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Polymerization of 2-(4-halophenyl)-1,3-butadiene(2-XPB)and their copolymerization with isoprene using a yttrium catalyst have been examined.The β-diketiminato yttrium bis(alkyl)complex(1)activated by[Ph3C][B(C6F5)4]and Al'Bu3 shows high cis-1,4-selectivity(＞98％)for the polymerization of 2-XPB(2-XPB = 2-FPB,2-CIPB and 2-BrPB)to afford halogenated plastic poly(dienes)with glass transition temperatures of 30-55 ℃.Moreover,the copolymerization of 2-XPB with isoprene(IP)has also been achieved by this catalyst,and the insertion ratios of 2-XPB can be facilely tuned in a full range of 0％-100％simply by changing the 2-XPB-to-IP ratio.Quantitative hydrogenation of cis-1,4-poly(2-XPB)results in perfect alternating ethylene-halostyrene copolymers,and an alternating copolymer of 4-vinylbenzoic acid with ethylene is obtained by a consecutive reaction of ethylene-4-bromostyrene copolymer with nBuLi,CO2 and HCI.