Monomers and Resulting Polymers from Biomass - Introduction to Chemicals from Biomass - page 172

5.3.4 Furfuryl Alcohol

In light of the fact that most furfural derivatives used for the described polymer
chain reactions have low efficiency, it may seem odd that furfural is a commodity
product [69]. However, furfural is almost exclusively produced for FA. The
condensation of FA results in a very useful cross-linked material. What should be
a straightforward acid-catalyzed condensation reaction is complicated by two
unavoidable side reactions, the scope of which is discussed elsewhere [65, 67, 75].
As a result of the side reactions, the product is a dark thermoset instead of a clear
thermoplastic [67]. The resins produced by condensation of FA have found a
number of applications, including metal casting cores, corrosion-resistant coat-
ings, polymer concretes, wood adhesives, low flammability materials, and porous
carbon [67, 76-80]. They are also used in hybrid materials such as carbon-silica,
nanocomposite carbons, PFA-silica, Nafion-PFA, and sol-gel-based nanocomposites
[67, 80-87].

5.3.5 Polyesters

Polyesters are one of the most promising markets for furan-based polymers.
Despite the fact that a patent for polyesters from furan-based monomers was filed
as early as in the middle of the twentieth century [88], the potential for these mate-
rials has only recently been realized [64, 89-92]. A specific target is poly(ethylene
terephthalate) (PET), which is a fossil-based polyester with a market volume of
50 million tons per year [93]. Several groups have investigated furan analogs
to PET using the 2,5-FDCA furan derivative [89, 91, 92, 94-97]. There are several
synthetic routes to polyesters based on FDCA, including solution polycondensa-
tion, polytransesterification, and solid-state postcondensation [91, 92]. Each route
requires the participation of a comonomer with FDCA. Here, ethylene glycol is of
particular interest as it can also be derived from renewable resources, offering an
alternative to PET with a completely renewable carbon content [89].
Gomes et al. investigated a variety of FDCA-based polyesters using different
diols, including biobased ethylene glycol, propylene glycol, isosorbide, isoidide,
and bis(2,5-hydroxymethyl)furan [91]. Scheme 5.3 provides an overview of
the reaction steps. The work investigated both solution polycondensation and
polytransesterification synthesis of polyesters; the molecular weights of the
produced polymers were studied by size exclusion chromatography and perfluor-
inated end-groups [91]. The molecular weights of the polymers produced ranged
from low (2 kDa) to moderately high (45 kDa). Transesterification was the
preferred technique because it allowed for the production of the higher-molecular-
weight polymers [91]. The thermal properties of the polyesters were studied
using thermal gravimetric analysis (TGA), differential scanning calorimetry
(DSC), and X-ray diffraction and it was shown that poly(ethylene 2,5-furandicar-
boxylate) (PEF) exhibited a glass transition temperature T g = 80°C, a melting