The ring-opening polymerization (ROP)
of cyclic carbonates with
diphenyl phosphate (DPP) as the organocatalyst and 3-phenyl-1-propanol
(PPA) as the initiator has been studied using trimethylene carbonate
(TMC), 5,5-dimethyl-1,3-dioxan-2-one, 5,5-dibromomethyl-1,3-dioxan-2-one,
5-benzyloxy-1,3-dioxan-2-one, 5-methyl-5-allyloxycarbonyl-1,3-dioxan-2-one,
and 5-methyl-5-propargyloxycarbonyl-1,3-dioxan-2-one. All the polymerizations
proceeded without backbiting, decarboxylation, and transesterification
reactions to afford polycarbonates having narrow polydispersity indices.
In addition, 6-azido-1-hexanol, propargyl alcohol, and N-(2-hydroxyethyl)maleimide were used as functional initiators for
the DPP-catalyzed ROP to produce the end-functionalized poly(trimethylene
carbonate)s. For further modification of the azido end-functionlized
polycarbonate, the macrocyclic poly(trimethylene carbonate) was synthesized
by the intramolecular click cyclization of the α-azido, ω-ethynyl poly(trimethylene carbonate). The DPP-catalyzed
ROP was applicable for the block copolymerization of TMC and δ-valerolactone or ε-caprolactone
to afford poly(trimethylene carbonate)-block-poly(δ-valerolactone)
and poly(trimethylene carbonate)-block-poly(ε-caprolactone),
and for that of TMC and l-lactide using DPP coupled with
4-dimethylaminopyridine without quenching to produce poly(trimethylene
carbonate)-block-poly(l-lactide).
The ring-opening polymerizations (ROPs) of e-caprolactone (e-CL) and L-lactide (LLA) have been studied using the organocatalysts of diphenyl phosphate (DPP) and 4dimethylaminopyridine (DMAP). The "dual activation" property of DPP and the "bifunctional activation" property of DPP/DMAP were confirmed by the NMR measurement for e-CL and its chain-end model of poly(e-caprolactone) and for LLA and its chain-end model of poly(L-lactide) (PLLA), respectively. The molar ratio of DPP/DMAP was optimized as 1/2 for the ROP of LLA leading to the well-defined PLLA, such as the molecular weight determined from 1 H NMR measurement of 19,200 g mol 21 and the narrow polydispersity of 1.10. Additionally, functional initiators were utilized for producing the end-functionalized PLLAs. The DPP-catalyzed ROPs of e-CL and its analogue cyclic monomers and then the DPP/DMAP-catalyzed ROP of LLA produced block copolymers.
The
tris(pentafluorophenyl)borane- (B(C6F5)3-) catalyzed group transfer polymerization (GTP) of N,N-disubstituted acrylamide (DAAm) using
a moisture-tolerant hydrosilane (HSi) as part of
the initiator has been intensively investigated in this study. The
screening experiment using various HSis suggested
that dimethylethylsilane (Me2EtSiH) with the least steric
bulkiness was the most appropriate reagent for the polymerization
control. The chemical structure of the DAAms significantly affected
the livingness of the polymerization. For instance, the polymerization
of N,N-diethylacrylamide (DEtAAm)
using Me2EtSiH only showed better control over the molecular
weight distribution, while that of N-acryloylmorpholine
(MorAAm) with a more obstructive side group using the same HSi afforded precise control of the molecular weight as well
as its distribution. Given that the entire polymerization was composed
of the monomer activation, the in situ formation
of a silyl ketene aminal as the true initiator by the 1,4-hydrosilylation
of DAAm, and the GTP process, the polymerization mechanism was discussed
in detail for each specific case, e.g., the B(C6F5)3-catalyzed polymerizations of DEtAAm and MorAAm and
the polymerization of MorAAm using B(C6F5)3 and Me3SiNTf2 as a double catalytic
system. Finally, the convenient α-end-functionalization of poly(N,N-disubstituted acrylamide) (PDAAm) was
achieved by the in situ preparation of functional
silyl ketene aminals through the 1,4-hydrosilylation of functional
methacrylamides, which has no polymerization reactivity in the Lewis
acid-catalyzed GTP, followed by the Me3SiNTf2-catalyzed GTP of DAAms.
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