Highlights
New CO2 copolymers

Angewandte
Chemie

DOI: 10.1002/anie.200((will be filled in by the editorial staff))

“This is the peer reviewed version of the following article: Angew. Chem. Int. Ed. 2014, 53, 7402-7404, which has been published in
final form at https://doi.org/10.1002/anie.201403969. This article may be used for non-commercial purposes in accordance with Wiley
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Preparation of CO2-diene copolymers: advancing carbondioxide based materials**
Giulia Fiorani and Arjan W. Kleij*
((Dedication----optional))
Keywords:
Carbon dioxide · dienes · radical
polymerization · CO2 telomerization · Pd
catalysis

Despite its physical and chemical inertness, carbon dioxide (CO2)
continues to be an attractive and alternative carbon synthon being
abundant, renewable, readily available and cheap.[1] The inertness of
CO2 poses a huge challenge given the energy input required for its
transformation and/or functionalization. A successful example of CO 2
reutilization is represented by the development of atom-economical
catalytic processes based on high-energy reactants (such as epoxides
and oxetanes) leading to new functional molecules such as organic
carbonates,[2] polycarbonates and polyether-polycarbonate based
polymers.[3] Various efficient catalysts active towards CO2/epoxide
couplings have been developed in the last ten years,[2-4] aiming at the
stereo-controlled preparation of functional, cyclic carbonates[5] as
well as stereo-regular functional polymers.[6] Further to this, some of
these promising catalytic systems are currently employed in
commercially feasible, industrial processes exploiting CO2 fixation
using ethylene and propylene oxide as reaction partners.[6c] These
processes furnish polyethylene carbonate, polypropylene carbonate
and poly(ether)carbonate-polyols mixtures with a tailored, narrow
molecular weight distribution of further (potential) use in
polyurethane synthesis.[7] The applicability of this type of
polymerization
reaction
is
still
limited
to
polycarbonates/poly(ether)carbonates synthesis and, so far, has not
been extended to another ambitious and challenging (commercial)
target, the preparation of polyesters by direct copolymerization of
CO2 with ethylene or dienes. This copolymerization reaction is
particularly appealing since it represents a link between different
renewable resources such as CO2, and cheap, widely available
petroleum-derived alkenes allowing a potential evolution towards
more sustainable materials. The principal obstacles preventing a
successful copolymerization of these monomers include (1) a high
energy barrier associated to the alternating copolymerization between
ethylene/polyene and CO2 requiring excess ethylene insertion to

[]

Dr. Giulia Fiorani, Prof. Dr. Arjan W. Kleij
Institute of Chemical Research of Catalonia (ICIQ)
Av. Països Catalans 16, 43007 Tarragona (Spain)
Fax: (+34)977-920-828
E-mail: akleij@iciq.es
Homepage: www.iciq.es
Prof. Dr. Arjan W. Kleij
Catalan Institute of Advanced Studies (ICREA)
Pg. Lluís Companys 23, 08010 Barcelona (Spain)

[]

GF kindly acknowledges financial support from the
European Community through FP7-PEOPLE-2013-IEF
project RENOVACARB (grant agreement N°622587). ICIQ,
ICREA and the Spanish MINECO (CTQ2011-27385) are
thanked for financial support.

ensure endergonic CO2 insertion, and (2) a kinetic barrier represented
by the high activation energy for CO2 insertion in the growing
polymeric chain versus chain growth of the poly(ethylene) or
poly(propylene).[8]
Nozaki and co-workers have now reported a reproducible and
highly customizable procedure for the preparation of CO2-diene copolymers.[8b,c] Key to this success is the innovative use of an
alternative
polymerization
strategy,
circumventing
the
thermodynamic and kinetic barriers associated to direct CO2butadiene co-polymerization. In particular, they have employed a
known meta-stable -lactone, 3-ethylidene-6-vinyltetrahydro-2Hpyran-2-one (1)][9] that can be easily obtained by telomerization of
CO2 and butadiene in the presence of a Pd/phosphine ligand catalytic
system (Scheme 1). Lactone 1 has been extensively studied by Behr
and others in the past 30 years as a promising functional organic
intermediate and versatile synthetic building block. The optimized
preparation of 1 both on lab and pilot-plant scale, thereby minimizing
the formation of undesired telomerization side-products, should thus
be regarded as a milestone in this area.[10]

Scheme 1. Synthesis of -lactone 1; the allylic moiety and the vinyl
moiety are highlighted in blue and green, respectively.

