Vinylidene Chloride Polymers

Abstract

Vinylidene chloride is a versatile monomer used primarily for making Vinylidene chloride copolymers. These copolymers are mostly used in food packaging to provide a good barrier‐to‐mass transport. Most applications rely on the low permeation of oxygen, carbon dioxide, and water vapor. However, the polymers have also been shown to have good barrier to flavors and aromas. Thus, a barrier layer of one of these copolymers in a package structure not only prevents spoilage of the food item but prevents flavor “scalping” on the supermarket shelf. These copolymers are available in three forms. First, the resin for extrusion into film or sheet represents the largest segment. This segment includes monolayer and coextruded film and coextruded sheet. Second, a number of emulsion resins are used for solution applications. A thin layer is coated onto a substrate. Third, copolymer latexes are used for paper coatings, etc. The coatings from solution or latex dry clear. Vinylidene chloride homopolymer does not have commercial application because its melting temperature is too high to permit extrusion without degradation, and it does not dissolve in a suitable solvent for coating.

Ab initio emulsion RAFT polymerization of vinylidene chloride mediated by amphiphilic macro‐RAFT agents

“…In this article, we developed a method to prepare VDC copolymer with high, controlled molecular weight (>25 kg mol −1 ) and well‐defined structure via the surfactant‐free Ab initio RAFT emulsion polymerization using the amphiphilic poly(acrylic acid‐ b ‐styrene) macro‐RAFT agent. Methyl acrylate (MeA) was chosen as the comonomer as it is commonly used in PVDC modification and has a near copolymerization reactivity ratio to VDC ( r VDC = 1.0, r MA = 1.0) . Effects of the macro‐RAFT structure and concentration on the colloidal stability, kinetics, and controllability of polymerizations were investigated.…”

“…Because of the significant chain transfer reaction from the growing macromolecular radicals to VDC monomer, VDC polymers prepared by the conventional free radical polymerization exhibit the structural defects and poor thermal stability . Moreover, the PVDC latex usually shows even lower thermal stability than the PVDC powder prepared by the suspension polymerization, due to the presence of a greater amount of emulsifier and other additives accelerating the polymer degradation. During the storage of PVDC latex, the hydrogen chloride produced by thermal degradation of PVDC and formation of oxygen‐containing defect structures would lead to the coloration and coagulation of latex .…”

“…Moreover, the PVDC latex usually shows even lower thermal stability than the PVDC powder prepared by the suspension polymerization, due to the presence of a greater amount of emulsifier and other additives accelerating the polymer degradation. During the storage of PVDC latex, the hydrogen chloride produced by thermal degradation of PVDC and formation of oxygen‐containing defect structures would lead to the coloration and coagulation of latex . Conversely, the emulsifier existed in the latex would transfer into the VDC polymer film after coating.…”