Block Copolymers of Macrolactones/Small Lactones by a “Catalyst-Switch” Organocatalytic Strategy. Thermal Properties and Phase Behavior

Abstract

Poly(macrolactones) (PMLs) can be considered as biodegradable alternatives of polyethylene; however, controlling the ring-opening polymerization (ROP) of macrolactone (ML) monomers remains a challenge due to their low ring strain. To overcome this problem, phosphazene (t-BuP 4), a strong superbase, has to be used as catalyst. Unfortunately, the one-pot sequential block copolymerization of MLs with small lactones (SLs) is impossible since the high basicity of t-BuP 4 promotes both intra-and intermolecular transesterification reactions, thus leading to random copolymers. By using ROP and the "catalyst-switch" strategy [benzyl alcohol, t-BuP 4 /neutralization with diphenyl phosphate/(t-BuP 2)], we were able to synthesize different well-defined PML-b-PSL block copolymers (MLs: dodecalactone, ω-pentadecalactone, and ωhexadecalactone; SLs: δ-valerolactone and ε-caprolactone). The thermal properties and the phase behavior of these block copolymers were studied by differential scanning calorimetry and X-ray diffraction spectroscopy. This study shows that the thermal properties and phase behavior of PMLs-b-PSLs are largely influenced by the PMLs block if PMLs components constitute the majority of the block copolymers.

Dual Polymerizations: Untapped Potential for Biomaterials

“…However, this poses a problem for the synthesis of block copolymers as strong bases also catalyze intra‐ and intermolecular chain transfer via transesterification, scrambling the polymer sequence. One strategy that has eliminated transesterification‐induced sequence scrambling when copolymerizing low and high ring strain lactones is to first polymerize low ring strain macrolactones with a strong base, quench the active chain, and subsequently reinitiate the polymerization of a higher ring strain monomer with a weaker base . The weaker base could be used to polymerize higher ring strain lactones but did not induce transesterification and the block copolymer sequence was preserved.…”

Tetracrystalline Tetrablock Quarterpolymers: Four Different Crystallites under the Same Roof

“…[18] We also developed an organic/organic catalyst switch strategy from PSB 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylid-enamino]-2l 5 ,4l 5 catenadi(phosphazene) (t-BuP 4 ,p K a,ACN = 42.7) to an organic acid (diphenyl phosphate [DPP], pK a,DMSO = 3.88) or t-BuP 2 . [19] First, an alcohol initiator was activated by t-BuP 4 (suitable for polymerizing epoxides [EXs] and macrolactones [MLs]), which promoted the ROPofEXs or MLs to high conversion. Tw ostrategies were subsequently performed.…”

Homo‐ and random copolymerizations of ω‐pentadecalactone with ε‐caprolactone using isothiourea‐based dual catalysis

“…Biodegradable aliphatic polyesters have received tremendous attention due to the growing demand of environment‐friendly and biodegradable polymers during the past few decades . Among them, poly(ω‐pentade‐calactone) (PPDL) and its copolymers, which exhibit promising physico‐chemical properties, such as biocompatibility and controllable biodegradability, have fuelled interest in their applications in the field of medicine . Polyesters derived from 16‐membered macrolactone ω‐pentadecalactone (PDL) display ductility and toughness, which resemble low‐density polyethylene (LDPE) .…”