Chemistry Reference
In-Depth Information
bonds.
47
On the basis of the above results establishing the reactivity of
vinyl and allyl ether in donor-acceptor copolymerization, we have studied
the relative reactivity of a series of allyl and vinyl ether compounds of
increasing complexity (from commercial model compounds with a sim-
ple structure to new synthesized glucidic monomers) in donor-acceptor
copolymerization with diethyl fumarate and diethyl maleate. These un-
saturated diesters were chosen as acceptor comonomers were chosen
because they can be obtained from bio-based intermediates which
allowed to minimize the non-renewable carbon atoms content within the
final polymeric material.
48
4 Donor-acceptor copolymerization of allyl and vinyl
pentosides
4.1 Reactivity of allyl vs. vinyl ether in donor-acceptor
copolymerization
We have explored in some detail the structure-reactivity relationships for
vinyl- and allyl-ethers derived from polyhydroxylic compounds (mainly
isopropylideneglycerol or ribose derivatives) for the free radical donor-
acceptor copolymerization with diethyl fumarate (DEF) and diethyl mal-
eate (DEM). Other allyloxy and vinyloxy monomers with a more simple
structure were also used as model compounds. The synthesis of non
commercial but known monomers (ACG, AHE, AIG, HVE, VCG, VIG), as
well as of the original pentose-based monomers (AIR, AR, ATMR, VIR,
VTMR) was achieved by conventional laboratory methods, using appro-
priate catalysts and trying to minimize the use of solvents for chemical
modification and for separation.
The variety of structural features exhibited by the selected allyloxy and
vinyloxy monomers can be assessed from Scheme 7: linear structures
with different chain lengths (alkyl allyl ethers) or oxygenated cyclic
structures (derivatives of solketal or glycerol carbonate, whose structure
is close to a carbohydrate backbone, as well as pentosides) with or
without hydroxylic functions in order to evaluate their influence on
reactivity in donor-acceptor copolymerization.
Photochemical initiation of the free radical process was selected
for its experimental convenience in terms of limited sample size and of
eciency.
49
Hence Darocur 1173 (2-hydroxy-2-methylphenylpropanone)
was used as Norrish type I photo-initiator
(PI), as
shown in
Scheme 8.
50
In order to minimize the influence of irradiation conditions on pos-
sible side reactions, photochemical initiation has been conducted under
mild conditions: at room temperature, in the absence of oxygen, under
low to medium intensity 365 nm irradiation, and in absence of short
wavelength contribution. The reactivity of both types of olefinic mono-
mers in copolymerization with acceptor monomers was studied. Several
competing processes previously presented can possibly occur. For this
reason, the consumption rate of each comonomer as well as the mo-
lecular weight of the final polymers were considered with attention and
compared for both types of donor function.
Search WWH ::
Custom Search