Isoprene Chain Shuttling Polymerization Mediated by a Heterobimetallic System Comprising La and Sc Amidinate Complexes: A One-Pot Process to Advanced Thermoplastic Elastomers

This study introduces a one-pot approach for synthesizing
regio-multiblock
copolymers with two tunable Tg values
from single conjugated dienes. A convenient acid–base reaction
was used to synthesize mononuclear rare-earth metal complexes R1C6H4C(N-2,6-iPr2–C6H3)2RE(o-CH2C6H4NMe2)2 (R1 = −OMe, RE = Sc (1), La (2); R1 = −H, RE = Sc (3), La
(4); R1 = −CF3, RE = Sc
(5), La (6)) in high yields. By carefully
tuning the ratios of catalytic precursors 1 and 2 in conjunction with AlEt3 and [Ph3C][B(C6F5)4] (borate), we achieved
precise control over the 1,4- and 3,4-regioselectivity in isoprene
chain shuttling polymerization. This approach yielded materials with
enhanced elongation at break (ε) compared to blends with similar
3,4-contents. Notably, the combination of catalytic precursors 5, 6, AlEt3 and borate further enabled
the synthesis of multiblock copolymers, which exhibit thermoplastic-elastomer
properties. By varying the reaction solvents and utilizing catalytic
precursor pairs (1, 2)/(3, 4)/(5, 6) in conjunction with borate
and AlEt3, all resulting copolymers exhibit dual-Tg values. These results highlight the versatility
and potential utility of the chain shuttling polymerization strategy
for designing polymer structures and tailoring the physical properties
of polymers.