Intramolecular branching in polyvinyl acetate

Abstract

The polymerisation of vinyl acetate at various temperatures between+l8 "C. and -50°C. to various conversions has been carried out to obtain polymers with different degrees of branching. All polymer samples showed a fall in intrinsic viscosity after hydrolysis and reacetylation. This change is related to the amount of branching in the original polymer. but the relationship did not become clear for unfractionated material. One sample was fractionated, and the fractions studied by following the changes in intrinsic viscosity and osmotic molecular weight occurring on hydrolysis and reacetylation. The fractionated sample was made from radio-active initiator, which enabled the number of catalyst-fragments per molecule to be counted, An intramolecular branching mechanism is proposed to explain the incidence of branch points in molecules which are in effect linear. ZUSAMMENFASSUNG: Um Polymere mit verschiedenem Verzweigungsgrad zu erhalten, wurde die Polymerisation des Vinylacetats bei verschiedenen Temperaturen zwischen + 18°C und -50°C und mit verschieden groBen Umsatzen dnrchgefiiit. Alle diese Polymeren zeigten nach ihrer Hydrolyse und Reacetylierung einen Viskositatsabfall. Der Abfall hiingt vom Grad der Verzweigung im urspriinglichen Polymeren ab, doch lieB sich fiir unfraktionierte Produkte keine klare Beziehung erkennen. Daher wurden an den Fraktionen einer Probe die dnderungen der Viskositat und des osmotischen Molekulargewichts bei der Hydrolyse und Reacetylierung verfolgt. Da die fraktionierte Probe mit radioaktivem Initiator hergestellt worden war, konnte die Zahl der Initiator-Bruchstiicke pro Molekiil ausgezlihlt werden. Urn das Auftreten von Verzweigungspunkten in wirklich linearen Molekiilen zu deuten, wird ein intramolekularer Verzweigungsmechanismus vorgeschlagen.

Challenges in the Emulsion Co- and Terpolymerization of Vinylidene Fluoride

“…After C2 injection at t=15 min, a clear decrease of temperature followed by the increase and stagnation of pressure ( Figure 5) implied that the growing VDF-radicals were consumed by C2 units and no further propagation occurred. This is further confirmed by alike 1 H ( Figure 6) and 19 F (Figure 7) NMR spectra chemical shifts.…”

“…The 1 H NMR spectra obtained were calibrated with the aid of d6-DMSO peak (2.5 ppm). 19 F NMR were calibrated utilising a CF 3 peak from the fluorinated surfactant. 19 F NMR was used to determine the types of VDF additions in the polymer chain (i.e.…”

“…Functionality, copolymer sequences, copolymer composition and type of VDF addition were evaluated by19 F and 1 H Nuclear Magnetic Resonance (NMR), recorded on a Bruker…”

Emulsion Polymerization of Vinyl Acetate

“…Long chain branching is not easily quantified by NMR spectroscopy alone as the branch points are liable to be confused with those of the short branches produced by backbiting. It has also been shown that significant backbiting occurs in the polymerization of VAc [75][76][77] . Bugada et al 69 employed 13 C and 1 H NMR to determine total, i.e.…”

New Aldehyde‐Functional Methacrylic Water‐Soluble Polymers

“…One well‐known route to aldehyde‐terminated water‐soluble polymers is the selective oxidation of the minor fraction of cis ‐diol units within poly(vinyl alcohol) [42] . This water‐soluble polymer can be obtained via hydrolysis of poly(vinyl acetate), which contains such cis ‐diols as defect sites resulting from a small amount of head‐to‐head coupling during the free radical homopolymerization of vinyl acetate [43] . Oxidation is readily achieved in aqueous solution under mild conditions using sodium periodate to afford aldehyde‐capped poly(vinyl alcohol) chains [44] .…”