a highly efficient polyurethane-type polymeric photoinitiator containing in-chain benzophenone and...

Full Paper DOI: 10.1002/macp.200600436 2321

Summary: A novel polyurethane-type polymeric photoini-tiator (PUIOA) was synthesized through polycondensationof a novel diamine AAPBP, TDI and MDEA. The BP andcoinitiator amine structures were successfully introducedinto the backbones of PUIOA. A polymeric photoinitiatorwithout the coinitiator amine in the polymer chain (PUIO)was also synthesized for comparison. FT-IR, 1H NMR andGPC analyses confirmed the structures of polymeric photo-initiators. The UV-vis spectra of PUIOA and PUIO are

similar to the parent AAPBP, and both exhibit high red-shifted maximal absorption as compared with BP. ESRspectra indicate that PUIOA can generate free radicals mostefficiently. Photopolymerization of the Polyurethane prepo-lymer, initiated by PUIOA, PUIO/MDEA, AAPBP/MDEAand BP/MDEA, was studied by photo-DSC. The resultsshow that PUIOA is the most efficient photoinitiator for PUprepolymer.

Synthesis routes for polymeric photoinitiators.

A Highly Efficient Polyurethane-Type

Polymeric Photoinitiator Containing In-chain

Benzophenone and Coinitiator Amine for

Photopolymerization of PU Prepolymers

Jun Wei, Hongyu Wang, Xuesong Jiang, Jie Yin*

Research Institute of Polymer Materials, School of Chemistry and Chemical Technology, State Key Laboratory for CompositeMaterials, Shanghai Jiao Tong University, Shanghai 200240, ChinaFax: þ86 21 5474 7445; E-mail: [email protected]

Received: August 24, 2006; Revised: September 29, 2006; Accepted: October 9, 2006; DOI: 10.1002/macp.200600436

Keywords: benzophenone; coinitiator amine; photopolymerization; polymeric photoinitiator; polyurethanes

Introduction classified into two types: photofragmentation (type-I

In order to circumvent some drawbacks derived from

conventional low molecular weight photoinitiators, such as

odor, yellowing and migration in the post-cured materials,

polymeric photoinitiators have been studied as good alter-

natives and they have attracted remarkable interest

recently.[1–16] Compared with the low molecular weight

analogues, the presence of polymer chain can improve

the compatibility in the formulation in many cases and

reduce the migration onto the film surface, which contri-

bute to the synthesis of low-odor and non-toxic pro-

ducts.[17–26] These polymeric photoinitiators have been

Macromol. Chem. Phys. 2006, 207, 2321–2328

photoinitiators) and hydrogen-abstraction chromophores

(type-II photoinitiators). Most of type-II polymeric

photoinitiators are based on benzophenone (BP) deriva-

tives,[12,26–28] and their photoefficiency can be promoted in

the presence of a hydrogen donor such as tertiary

amines.[16–18,29–32] The incorporation of both BP and

coinitiator amine into the same polymer chain has obvious

advantages, such as intramolecular reactions responsible

for the formation of more reactive species, protecting the

active species by macromolecular chain[8,13,33–36] and

avoiding the migration of low molecular weight coin-

itiators in the post-cured materials.

� 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2322 J. Wei, H. Wang, X. Jiang, J. Yin

From the viewpoint of the applications of polymeric

photoinitiators, UV radiation is a well-accepted technology

for the fast curing of polymeric materials.[33] Among

them, UV-curable coating is one of the substitutes for

the conventional solvent-based coating[34–36] because of

the fast cure response, good weathering characteristics,

excellent chemical resistance and the possibility of reduc-

ing environmental pollution. Coatings based on polyur-

ethanes (PUs) are one of the most widely used in industrial

applications due to their well-balanced properties, such

as high impact and tensile strength, abrasion resistance,

toughness and excellent resistance to chemicals and sol-

vents.[37] Moreover, different properties of PU can be

easily tailored by the variation of soft or hard segments

in its structure.[38] Therefore, it may be very valuable to

synthesize amino-terminated or hydroxyl-terminated PU-

type polymeric photoinitiators to initiate PU prepolymers.

