Erling M. Sörvik

Formation of anomalous structures in PVC and their influence on the thermal stability: 2. Branch structures and tertiary chlorine

Abstract Branch structures were determined in fractions of a commercial suspension of PVC (S-PVC) and experimental PVC samples obtained at subsaturation conditions (U-PVC). The analyses were performed with 13 C n.m.r. spectroscopy at 50.31 MHz after reductive dehalogenation with tributyltinhydride. With increasing monomer starvation U-PVC was found to have an increasing amount of butyl and long chain branches (LCB). A polymer prepared at 55°C and 59% of the saturation pressure of vinylchloride had 3.4 butyl branches and 2.0 LCB per 1000 monomer units. In the S-PVC series the total content of these two structures varied between 0.5 and 1.0 per 1000 monomer units. By using tributyltindeuteride as reducing agent the structure of the butyl branches could be determined as ∼CHClCH 2 CCl(CH 2 CHClCH 2 CH 2 Cl)CH 2 CHCl∼. A major part of the LCB points also contained tertiary chlorine. The formation of LCB is suggested as occurring after abstraction of hydrogen from the polymer chain by macroradicals and chlorine atoms. The latter will lead to LCB points with tertiary hydrogen and internal double bonds. The rate of dehydrochlorination at 190°C in nitrogen could be related to the amount of tertiary chlorine (correction coefficient=0.97). It was assumed that tertiary chlorine is the most important labile structure in PVC.

Formation of anomalous structures in PVC and their influence on the thermal stability: 3. Internal chloroallylic groups☆

Abstract Internal double bonds were determined by oxidative cleavage in fractions of a commercial suspension PVC (S-PVC) and experimental PVC samples obtained at subsaturation conditions (U-PVC). The changes in molecular weight were measured by g.p.c. and viscometry. The oxidation was performed by ozonolysis in tetrachloroethane solution at −20°C. Oxidation by potassium permanganate in dimethylacetamide solution at −10° to +50°C was also studied. However, this method was found to give erratic results. With increasing monomer starvation the number of internal double bonds increased. In the original S-PVC sample the internal double bond content was 0.2 1000 VC . The formation of double bonds is assumed to be the result of an increased tendency, by chlorine atoms, to attack on the methylene groups in the chain. Hydrolytic cleavage and 1H n.m.r. measurements did not give any evidence of ketoallylic groups. With increasing chloroallylic group content the U-PVC samples showed an increased rate of dehydrochlorination at 190°C in nitrogen. The S-PVC fractions, however, showed a decreased rate. However, the thermal stability in both series of samples could be related to the tertiary chlorine content. Butyl and long chain points with tertiary chlorine are more frequent than the internal chloroallylic groups. It was assumed that tertiary chlorine is the most important labile structure not only in U-PVC but also in ordinary PVC.

Formation of Anomalous Structures in PVC and Their Influence on Thermal Stability. I. Endgroup Structures and Labile Chlorine Substituted by Phenol

Abstract The thermal stability and structural details were compared for fractions of S-PVC and a series of “U-PVC” prepared at sub-saturation conditions. Molecular weights and long chain branching were obtained by GPC and viscometry. “Labile chlorine” was determined by phenolysis, double bonds by bromination, and endgroup structure by NMR. The rate of thermal dehydrochlorination was determined in nitrogen at 190°C. In S-PVC there are few tertiary chlorine, and phenolysis therefore measures allylic chlorine. By NMR it was found that ∼CH2-CH[dbnd]CH[sbnd]CH2Cl is the main unsaturated structure. Phenolysis and bromination therefore mainly give a measure of this group. The main saturated chain end is ∼CHCl[sbnd]CH2Cl. These groups account for 80% of the endgoups and are the result of the mechanism of chain transfer to monomer: head-to-head addition followed by 1,2-Cl migration and Cl· elimination. They have only a weak influence on the thermal stability, however. U-PVC, on the other hand, shows a strong relat...

Polymerization of Vinyl Chloride at Reduced Monomer Accessibility. I. Polymerization at Subsaturation Pressure with Suspension PVC as a Seed

Abstract Vinyl chloride was polymerized at 40–96% of saturation pressure in water suspended systems at 55°C with suspension PVC as a seed. The monomer was continuously charged as vapor from a storage vessel kept at lower temperature. Characterization included molecular weight distribution (MWD) and degree of long-chain branching (LCB) by GPC and viscometry, thermal dehydrochlorination, microscopy, and technical standard tests. A granular seed was necessary to obtain granular polymer and reasonable polymerization rate. In properly seeded systems with monomer-soluble initiator, crust formation is very low. With monomer-soluble initiator the polymerization reactions are restricted to the seed polymer, comprise its total structure, reducing its porosity. At pressure near saturation, molecular weight increased with conversion, and autoacceleration occurred. The changes in molecular weight are presumably due to the lack of a liquid monomer phase, which reduces the mobility of the radicals leading to decreased t...