Poly Vinyl Chloride Homopolymer

Siding. The resin most used for siding is poly(vinyl chloride) homopolymer, compounded with modifiers, stabilizers, and pigments. Modifiers are most often acryhc esters, followed by chlorinated polyethylene or ethylene—vinyl acetate, used at 6—8 phr (parts per hundred resin). The modifier increases the impact strength of the rigid PVC. 

The polymerization reaction in aqueous suspension of vinyl chloride in the presence of an ethylene-propylene saturated elastomer occurs with the formation of poly (vinyl chloride) homopolymer and rubber-poly (vinyl chloride) grafted copolymers. The first grafting reaction proceeds as far as diffusion of the monomer inside the particles in suspension is possible afterwards, some chain branching of grafted PVC is possible. Under our experimental conditions the amount of grafted rubber does not exceed 60% of the initial rubber and is little influenced by the type of initiator used. 

The vinyl acetate content of such materials ranges between 3 and 40%, and the copolymers are more soluble and pliable than poly(vinyl chloride) homopolymer. They can be shaped mechanically at lower temperatures than homopolymers with the same degree of polymerization and are used mainly in surface coatings and products where exceptional flow and reproduction of details of a mold surface are needed. 

Commercially, by far the biggest amount of poly(vinyl chloride) homopolymer is produced by suspension polymerization and, to a lesser extent, by emulsion and bulk polymerization. Very little polymer is formed by solution polymerization. 

Schmidt, J.J., Gardella Jr., J.A., Salvati Jr., L. Surface studies of polymer blends. 2. An ESCA and IR study of poly(methyl methacrylate)/poly(vinyl chloride) homopolymer blends. Macromolecules 22(12), 4489 1495 (1989)... 

D3749 Residual Vinyl Chloride Monomer in Poly(Vinyl Chloride) Homopolymer Resins by Gas Chromatographic Headspace Technique 6401... 

Poly(vinyl chloride) is Hsted on the TSCA inventory and the Canadian Domestic Substances List (DSL) as ethene, chloro-, homopolymer [9002-86-2]. Because polymers do not appear on the European Community Commercial Chemical Substances listing or EINECS, poly(vinyl chloride) is listed through its monomer, vinyl chloride [75-01-4]. In the United States, poly(vinyl chloride) is an EPA hazardous air pollutant under the Clean Air Act Section 112 (40 CER 61) and is covered under the New Jersey Community Right-to-Know Survey N.J. Environmental Hazardous Substances (EHS) List as "chloroethylene, polymer" with a reporting threshold of 225 kg (500 lb). 

Commercial interest in poly(vinyl chloride) was revealed in a number of patents independently filed in 1928 by the Carbide and Carbon Chemical Corporaration, Du Pont and IG Farben. In each case the patents dealt with vinyl chloride-vinyl acetate copolymers. This was because the homopolymer could only be processed in the melt state at temperatures where high decomposition rates occurred. In comparison the copolymers, which could be processed at much lower temperatures, were less affected by processing operations. 

Mixtures of two or more monomers can polymerize to form copolymers. Many copolymers have been developed to combine the best features of each monomer. For example, poly(vinyl chloride) (called a homopolymer because it is made from a single monomers) is brittle. By copolymerizing vinyl chloride with vinyl acetate, a copolymer is obtained that is flexible. Arrangement of the monomer units in a copolymer depends on the rates at which the monomers react with each other. Graft copolymers are formed when a monomer is initiated by free radical sites created on an already-formed polymer chain. 

ISO 305, Plastics - Determination of thermal stability of poly(vinyl chloride), related chlorine-containing homopolymers and copolymers and their compounds - Discoloration method, 1990. 

Core-shell emulsion polymers with a core or rubbery stage based on homopolymers or copolymers of butadiene are used as impact modifiers in matrix polymers, such as ABS, for styrene acrylonitrile copolymer methyl methacrylate (MMA) polymers, poly(vinyl chloride) (PVC), and in various engineering resins such as polycarbonate) (PC) poly(ester)s, or poly(styrene)s, further in thermosetting resins such as epoxies. 

A comparison was accomplished with a conventional poly (vinyl chloride) (Table VII) having a molecular weight comparable with that of the homopolymer present in the crude grafting product. 

The thermal stability of poly(vinyl chloride) is improved greatly by the in situ polymerization of butadiene or by reaction with preformed cis-1,4-polybutadiene using a diethyl-aluminum chloride-cobalt compound catalyst system. The improved thermal stability at 3-10% add-on is manifested by greatly reduced discoloration when the modified poly-(vinyl chloride) is compression molded at 200°C in air in the absence of a stabilizer, hydrogen chloride evolution at 180°C is retarded, and the temperature for the onset of HCl evolution and the peak decomposition temperature (DTA) increase, i.e. 260°-280°C and 290°-325° C, respectively, compared with 240°-260°C and 260°-280°C for the unmodified homopolymer, in the absence of stabilizer. The grafting reaction may be carried out on suspension, emulsion, or bulk polymerized poly(vinyl chloride) with little or no change in the glass transition temperature. 

A similarly poor efficiency in extraction can also be seen in Fig. 11, where the extraction result for the product obtained by the radiation grafting of styrene onto polyethylene terephthalate)(PET) fibers13 is shown. In this case the unreacted PET can be extracted after most of PS homopolymer has been extracted by repeated solution-precipitation of the sample. It should be mentioned here that the solution procedure is also necessary to extract the unreacted PET. Such a solution-precipitation procedure is also necessary for nylon-styrene13 and poly(vinyl chloride)-acrylo-nitrile14 graft products so as to remove the homopolymers to a sufficient extent. 

When the polymers were analyzed for their content of homopolymer, it was found that the acrylonitrile polymer is soluble in chlorobenzene and the vinyl chloride polymer in toluene. Since chlorobenzene is unable to dissolve polyacrylonitrile and toluene cannot dissolve poly (vinyl chloride), it must be assumed that no homopolymer has been formed. This has been verified by fractionations. It is possible to extract with methanol from the vinyl acetate polymer 33% of a substantially pure polyvinyl acetate with a vinyl acetate content of 95%. Hence, acrylo-... 

Except for the acetic acid peak, the pyrogram of poly(vinyl chloride-co-vinyl acetate) is very similar to that of poly(vinyl chloride). However, this is easily explained by the fact that both poly(vinyl chloride) and poly(vinyl acetate) homopolymers have a similar pyrolysis mechanism, with the elimination of side chain groups and formation of double bonds along the polymeric backbone. After the acetic acid and/or HCI elimination the remaining polymeric structure undergoes the same process of formation of unsaturated and aromatic molecules. This explains the presence of a number of aromatic compounds that are identical in the pyrolysate of the two homopolymers (see Section 6.5 for the pyrolysis of poly(vinyl acetate)). 

Poly(vinyl chloride) may also be internally plasticized by copolymerization of vinyl chloride with vinyl acetate, as mentioned earlier. It is not possible to obtain the same result from a mixture of the same proportions of PVC and poly(vinyl acetate) homopolymers. Incorporation of vinyl acetate into the polymer chains produces the intimate association of components needed to lower the temperature required for processing in much the same way as an added plasticizer does. Important end uses for poly(vinyl chloride-co-vinyl acetate) at low levels of vinyl acetate incorporation are phonograph records and floor tiles, and also for sheeting, when added filler will also be used. 

More pounds of homopolymers are produced than any other vinyl resin. Figure 1 shows the typical reaction of monomeric vinyl chloride to form poly (vinyl chloride). Polymers of this nature represent the ultimate in chemical and physical properties. 

---