Phosphorus compounds as photoinitiators for radicalic polymerization

Article abstract of DOI:10.1080/15421400490478957

p-Methoxybenzoyldialkylphosphonates, where alkyl = methyl, ethyl and p-methoxy-benzoyldiphenylphosphine oxide were synthesized by Michaelis-Arbuzov reaction. These compounds were used as photoinitiators for radicalic polymerization of acrylic monomers. Th

Full text of DOI:10.1080/15421400490478957

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Phosphorus Compounds as
Photoinitiators for Radicalic
Polymerization
Lavinia Macarie a , G. Ilia a , Smaranda. Iliescu a
,
Adriana. Popa a , G. Dehelean a , I. Manoviciu b , A.
Petrean b & M. J. M. Abadie c
a Institute of Chemistry , Romanian Academy ,
Timisoara, 1900, Romania
b University “Politehnica” , Timisoara, 1900,
Romania
c University Montpellier 2 , Montpellier, France
Published online: 18 Oct 2010.
To cite this article: Lavinia Macarie , G. Ilia , Smaranda. Iliescu , Adriana. Popa , G.
Dehelean , I. Manoviciu , A. Petrean & M. J. M. Abadie (2004) Phosphorus Compounds
as Photoinitiators for Radicalic Polymerization, Molecular Crystals and Liquid Crystals,
416:1, 165-173, DOI: 10.1080/15421400490478957
To link to this article: http://dx.doi.org/10.1080/15421400490478957
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Mol. Cryst. Liq. Cryst., Vol. 416, pp. 165=[421]–173=[429], 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080=15421400490478957
PHOSPHORUS COMPOUNDS AS PHOTOINITIATORS
FOR RADICALIC POLYMERIZATION
Lavinia Macarieꢀ, G. Ilia, Smaranda. Iliescu, Adriana. Popa,
and G. Dehelean
Romanian Academy, Institute of Chemistry,
1900 Timisoara, Romania
I. Manoviciu and A. Petrean
University ‘‘Politehnica’’, 1900, Timisoara, Romania
M. J. M. Abadie
University Montpellier 2, Montpellier, France
p-Methoxybenzoyldialkylphosphonates, where alkyl ¼ methyl, ethyl and
p-methoxy-benzoyldiphenylphosphine oxide were synthesized by Michaelis-
Arbuzov reaction. These compounds were used as photoinitiators for radicalic
polymerization of acrylic monomers. The photoreactivity parameters were de-
termined by differential photocalorimetry (DPC), in isothermal conditions,
using 1,6-hexandioldiacrylate (HDDA) as monomer, in the presence and
absence of amine. The influence of concentration on film pendulum hardness
was studied.
Keywords: acylphosphonates; acylphosphine oxides; differential photocalorimetry
INTRODUCTION
In the field of photoinitiators, phosphorus compounds of type acylpho-
sphine oxides and acylphosphonates have been developed as a new class
of UV photoinitiators. These compounds are effective as photoinitiators
for various unsatured systems, especially they are reactive towards acry-
lates [1,2]. On UV irradiation acylphosphonates and acylphosphine oxides
undergo a Norrish type I a-scission to form carbonyl and phosphonyl radi-
cals able to initiate polymerization [3].
ꢀCorresponding author. E-mail: lavi mac@yahoo.com
165=[421]

166=[422]
L. Macarie et al.
The aim of this paper is to present the synthesis of p-metoxybenzoyl-
dialkylphosphonates (alkyl ¼ methyl, ethyl) and p-metoxybenzoyldiphe-
nylphosphine oxide, and their applications as photoinitiators for radical
polymerization of acrylic monomers.
Differential photocalorimetry was used to monitor polymerization reactions.
Their photoinitiating efficiency was compared with commercial products.
The influence of concentration on pendulum hardness was determined.
EXPERIMENTAL
Acylphosphonates were synthesized by Michaelis-Arbuzov reaction be-
tween acidic chlorides and trialkylphosphites (reaction 1) and acylpho-
sphine oxide was synthesized by Michaelis-Arbuzov reaction between
acidic chlorides and diphenylmethylphosphinite (reaction 2) [1,2]:
Reagents
Trialkylphosphites were used as received from Aldrich.
Acidic chlorides were obtained in laboratory from p-methoxybenzoic
acid and thionyl chloride in molar ratio 1:1.5, respectively [4]. In such cases
all thionyl chloride must be removed from acidic chloride before addition of
the trialkylphosphite.
Diphenylmethylphosphinite was obtained from diphenylchlorphosphine
and methanol in petroleum ether, in the presence of N,N-diethylaniline,
as previously reported [5].

