Photocationic Curable Silsesquioxanes Having Oxetanyl Group

Chapter 27

Photocationic Curable Silsesquioxanes Having Oxetanyl Group

Downloaded by CORNELL UNIV on August 3, 2016 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch027

Hiroshi Suzuki, Seitarou Tajima, and Hiroshi Sasaki Corporate Research Lab, Toagosei Company Ltd., 1-1 Funami-cho, Minato-ku, Nagoya-shi, Aichi 455-0027, Japan

Novel oxetanyl-functional silsesquioxanes (SQs) were synthesized and investigated as UV-curable materials. The multi-functional monomer (OX-SQ) was prepared by hydrolytic condensation of 3-ethyl-3-((tri-ethoxysilyl) propoxy)methyloxetane (TESOX). OX-SI-SQ, having a silicone chain partially introduced into SQ skeleton, was also synthesized through polycondensation of TESOX with α, ω -Dihydroxy poly(dimethylsiloxane). OX-SQs (OX-SQ and OX -SI-SQ) were colorless highly viscous liquid and soluble in common solvents. From the H and Si-NMR spectra, the SQ unit in OX-SQs was considered to be a mixture of several structures with a random, ladder or cage structure. OX-SQs exhibited good compatibility with cycloaliphatic diepoxide and gave formulations with high reactivity. OX-SQ gave photocured products of high hardness and OX-SI-SQ added silicone characteristics to the surface of the cured products, which showed excellent pollution-free properties. OX-SQs also exhibited high modulus at high temperature and rather high thermal stability. 1

306

29

© 2003 American Chemical Society

Belfield and Crivello; Photoinitiated Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

307


Introduction Photo-cationic curable materials, using epoxides and vinyl ether derivatives, have been widely investigated. Among them, oxetanes have been proved to possess many good properties, such as safety (AMES Test negative) and high reactivity (I, 2). Based on this chemistry, application of oxetanes as photocurable materials are spreading extensively. In the development of photocurable materials, not only the reactive group but also the structure of the main chain of the oligomer is important. Silicones are very attractive due to their high flexibility and chemical resistance. The introduction of oxetanyl groups into dimethylsiloxane derivatives has already been reported (3, 4). Meanwhile, organic silsesquioxanes (SQ) represented by the formula, (RS1O3/2),,, are a well-known class of compounds for the preparation of both nano-composite and nano-structured organic-inorganic hybrid materials, in which the inorganic silica matrix is covalently bound to the organic moiety (5, 6). SQ can be obtained by hydrolytic polycondensation of organic trichlorosilanes or organic trialkoxysilanes. In recent years, there has been a great deal of interest to functionalize SQ with polymerizable groups, for example, vinyl functional-SQ, allyl-SQ, methacryl-SQ, epoxy-SQ and so on (5, 7). It should be interesting to investigate oxetanyl-functional SQ (OX-SQ) which can be considered a novel multifunctional oxetane compounds possessing the SQ backbone. The present work focuses on the preparation and application of OX-SQ and its derivative having a silicone chain partially introduced into SQ skeleton (OXSI-SQ). The properties of photocured coatings of OX-SQs (OX-SQ and OX-SISQ) were also investigated.

Experimental Materials and experimental conditions used in this study are listed below.

Materials. All reagents were used without a further purification. Triethoxysilane (TRIES) and 3-ethyl-3-allyloxymethyloxetane (AOX) were available from Toagosei Co. a, ω-Dihydroxy poly(dimethylsiloxane) (OH-Silicone) was purchased from Shin-etsu Chemical Co. 3, 4-epoxycyclohexylmethyl-3 , 4epoxycyclohexane carboxylate (UVR-6110) was obtained from Union Carbide f


308 Co. The iodonium salt cationic photoinitiator having hexafluoroantimonate as the counteranion (UV9380C) was availablefromG.E. Toshiba Silicone Co.

Instrumentation.

