Synthesis of multifunctional hyperbranched polymers (HPs) with simultaneously precisely modulated degrees of branch (DBs) and multibiorelevant signal-triggered sensitivities generally suffers from multistep preparation and purification procedures and uncontrolled DB. To develop a facile yet robust approach toward multifunctional HPs with a precisely modulated DB, we reported herein the synthesis of a reducible hyperbranched polymer template (HPT) with a fixed DB via an [A 2 + B 3 ]-based click polymerization and its further mediation of reversible addition−fragmentation chain transfer (RAFT) polymerization for the facile preparation of well-defined multifunctional HPs with a uniform DB, predetermined polymer compositions, and wellmodulated molecular weights (MWs) and low dispersity (Đ) indexes. The breakthrough of this study is the design of a bioreducible HPT-based multimacro chain transfer agent (multimacro-CTA) with a fixed DB of 0.45 via click polymerization between an A 2 unit containing a central trithiocarbonate group for further conduction of RAFT polymerization of any vinyl-based monomers, two disulfide links for reduction sensitivity, and two azide groups and a branched B 3 unit with three highly reactive alkynyl functions. The resulting HPT was further adopted as a multimacro-CTA to mediate RAFT polymerization of a previously reported acidic pH cleavable oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA) monomer, α-OEGMA, affording reduction and acidic pH dual sensitive HPT-P(α-OEGMA). Notably, the resulting polymer panel of HPT-P(α-OEGMA)s could self-assemble into stabilized unimolecular micelles with MW-dependent mean hydrodynamic size in a range from 18.9 to 27.0 nm. The drug-loaded HPT-P(α-OEGMA) micelles incubated in a reducing or an acidic pH condition showed accelerated drug release due to the reduction-triggered cleavage of the disulfide links or an acidic pH induced breakage of the acetal links for polymer degradation. Therefore, the universal HPT platform provides a facile yet robust approach toward well-defined multifunctional HPs with a uniform DB, well-controlled MWs, and low Đ indexes for biomedical applications.
We
report a poly(norbornene-graft-styrene) (PNB-g-PS) supported mono(phenoxy–imine) metal complex
for ethylene polymerization. As a molecular bottlebrush (MB), PNB-g-PS was prepared via grafting-through ring-opening metathesis
polymerization (ROMP) of the norbornenyl macromonomer. Postmodification
reactions of PNB-g-PS were performed to incorporate
phenoxy–imine type ligands in PS side chains, which were then
coordinated with early transition metals to generate a series of MB
supported mono(phenoxy–imine) catalysts. The loading efficiency
of the metals was assessed by inductively coupled plasma mass spectrometry.
Using these catalysts with four types of phenoxy–imine ligands
and two metals (Ti and Zr), we evaluate their catalytic performances
(activity, M
w, and the crystallinity of
polyethylenes) for ethylene polymerization. Improved catalytic activities
were observed for the catalysts bearing bulky substituents ortho to the phenolic oxygen in the ligands. The highest
ones are 369 and 461 kg PE mol–1 h–1 for the Ti and Zr catalysts with a cumyl group. The obtained polyethylenes
(PEs) have high crystallinities and tunable molecular weights ranging
from 80 to 2000 kDa. We also successfully prepared bimodal PEs in
one pot by rationally combining two different phenoxy–imine
ligands in the MB supported catalysts.
A novel oligomeric P–N synergistic flame retardant (FR) poly(phenyl O–(2–aminoethyl) phosphonamidoate) (PPAP) was synthesized and characterized by fourier transform infrared spectrometry (FT–IR) and 1H nuclear magnetic resonances (1H NMR). Application of PPAP on cotton fabric was studied, and the results showed that the best dosage of PPAP and coupling agent tetraethyl orthosilicate (TEOS) were 350 g/L and100 g/L respectively. Under these conditions, the treated cotton fabric was tested with 10.6 cm of char length. The results of thermogravimetric analyser (TGA) indicated that the fabrics treated with PPAP were more stable in high temperature compared with original fabrics. All the results implied PPAP can be used as a promising FR.
The manipulation of the crystallization kinetics and
crystallinity
of polymers without altering their chemical composition, chain structure,
or average molecular weight is challenging, while little attention
is paid to the role of molecular weight distribution (MWD) shape.
In this work, a series of well-defined linear unimodal and bimodal
polyethylenes (PEs) with molecular weights ranging from 300 k to 1200
k g/mol were synthesized to serve as a model system to study the impact
of bimodal MWD shape on the crystallization kinetics of semicrystalline
polymers in comparison with unimodal MWD shape at the same weight-average
molecular weight (M
w). It is shown that
PEs with a bimodal shape exhibit a faster nucleation rate and crystallization
rate with a smaller lamellar width at low isothermal temperatures.
A higher crystallization enthalpy of bimodal PEs is shown in non-isothermal
experiments. The mechanism behind this is elucidated, which suggests
that MWD shapes mainly affect the small-scale nucleation process without
altering the large-scale growth process. This first systematic comparative
study on the crystallization kinetics of linear unimodal and bimodal
PEs gives insight into tailoring the crystallization behavior of semicrystalline
polymers from an MWD shape perspective.
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