Highly Thermally Stable and Miscible CO2‑Based Block Copolymers by the Combination of Ring-Opening and RAFT Copolymerizations through Mediated Hydrogen Bonding Interactions

TL;DR

Scientists created a new type of CO2-based block copolymer that is thermally stable and has unique hydrogen bonding interactions.

Contribution

The study introduces a novel method to synthesize CO2-based block copolymers with enhanced thermal stability and miscibility.

Findings

The PCHC-b-PSHPMI copolymers showed a single Tg value, indicating miscibility.

Hydrogen bonding interactions were observed via FTIR and NMR spectroscopy.

Relaxation times from NMR indicated complete miscibility at a nanoscale.

Abstract

In this study, the chain end of a reversible addition–fragmentation
chain transfer (RAFT) polymerization agent of poly­(cyclohexene carbonate)
(PCHC) was synthesized via the ring-opening copolymerization of CO2 and cyclohexene oxide (CHO) by using s-dodecyl-s’-(α,α′-dimethyl-α″-acetic
acid) trithiocarbonate (DDMAT) as a chain transfer agent. Various
block copolymers of poly­(cyclohexene carbonate)-b-poly­(styrene-alt-N-(hydroxyphenyl)­maleimide) (PCHC-b-PSHPMI) were subsequently synthesized by the RAFT copolymerization
of styrene and N-(hydroxyphenyl)­maleimide (HPMI)
in the presence of azobis­(isobutyronitrile) (AIBN), which were characterized
by using differential scanning calorimetry (DSC), thermogravimetric
analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, nuclear
magnetic resonance (NMR), and gel permeation chromatography (GPC).
DSC thermal analyses indicated that the single T
g values were observed for all PCHC-b-PSHPMI
copolymers, indicating miscible behavior, and the T
g value was 194 °C for the PCHC-b-PSHPMI78 copolymer. One- and two-dimensional (2D) FTIR spectroscopy
revealed that these PCHC-b-PSHPMI copolymers actually
provide relatively weak intermolecular O–H···OC
hydrogen bonding, which was attenuated by the self-association of
hydrogen bonding within the pure PCHC and pure PSHPMI segments. In
the solid-state 13C NMR spectra, a pronounced chemical
shift variation of the C–OH and CO units of the PSHPMI
segment and CO units of the PCHC segment was also observed,
which is attributable to the intermolecular hydrogen interactions
in these PCHC-b-PSHPMI copolymers. Rotating-frame 1H spin–lattice relaxation [T
1ρ(H)] analyses also indicated the complete miscible behavior of these
block copolymers within the 2–3 nm length scale, and the relaxation
times exhibited positive deviations from the linear predicted rule.
These results suggest that the loose chain structure was formed because
of the weaker intermolecular hydrogen bonding between the PCHC and
PSHPMI segments in the block copolymers.

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