Gel permeation chromatography (GPC) analysis was carried out using a TOSOH HLC-802A equipped with two polystyrene gel columns (TSK-GEL, 2500HXL+100HXL) to determine the molecular weight of OX-SQs. H and Si-NMR spectra were obtained on a JEOL JNM-400 spectrometer. Photocuring was carried out using an Iwasaki Electric UB062-5B UV processor equipped with a high-pressure mercury lamp (80 W/cm). The viscoelasticity of the cured samples was measured by Dynamic Mechanical Spectrometer (DMS 6100: SEIKO Instruments). TG/DTA320 (SEIKO Instruments) was used for the thermal degradation measurements of cured samples. !


29

Synthesis of3-ethyl-(tri-ethoxysiiylpropoxy)methyl

oxetane

(TESOX).

Under dry nitrogen, 103.1 g (660 mmol) of AOX and 0.3 mL of H PtCl 6H 0 in benzonitrile (0.05 mol/L) were introduced into a 500 mL flask fitted with a mechanical stirrer, dropping funnel and a reflux condenser. The mixture was heated to 70°C and 98.6 g (600 mmol) of TRIES was added dropwise. The reaction mixture was maintained at 80°C for 4 hours. After the reaction was completed, the product was isolated by distillation at 130-140°C under 0.1 mmHg. Yield: 70%. 2

6

2

Preparation

of Oxetanyl-functional

SQ (OX-SQ).

A 300 mL of flask equipped with magnetic stirrer was charged with 19.2 g (60 mmol) of TESOX and 50 mL of isopropyl alcohol (IPA). To the flask, 3.4 g of an aqueous 5.1% solution of Me NOH (Me NOH: 2 mmol, H 0 : 180 mmol) was added dropwise. The reaction mixture was left under stirring at room temperature. The reaction process was followed by GPC, and the reaction was over at the time when the TESOX had almost disappeared, i.e., about 20 hours after addition of the mixture. After the reaction was over, the solution was diluted with 200 mL of toluene and washed with an aqueous saturated sodium chloride. The washing was repeated until the aqueous layer became neutral, and the organic layer was fractionated and dehydrated over anhydrous sodium sulfate. Evaporation of the toluene in vacuo gave the desired condensation product (OXSQ) with quantitative yield. 4

4

2


309

Preparation of OX-SQ having a partial silicone chain (OX-SI-SQ). OX-SI-SQ was obtained by hydrolytic co-polycondensation of TESOX with α,ω-dihydroxy poly(dimethylsiloxane) (OH-Silicone). A 300 mL of flask equipped with a magnetic stirrer was charged with 64.1 g (200 mmol) of TESOX, 10.47 g of OH-Silicone (Mn = 1,000-1,500) and 100 g of IPA. The mixture was allowed to stir at room temperature, and 21.9 g of an aqueous 1.3% solution of Me NOH (Me NOH: 3 mmol, H 0 : 1,200 mmol) was added dropwise. The subsequent procedure was the same as OX-SQ and the objective OX-SI-SQ containing 20 wt% silicone chain was obtained with quantitative yield.


4

4

2

Photopolymerization and evaluation methods. The formulations were prepared by mixing the monomers (OX-SQs and UVR-6110) with UV9380C (2 wt% for film coating and 1 wt% for viscoelastic mesurements) as photoinitiator in an amber vial at 40°C. For film coating evaluations, liquid samples were coated on glass substrate using #5 bar applicator (approximately 10 μπι thickness) and irradiated using a conveyor type UV irradiator equipped with 80 w/cm of high pressure Hg lamp at 10 m/min. of conveyor speed. For viscoelastic measurements, a lmm-thickness samples were cured using UV irradiator equipped with 80 w/cm of high pressure Hg lamp for 1 minute. The total irradiated UV energy under this condition was 2.85 J/cm . The viscoelasticity of the cured samples was measured using vibration mode (expansion) at 10 Hz. Using a small piece (approximately 10 mg) of the sample used for viscoelastic measurement, thermal degradation of cured samples was measured in air. 2

Results and Discussion

Synthesis of TESOX. Hydrosilylation of TRIES with AOX in the presence of H PtCl - 6H 0 led to TESOX (Figure 1). ^ - N M R (in C D ) δ (ppm): 1.21 (t, 9H, Çfl CH OSi); 3.84 (q, 6H, C H ££f -OSi); 0.78 (m, 2H, -Cfl Si); 1.88 (m, 2H, CH -Cfl -CH Si); 3.39 (t, 2H, 0-Çfî -CH ); 3.39 (s, 2H, -£ïï -0-CH CH ); 0.75 (t, 3H, C&-CH -C); 1.65 (q, 2H, CH3-JC&-C); 4.37 (2d, 4H, C - C H O in oxetane ring). 2

