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\begin{document}

\title{Crosslinked Polymers Based on Monomers Derived from Renewable Resources
and Their Application Potential}



\author[1]{Veronika Strehmel}%
\author[1]{Bernd Strehmel}%
\affil[1]{Hochschule Niederrhein}%


\vspace{-1em}



  
  \date{May 30, 2024}


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\selectlanguage{english}
\begin{abstract}
Possible structural variation of a bio-based dimethacrylate derived from
oleic acid and ethylene glycol is discussed as well as sources to obtain
the starting material for manufacturing of this monomer. Furthermore,
aspects influencing the transfer of a newly developed product or further
scientific result to application are included into the discussion as
well focusing to manufacturing processes and development of a new
product for the market.%
\end{abstract}%



\sloppy


Perspective

Crosslinked Polymers Based on Monomers Derived from Renewable Resources
and Their Application Potential

Veronika Strehmel* and Bernd Strehmel

Niederrhein University of Applied Sciences, Faculty of Chemistry and
Institute for Coatings and Surface Chemistry, Adlerstrasse 32, D-47798
Krefeld, Germany

E-mail: veronika.strehmel@hsnr.de

Abstract

Possible structural variation of a bio-based dimethacrylate derived from
oleic acid and ethylene glycol is discussed as well as sources to obtain
the starting material for manufacturing of this monomer. Furthermore,
aspects influencing the transfer of a newly developed product or further
scientific result to application are included into the discussion as
well focusing to manufacturing processes and development of a new
product for the market.

KEYWORDS

bio-based monomer, dimethacrylate, photo-initiated polymerization,
crosslinked polymer, application potential

INTRODUCTION

Nowadays, there is no doubt that the modern society demands to search
for alternative materials having the capability to replace fossil
resources partially or completely in the future. Generation of fossil
resources has needed a long period in the earth's history. Nevertheless,
they have been used with continuous increasing amount in the last two
centuries to generate materials. Thus, this topic closely relates to the
chemical industry that has used fossil resources as both starting
material for product manufacturing and energy source, which appears as
very important for the usually highly energy intensive chemical
processes. Two ways appear purposeful to solve this problem. These ways
include both renewable energy sources and renewable materials. Sunlight
seems useful as direct or indirect renewable energy source. Various
plants produce a broad variability of biomass catalyzed by enzymes in
the presence of sunlight as well. Discussions have continued in the
literature to search regarding selection of available plant species
outside the competition with food production for humans and animals,
efficiency of product manufacturing from biomass, and re-using the
material after its application.\textsuperscript{{[}1-4{]}} Beside the
high molecular weight natural products, such as cellulose, hemicellulose
and lignin, low molecular weight compounds have received increased
interest recently.\textsuperscript{{[}4-6{]}} The latter include
terpenes and triglycerides, as well as products derived from
triglycerides like glycerin and various fatty acids. Nevertheless, some
of them interfere the food chain, which appears critical in countries
with high population density or regions with food shortage. Thus,
resources based on waste have moved into the focus.

Furthermore, several bio-based linear aliphatic, aromatic, and
cycloaliphatic compounds have been successfully converted into
(meth)acrylates that are interesting monomers for manufacturing of
polymers.\textsuperscript{{[}7-14{]}} Among these bio-based monomers is
a new dimethacrylate synthesized in three steps as shown in Scheme 1.
The synthesis starts with esterification of oleic acid with ethylene
glycol, it continues with epoxidation of the two double bonds of the
ethylene dioleate, and ring opening reaction of the resulting diepoxy
compound with methacrylic acid is the final
step.\textsuperscript{{[}12{]}} Moreover, the new bio-based
dimethacrylate was polymerized in thin film using photoinitiated radical
polymerization mechanism applying ultraviolet-technology (Scheme 1) to
form an insoluble crosslinked polymer film showing high hydrophobicity
detected by contact angle
measurements.\textsuperscript{{[}12{]}}Crosslinking polymerization of
the bio-based dimethacrylate alone or in the presence of further
bio-based methacrylates comprising aromatic structures resulted in glass
transition temperature increase of the highly hydrophobic crosslinked
polymer films that makes them interesting for application e. g. as
water-repellent coating for surface protection. The latter may be of
importance for surface protection against corrosion. Such materials
possess additionally potential in medical application as long as the
natural origin would not cause incompatible responses of the body that
synthetic materials sometimes do.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Scheme 1. Synthetic way to a bio-based dimethacrylate starting by
esterification of oleic acid with a diol (e. g. ethylene glycol)
catalyzed by \emph{p} -toluene sulfonic acid (1. step), epoxidation of
the double bonds of the diester with hydrogen peroxide in the presence
of formic acid (2. step), and epoxy ring opening reaction with
methacrylic acid catalyzed by 1,4-diazabicyclo{[}2.2.2{]}octane (DABCO,
3. step) resulting in three isomers (i1, i2, and i3) of the bio-based
dimethacrylate. Photoinitiated radical polymerization of the
dimethacrylate alone or in the presence of bio-based methacrylates
comprising aromatic structures resulted in crosslinked polymer films
showing water-repellent properties as detected by contact angle
measurements.\textsuperscript{{[}12{]}}