Nozaki and co-workers have found that -lactone 1 can easily
undergo thermally initiated radical polymerization under aerobic
conditions in the presence of an appropriate, thermally activated
radical initiator [1,1’-azobis(cyclohexane-1-carbonitrile), V-40],
observing a moderate conversion (17%) and producing a polymer,
poly-1 (Scheme 2), containing exclusively -subunits formed by
attack of the radical chain-end on the allylic ester unit of 1 (Scheme
2). Poly-1 was characterized by a moderate Mn (5.7 kDa) and a narrow
polydispersivity Mw/Mn of around 1.3. The presence of Lewis acid
additives such as ZnCl2 and additional solvent such as ethylene
carbonate (EC) accelerated the reaction rate and improved
substantially the overall yield (48%) and Mn values (6285 kDa)
while retaining a good Mw/Mn distribution, but affected significantly
the morphology of the resulting polymer (poly-1’); poly-1’ comprises
different isomeric subunits (,  and  in Scheme 2) and their
presence is mediated by Lewis acid stabilization of the radical in the

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-position to the ester carbonyl group or hydrogen abstraction in the
vinyl moiety of 1. Both poly-1 and poly-1’ polymers display
relatively high CO2 incorporation (29% w/w) and high glass
transition temperatures (Tg = 178192 ºC) making these novel
polymers likely suitable as engineering plastics.

Scheme 2. Synthesis of and details for poly-1 and poly-1´.

To simplify and speed up the synthetic procedure, poly-1’ was
also prepared in a one-pot fashion, starting from butadiene and CO2.
The scope of these one-pot polymerization reactions was extended to
the incorporation of more complex diene structures (viz. 1,3pentadiene and isoprene) within the polymeric chain. The mixed
telomerization of butadiene, CO2 and other C5 dienes was
characterized by a lower reactivity, mainly ascribed to steric
hindrance issues; however, after optimization, CO2-rich terpolymers
could be obtained in good yields (46 and 35% yield for isoprene and
1,3-pentadiene, respectively) with relative high CO2 incorporation
(2024% w/w) and varying polymer properties (Mn = 5.516 KDa,
Mw/Mn = 2.02.5; Tg = 3363 ºC).
By exploiting this facile aerobic radical homo-polymerization of

-lactone 1, Nozaki and co-workers have elegantly overcome the

thermodynamic barrier preventing direct CO2/butadiene copolymerization, while expanding the library of useful high-energy
CO2 co-reactants. However, further characterization data (cf.,
mechanical and thermal stability, biodegradability) of the resulting
CO2-rich polymeric materials is required to estimate their full
potential and properties. Despite the slow reaction rates and the use
of an excess Lewis acid co-catalyst, the possibility of obtaining
CO2/diene copolymers with a high CO2 content (between 2029 %
w/w) is a significant step forward towards the preparation of more
sustainable plastics and could potentially lead to a bulk utilization of
CO2 as a chemical feedstock. Moreover, extensive studies on the
optimization of preparation procedures for intermediates of type 1
could be an excellent starting point for further process scale-up and
providing new research opportunities. The combination of new,
(bio)renewable based monomers with the concomitant development
of one-pot polymerization strategies applicable to a discrete family of
low molecular weight dienes could potentially lead to the preparation
of new CO2-based copolymers with novel innovative structures,
enhancing their application potential in existing and new areas of
polymer science.

[1]

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Entry for the Table of Contents:

New CO2 copolymers
Giulia Fiorani and Arjan W. Kleij*
__________ Page – Page

Preparation of CO2-diene copolymers:
advancing carbon-dioxide based
materials

Expanding the family of CO2 based materials: meta-stable CO2-diene based
lactones, prepared by Pd-catalyzed telomerization of CO2 and dienes, easily undergo
aerobic radical homo-polymerization to give novel CO2-rich polymers (see Scheme).
This two-step reaction set-up expands the potential applications of CO2-based copolymers adding innovative compositions, structures and properties.

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