It has long been recognized that internal necessary for the processing of polyvinyl chloride resins.  These materials reduce the internal friction within the polymer melt and, in turn, the heat build-up when the polymer is subjected to stress.  Because of the characteristic high melt viscosities of rigid PVC, an internal lubricant is considered necessary to improve flow properties.  Its use results in an economic advantage in that less work need be expended at a given set of processing conditions.  In addition, the appearance of the product is improved.  An internal lubricant also promotes fusion.  Conversely, a lack of lubricant causes heat build-up during processing and results in a rough surface and a degraded product. 
Perhaps the most widely used internal lubricants are the oleate and stearate esters of glycerol, though numerous other materials have been taught by the prior art.  For example, U.S. Pat.  No.  3,479,309 describes the use of fatty acid or ester lubricants such as stearic, palmitic, myristic and hydrogenated tallow fatty acid and the glycerides thereof.  The addition of unsaturated fatty acids or the polyvalent metal salt thereof is also described so that the blend has an iodine number of from 2.5 to 20. 
U.S. Pat.  No.  3,679,619 mentions the use of long chain acids and alcohols such as stearic acid, nonadecanoic acid, arachidic acid, montanic acid, stearyl alcohol, carnaubyl alcohol, cetyl alcohol and montanyl alcohol; esters of polyhydric alcohols and short chain monocarboxylic acids such as glycerol monostearate, ethylene glycol dilaurate, 2-ethylhexane diol-1,3-distearate, ethylene glycol di-2-ethylhexanoate and octylene glycol dicaprylate and esters of dicarboxylic acids with short chain monohydroxy-alcohols, such as diisooctyl sebacate and dilauryl azelate. 
Monoglycerine esters, stearic acid and stearic alcohol are noted in U.S. Pat.  No.  3,981,838 and derivatives of trimellitic acid or anhydride are proposed. 
In U.S. Pat.  No.  3,988,330 it is claimed that the reaction product of mono- and polyfunctional alcohols with high molecular weight branched and straight chain aliphatic monocarboxylic acids obtained from alpha-olefins containing 22 or more carbon atoms are particularly useful for internal-external lubrication of PVC homopolymers and copolymers.  The mono- and polyfunctional alcohols include monohydric alcohols, di- and higher polyhydric alcohols and ether alcohols, which can be either mono- or polyfunctional.  The aliphatic monohydric alcohols include ethanol, n-propanol, sec-propanol, n-butanol, t-butanol, isoamyl alcohol, n-hexanol, 2-ethylhexanol, n-octanol, isodecanol, capryl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol and oxo alcohols such as tridecyl alcohol, which is mainly tetramethyl-1-nonanol, and hexadecyl alcohol, which is a complex mixture of primary alcohols.  The aliphatic polyols named are ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2,3-dimethyl-2,3-butanediol, trimethylol propane, mannitol, sorbitol, glycerol and pentaerythritol. 
Known PVC lubricants are described in U.S. Pat.  No.  4,081,413 including mineral oil; fatty acids; synthetic waxes of the fatty amide and ester type; octyl stearate; calcium stearate; the corresponding citrates and citrate esters, particularly the citrate esters of medium- (e.g., 10 carbon atoms and above) and long-chain carboxylic acids; and the glyceride esters of the medium- and long-chain saturated and unsaturated carboxylic acids. 
Ethylene oxide-capped polyether propylene glycol block copolymer lubricants for PVC are taught in U.S. Pat.  No.  4,168,256.  Graft polyblends of acrylate esters to improve PVC flow properties are described in U.S. Pat.  No.  4,212,958. 
Though the above-described internal lubricants have achieved the intended result, they have not been ideal for a variety of reasons.  For example, compounds containing the glycerol esters can degrade during processing, which causes yellowing to occur in clear applications.  This initial degradation is accelerated by the presence of unreacted.  glycerol.  Furthermore, where the compound is initially transparent, the optical properties (clarity and haze) are often adversely affected by contact with various fluids such as water, vinegar and alcohol.