Reactivity of allyl and vinyl pentosides in photo-initiated donor-acceptor copolymerization - Carbohydrate Chemistry: Chemical and Biological Approaches - page 291

copolymerization of monofunctional monomer with DEF, leading to re-
strictions to chain mobility. The maleate hybrid monomer, MAIR, ap-
peared to be less reactive than its fumarate analog, FAIR, the initial rates
of polymerization for both type of unsaturations in MAIR being almost
ten times lower than polymerization rates measured for FAIR.
In order to balance the hasty disappearance of acceptor unsaturations
but also to reduce the vitrification of the blend, the acceptor monomer,
diethyl fumarate or maleate was introduced in excess, as reactive diluent
of the polymerizable mixture. As expected, the final conversion increased
and the butenedioate unsaturations disappeared twice faster than the
donor unsaturation for FAIR-DEF blend, confirming the plasticizing ef-
fect of excess DEF (Table 6). In blends diluted with DEM (FAIR-DEM,
MAIR-DEM), the maleate function was shown to undergo limited con-
version, confirming the poor reactivity in homopropagation for the
butenedioate unsaturation with a Z configuration, though behaving well
in donor-acceptor copolymerization.

Tetra-allyl monomer. The crosslinking copolymerization of allyl-
2,3,5-tri-O-allyl- D -xylopyranoside, TAX, with four equivalent of DEF as the
acceptor comonomer was monitored similarly by FTIR spectroscopy.
Final conversions for allylether unsaturations were about 40%, whereas
final conversion for DEF was higher (65%), due to homopropagation,
both values being limited by the early vitrification of the reactive film
(Table 7). Using excess DEF (6 eq. for 1 eq. TAX) enabled to reduce the
viscosity of polymerization mixture and to delay the solidification, thus
yielding networks with lower crosslink density. However, the conversion
of allyl unsaturations did not increase significantly, as a consequence of
the multiple functionality of TAX, isolating the unreacted functions of
monomers included in the network by reaction of one or two of its other
allyl groups. On the other hand, copolymerization conducted with DEM
led to alternating polymer with high crosslinking density but weak final
conversions (20%) explained by the rapid vitrification of polymer blend.

4.4.2 Network properties. The UV-cured materials obtained by
crosslinking polymerization of mixed donor-acceptor monomers or by
crosslinking copolymerization of multifunctional allyl monomer with an
acceptor comonomer in presence of 1 wt-% of TPO (diphenyl-(2,4,6)-tri-
methylbenzoyl)phoshine oxide) as photo-initiator were placed between
glass lids allowing for the formation of 1mm-thick samples after

Table 7 Kinetic data for the photopolymerization of TAX (1 wt-% of TPO as PI; P = 150W).

Initial rate
(mmol kg 1 s 1 )

Final
conversion (%) Molar ratio a

(R p ) 0 (R p ) 0 p A N p D N Polymer blends f A f D

TAX-DEF 0.2 0.8 1 0.6 65 40

TAX-DEF 0.15 0.85 1.1 0.5 76 43

TAX-DEM 0.2 0.8 0.4 0.4 20 20

a Molar ratios in functions.