HPG-C4s) are fairly miscible with PVC irrespective of their degree of polymerization (DP). The obtained PVC/HPG-C4 films exhibit similar flexibility and stretchability with the corresponding properties of PVC/DEHP films. In particular, PVC/HPG3-C4, the blend with the smallest DP, has excellent plasticization efficiency and low apparent activation energy (E-a) for a relaxation comparable to those of PVC/DEHP owing to its high concentration of chain ends. The transparency and thermal stability of PVC/HPG-C4 are rather better than those of PVC/DEHP, and HPG-C4s are biologically safe without acute toxicity. Moreover, PVC/HPG-C4 shows an extremely small degree of migration in leaching tests, more than 80% lower than that of PVC/DEHP.