Photosensitive polymers with cinnamate units in the side position of ...

2396 R. Mahy et al. / European Polymer Journal 42 (2006) 2389–2397
Ultraviolet lamp. IR and UV spectra of the copolymer
6b recorded after various times of irradiation
are given in Fig. 7. The UV analyses show that
the intensity of absorbance at k = 310 nm due to
cinnamate moieties decreases during exposure.
While that at k = 260 nm due to the cyclobutane
formation increases gradually. The insolubility of
the studied films in organic solvents after the irradiation
confirms that photocrosslinking took place. In
IR analysis, the decrease of C@C absorption band
at 1613 cm 1 upon irradiation was assigned to the
cyclobutane formation by dimerization of C@C cinnamate
groups.
More detailed studies on the ability of homopolymer
5 and copolymers 6 to crosslink under UV
irradiation are under investigation. The results of
these studies will be reported elsewhere.
4. Conclusion
Absorbance
a b
1.0
0.8
0.6
0.4
200 300 400 500
Wavelength
- 0 min
- 10 min
- 30 min
- 50 min
- 75 min
- 115 min
Photosensitive polymers with cinnamate units
in side position of chains were prepared by homopolymerization
and copolymerization of ethyl acyano-4-(methacryloxy)cinnamate
with methyl
methacrylate. Homopolymerization and copolymerizations
were carried out at 65 °C in chloroform.
The structures of the formed polymers were characterized
by IR and 1 H NMR. Homo- and co-polymers
of medium molecular weights were obtained
with good yields (60–95%). They were easily soluble
in most of the organic solvents such as butanone,
THF, CH 2Cl 2, CHCl 3, benzene, toluene, DMF
and dioxane.
Absorbance
0.4
0.3
0.2
0.1
0.0
- 210 min
- 170 min
- 110 min
- 55 min
- 15 min
- 0 min
1600 1650 1700 1750
Kinetic studies of homo- and co-polymerization
were performed in deuterated chloroform under
nitrogen atmosphere. In the case of the homopolymerization
of 4, the plot of Ln(M0/Mt) versus
[1 exp( kd Æ t/2)] leads to a kp= ffiffiffiffi p
kt ratio value of
0.04 mol 1/2 l 1/2 s 1/2. By comparing with that
determined for MMA (kp= ffiffiffiffi p
kt ¼ 0:12), it was
deduced that 4 is about three times less reactive than
MMA. This difference of reactivity between 4 and
MMA can be explained both by steric hindrance
and radical resonance stabilization of cinamate unit.
The lower reactivity of 4 compared with that of
MMA was confirmed by the results of copolymerizations
performed between 4 and MMA, more
especially by reactivity ratios of 4 (r1 = 0.08) and
MMA (r2 = 2.8) determined from the Finneman–
Ross method.
A first test of photoreactivity performed with 6b
showed that the synthesized polymers can crosslink
in the solid state when they are exposed to UV
irradiation.
The insolubility of the film at the end of the exposure
to UV irradiation and the disappearance of the
UV absorbance at k = 310 nm characteristic of the
cinnamate functions, are significant that crosslinking
occurred probably according to a mechanism
similar to that found for cinnamate acid and its
derivatives [17].
Acknowledgement
Wavelength
Fig. 7. UV and IR spectra of copolymer 6b (f = 0.3) recorded after each exposure interval.
The authors thank the ‘‘Comité Mixte Franco-
Marocain’’ for its financial support through the