6

2

6

r

r

2

2

2

2

2

2

2

6

2

3

2

2

2

r


310 OEt 0

OEt

χ-Ν^

R

C

a

t

/V^O^^Si-OEt

V Ο

I OEt

AOX

ÔEt

TRIES

TESOX

Figure 1. Synthesis of TESOX by hydrosilylation of TRIES with AOX


Preparation of OX-SQ. The preparation of OX-SQ was carried out by hydrolytic polycondensation of TESOX using an alkaline catalyst (Figure 2). OX-SQ was colorless highly viscous liquid and soluble in toluene, ether, hexane, acetone and other common solvents in any ratio. The number average molecular weight (M„) of OX-SQ obtained from GPC measurement was about 2,000. A ^ - N M R spectrum of OX-SQ is shown in Figure 3.

TESOX

OX^SQ

Figure 2. Preparation of OX-SQ by hydrolytic polycondensation of TESOX.

ι

ι ι—I 5

I I j

4

ι

ι—I I j ι—I f I j ι ι ι ι

3

2

ι 1

ι

ι

ι

ι

I r

0

Figure 3. ^-NMR spectrum of OX-SQ


311

The appearance of peaks at 4.3 to 4.5 ppm showed the persistence of oxetane ring and no peak corresponding to the ethoxy group (Si-0-C H ) was observed. The *H-NMR spectrum indicated that substantially all of the ethoxy groups in TESOX were condensed without decomposition of oxetane ring. Since the oxetane ring is stable to water under alkaline conditions, oxetanyl-SQ can be prepared by hydrolysis of the corresponded oxetanyl-alkoxysilanes. On the other hand, unlike oxetane derivatives, it is difficult to prepare of epoxy-functional SQ by hydrolytic condensation of epoxy-alkoxysilanes due to decomposition of epoxy ring. Epoxy-SQ was prepared, for example, by hydrosilylation of allylglycidyl ether with hydrogen-functional SQ (7). As seen in the Si-NMR spectrum of OX-SQ (Figure 4), the signals due to the Si-O-Si of SQ structures were observed around -60 to -70 ppm region. The sharp peak at -67.4 ppm showed the existence of a regular SQ structure . The fact that broad and sharp peaks were concurrently observed in the *H and Si-NMR chart suggested that OX-SQ consisted of a mixture of several structures with random, ladder and cage structures. Among these peaks, sharp peaks were assumed to be due to a regular cage structure and broad peaks should indicate the existence of ladder or random structures. 2

5


29

29

Preparation

of

OX-SI-SQ.

OX-SI-SQ was prepared by the hydrolytic co-polycondensation of TESOX with OH-Silicone according to Figure 5.

- 67.

*

~t -50

A

«

ppm

•

·

r~ -tQQ

29

Figure 4. Si-NMR

spectrum of OX-SQ


312

H

Cat H 0

OX-SI-SQ

2

TESOX

OH-Silicone

Figure 5. Preparation of OX-SI-SQ by hydrolytic copolycondensation of TESOX with OH-Functional Silicones

OX-SI-SQ was soluble in conventional solvents and had a M of about 2,000. In Si-NMR spectrum of OX-SI-SQ, the signals due to the silicone and SQ structure were observed at -21.5 ppm and -66 to -68 ppm respectively. The OX-SI-SQ obtained using OH-Silicone was low molecular weight (M„ < 2,000) was colorless and clear. On the other hand, the OX-SI-SQ prepared using a higher molecular weight OH-Silicone (Mn>4,000) was turbid in appearance. n