Photoinitiators for Radicalic Polymerization
167=[423]
Synthesis of p-methoxybenzoyldialkylphosphonates
In a flask equipped with mechanical or magnetic stirrer, dropping funnel
and condenser was added the acidic chloride in toluene. Trialkylphosphite
(alkyl ¼ methyl, ethyl), in stoichiometric ratio, was added drop wise over
20 min by stirring continuously. The reaction mixture was heated for 2
hours over an oil bath at 40ꢁC when the reagent is trimethylphosphite,
and for 8 hours at 80ꢁC when the reagent is triethylphosphite, with continu-
ous stirring. Acyldialkylphosphonate was purified by vacuum distillation
(90ꢁC=12 mmHg).
Synthesis of p-methoxybenzoyldiphenylphosphine Oxide
In a flask equipped with mechanical or magnetic stirrer, dropping funnel
and condenser was added 0.1 mol p-metoxibenzoyl chloride in toluene.
0.1 mol diphenylmethylphosphinite was added to p-metoxibenzoyl chloride
drop wise, over 20 min, with continuous stirring. The mixture was heated at
60ꢁC for 2 hours. The obtained compound were recrystallized from cyclo-
hexane.
The synthesized compounds were characterized by IR spectroscopy
using FTIR Nicolet 710 spectrometer.
Photoinitiating Activity
Materials
1,6-hexanedioldiacrylate (HDDA) (Aldrich) was used without further
purification. The photoinitiators were the synthesized compounds: p-meth-
oxybenzoyldialkylphosphonates alkyl ¼ methyl, ethyl and p-methoxy
benzoyldiphenylphosphine oxide (Scheme 1). Commercial photoinitiator
Lucirin TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) (BASF)
was used as received (Scheme 1). Secondary and tertiary amines: diethy-
lamine (DEA), triethylamine (TEA) and N,N-dimethylbenzylamine
(BDMA) (Aldrich) were used as synergist additives.
Technique
Differential scanning photocalorimetry was performed using a DuPont
930 irradiation unit with a double head differential calorimeter 912
calibrated with indium metal standard. A standard high pressure Hg lamp
with 3 mW=cm2 light intensity was used for sample UV exposure.
Sample Preparation
About 1.5 ꢂ 0.5 mg sample containing monomer HDDA, photoinitiator in
a concentration of 3% weight versus monomer, and amine 3% versus

168=[424]
L. Macarie et al.
SCHEME 1 Monomer and photoinitiators.
monomer, were added in an aluminium DPC pan, and than covered with a
PET film in order to minimize oxygen inhibition effect. Another sample is
the reference which contains only HDDA, crosslinked before, to became
inert.
Measurement
DPC experiments were carried out using computer controlled isothermal
methods. Before irradiation, the sample and the reference were placed in
the DPC furnace for 5 min under nitrogen to remove residual oxygen and
to allow temperature stabilization. Then the sample and the reference
were irradiated for 5 min in an inert atmosphere. The heat flow (W=g)
versus exposure time (min) was recorded for each sample to obtain
photoreactivity parameters: polymerization enthalpy, time to reach
maximum, percentage reacted at peak maximum, induction time (time
to reach 1% conversion) and rate constant. Induction time is shorter
when the photoinitiator is more reactive.
RESULTS AND DISCUSSION
In Table 1 are presented data concerning synthesis and characterization of
acyldialkylphosphonates and acylphosphine oxide.
The synthesized compounds were characterized by IR spectroscopy. The
P
B
O and PꢃOꢃC(phosphonate) are the functional groups which is most

