Copolymers of Vinyl Acetate and Vinyl Carboxylates Bearing Branched C₇–C₉ Chains: Synthesis, Alcoholysis, and Properties

This contribution reported the radical copolymerization of vinyl acetate (VAc) with vinyl carboxylates bearing branched C₇–C₉ chains, including vinyl neononanoate (VV-9), vinyl neodecanoate (VV-10), and vinyl 2-ethylhexanoate (VV-EH), and the VAc units of the as-prepared copolymers were subsequently hydrolyzed to vinyl alcohol units in a base medium. With reactivity ratios of r₁ = 0.94 (VV-9) and r₂ = 0.96 (VAc), the copolymerization of VV-9 and VAc demonstrates an ideal azeotropic copolymerization. By simply adjusting the initial feed ratios, terpolymers of VV-9, VAc, and vinyl alcohol (PVVOH) with different compositions have been successfully prepared. As a proof-of-concept, their application as modifiers to improve the adhesive, hydrophilic, and oxygen barrier properties of low-density polyethylene (LDPE) was evaluated. When the PVVOH with 40 wt % VV-9 units was blended with LDPE, the dispersed PVVOH phase formed microdomains with a size of about 1 μm, and there was no observable two-phase structure. The water contact angles of the PVVOH/LDPE blends were reduced from 103.7 ± 0.9° to 51.1 ± 1.3° and retained after being soaked in water at ambient conditions for 30 days. PVVOH is also effective in improving the adhesion between LDPE and aluminum alloys. With the addition of 25 wt % PVVOH (20 wt % VV-9), the ultimate shear strength of the lap joint was effectively enhanced from 3.60 ± 0.17 MPa (pristine LDPE) to 4.87 ± 0.02 MPa. Furthermore, the addition of 20 wt % PVVOH reduced the oxygen transmission rates (OTR) of LDPE film from 145.3 to 52.2 cm³·mm·m^–2·day^–1·bar^–1.