SOURCES FOR THE STARTING MATERIAL

Plant oil and fat represent main resources for triglycerides that are
hydrolyzed into fatty acids and glycerol by chemical or enzymatic
processes.\textsuperscript{{[}4,15{]}} Though industrial use of plant
oil and fat e. g. for biodiesel production from triglycerides as
alternative to petrochemical diesel or for monomer synthesis compete
with food production, only cooking oil available as waste from industry,
restaurants or household should be utilized for fatty acid
manufacturing. Furthermore, the glycerol formed as by-product in the
biodiesel production may be useful for esterification of oleic acid
instead of using ethylene glycol as shown in Scheme
1.\textsuperscript{{[}12{]}} Ethylene glycol is obtained in two
different ways; that is a petrochemical and a bio-based way. The latter
is described as hydrolytic hydrogenolysis reaction of
cellulose.\textsuperscript{{[}16,17{]}} Lignin available in bark, wood
and plants provides compounds comprising aromatic moieties derived from
natural resources.\textsuperscript{{[}18,19{]}}

STRUCTURAL VARIABILITY OF THE CROSSLINKABLE BIO-BASED MONOMER

Various structural modifications of the bio-based dimethacrylate may be
possible by choosing different diol compounds for esterification with
oleic acid resulting in variation of the bridge between the oleate
structures on the one hand and by selection of different reagents for
ring opening reaction of the epoxidized di-oleates that give a
structural variation of the substituents R\textsubscript{1},
R\textsubscript{2}, R\textsubscript{3}, and R\textsubscript{4} on the
other hand (Scheme 1). The latter may contain either an OH-group or
aromatic structure and two (meth)acrylate groups. As a result, the
structure depicted in Scheme 2 represents only some possible structural
modifications of the dimethacrylate derived from oleic acid and ethylene
glycol, which was firstly described in 2021.\textsuperscript{{[} 12{]}}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

Scheme 2. Possible structural modification of the dimethacrylate derived
from oleic acid and ethylene glycol (Scheme 1) includes variation of
both the linking moiety R and the substituents R\textsubscript{1},
R\textsubscript{2}, R\textsubscript{3}, as well as
R\textsubscript{4}resulting in numerous possible bio-based
dimethacrylates that may differ in the properties of both monomers and
polymers made of them e. g. by photoinitiated polymerization. The
efficiency of both processes, monomer manufacturing and polymer
formation as well as the properties of the crosslinked polymer materials
obtained are important for selection of the new materials for
application.

APPLICATION POTENTIAL

Aspects for introduction of new starting materials in existing
production processes for manufacturing of new products include
availability and current economic affordability of the new raw material,
efficiency of the manufacturing processes for both the product, e. g.
monomer and further material derived of the product, e. g. crosslinked
material. Furthermore, the manufacturing processes should agree with the
principles of green chemistry.\textsuperscript{{[}20{]}} Quantification
of the efficiency of manufacturing processes includes for example the
energy balance, atom economy, yield, reaction mass efficiency, process
mass intensity, and environmental
factor.\textsuperscript{{[}21-26{]}}Moreover, the new products should
address to gaps existing on the market or may be replacements showing
improved properties relative to existing products. Though fossil
resources are limited, partial or complete substitution of the fossil
resources will be necessary sooner or later. Therefore, the new
bio-based dimethacrylate described in the
reference\textsuperscript{{[}12{]}} is going to contribute to this
topic. The new journal \emph{Applied Research} was selected for
publication of the scientific results obtained regarding the new
bio-based dimethacrylate manufacturing and photocrosslinking resulting
in hydrophobic crosslinked films to draw attention particularly for the
use in practice. Here, the new highly hydrophobic material received from
the dimethacrylate alone or in the presence of a bio-based methacrylate
comonomer comprising an aromatic structure possesses huge potential. The
two long alkyl substituents, which are available in each segment of the
crosslinked polymer, contribute to the high hydrophobicity of the
material derived from the bio-based dimethacrylate. Furthermore, the
high hydrophobicity of the material makes it attractive for applications
in corrosion protection e. g. of metal surfaces. At the present time,
fluorinated polymers are commonly used to increase the hydrophobicity of
surfaces although their manufacture has a negative impact on the
environment.\textsuperscript{{[}27{]}} Nowadays, substitution of
fluorine comprising materials has received increased priority to solve
this environmental issue. Here, the new bio-based dimethacrylate (Scheme
1) and a modified structure of the bio-based dimethacrylate e. g. as
shown in Scheme 2, respectively, may become interesting alternatives to
the currently used fluorinated polymers. 3D Printing can be seen as an
additional application field where these monomers could receive
additional attraction.\textsuperscript{{[}28-32{]}} Particular
manufacture of prothesis for medical uses or dental restauration
addresses interesting challenges.\textsuperscript{{[}31,32{]}}

