Copolymerization of dif fer ent amounts of sty rene (St) and 4-methylstyrene (MSt) us ing Cp*Ti(OBu)3/ MAO/TIBA cat a lyst was per formed in bulk state un der hy dro gen at mo sphere. With out the par t ic i pa tion of a re ac tion sol vent, poly mer iza tion pro ceeded well with better yield as com pared to those with to lu ene or cyc lohex ane as re ac tion sol vent. The sharp peaks in the 13 C NMR spec tra in di cate that both the St and MSt units in the co pol y mers are co-syndiotactic in na ture. The re ac tiv ity ra tio eval u ated from a Fineman-Ross plot suggests a better re ac tiv ity of MSt than St mono mers. Ex per i ments also in di cate that the de c rease of M n and M w , and the broad en ing of mo lec u lar weight dis tri bu tion were ac com pa nied by the higher hy dro gen pres sure employed in the poly mer iza tion stage, a re sult at trib uted to the chain trans fer re ac tion pro moted by the hy dro gen gas.
IN TRO DUC TIONSyndiotactic poly sty rene (sPS) pre pared from the methallocene cat a lysts has given rise to in dus trial and ac ademic in ter est due to its unique char ac ter, such as high thermal sta bil ity and low di elec tric con stant.1,2 To tai lor its proper ties, sev eral comonomers have been used to copolymerize with sty rene. 3-5 Among them, sub sti tuted styrenes such as methyl-, methoxy-, and chloro-substituted sty rene are ex amples of a con stant re search fo cus in view of their close re semblance to sty rene mono mers. Pre vi ously, poly(sty rene-co-4-methylstyrene)(PS-PMS) had been pro duced with syndiospecific titancene cat a lysts [2][3][4][5] (e.g. η 5 -CpTiCl3, η 5 -Cp*TiCl3, Ti(Bz)4, Ti(OMen)4, where Cp = C5H5, Cp* = C5Me5, Bz = C5H5CH2, Men = L-(-)-menthol) com bined with cocatalyst, methylalumoxane (MAO) in the pres ence of to lu ene as re ac tion sol vent. The re ac tiv ity ratios, r 1 and r2, of sty rene (St) and 4-methylstyrene (MSt) were thus eval u ated and val ues de pend ent on the cat a lysts ap plied. Judged from the sharp res o nance peaks in 13 C NMR spec tra, the re sult ing PS-PMSs were con sid ered to be co-syndiotactic in na ture. X-ray study on PS-PMS co pol y mers of dif fer ent com po si tions showed com pli cated poly mor phism be hav ior.
6In gen eral, the in crease of MSt con tent fa vors the α-form over the β-form and no β-form was ob tained once the MSt con tent ex ceeds 20 mol%. In this re search, syn the sis of PS-PMS co pol y mers were also at tempted, how ever, with a dif fer ent cat a lyst sys tem (CP*Ti(OBu)3/MAO/triisobutylaluminum(TIBA)) and without the pres ence of re ac tion sol vent. Cp*Ti(OBu)3 cat a lyst was em ployed in view of its good re ac tiv ity to ward MAO, and TIBA was used as scav en ger to pro mote both the cat a lyst ac tiv ity and syndio-specificity. 7,8 In this study, bulk poly meriza tion was per formed to dis tin guish from the so lu tion process used pre vi ously. [2][3][4][5] Here, the liq uid sty rene (St) and 4-methylstyrene (MSt) mono mers can func tion as re ac tion solvents dur ing poly mer iza tion. Bulk ...