Morpholine-2,5-diones are increasingly
attractive monomers derived
from amino-acids whose copolymerization with other monomers produces
interesting biodegradable materials. In this study, the rapid and
controlled organocatalyzed ring-opening polymerization of 3S-(isobutyl)morpholine-2,5-dione
(MD) and its copolymerization with lactide (LA) was accomplished using
1,8-diazabicyclo(5,4,0)undec-7-ene and a thiourea (TU) cocatalyst.
The amount of TU used for the polymerization was found to be fundamental
for achieving good control. A range of polymers with molecular weights
between 8.1 and 25.2 kg mol–1 was thus produced
with narrow chain distributions (Đ = 1.13–1.18)
in short periods (5 to 10 min). Secondly, copolymers with varying
compositions (MD:LA = 25:75;50:50; 75:25) were prepared (11.2 to 12.7
kg mol–1;
Đ = 1.09–1.26).
The kinetics of these polymerizations suggest that concurrent thioimidate
and cyclic imidate mechanisms are occurring and that these are governed
by the quantity of TU in respect to MD.
There is a growing interest surrounding morpholine-2,5-dionebased materials due to their impressive biocompatibility as well as their capacity to break down by hydrolytic and enzymatic pathways. In this study, the ringopening (co)polymerization of leucine-derived 3S-(isobutyl)morpholine-2,5dione (MD) and lactide (LA) was performed via ball-milling using a catalytic system composed of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 3-[3,5bis(trifluoromethyl)phenyl]-1-cyclohexylthiourea (TU). Once the homopolymerizations of MD and LA optimized and numerous parameters were studied, the mechanochemical ring-opening copolymerization of these monomers was explored. The feasibility of ring-opening copolymerizations in mechanochemical systems was demonstrated and a range of P(MD-co-LA) copolymers were produced with varying proportions of MD (23%, 48%, and 69%). Furthermore, the beneficial cocatalytic effects of TU with regards to ROP control were found to be operative within mechanochemical systems. Further parallels were observed between solution-and mechanochemical-based ROPs.
Well-defined double hydrophilic block copolymers (DHBCs) of poly(ethylene glycol)-block-poly(N,Ndiethylacrylamide) (PEG-b-PDEAm) were synthesized via a reversible addition-fragmentation chaintransfer (RAFT) polymerization of N,N-diethylacrylamide (DEAm) using dithioester terminated PEG of different chain lengths as macro-chain transfer agents. Controlled molecular weight and narrow molecular weight distribution were achieved as proven by size exclusion chromatography (SEC). Cloud points (CP) were determined via turbidity measurements with ultraviolet-visible spectroscopy (UV-vis) and LCST by differential scanning micro-calorimetry (micro-DSC). They range from 32 to 40°C depending on the PDEAm length block and its concentration. Above the LCST, fluorescence spectroscopy and dynamic light scattering (DLS) demonstrated that the PEG-b-PDEAm copolymers self-organized into large aggregates. More interestingly, copolymers pre-aggregated at relatively high concentrations below the LCST.
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