High molecular weight, medium density polyethylene

A multiple zone process which comprises:

• (a) polymerizing an olefin mixture that comprises:
• (i) from about 85 to about 98 wt % of ethylene;
• and
• (ii) from about 2 to about 15 wt % of a C3 to C10 α-olefin in a first reaction zone in the presence of a Ziegler catalyst at a temperature within the range of about 60° C. to about 110° C. at a hydrogen to ethylene molar ratio in the vapor space within the range of about 0.0005/1 to about 0.8/1 to produce a first polymer that has a density within the range of about 0.90 to about 0.944 g/cc and an MI2 less than about 0.5 dg/min;
• (b) removing volatile materials from the first polymer;
• and
• (c) transferring the first polymer to a second reaction zone and continuing the polymerization in the second reaction zone by adding more of the olefin mixture at a hydrogen to ethylene molar ratio in the vapor space within the range of about 1/1 to about 10/1 at a temperature within the range of about 65° C. to about 110° C. to produce a second polymer having a density within the range of about 0.92 to about 0.944 g/cc and an MI2 within the range of about 0.01 to about 0.5 dg/min;
• wherein about 35 wt % to about 65 wt % of the total polymer is produced in the first reaction zone.

A multiple zone process which comprises:

• (a) polymerizing an olefin mixture that comprises:
• (i) from about 85 to about 98 wt % of ethylene;
• and
• (ii) from about 2 to about 15 wt % of a C3 to C10 α-olefin in a first reaction zone in the presence of a Ziegler catalyst at a hydrogen to ethylene molar ratio in the vapor space within the range of about 1/1 to about 10/1 at a temperature within the range of about 65° C. to about 110° C. to produce a first polymer having an MI2 within the range of about 50 to about 600 dg/min and density within the range of about 0.94 to about 0.97 g/cc;
• (b) removing volatile materials from the first polymer;
• (c) transferring the first polymer to a second reaction zone and continuing the polymerization in the second reaction zone by adding more of the olefin mixture at a temperature within the range of about 60° C. to about 110° C. at a hydrogen to ethylene molar ratio in the vapor space within the range of about 0.0005/1 to about 0.8/1 to produce a second polymer having a density within the range of about 0.92 to about 0.944 g/cc and an MI2 within the range of about 0.01 to about 0.5 dg/min;
• and
• (d) thermally processing the second polymer in the presence of oxygen into a final polymer.

A multiple zone process which comprises:

• (a) polymerizing an olefin mixture that comprises:
• (i) from about 90 to about 100 wt % of ethylene;
• and
• (ii) from 0 to about 10 wt % of a C3 to C10 alpha olefin in a first reaction zone in the presence of a Ziegler catalyst at a hydrogen to ethylene molar ratio in the vapor space within the range of about 0.2/1 to about 10/1 at a temperature within the range of about 65° C. to about 110° C. to produce a first polymer;
• (b) removing volatile materials from the first polymer;
• and
• (c) transferring the first polymer to a second reaction zone and continuing the polymerization in the second reaction zone by adding more of the olefin mixture at a temperature within the range of about 60° C. to about 110° C. at a hydrogen to ethylene molar ratio within the range of about 0.05/1 to about 5/1 to produce a second polymer having a density lower than that of the first polymer and within the range of about 0.944 to about 0.965 g/cc and an MI2 lower than that of the first polymer and within the range of about 2 to about 100 dg/min;
• wherein about 35 to about 65 wt % of the total polymer is produced in the first reaction zone.