Synthesis of a Vinyl Chloride-Methyl Acrylate Random Copolymer with Controllable Copolymer Composition and Its Processing Features in Rigid PVC

The copolymers of vinyl chloride (VC) with acrylates are widely used as special resins in multiple fields such as coatings, adhesives, and polymer processing aids. Nevertheless, the controllability in the copolymer composition is still a challenge owing to the big gap in reactivity ratio. In this paper, we conducted the nonaqueous copolymerization of VC with methyl acrylate (MA) in a mixed organic solvent (hexane/ethanol) without any suspending agent or emulsifier and intended to regulate the copolymer composition by dropping MA in a continuous mode. The promising results showed that a powdery vinyl chloride-co-methyl acrylate (PVMA) with ultralow number-average molecular weight (Mn, 9000–11 000) and submicrometer size (0.2–0.5 μm) is synthesized successfully, which is highly different from those of conventional aqueous polymerizations such as suspension and emulsion. More interestingly, varied PVMAx (x represents the actual mass fraction of MA in the copolymer) with relatively uniform and narrow dispersity in copolymer compositions (x = 1.7 ± 0.4, 3.2 ± 0.5, 5 ± 0.7, and 8.2 ± 0.4%) are obtained during the whole polymerization stage. In the batch process, the content of MA units in the copolymer decreased significantly with the increase of monomer conversion. Subsequently, the PVMA copolymers were employed as processing aids in rigid PVC and exhibited unique features. Stemming from its low Mn and the excellent compatibility with PVC matrix, the addition of PVMA can improve the plasticization efficiency significantly and thereby further enhance the mechanical performance. For instance, addition of 3 phr PVMA8.3 in the rigid PVC system can shorten the plasticization time from 104 to 52 s, enhance the tensile strength from 65 to 74 MPa, and increase the elongation at break 2-fold in comparison to the controlled PVC. In summary, this study provides a novel polymerization technique and strategy for the preparation of a vinyl chloride based copolymer resin with a low Mn and further composition control.