Highly Branched Polycaprolactone/Glycidol Copolymeric Green Plasticizer by One-Pot Solvent-Free Polymerization

Abstract

This study aims to develop a simple, low-cost method for synthesis of highly branched polycaprolactone (hbPCL) for use as effective “green” plasticizers for poly­(vinyl chloride) (PVC). We demonstrate the facile synthesis of hbPCL with tunable molecular architecture using glycidol as a branching monomer. A series of hbPCLs is prepared via one-pot, solvent-free copolymerization of ε-caprolactone and glycidol, wherein the molecular architecture is readily controlled by varying the molar ratio of glycidol to ε-caprolactone. Further, studying the kinetics of copolymerization reveals the preferential reaction of glycidol over ε-caprolactone, resulting in a multiarm star-like copolymer after the ring-opening of the two monomers. The crystallization ability of hbPCL is found to gradually weaken with the introduction of the branching structure, and its molecular mobility is improved substantially by esterification with butyric anhydride, following which a maximum mobility is realized at an intermediate level of branching. The butyl-esterified hbPCL (hbPCL-C4) is miscible with PVC, and their mixtures have excellent flexibility comparable to that of PVC/bis­(2-ethylhexyl) phthalate (DEHP). In particular, the stretchability of PVC/hbPCL-C4 is superior to that of PVC/DEHP, owing to its better structural homogeneity. Furthermore, PVC/hbPCL-C4 shows outstanding migration stability with the weight loss after extraction being >85% lower than that of PVC/DEHP.

Plasticizers Derived from Biomass Resources: A Short Review

“…Glycidol can be derived from glycerol, which is a major compound generated during the production of biodiesel from the transesterification of plant oils and lipid-rich surplus streams from slaughterhouses and the rendering industry [43]. Recently, hyperbranched esters deriving from glycidol via a green one-pot process using neither toxic solvents nor expensive catalysts have been used to replaced DOP as main plasticizer [44,45]. Figure 8 and Figure 9 show the two kinds of hyperbranched esters: alkyl terminal hyperbranched polyglycerol (alkyl-HPG) and butyl-esterified highly branched polycaprolactone.…”

Recent Attempts in the Design of Efficient PVC Plasticizers with Reduced Migration

“…In comparison to their linear counterparts, hyperbranched plasticizers exhibit high terminal functional group concentrations and, therefore, are able to increase free volume in polymer matrices. On the other hand, a high molecular weight plasticizer is usually difficult to process, especially because of its higher viscosity [ 48 , 49 , 50 , 51 ].…”

Preparation of Biomass-Based Ester End-Capped Hyperbranched Poly(ether)s via Facile One-Pot Reaction and Their Performance as Non-Toxic Plasticizers

“…In order to further track the facile one-pot reaction, 1 H NMR and 13 C NMR of BHP and BHE were investigated; they are shown in Figure 2b,c. In the 1H NMR of triethyl citrate, the strong peak ( Figure 2a) appearing at 1.25 ppm is associated with methyl protons, the peak ( Figure 2b) appearing at 2.89 ppm is attributed to protons of methylene next to the carbonyl group, and the two strong peaks (Figure 2c [25]. In the 1 H NMR of BHE, a new strong peak (Figure 2g) at 2.4 ppm is assigned to protons of methyl groups next to a carbonyl group, illustrating that esterification was finished.…”

“…The signal (Figure 2e) of carbons connected to hydroxyl groups appears at 73.30 ppm. The signals (Figure 2f,g) at 169.77 and 173.40 ppm correspond to carbons of carbonyl groups [25,26]. Compared with the 13 C NMR of triethyl citrate, new signals appear in the 13 C NMR of BHP; the new signals (Figure 2i,j) appearing at 21.50 ppm and 31.10 ppm are assigned to carbons next to ether groups, and the peaks at around 64 ppm and 72 ppm are attributed to carbons connected to hydroxyl groups that are derived from glycidyl units, indicating that the ring-opening polymerization was complete.…”