These PUs can work both as efficient polymeric photo-

initiators and functional prepolymers due to the residual

hydroxyl or amino group. For example, if they are further

introduced into another UV-curable backbone as prepoly-

mers, they may undergo self-initiation upon UV irradia-

tion. Moreover, this PU type photoinitiator may also have

good compatibility to the PU-based photo-curing systems.

In this context, taking account of the advantages of

polymeric photoinitiators and their potential applications

in UV-curable systems, we provide a facile way to achieve

functional PU type polymeric photoinitiators. Through

polycondensation of a novel diamine monomer of 4-amino-

40-[4-aminophenoxyl]benzophenone (AAPBP), toluene-2,

4-diisocyanate (TDI) andN-methyldiethanolamine (MDEA),

we obtained a PU-type polymeric photoinitiator containing

in-chain BP and tertiary amine (PUIOA). UV-vis and

electron spin resonance (ESR) spectra were studied to

investigate their photochemical behavior. A difunctional

PU prepolymer was initiated by PUIOA through differ-

ential scanning photocalorimetry (photo-DSC). In order

to investigate the photoinitiation mechanism, a polymeric

photoinitiator without coinitiator amine in the poly-

mer chain (PUIO), as well as the small molecule BP

and AAPBP, were also synthesized for comparison.

Experimental Part

Materials

4-Aminophenol, TDI, N,N-dimethylformamide (DMF), anhy-drous potassium hydroxide, N-methyl-2-pyrrolidone (NMP),dibutyltindilaurate (T12) (from Medicine Group of China),MDEA (from Kewang Chemical Reagent Company), PUprepolymer (UA-4200, CAS No. 199875-93-9, functionality2, from Shin-Nakamura Chemical Co. Ltd.) and 4-amino-40-chlorobenzophenone (ACBP; synthesized in our laboratoryaccording to our previous work[39]) were used in the presentedstudy. Other chemicals were of analytical grade except asnoted.

Macromol. Chem. Phys. 2006, 207, 2321–2328 www.mcp-journal.de

Monomer Preparation

Synthesis of AAPBP

A three-necked flask that contained 12.00 g (0.11 mol) of4-aminophenol, 23.16 g (0.10mol) of ACBP, 6.72 g (0.12 mol)of KOH, 15 mL of toluene and 40 mL of NMP was equippedwith a nitrogen pad and a Dean-Stark trap. The mixture washeated at 130 8C for 3 h to strip off most of the toluene anddehydrate the reaction system, and then the temperature waskept at 170–175 8C for an additional 6 h. After cooling downto ambient temperature, the resultant viscous solution wasfiltered to remove most of the salt before being poured into500 mL of 6 N HCl aqueous solution. The precipitate wascollected by filtration before pouring into 200 mL of water,and then ammonia water was added dropwise to the solutionuntil the pH value is over 7. The precipitate was filtered andwashed with a large amount of water. The crude productwas recrystallized from mixed solvent of isopropyl alcoholand water, and dried under vacuum at 50 8C for 48 h to yield22.94 g of AAPBP. Yield: 75.4%.

mp: 147.5 8C (DSC in N2). EIMS (70 eV): m/e¼ 304.1H NMR (DMSO-d6, 400 MHz): d¼ 7.60–7.57 (2H,

aromatic), 7.50–7.47 (2H, aromatic), 6.92–6.89 (2H, aro-matic), 6.83–6.81 (2H, aromatic), 6.63–6.56 (4H, aromatic),6.07 (2H, NH2), 5.13 (2H, NH2).

FT-IR (KBr, cm�1): 3 358 (NH2), 1 676 (C––O), 1 236 (Ar–O–

Ar).

Elemental analysis, C19H16N2O2: Calcd. C 74.98, H 5.30,N 9.20; Found C 74.86, H 5.30, N 9.14.

Polymer Preparation

Synthesis of Polymer ContainingIn-Chain BP (PUIO)

A three-necked flask that contained 5.40 mmol (0.940 g) TDIand 10 mL of DMFwas equipped with magnetic stirring undernitrogen atmosphere. A solution of 6.00 mmol (1.826 g)AAPBP in 10 mL of DMF was added dropwise through adropping funnel over 15 min. In this process, the molar ratio ofamino group (NH2) to isocyanate group (NCO) was main-tained at 1:0.9. The mixture was stirred at room temperaturefor 1 h and then it was heated at 50 8C for an additional 1 h.After it was cooled down to ambient temperature, the resultantsolution was poured into ten-fold diluted aqueous solution ofammonia water. The solution was filtered to collect an yellowproduct, which was dried in vacuum to obtain polymericphotoinitiator containing in-chain BP (PUIO).

