Zn^II Chlorido Complexes with Aliphatic, Chiral Bisguanidine Ligands as Catalysts in the Ring‐Opening Polymerisation of rac‐Lactide Using FT‐IR Spectroscopy in Bulk

Abstract

Eight new zinc complexes of bisguanidine ligands have been structurally characterised and tested for the polymerisation of lactide. Initially this necessitated the preparation of the new six bisguanidine ligands [TMG 2 thf, DMEG 2 thf, trans-TMG 2 (1,2)ch, trans-DMEG 2 (1,2)ch, R,R-TMG 2 (1,2)ch, R,R-DMEG 2 (1,2)ch]. With these ligands in hand, zinc chlorido complexes could be obtained, which were characterized by X-ray crystallography and NMR spectroscopy. Furthermore, two new zinc chlorido complexes are reported, based on previous bisguanidine ligands [TMG 2 (1,3)ch, DMEG 2 (1,3)ch]. All complexes show a distorted tetrahedral coordination geometry. These eight complexes are utilised as catalysts in melt polymerization

Reactivity of Zinc Halide Complexes Containing Camphor-Derived Guanidine Ligands with Technical rac-Lactide

“…As initiating systems, a co-initiator, which can be benzyl alcohol or water, has the task of starting the polymerization catalyzed by the zinc guanidine complexes. In comparison to other zinc N,N-guanidine complexes, these systems show by far the highest activity in polymerization [65,69,70,72]. N gua ,O zinc chlorido complexes show the same reaction constants but yield polymers with molar masses, in good accordance with the theoretical ones, which demonstrates excellent reaction control [71].…”

“…After integration over these two regions, the conversion can be determined. In the recent study we could show that the two different setups (oil bath: conversion determined by 1 H NMR spectroscopy (polymerization method b) or jacketed vessel: conversion determined by FT-IR spectroscopy (polymerization method c) make no difference to the polymerization activity and reaction constant [70]. investigations is that all catalysts show similar reaction constants in polymerization and a higher yield can be obtained for C2 (which is important for industrial use).…”

“…In C1 the averaged angle lies in the region of 35.6 • , whereas in C2 and C3 the value is 13.1 • and 7.1 • . In C2 and C3 the free rotation in the guanidine moiety is hindered, which leads to smaller angles [69][70][71]. All complexes were fully identified by NMR, IR spectroscopy, and MS measurements.…”

“…Benzyl alcohol was added to one polymerization to determine if it can open the ring of the lactide monomer and to see the impact on the molar masses (polymerization method c) ( Table 4). In recent reports [70] it could be shown that the quality of lactide (technical or recrystallized) has no major impact on the activity of the polymerization. As a result, in polymerization methods b and c different qualities of lactide are used (Table 4).…”

“…The final reaction time in b was 13 h and in c 7 h. In polymerization method b technical lactide was used and in polymerization method c recrystallized lactide was used. In a recently published study it was shown that the quality of recrystallized vs. technical lactide makes no difference for our systems [70]. The conversion in polymerization method b was determined via 1 H NMR spectroscopy and in polymerization method c with FT-IR spectroscopy.…”