9 Developments in Vinyl Chloride Polymerization Kinetics and Technology Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 09/11/18. For personal use only.
Graft Copolymers F. WOLLRAB, OBSOMER
J.
DUMOULIN,
F.
DECLERCK,
P.
GEORLETTE,
and
M.
Solvay et Cie S.A., Centre Recherche, rue de Ransbeek, 310, 1120 Brussels, Belgium
To obtain vinyl chloride graft copolymers with a high backbone-polymer content of the desired homogeneous morphology, all of the liquid vinyl chloride must be absorbed by the backbone polymer during polymerization. This condition is realized when, at polymerization temperature, the partial pressure of vinyl chloride in the autoclave is lower than the vapor pressure of pure vinyl chloride. On this basis, a graft polymerization process for the production of homogeneous vinyl chloride/polyethylene graft copolymers with high backbone-polymer content has been developed. One of these graft copolymers has already found industrial application as a peroxide-crosslinkable material in cable insulation. The graft polymerization process also applies to rubbery ethylene-propylene copolymers and amorphous epichlorohydrin polymers.
rafting of vinyl chloride ( V C ) onto various polymer backbones is a useful way of preparing modified polyvinyl chloride ( P V C ) type resins. This paper deals with the grafting of vinyl chloride onto polyethylene ( P E ) , onto rubbery ethylene-propylene copolymers ( E P R ) , and onto amorphous epichlorohydrin polymers. This kind of P V C modification should lead to resins with improved processability or i m pact strength, or to crosslinkable polymers. Among the various techniques of grafting vinyl chloride described in the literature ( 1 ), we chose the one based on the polymerization, i n aqueous suspension, of vinyl chloride in the presence of the backbone polymer with an organic peroxide. Some important improvements i n this technique are the main subject of this paper. 135
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P O L Y M E R I Z A T I O N
KINETICS
A N D
T E C H N O L O G Y
W i t h a polyethylene backbone, this grafting technique w i l l not yield pure poly(ethylene-g-vinyl chloride)—"pure graft copolymer'—but a mixture of this compound with PVC homopolymer and unmodified poly ethylene. W e call this raw graft polymerization product " V C / P E graft copolymer." Sometimes, we add its gross composition between parentheses—for example, V C / P E (50-50) graft copolymer. The same statement applies to the other backbone polymers. The grafting of vinyl chloride onto polyethylene by following these principles has already been studied i n several industrial laboratories (25 ) . In the case of the EPR backbone, earlier work was essentially done by Natta (6) and Severini (7), and processes are described i n the pat ents literature (8,9). As far as we know, that work d i d not lead to com mercial applications. Graft Polymerization
Processes
Our own work i n this field followed two lines: preparation of graft copolymers with high backbone-polymer content, such as V C / E P R (5050) graft copolymers; and preparation of products with low backbonepolymer content, such as V C / E P R (95-5) graft copolymers. Graft Copolymers with High Backbone-Polymer Content. Work on V C / P E graft copolymers of this type led to a process (10) now being tested on pilot-plant scale. Its industrial application is being considered. The process is also applicable to other backbone polymers that are suffi ciently swelled by this monomer. Most grades of ethylene-propylene Table I.
Characteristics of the Polyethylene Backbone Polymers Type
Microthene Ν 710
Process
Alkathene WRM 19
H i g h Pressure
Particle F o r m Producer Density g / c m ( A S T M D 1505) M e l t index g/10 min ( A S T M D 1238) Crystallinity, % (differential thermal analysis) Double bonds/1000 C atoms trans vinyl vinylidene CH3/IOOO C atoms 3
Powder USI 0.916
Pellets ICI 0.916
22
20
26
28
0.09 0.04 0.64 15
0.09 0.02 0.53 16
EUex 6087 Low Pressure Fluff Solvay 0.960 3.7 73