PUIO: Mn ¼ 5.2� 103, Mw=Mn ¼ 1.36 (determined byGPC using DMF as eluent).

1H NMR (DMSO-d6, 400 MHz): d¼ 8.75–8.74 (1H, NH),8.62–8.61 (1H, NH), 7.74–7.71 (2H, aromatic), 7.64–7.62(2H, aromatic), 7.54–7.50 (4H, aromatic), 7.07–7.04 (3H,aromatic), 6.59–6.58 (2H, aromatic), 6.09 (2H, aromatic),2.18–2.16 (3H, CH3).

FT-IR (KBr cm�1): 3 354 (N–H), 1 660 (C––O of –NHCO–),1 596 (C––O of Ar–CO–Ar), 1 226 (Ar–O–Ar).


A Highly Efficient Polyurethane-Type Polymeric Photoinitiator Containing . . . 2323

Synthesis of Polymer Containing In-Chain BP andCoinitiator Amine (PUIOA)

A three-necked flask that contained 6.00 mmol (1.045 g) TDIand 10 mL of DMFwas equipped with magnetic stirring undernitrogen atmosphere, and a solution of 3.00 mmol (0.913 g)AAPBP in 10 mL of DMF was added dropwise in 10 min andstirred at room temperature for 1 h, then the mixture washeated at 50 8C for an additional 1h. During this process, themolar ratio of NH2 to NCO was maintained at 1:2. After it wascooled down to ambient temperature, a solution of 4.5 mmol(0.536 g) MDEA in 5 mL of DMF and a drop of T12 wereadded, and the molar ratio of NCO to OH was maintained at1:1.5. The mixture was heated at 60 8C for 6 h. The resultantsolution was poured into ten-fold diluted aqueous solutionof ammonia water. The solution was filtered to collect anyellow product, which was washed twice with water anddried in vacuo to obtain polymeric photoinitiator containingin-chain BP and coinitiator amine (PUIOA).

PUIOA: Mn ¼ 4.9� 103, Mw=Mn ¼ 1.28 (determined byGPC using DMF as eluent).

1H NMR (DMSO-d6, 400 MHz): d¼ 8.81–8.80 (1H, NH),8.63–8.62 (1H, NH), 7.74–7.71 (2H, aromatic), 7.64–7.60(2H, aromatic), 7.52–7.48 (4H, aromatic), 7.08–7.04 (3H,aromatic), 6.59–6.57 (2H, aromatic), 6.09 (2H, aromatic),4.31(2H, CH2), 4.13–4.11 (2H, CH2), 3.46–3.45 (2H, CH2),2.64–2.63 (2H, CH2), 2.24 (3H, Ar-CH3), 2.11–2.08 (3H,NCH3). FT-IR (KBr, cm�1): 3 346 (NH), 2 954, 2 860 (CH2),1 702 (C––O of –NHCO–), 1 596 (C––O of Ar–CO–Ar), 1 226(Ar–O–Ar).

Measurements

Physicochemical Measurements

Molecular weights were determined by gel permeationchromatography (GPC) on a Perkin Elmer Series 200apparatus on the basis of linear polystyrene (PS) standards.DMF was used as eluent. 1H NMR spectra were recorded on aMercury Plus 400 MHz spectrometer with DMSO-d6 as thesolvent. Fourier-transform infrared (FT-IR) spectra wererecorded on a Perkin-Elmer Paragon1000 FT-IR spectrometer.The samples were prepared as KBr discs. UV-vis spectra wererecorded in chloroform solution by Perkin-Elmer Lambda20 UV-vis spectrophotometer.

