Thermal degradation of PVC synthesized with a titanocene
catalyst II. Complementary isothermal results
, R. Benavides
, G. Cadenas-Pliego, H. Maldonado
Centro de Investigacio´n en Quı´mica Aplicada, Blvd. Enrique Reyna H. 140, Saltillo Coahuila 25100, Mexico
Received 30 June 2006; received in revised form 17 January 2007; accepted 17 January 2007
Available online 9 February 2007
The use of an isothermal degradation method on metallocene produced PVC and commercial PVC, under nitrogen and air atmospheres, re-
veals more details about degradation routes. Without regard to the polymer origin, the hydrochloric acid release occurs in two steps, which are
reﬂected in molecular weight only under a nitrogen atmosphere; otherwise, the oxygen appears to be included in the scission/crosslinking pro-
cess. On the one hand, Met PVC has unsaturations from its synthesis, producing a faster HCl release compared to Com PVC; consequently, its
degradation resistance is lower. On the other hand, Com PVC has more oxidized species and has a natural tendency to include more of them.
Surface area seems to have an important effect and is directly related to the rate of hydrochloric acid release. The latter is not supported by the
chain oxidation mechanism, making the effect of the applied atmosphere more critical to the results obtained from the degradation experiments.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Synthesis; Poly(vinyl chloride); Degradation; Metallocene catalyst
The low-heat resistance of PVC is known to be caused by
the structural defects inherent in this material because the tra-
ditional polymerization method permits the eventual monomer
head-to-head linking, instead of the correct head-to-tail bond.
These abnormal sequences are the sites of such defects,
namely double bonds, tertiary chlorine (branching) and allylic
chlorine, where each one of these is able to begin the hydro-
chloric acid release by the well-known zipper mechanism.
The latter produces colouration, chain scission and loss of
many desirable properties [1,2]. Nowadays it is believed that
these structural defects can be eliminated in PVC by limiting
the bonding to only head-to-tail vinyl chloride units during the
polymerization reaction. This would be possible mainly by
substituting the radical reaction mechanism with a different
mechanism. Using this approach attempts have been made us-
ing anionic polymerization [3,4], coordination chemistry poly-
merization [5e7], photopolymerization  and living radical
polymerization ; but, as can be seen from the papers, the
degradation feasibility still remains without showing related
results. This paper describes the thermal degradation of PVC
produced by coordination polymerization of vinyl chloride
using a half sandwich titanocene catalyst activated with low
catalyst/MAO ratios  and is a continuation of previously
reported thermal degradation behaviour , where the resis-
tance of the metallocene produced polymer was higher during
dynamic evaluations (TGA) but lower for static degradation
methods. The difference in chemical origin and inherent mor-
phology between produced and commercial PVC is believed
to be the reason.
The Met PVC was produced in the laboratory as described
in detail elsewhere [10,11], and compared with a commercial
* Corresponding author.
E-mail address: firstname.lastname@example.org (R. Benavides).
Working now for Enertec Me
xico e Johnson Controls Inc.
0141-3910/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
Polymer Degradation and Stability 92 (2007) 1133e1140