Photoinitiators for Radicalic Polymerization
169=[425]
TABLE 1 Synthesis of Acylphosphonates and Acylphosphine Oxide
Phosphorus
contain
Nr.
crt.
Compound
Aspect
Yields, %
exp.
teor.
12.70
10.91
9.22
1.
p-methoxybenzoyldimethyl-
phosphonate MBDMP
liquid p.f.2.5 170ꢁC
liquid p.f.0.4 158ꢁC
83
71
77
12.12
11.4
8.98
2.
p-methoxybenzoyldiethyl
phosphonate MBDEP
3.
p-methoxybenzoyl diphenyl
phosphineoxide MBDPPO
white crystals
m.p. 180–182ꢁC
readily recognized from its IR strong absorption bands in the region 1320–
1200 cmꢃ1 and 1088–950 cmꢃ1, respectively [6]. The absorption band of
PꢃC(alkyl) bond can be identified in the region 785–680 cmꢃ1, which have
weak intensity. In the case of acylphosphine oxides, a strong absorption
band can be identified at 1440 cmꢃ1 (Table 2).
In Figure 1 is shown a typical thermogram with photoreactivity para-
meters for the photoinitiated polymerization of HDDA using MBDPPO as
photoinitiator in a concentration of 3%, in the presence of 3% TEA.
From the thermograms it can obtain photoreactivity parameters of
photoinitiated polymerization of HDDA with synthesized photoinitiators.
Photoreactivity parameters for synthesized compounds, recorded by dif-
ferential photocalorimetry, are shown in Table 3. Theoretical polymeriza-
tion enthalpy for HDDA is 710.5 J=g [7].
From Table 3 it can observe that MBDPPO shows the better values of
photoreactivity parameters (in the presence of TEA), especially the induc-
tion time (ti ¼ 1.3 s) and the enthalpy of polymerization (DH ¼ 533.3 J=g).
That means that MBDPPO is an effective photoinitiator, as effective as
commercial product Lucirin TPO(ti ¼ 1.3 s, DH ¼ 517.37 J=g). MBDMP
TABLE 2 Characteristic IR Absorption Bands of Synthesized Compounds
PꢃC
(aliphatic)
cmꢃ1
PꢃC
(aromatic)
cmꢃ1
PꢃOꢃC
(phosphonate)
cmꢃ1
Nr.
crt.
P BO
Compound
cmꢃ1
1.
2.
3.
MBDMP
MBDEP
MBDPPO
1262
1257
1252
697
696
650
–
–
1028
1023
–
1440

170=[426]
L. Macarie et al.
FIGURE 1 Typical thermogram of photoinitiated polymerization of HDDA with
MBDPPO in the presence of TEA.
TABLE 3 Photoreactivity Parameters for the Polymerization of HDDA with
Synthesized Photoinitiators, in Isothermal Conditions (tꢁ ¼ 30ꢁC), in the Presence
of Various Amines
Peak
Enthalpy, maximum,
Reacted at Induction
time,
sec
peak,
%
k,
1=min
Photoinitiator Amine
J=g
sec
MBDMP
TEA
DEA
536.9
472.0
480.2
527.2
6.0
6.4
20.4
19.5
21.0
24.0
2.1
2.4
2.6
6.9
13.721
13.283
10.066
3.572
BDMA
without amine
8.0
21.2
MBDEP
TEA
DEA
504.5
454.8
491.8
6.4
6.8
9.0
20.7
19.0
23.9
2.4
2.6
2.9
12.175
11.734
9.877
BDMA
MBDPPO
TEA
DEA
533.3
504.0
416.6
2.8
3.4
5.2
15.6
16.8
15.8
1.3
1.5
2.5
27.312
22.618
16.644
BDMA
Lucirin TPO
–
517.37
2.8
16.3
1.3
26.281

Photoinitiators for Radicalic Polymerization
171=[427]
FIGURE 2 Conversion (a) and rate of polymerization (b) of HDDA with synthe-
sized photoinitiators at a concentration of 3%, in the presence of 3% TEA.
and MBDEP have also short induction time and they perform good photo-
initiating activity.
In Figures 2 and 3 are shown the variation of conversion and polymeriza-
tion rate versus time of UV exposure in comparison with Lucirin TPO.
It can observe that the best values of conversion and rate were obtained
using MBDPPO, better than Lucirin TPO.
The photoreactivity parameters depend on amine. In the case of photo-
initiated polymerization of HDDA using MBDMP without amine, the induc-
tion time is greater that in case when amine is added. The role of amine is
of an oxygen scavenger. It is well known that phosphorus radicals rapidly
react with oxygen and thus probably partially consumed by this reaction
[8]. The best results were obtained by adding TEA and DEA (Figure 3 a, b).
FIGURE 3 Conversion (a) and rate of polymerization (b) of HDDA with MBDMP
photoinitiator at a concentration of 3%, in the presence of various amines 3%
and without amine.