ESR experiments were carried out with a Bruker EMX EPRspectrometer at 9.77 GHz with a modulation frequency of100 kHz with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) asradical capturing agent. A high-pressure mercury lampwas used for irradiation in the ESR spectrometer cavity.The concentration of polymeric photoinitiators dissolved indichloromethane was 1� 10�3

M, and 0.5 mL of each samplewas transferred into a quartz ESR tube and then purged withnitrogen to remove the oxygen.

Photocalorimetry (Photo-DSC)

The photopolymerization of PU prepolymer was carried outby a DSC 6200 (Seiko Instrument Inc.) photo-DSC according


to ref.[18] Approximately 2 mg of sample mixture was placedin the aluminum DSC pans.

Heat flow versus time (DSC thermogram) curves wererecorded in an isothermal mode under a nitrogen flow of50 mL �min�1. The reaction heat liberated in the polymeriza-tion was directly proportional to the number of vinyl groupsreacted in the system. By integrating the area under the exo-thermic peak, the conversion of the vinyl groups (C) or theextent of reaction could be determined according to theequation

C ¼ DHt=DHtheor0 (1)

where DHt is the reaction heat evolved at time t, and DHtheoro is

the theoretical heat for complete conversion. DHtheoro ¼ 86

kJ �mol�1 for an acrylic double bond.[40] The rate ofpolymerization (Rp) is directly related to the heat flow (dH/dt) by the following equation

Rp ¼dC

dt¼ dH

dt

� �1

DHtheor0

(2)

Results and Discussion

Monomer Synthesis

In the presence of a strong base (KOH), the diamine

AAPBP was synthesized through nucleophilic substitution

reaction of 4-amino-40-chlorobenzophenonewith 4-amino-

phenol in one step, as shown in Scheme 1. In order to attain

high yield of AAPBP, toluenewas used to remove thewater

produced from the reaction system and accelerate the

velocity of the reaction. The structure of AAPBP was

characterized by 1H NMR and FT-IR spectra, and further

confirmed by mass spectral and elemental analysis.

Polymer Synthesis

Two polymers were synthesized by polycondensation

according to Scheme 1. By keeping the molar ratio of

amino group (NH2)/isocyanate group (NCO) at 1:0.9,

NH2-terminated polymeric photoinitiators containing

in-chain BP (PUIO) were synthesized through the poly-

condensation of AAPBP with TDI. PUIOA was synthe-

sized through two steps: at first, NCO-terminated polymer

was synthesized through polycondensation of AAPBP and

TDI by keeping the molar ratio of NCO/NH2 at 2:1, then

through a chain-extending reaction of NCO-terminated

polymer with MDEA (NCO/OH¼ 1:1.5), coinitiator amine

was successfully incorporated into the macromolecular

backbone. FT-IR, 1H NMR and GPC spectra confirmed

the structures of the two polymers. The appearance of

signals related to the urethane and urea group in IR and1H NMR spectra of polymers, was considered as evidence



Scheme 1. Synthesis routes for polymeric photoinitiators.

of completion of the reaction, which is also shown by

the molecular weight of polymers as determined by GPC.

As for the OH-terminated polymeric photoinitiator

(PUIOA), it can work as an efficient photoinitiator, as

well as a functional prepolymer due to the residual reactive

hydroxyl group.

Figure 1. UV-vis absorption spectra of photoinitiators inchloroform solution. (The concentration was 0.025� 10�3

M interms of benzophenone (BP) moieties.)

UV-Vis Spectra

UV absorption spectra of BP, BP/MDEA, AAPBP, PUIO

and PUIOA in chloroform of low concentration (0.025�10�3

M) are shown in Figure 1. Their maximum absorption

(lmax) and the values of molar extinction coefficient e atlmax are summarized in Table 1. The maximal absorption

of these photoinitiators is important in terms of their

photochemical activity.

In Figure 1 and Table 1, the maximal absorption of BP is

254 nm. Because the UV spectra of photoinitiators were

measured at a very low concentration, this transition can

be attributed to the main benzenoid p-p� type transition

of BP.[41] Taking into account that the polarity of the

microenvironment of BP moieties will increase in the


presence of amino group (nitrogen atom), and the

increasing polarity may affect its maximal absorption,

the UV spectra of BP/MDEA was also measured for

comparison. Compared with BP and BP/MDEA, AAPBP



Table 1. Absorption properties of photoinitiators in chloroformsolution.