29

Photopolymerization of OX-SQ and OX-SI-SQ The prepared OX-SQs are a kind of multifunctional oxetane compounds, which can produce photocured products. SQ itself and functionalized SQ are known to be easily used to formulate homogeneous resin compositions due to their high compatibility with organic compounds. OX-SQ and OX-SI-SQ were soluble in various organic compounds and may contain reactive monomers such as typical cycloaliphatic diepoxide monomers (eg. UVR-6110). As the initiation of oxetane homo-polymerization is known to be slow and accelerated by epoxides (2), the curing properties of OX-SQ were investigated in formulations with UVR-6110 (Table I). With higher amount of OX-SQ, the surface hardness and acetone resistance were improved, owing to the SQ skeleton structure and the high crosslink density. UVR-6110 alone exhibited poor acetone resistance even upon standing for 24 hours after UV exposure. Addition of OX-SQ gave good acetone resistance even after 1 hour standing. The improvement effect could be explained by the fast generation of crosslinked network of oxetanes accelerated by epoxide. The formulation of OX-SQ and OX-SI-SQ with UVR-6110 are shown in Table II. In spite of the silicone chain, OX-SI-SQ exhibited good compatibility with UVR-6110. Though OX-SQ gave inferior pollution-free properties, all of the cured films from the OX-SI-SQ showed excellent pollution-free properties, i.e. silicone characteristics were given to the surface. These coatings had fairly good surface hardness too. Furthermore, even after wiping 2,000 times under a 500 g load with dry gauze, the ink-repellency was still good. The maintenance of excellent pollution-free properties should be provided by the remaining silicone chain on the coating which is covalently bounded to the SQ structure.


313

Table I. Formulation of Cycloaliphatic Epoxide (UVR-6110) with or without OX-SQ a )

UVR-6110 (wt%)

No.

Bl

OX-SQ (wt%)

100 90

SQ-1 Downloaded by CORNELL UNIV on August 3, 2016 | http://pubs.acs.org Publication Date: March 3, 2003 | doi: 10.1021/bk-2003-0847.ch027

b )

c)

10

3H 3H

d)

Acetone Resistance

Pencil Hardness

lh

2h

6 h

24 h

0 40

30 50

50

>200

>200

>200

SQ-2

80

20

4H

60

>200

>200 >200

SQ-3 SQ-4

60

40

5H

>200

>200

10

90

6H

>200

>200

>200 >200 >200 >200

a) 2 wt% of UV9380C (GE Toshiba Silicone Corp.) was added and coated on glass substrate to 5 μπι thickness with a bar applicator and cured with 80 W/cm of high pressure Hg lamp at lOm/min. conveyor speed b) Cycloaliphatic epoxy monomer, availablefromUnion Carbide Corp. c) According to JIS Κ 5400. d) Number of rubbing times with a cotton ball wetted with acetone.

Table II. Formulation of OX-SQ and OX-SI-SQ with UVR-6110 Sample. No.

UVR-6110 OX-SI-SQ

b )

Transparency of resin c)

Pencil hardness Pollution-free

initial

property

after wiping

Exp-2

Exp-3

Exp-4

100

80

90

80

-

20

-

-

Exp-1

OX-SQ

e)

a)

-

10

20

Clear

Clear

Clear

Clear

3H

4H

4H

5H

NG

NG

OK

OK

NG

NG

OK

OK

a) 2wt% of UV9380C was added and coated on glass substrate to 10 μπι thickness with a #5 bar applicator and cured in the same way as Table 1. b) Containing 20 wt% of silicone. c) According to JIS Κ 5400. d) Lines were drawn using oil marker pen, OK : completely repellent, NG : no repellent. e) Wiping with dry gauze was performed 2,000 times under a 500 g load.


314 Thermal properties ofphoto-cured OX-SQs The storage modulus (F) and tan δ plots against temperature for the photocured formulations of SQs with 10 wt% of UVR-6110 and 1 wt% of UV9380C as photoinitiator were shown in Figure 6. The TGA results measured in air for the same materials are exhibited in Figure 7. The formulations and results were summarized in Table III.


Table III. Thermal Properties of OX-SQs Formulated with UVR-6110 UVR-6110 (wt%)

OX-SQ (wt%)

OX-SI-SQ (wt%)

90

-

-

90

10 10

.b>

E

at250°C 5.45E+8 4.93E+8

a)

c>

Thermal Degradation TD5

Photocationic Curable Silsesquioxanes Having Oxetanyl Group

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