172=[428]
L. Macarie et al.
By adding TEA and DEA it was obtained more efficient photoinitiating
activity of MBDMP than by adding BDMA or without amine. BDMA is steric
hindered and reacts slower with atmospheric oxygen.
Photoinitiator Applications
The synthesized compounds were used as UV curing photoinitiators of dia-
crylate Photomer 3015 (Henkel) films. Photopolymerizable formulation
containing monomer, photoinitiator and additive (amine) was laid down
on a glass panel with a film applicator. UV curing was carried out using
¨
Hg lamp, situated 15 cm above surface of formulation. The Konig pendulum
hardness of cured film was determined using pendulum hardness test
according with DIN 53157. The results are shown in Table 4.
It can observe from Table 4 that by adding amine the values of the pen-
dulum hardness decrease, although in differential photocalorimetry experi-
ments, by adding amines, were obtained better values for photoreactivity
parameters. However, there are small differences between photoreactivity
parameters obtained at photoinitiated polymerization with and without
amine. In practical applications, great values of pendulum hardness means
good resistance of the films to solvents and weathering.
The influence of photoinitiator concentration on pendulum hardness of
acrylate films was studied.
In the Figure 4 are shown the variation of the pendulum hardness of
Photomer 3015 films, using MBDMP as photoinitiator.
The pendulum hardness of the film pronounced increases from a con-
centration of 1% to 1.5% and slowly up to 1.5%. Good values for pendu-
lum hardness were obtained from a concentration of 3%.
TABLE 4 Pendulum Hardness of UV Cured Films of Photomer 3015 in the Absence
and in the Presence of TEA as Additive, After 1 min. Exposure Time
Pendulum hardness, s
Photoinitiator
MBDMP
Film thickness, mm
Without TEA
With TEA
120
300
254
265
149
153
MBDEP
120
300
231
239
143
148
MBDPPO
120
300
242
264
235
259

Photoinitiators for Radicalic Polymerization
173=[429]
FIGURE 4 The influence of concentration on pendulum hardness.
CONCLUSION
p-Methoxybenzoyldialkylphosphonates, where alkyl ¼ methyl, ethyl and
p-methoxy-benzoyldiphenylphosphine oxide were synthesized by Michaelis-
Arbuzov reaction. These compounds were tested as photoinitiator for
radicalic polymerization of diacrylate monomer HDDA by differential
photocalorimetry method. They showed a very good photoreactivity
efficiency, comparable with commercial product Lucirin TPO. The influ-
ence of amine on photoreactivity parameters was studied. The best
results were obtained in the presence of TEA. The influence of concen-
tration on pendulum hardness was studied.
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ihre Verwendung, DE 2830927.
[2] Lechtken, P., Buethe, I., Jacobi, M., & Trimborn, W. (1980) (BASF): Acylphosphinoxidver-
bindungen, ihre Herstellung und Verwendung, DE 2909994.
[3] Sumioshi, T. & Schnabel, W. (1985). Laser flash photolysis of acyl phosphonic acid ester.
J. of Photochemistry, 30, 63.
˘
[4] Nenitescu, C. (1980). Chimie Organica, Did. s¸i Ped. Bucures¸ti, (Ed.), Vol. I, p. 789.
[5] Meerweein, H. (1965). Houben Weyl, Vol. VI=3, p. 295.
[6] Thomas, L. C. (1974). The Identification of Functional Groups in Organophosphorus
Compounds, Academic Press, p.23.
[7] Moore, J. E. (1980). Calorimetric Analysis of UV Curable Systems from UV Curing: Science
and Technology, (Ed.) Tech. Market Corp. USA.
[8] Davidson, R. S. (1993). The Role of Amines in UV Curing Radiation in Polymer Science
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