Photoinitiatora) lmax e

nm 104 mol�1 � cm�1 �L

PUIOA 315 2.486PUIO 316 1.903AAPBP 316 2.204BP 254 1.738BP/MDEA 256 1.733

a) The photoinitiator concentration was 0.025� 10�3M in terms

of BP moieties.

possesses a significantly red-shifted maximal absorption of

316 nm, which may be ascribed to the electron donation via

the phenoxy group. As for AAPBP, PUIO and PUIOA

also possess a greatly red-shifted maximal absorption as

compared with BP. This red-shifted maximummakes these

polymers attractive as photoinitiators, suitable for UV-

curing near the visible light. Meanwhile, they possess an

absorption similar to AAPBP, which indicates that the

macromolecular structure has no obvious influence on

UV-vis absorption of BP moieties of polymeric photo-

initiators.

ESR Spectroscopy

To get information on the photoinitiation mechanism, ESR

studies of AAPBP/MDEA, PUIO/MDEA and PUIOAwere

carried out in dichloromethane, with DMPO as a radi-

cal trapper, and the results are shown in Figure 2. The

mechanism of radicals trapping by DMPO is depicted in

Figure 2. ESR spectra of photoinitiators in dichloromethane,irradiated for 5 min. (a) AAPBP/MDEA, (b) PUIO/MDEA and(c) PUIOA.


Scheme 2. As shown in Figure 2(b), ESR signals usually

have six-line hyperfine splitting, which is explained by

a triplet with a-nitrogen and a further split into a doublet

with a b-proton.[16] Because of the stronger electron-

donating ability of methylene groups with respect to

methyl groups in the MDEA, the excited triplet BP

moieties may abstract hydrogen mainly from the methyl-

ene groups.[42] Therefore, the amine radical (1) (depicted

in Scheme 3) marked in Figure 2(b) is the main radical. In

Figure 2, ESR spectrum of PUIO/MDEA system is more

complicated, which indicates that some other radicals may

be trapped by DMPO besides the main radical (1). This

result implies that the excited state of BP moieties may

partly abstract hydrogen from the methyl group of MDEA.

However, compared with the main six-line hyperfine

splitting, the signal intensity of these radicals is very weak.

In Figure 2(c), PUIOA has the highest single intensity

among the three photoinitiator systems. This result may

be addressed to its macromolecular structure, which favors

the possibility of intramolecular energy transfer and

hydrogen-abstraction between the excited state of BP

and MDEA moieties along the polymer chain.

Compared with the AAPBP/MDEA system, PUIO/

MDEA possesses a slightly higher signal intensity. This

result may be ascribed to the dramatic difference between

the structures of small molecule and polymer. As for

AAPBP, because of the electron-donating effects of amino

group and phenoxy group towards BP moieties, the

electronegativity of carbon atom in carbonyl group would

be increased. However, the bimolecular hydrogen-abstrac-

tion reaction between BP moieties and MDEA belongs to a

nucleophilic reaction. Thus, the increased electronegativity

of carbon atom would certainly disfavor the hydrogen-

abstraction reaction, leading to low concentration of free

radicals to be generated and relatively lower signal

intensity in ESR spectrum. On the contrary, when AAPBP

was introduced into PUIO, the amino groups were con-

verted to urea groups. The electrophilic effect of urea groups

would decrease the electronegativity of carbon atom in

carbonyl group, and favor the hydrogen-abstraction reac-

tion. As a result, the PUIO/MDEA system can produce a

relatively higher concentration of free radicals than the

AAPBP/MDEA system.

Photopolymerization of PU Prepolymer

Photolysis of BP derivatives, in the presence of coinitiators

such as tertiary amine, leads to the formation of a radical

generated from a carbonyl compound (ketyl-type radical)

and another radical derived from the coinitiator amine.[16,43]

The ketyl radicals are usually inactive for the photo-

polymerization of vinyl monomers, because of the steric

hindrance and the delocalization of unpaired electron.

Therefore, the amine radicals may mainly initiate the vinyl



Scheme 2. Mechanisms for the radicals trapped by DMPO.

photopolymerization.[29,30] The overall photoinitiation

mechanism is presented in Scheme 3, from which we can

deduce that the quantity and the activity of amine radicals

determine the photopolymerization rate.

