11 Preparation of Acrylonitrile-Styrene Copolymers by Calorimetrically Controlled
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Monomer Feeding B.
N.
HENDY
Research Department, Imperial Chemical Industries, L t d . , Plastics Division, W e l w y n Garden C i t y , Hertfordshire, E n g l a n d
A fairly general solution to the problem of composition drift during batch copolymerization permits making copolymer in sufficient quantities for evaluation as a thermoplastic. By polymerizing in a calorimeter, it was possible to control monomer feed accurately in relation to rate of polymerization. The apparatus has a 2-l reaction vessel which is basically a distillation calorimeter that controls the batch temperature and measures the reaction rate and the total integrated amount of reaction, or heat, to which is aligned the monomer feed. Acrylonitrile-styrene copolymers rich in acrylonitrile were prepared by feeding styrene. The heterogeneous product formed without feeding was useless as a thermoplastic, but the homogeneous product made by feeding was very good. The mechanical properties of these copolymers improved with increasing acrylonitrile content.
T
he composition of a copolymer produced b y simple batch copolymerization of monomers w i t h very different relative reactivities changes as the reaction proceeds so that a heterogeneous product is obtained. This is w e l l illustrated b y the copolymerization of acrylonitrile ( A N ) and styrene (S) because mixtures of these monomers consisting mainly of A N form instantaneous copolymers that contain m u c h more styrene than the parent mixture. Thus, as such polymeriza tions proceed, the concentration of styrene i n the remaining monomer mixture falls progressively, and consequently the composition of the copolymer changes accordingly. This tendency to styrene enrichment is tabulated i n Table I w h i c h summarizes the whole composition range from acrylonitrile-rich mixtures to styrene-rich mixtures. In the former, styrene enrichment is pronounced. H o w ever, it is almost nonexistent i n the latter, a n d thus styrene-rich copolymers can be made without the problem of composition drift. I n light of this, it is noteworthy that, whereas styrene-rich copolymers have long been established commercially, acrylonitrile-rich copolymers have only recently been investi gated i n detail ( I ) . 115
In Copolymers, Polyblends, and Composites; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.
116
COPOLYMERS,
Table I.
Downloaded by UNIV OF MINNESOTA on July 18, 2013 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0142.ch011
Sp , mole %
Sp:S
