Process for controlling production of in-situ thermoplastic polyolefins and products

In a gas-phase process for producing thermoplastic polyolefins in multiple reactors wherein propylene is homopolymerized in a first reactor maintained at 50.degree. C. to 100.degree. C. and 250 psig to 650 psig in the presence of a supported high activity Ziegler-Natta catalyst comprised of a titanium-containing catalyst component and organoaluminum cocatalyst component and the product produced therein is fed to a second reactor maintained at 25.degree. C. to 80.degree. C. and 100 psig to 500 psig where propylene is copolymerized with ethylene, to obtain high rubber content modified polypropylene having reduced hexane extractables and improved paintability, the improvement comprising:

• (a) calculating a control parameter Q.sub.c using eight integrated areas of the .sup.13 C NMR spectrum corresponding to molecular structural features for copolymers of propylene and ethylene in accordance with the equation:
• ##EQU3## where A=1.167R.sub.1 +0.75R.sub.2 +1.5R.sub.3 +1.5R.sub.4 +1.167R.sub.8
• B=0.667R.sub.1 +0.5R.sub.2 +R.sub.5 +R.sub.6 +R.sub.7 +0.667R.sub.8
• and R.sub.1 through R.sub.8 have the following peak assignments:
• ______________________________________ R.sub.1 37.9 PPM R.sub.2 37.5 PPM R.sub.3 33.2 PPM R.sub.4 31.2-30.9 PPM R.sub.5 30.4 PPM R.sub.6 30.0 PPM R.sub.7 27.4 PPM R.sub.8 24.9 PPM;
• ______________________________________
• (b) selecting limits of Q.sub.c for the process within the range 0.65 to 1.0;
• (c) determining the actual value of the parameter, Q.sub.A, for the polymer obtained from the second reactor;
• and
• (d) controlling the ethylene feed to maintain Q.sub.A within the limits defined in (b).