The photo-DSC profiles of the polymerization of PU

prepolymer for BP/MDEA, AAPBP/MDEA, PUIO/MDEA

and PUIOA are shown in Figure 3. Their polymerization

behaviors appear similar to other multifunctional mono-

mers.[44–48] Figure 4(a) shows that the conversion corre-

sponding to time is dependent on photoinitiators. The data

for the maximal polymerization rate (Rp max) and final

conversion of PU prepolymer are summarized in Table 2. In

Figure 3 and 4 and Table 2, AAPBP/MDEA is the least

efficient photoinitiator system for the polymerization of PU

prepolymer. This result may be ascribed to the low concen-

tration of free radicals generated in the photoinitiator system

as discussed in ESR studies. Compared with the PUIO/

MDEA system, BP/MDEA can initiate the polymerization of

PU prepolymer more efficiently, which may be attributed to

the high viscosity of PU prepolymer (2 000mPa � s � 8C�1). In

order to attain efficient electron and proton transfer, both BP

moieties and MDEA must get as close as possible. It is

obvious that BP has a much higher mobility than the poly-

meric photoinitiator PUIO, leading to more efficient energy

transfer in the BP/MDEA system than that in the PUIO/

MDEA system. Therefore, the BP/MDEA system may

produce a relatively higher concentration of free radicals than

Scheme 3. Proposed initiation mechanisms for photoinitiatorsystems.


PUIO/MDEA system. It is noted that the polymerization rate

of a PU prepolymer depends on the efficiency of forming

primary radicals (amine radicals) by hydrogen-abstraction

reaction, as well as the efficiency of monomers for quenching

primary radicals and forming monomer radicals. Because the

active radicals generated in both BP/MDEA and PUIO/

MDEA systems are the lowmolecular amine radicals, there is

no significant difference in radical activities for initiating the

monomer. As a result, BP/MDEA possesses only a slightly

higher final conversion of PU prepolymer than PUIO/

MDEA.

In Figure 3 and 4 and Table 2, PUIOA is the most

efficient photoinitiator for the polymerization of PU pre-

polymer. This result may be ascribed to the more efficient

intramolecular electron and proton transfer between the

excited state of BP and MDEAmoieties in PUIOA than the

Figure 3. Photo-DSC profiles for polymerization of PU pre-polymer initiated by photoinitiator systems, cured at 25 8C by UVlight with an intensity of 50 mW � cm�2. (The photoinitiatorconcentration was 0.02 M in terms of BP moieties.)



Figure 4. (a) Rate versus conversion; (b) Conversion versustime for polymerization of PU prepolymer for BP/MDEA,AAPBP/MDEA, PUIO/MDEA, PUIOA systems, cured at25 8C by UV light with an intensity of 50 mW � cm�2. (Thephotoinitiator concentration was 0.02 M in terms of BP moieties.)

intermolecular reaction in BP/MDEA and PUIO/MDEA

systems, as discussed in ESR studies. Moreover, the steric

hindrance of the macromolecular coil could disfavor the

recombination reaction between the propagating radicals

Table 2. Photopolymerization of PU prepolymer initiated by photmW � cm�2.

Photoinitiatora) Rp max Final

10�2 s�1

PUIOA 2.045PUIO/MDEA 2.327BP/MDEA 2.720AAPBP/MDEA 0.365

a) The photoinitiator concentration was 0.02 M in term of BP moieties;flow, and Tmax: time to reach maximal heat flow.


