| 摘要 |
PCT No. PCT/GB96/00980 Sec. 371 Date Apr. 13, 1998 Sec. 102(e) Date Apr. 13, 1998 PCT Filed Apr. 24, 1996 PCT Pub. No. WO96/34018 PCT Pub. Date Oct. 31, 1996A polymeric material comprising at least first and second polymer parts, which first part has a number average molecular weight higher than that of the second part and which first and second polymer parts each comprise a respective polymer part derived from at least one ethylenically unsaturated monomer, is prepared by a process which comprises the steps of (1) preparing, by aqueous suspension polymerisation the first, higher molecular weight polymer part in the presence of a free radical initiator, but in the absence of a chain transfer agent to form a suspension of the first, higher molecular weight part and thereafter (2) preparing by aqueous suspension polymerisation the second, lower molecular weight part, which preparation step (2) is carried out in the presence of the suspension of the first, higher molecular weight part, a free radical initiator and a catalytic chain transfer agent (CCTA). Step (2) may be continued to provide, additionally, a third polymer of a molecular weight intermediate that of the first and second polymers. A polymeric material thus obtainable has a PDi of at least 5 and a skewed molecular weight distribution in which the first-third polymers are present in successively increasing amounts. The polymeric material is especially suitable for use as a binder in a toner composition. |
