The synthesis of well-defined and constant composition terpolymer containing multi-alternating modules via LAP

Abstract

The combination of “DPE-alternating chemistry” and “Pentadiene-alternating strategy” offers a novel LAP routine to afford well-defined and sequence-controlled copolymers with diversified alternating series modules. By adjusting the feed ratio of comonomers (1,1-diphenylethylene = D, 1,3-pentadiene = P, and styrene derivatives = S), the polymer composition can be controlled to prepare a series of sequence-controlled terpolymers with constant composition, ternary random sequence, and gradient alternating block structure. “One-pot” terpolymerization kinetic analysis indicated that the polymer yields and polymerization rates were strongly dependent on the feed composition and the type of the “alternating sequence.” Additionally, the instantaneous monomer composition containing a predominant alternating structure rather than a homopolymerization sequence was tracked by ¹H NMR analysis. The real-time ¹H NMR spectrum monitoring the characteristic peak change of [D]/[P]/[S] (i.e., [aromatic ring]/[C = C]/[alkyl-CH₃]) monomer units indicated the distinctive copolymerization behavior of the selected “alternating-modules” including [D/P], [D/S], and [S/P] repeating units. In addition, the thermal property of the resulting terpolymer was investigated by DSC analysis. The glass transition temperature (T_g) was very sensitive to the polymer composition, and most terpolymers had only one T_g. In contrast with poly([D/P]-ran-[S/P]) with high randomness distribution and strictly alternating modules, which had the lowest T_g, there were relatively higher T_gs in the DPE-rich and S-rich terpolymers. Moreover, poly([D/P]-co-[D/S]) copolymerization can be viewed as the random copolymerization of the standard [D/P] module and the default [D/S] module; therefore, the abundant residual D monomer was observed due to the unavoidable S homopolymerization. Meanwhile, poly([S/P]-gradient-[D/S]) with a special gradient block-alternating sequence can be obtained in an S-rich case due to the huge reactivity ratios of the two modules (r_[S/P] > > r_[D/S]). Finally, the “bond-forming initiation” theory was proposed to interpret the unique terpolymerization behavior.