and the macroradicals, thus strongly limiting the extent of

termination and preventing a reduction in the concentration

of active species. The major differences between BP/

MDEA and PUIOA systems are that the polymerization

rate of a BP/MDEA system is higher than that of PUIOA at

early stage, but slower at later stage. At early stage, the

mobility and activity of macromolecular amine radicals

may be relatively lower than low molecular amine radicals,

leading to slower polymerization rate and longer time

(Tmax) to reach the maximal polymerization rate (Rp max)

for PUIOA system. Meanwhile, because of the relatively

lower activity of macromolecular amine radicals, it may

form a three-dimensional gel structure with lower cross-

linking density than that of BP/MDEA system. As the

polymerization proceeds, the increased crosslinking level

will eventually limit the mobility of both macromolecular

radicals and double bonds. Therefore, the propagation

reaction may become diffusion controlled along with

radical termination. In this condition, due to the low

crosslinking density of gel structure formed at the early

stage, the polymerization rate of PUIOA may decrease

slowly as compared with BP/MDEA. In addition, the good

compatibility of the PU type photoinitiator with PU

prepolymer may favor the mobility of macromolecular

amine radicals. Therefore, the polymerization rate of PU

prepolymer for PUIOA is faster at the later stage. As a

result, PUIOA possesses a much higher final conversion of

PU prepolymer than BP/MDEA.

Conclusion

In this paper, we presented a facile way to obtain PU type

polymeric photoinitiators containing in-chain BP and

coinitiator amine (PUIOA) through polycondensation. To

investigate its photoinitiation mechanism, a polymeric

photoinitiator without coinitiator amine in polymer chain

(PUIO) was also synthesized for comparison. The results

show that both PUIOA and PUIO possess a greatly red-

shifted UVmaximal absorption as compared with BP. ESR

studies show PUIOA can generate free radicals most

efficiently. Photopolymerization of PU prepolymer, initiated

oinitiators, cured at 25 8C by UV light with an intensity of 50

conversion Hmax Tmax

% mW �mg�1 s

86.67 3.03 11.261.33 3.51 8.865.87 4.13 8.827.53 0.89 19.0

Rp max: the maximal polymerization rate, Hmax: the maximal heat



by PUIOA, PUIO/MDEA, AAPBP/MDEA and BP/MDEA,

was studied by photo-DSC. The results show PUIOA can

efficiently initiate the polymerization of PU prepolymer with

much higher final conversion than that of its low molecular

weight analogues, which indicates that this PU type

polymeric photoinitiator might possess enormous potential

for application in PU-based UV- curable systems.

Acknowledgements: The authors express their gratitude tothe Ministry of Science and Technology of China (no.:2004AA33H010), and theMinistry Education of China (KuashijiScholar Project) for their financial support.

[1] G. Temel, N. Arsu, Y. Yagci, Polym. Bull. 2006, 57, 51.[2] Q. F. Si, X. D. Fan, Y. Y. Liu, J. Kong, S. J. Wang,

W. Q. Qiao, J. Polym. Sci., Part A: Polym. Chem. 2006,44, 3261.

[3] J. W. Seok, Y. S. Han, Y. Kwon, L. S. Park, J. Appl. Polym.Sci. 2006, 99, 162.

[4] X. S. Jiang, H. J. Xu, J. Yin, Polymer 2005, 46, 11079.[5] I. Cakmak, T. Ozturk, J. Polym. Res. 2005, 12, 121.[6] M. Degirmenci, J. Macromol. Sci., Pure. Appl. Chem. 2005,

A42, 21.[7] M. Degirmenci, Polym. J. 2004, 36, 542.[8] C. Carlini, L. Angiolini, D. Caretti, E. Corell, P. A. Rolla,

Polym. Adv. Technol. 1997, 7, 379.[9] M. Degirmenci, G. Hizal, Y. Yagci, Macromolecules 2002,

36, 8265.[10] V. Castelvtro, M. Molesti, P. Rolla,Macromol. Chem. Phys.

2002, 203, 1486.[11] C. Decker, C. Bianchi, S. Jonsson, Polymer 2004, 45, 5803.[12] T. Corrales, F. Catalina, C. Peinado, N. S. Allen,

J. Photochem. Photobiol., A 2003, 159, 103.[13] X. S. Jiang, J. Yin, Macromolecules 2004, 37, 7850.[14] M. Visconti, M. Cattaneo, Prog. Org. Coat. 2000, 40, 243.[15] A. M. Sarker, K. Sawabe, B. Strehmel, Y. Kaneko,

D. C. Neckers, Macromolecules 1999, 32, 5203.[16] X. S. Jiang, H. J. Xu, J. Yin, Polymer 2004, 45, 133.[17] T. Corrales, F. Catalina, C. Peinado, N. S. Allen, A. M. Rufs,