The journal \emph{Applied Research} together with its broad interested
readership has accelerated scientific research in diverse fields, which
strongly relate to application aspects. This covers applied research in
industry for improving existing products and production processes as
well as for the development of new products whose production proceeds in
existing manufacturing plants. These facts may contribute to accelerate
the transfer of recently obtained scientific results and newly developed
products to manufacturing processes and making it feasible to bring new
products to the market. Furthermore, the application aspects of the
papers published in the journal \emph{Applied Research} are going to
widen the visual field of researchers working at institutes and
universities. Moreover, this may encourage these researchers to include
application aspects in their own work as well. The idea of applied
research is deep-seated in research institutes such as Fraunhofer
Institutes and Universities of Applied Sciences in Germany. The
journal\emph{Applied Research} may become the favorite journal for
publication of scientific results focusing on application aspects
derived from fundamental research. In addition, this journal represents
a valuable source to provide recent research results with applied
aspects for teaching in master and doctoral courses focusing on
sustainable and green aspects.

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ACKNOWLEDGMENT

Open Access funding enabled and organized by Projekt DEAL.

CONFLICT OF INTEREST

The authors declare no conflict of interest.

AUTHORS BIOGRAPHY

Veronika Strehmel accepted her professorship for Organic Chemistry
focusing on Macromolecular Chemistry at the Niederrhein University of
Applied Sciences in 2010. Beside \emph{Polymer Chemistry}
and\emph{Polymerization Technology} , she has taught \emph{Green Organic
and Polymer Chemistry} . Furthermore, she has been private lecturer for
Polymer Chemistry at the University of Potsdam since 2007, where she has
taught \emph{Photopolymerization} . As a member of the Institute for
Coatings and Surface Chemistry of the Niederrhein University of Applied
Sciences, her research has focused on ionic liquids as well as on
monomers and polymers based on renewable resources. Prior to this, after
completing her PhD at the Technical University of Merseburg, she pursued
both applied research (Leuna Company; Fraunhofer Institute for Applied
Polymer Research) and fundamental research (Stanford University;
Martin-Luther University Halle-Wittenberg, where she received her
habilitation in Polymer Chemistry in 2000; Institute for Thin Film
Technology and Microsensorics; University of Potsdam).

Picture: Veronika Strehmel\selectlanguage{english}
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\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

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Bernd Strehmel accepted his professorship for Coatings and New Materials
at the Niederrhein University of Applied Sciences in 2011. Since 2017,
he has chaired the Institute for Coatings and Surface Chemistry at the
same institution in Krefeld. In the master module \emph{Green Chemistry}
, he has taught \emph{Technical Photochemistry} since 2017. Prior to
this, after completing his PhD at the Technical University of Merseburg,
he pursued research at several national (TU Berlin, Humboldt-University
of Berlin, University of Potsdam) and international universities
(Stanford University, Bowling Green State University-Center for
Photochemical Sciences) before he moved to Kodak after completion his
habilitation at the Humboldt-University of Berlin. There, he worked in
R\&D for the development of Computer to Plate materials for the graphic
industry. He additionally has been a member of the reviewer board of the
German Research Council (DFG) in the field 406: Material Science
(Synthesis and Properties of Functional Materials) from 2016. In the
German Chemical Society (GDCh), he was a member of the board of the
Photochemistry division, which he chaired from 2018 to 2021.

Picture: Bernd Strehmel\selectlanguage{english}
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