In-situ branched Poly (butylene succinate-co-butylene terephthalate) for green preparation of ultralight foams: simultaneous enhanced mechanical and degradation properties

A series of PBST with the branching agent glycerol ranging from 0 mol.% to 1.5 mol.% were synthesized by in-situ polymerization, and different branched PBST foams were prepared using supercritical CO₂. The introduction of branching structure both improve the rheological, mechanical properties and crystallization behavior of PBST. The crystallinity, relaxation time and tensile modulus of branched PBST increase from 12.7 % to 15.2 %, from 0.0136 s to 2.288 s and from 63.9 MPa to 87.0 MPa, respectively. When the glycerol content was 1.0 mol.%, the degree of branching was optimal and the maximum initial and final expansion ratios of the prepared foams were 38.5 and 21.5, respectively. The addition of branching agent increases the rigidity and entanglement of the molecular chain and provides more hydroxyl groups as degradation sites, resulting in branched PBST foams exhibiting superior compression and degradation properties. Compared to linear PBST, the compressive modulus of branched PBST foams with an expansion ratio of 10 increases from 1.21 MPa to 2.92 MPa. Introduction of branching structure by in-situ polymerization can provide an effective strategy for the preparation of degradable foams with excellent mechanical and degradation properties, and adjustable cell parameters.