C. Bueno, M. V. Encinas, Polymer 2002, 43, 4591.[18] X. S. Jiang, J. Yin,Macromol. Rapid Commun. 2004, 25, 748.[19] L. Angiolini, D. Caretti, C. Carlini, E. Corell, E. Salatelli,

Polymer 1999, 40, 7197.[20] T. Corrales, F. Catalina, C. Peinado, N. S. Allen,

J. Photochem. Photobiol., A 2003, 159, 103.[21] L. Angiolini, D. Caretti, E. Salatelli, Macromol. Chem.

Phys. 2000, 201, 2646.


[22] C. Decker, Macromol. Rapid. Commun. 2002, 23, 1067.[23] C. Valderas, S. Bertolotti, C. M. Previtali, M. V. Encinas,

J. Polym. Sci., Part A: Polym. Chem. 2002, 40, 2888.[24] C. Peinado, A. Alonso, E. F. Salvador, J. Baselga,

C. Fernando, Polymer 2002, 43, 5355.[25] L. Angiolini, D. Caretti, E. Corelli, C. Carlini, P. A. Rolla,

J. Appl. Polym. Sci. 1997, 64, 2247.[26] X. S. Jiang, J. Yin, J. Photochem. Photobiol., A 2005, 174,

165.[27] C. Carlini, F. Gurzoni, Polymer 1983, 24, 101.[28] R. S. Davidson, H. J. Hageman, S. P. Lewis, J. Photochem.

Photobiol., A 1998, 118, 183.[29] T. Corrales, C. Peinado, F. Catalina, M. G. Neumann,

N. S. Allen, A. M. Rufs, M. V. Encinas, Polymer 2002,41, 9103.

[30] M. Aydin, N. Arsu, Y. Yagci, Macromol. Rapid Commun.2003, 24, 718.

[31] L. Cokbaglan, N. Arsu, Y. Yagci, S. Jockusch, N. J. Turro,Macromolecules 2003, 36, 2649.

[32] J. W. Yang, Z. H. Zeng, Y. L. Chen, J. Polym. Sci., Part A:Polym. Chem. 1998, 36, 2563.

[33] H. Yu, Q. L. Yuan, D. N. Wang, Y. H. Zhao, J. Appl. Polym.Sci. 2004, 94, 1347.

[34] W. K. Huang, K. J. Chen, J. T. Yeh, K. N. Chen, J. Appl.Polym. Sci. 2002, 94, 1980.

[35] N. Kayaman-Apohan, A. Amanoel, N. Arsu, A. Gungor,Prog. Org. Coat. 2004, 49, 23.

[36] C. Decker, F. Masson, R. Schwalm, Polym. Degrad. Stab.2004, 83, 309.

[37] A. Tauber, T. Scherzer, R. Mehnert, J. Coat. Technol. 2000,72, 51.

[38] C. Hepburn, ‘‘Polyurethane Elastomers’’, Applied SciencePublishers, New York 1982, p. 280.

[39] J. Wei, H. Y. Wang, J. Yin, J. Polym. Sci., Part A: Polym.Chem., in press.

[40] E. Andrejewska, M. Andrzejewski, J. Polym. Sci., Part. A:Polym. Chem. 1998, 36, 665.

[41] R. Liska, J. Polym. Sci., Part. A: Polym. Chem. 2002, 40,1504.

[42] G. J. Jiang, Y. Shirota, H.Mikawa, Polym. Photochem. 1986,7, 311.

[43] D. G. Anderson, J. Davidson, J. J. Elvery, Polymer 1996, 37,2477.

[44] K. S. Anseth, C. M. Wang, C. N. Bowman, Polymer 1994,35, 3243.

[45] L. Lecamp, B. Youssef, C. Bunel, Polymer 1999, 40,1403.

[46] Q. Yu, S. Nauman, J. P. Santerre, S. Zhu, J. Appl. Polym. Sci.2001, 82, 1107.

[47] W. D. Cook, Polymer 1992, 33, 2152.[48] W. D. Cook, Polymer 1992, 33, 600.


a highly efficient polyurethane-type polymeric photoinitiator containing in-chain benzophenone and...

Documents