Effects of Molecular Weight Distribution on the Thermal–Mechanical Performance and Recycling of CO2‑Derived Poly(cyclopentene carbonate)

TL;DR

This paper studies how the molecular weight distribution of a CO2-based plastic affects its strength, thermal properties, and recyclability.

Contribution

The study reveals how bimodal molecular weight distributions impact the performance and recycling of CO2-derived poly(cyclopentene carbonate).

Findings

PCPC samples with narrow-gap bimodal distributions retain high tensile strength and thermal properties.

Wide-gap bimodal PCPC samples show reduced performance unless low amounts of high molecular weight chains are added.

All high molecular weight PCPC samples can be rapidly depolymerized into cyclopentene oxide and CO2 within 15 minutes.

Abstract

Poly­(cyclopentene carbonate) (PCPC) is a recyclable,
CO2-derived thermoplastic with high tensile strength and
low entanglement
molecular weight. Such CO2-derived polycarbonates typically
show bimodal molecular weight distributions, but how these distributions
influence their properties is not yet understood. Here, the tensile,
mechanical, thermal, and recycling properties are investigated for
PCPC samples with different bimodal molecular weight distributions.
Samples with high molecular weights (M
n ∼ 81 kg mol–1) and narrow-gap bimodality,
showing a relative 1:2 chain length distributions, are prepared using
variable alcohol:diol ratios. These narrow-gap bimodality PCPC samples
all show the same high tensile strength (σmax ∼
60 MPa) and glass transition temperature (T
g,∞ = 88 °C). A second series features different relative amounts
of high molecular weight PCPC (M
n = 76
kg mol–1) blended with low molecular weight samples
(M
n = 9 or 16 kg mol–1). These wide-gap bimodality PCPC samples generally show compromised
thermal and mechanical performance, with properties only being retained
when low amounts of chains with molecular weights above chain entanglement
are added. All the high-M
n PCPC samples
are rapidly depolymerized, using neat polymer-catalyst blends, to
produce cyclopentene oxide and carbon dioxide, regardless of molecular
weight distribution. Complete conversion to epoxide (CPO) and CO2 is achieved in <15 min at 140 °C (1:300 catalyst:PCPC
repeat unit).

Figures