New Insight into the Formation of Structural Defects in Poly(Vinyl Chloride)

Abstract

The monomer conversion dependence of the formation of the various types of defect structures in radical suspension polymerization of vinyl chloride was examined via both 1H and 13C NMR spectrometry. The rate coefficients for model propagation and intra- and intermolecular hydrogen abstraction reactions were obtained via high-level ab initio molecular orbital calculations. An enormous increase in the formation of both branched and internal unsaturated structures was observed at conversions above 85%, and this is mirrored by a sudden decrease in stability of the resulting PVC polymer. Above this threshold-conversion, the monomer is depleted from the polymer-rich phase, and the propagation rate is thus substantially reduced, thereby allowing the chain-transfer processes to compete more effectively. In contrast to the other defects, the chloroallylic end groups were found to decrease at high conversions. On the basis of the theoretical and experimental data obtained in this study, this decrease was attributed to copolymerization and abstraction reactions that are expected to be favored at high monomer conversions. Finally, a surprising increase in the concentration of the methyl branches was reported. Although a definitive explanation for this behavior is yet to be obtained, the involvement of transfer reactions of an intra- or intermolecular nature seems likely, and (in the latter case) these could lead to the presence of tertiary chlorine in these defects.

Preparation of MgAl LDHs Intercalated with Amines and Effect on Thermal Behavior for Poly(vinyl chloride)

“…The peak in MgAl-CO(NH 2 ) 2 is a little stronger due to the greater concentration of carbonate. While other absorption bands below 800 cm −1 are associated with the stretching and bending modes of metal-oxygen bonds [23]. The results proved CO(NH 2 ) 2 , 4 …”

“…IR spectra of the samples were shown in Figure 2. FT-IR spectra display the characteristic bands for OH and CO bonds that are abundantly present in MgAl-LDH [23]. A broad band is visible (3436 -3487 cm −1 ) that may be attributed to stretching vibrations of the hydroxyl ions and hydroxyl groups of the intercalated water.…”

Structures of LDHs Intercalated with Ammonia and the Thermal Stability for Poly(vinyl chloride)

“…The broad ), the peak resulted from the asymmetric stretching vibration for C-O bond in 2 3 CO − group of LDHs appeared at 1320 -1380 cm −1 , significantly shifting to the lower wave number, which attests carbonate ion inserted between layers of LDHs are not really disengaged ions and have strongly interacted with interlaminar H 2 O molecules by hydrogen bonding. Other absorption peak appearing near 700 cm −1 are assigned to the bending and stretching vibration modes for metal-oxygen bonds [10]. …”

Ab Initio Study of Poly(vinyl chloride) Propagation Kinetics: Head‐to‐Head versus Head‐to‐Tail Additions

“…The studied aspects range from propagation kinetics, substituent effects, and solvent effects to properties of short chain branching. Relevant references published in this area during the last decade are the work of Radom, [15][16][17] Gilbert, [18][19][20] Heuts, [21,22] Aviyente, [23] and Coote [10] and their co-workers. Recently, a combined experimental and theoretical study was published concerning the formation of structural defects in PVC.…”

“…Recently, a combined experimental and theoretical study was published concerning the formation of structural defects in PVC. [10] The monomer conversion dependence of the formation of various types of defects was measured by 1 H and 13 C NMR spectroscopy. Ab initio calculations were performed on four model reactions in an attempt to explain certain trends in the measured defect concentrations that could not be understood via the commonly accepted reaction schemes for the formation of structural defects in PVC.…”