Poly(siloxyethylene glycol) for New Functionality Materials - ACS

Chapter 24

Poly(siloxyethylene glycol) for New Functionality Materials 1

Downloaded by UNIV OF ARIZONA on January 3, 2013 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch024

Yukio Nagasaki and Hidetoshi Aoki

2

2

1Department of Materials Science and Technology, Science University of Tokyo, Noda 278-8510, Japan Research and Development Center, Hokushin Corporation, Turumi, Yokohama 230-0003, Japan

Poly(siloxyethylene glycol)s, (PSEGs) which consist of alternating oligooxyethylene and oligosiloxane derivatives, were prepared via polycondensation reactions between oligoethylene glycol and bis(diethylamino)dimethylsilane. When the dimethylamino group was used as the leaving group of the electrophilic silyl compound, the polycondensations proceeded smoothly without any degradation. It should be noted that cleavage reactions takes place when dichlorodimethylsilane was used as an electrophile due to the liberated HCl. PSEGs thus prepared possesses alternating hydrophilic and hydrophobic unit in the main chain, which showed unique phase transition phenomena in aqueous media. Especially, the lower critical solution temperature (LCST) can be controlled by their Si -content. The glass transition temperature can also be varied by the Si-content. Thus, the unique structure and characteristic of PSEG derivatives can be utilized as matrix for functional materials such as hydrogels with stimuli-sensitivity, resists with high etching durability and water development and as a matrix for solid electrolytes. This paper reviews the synthesis and applications of P S E G derivatives.

Polymers having an organosilicon moiety show unique characteristics due to the nature of silicon atom.(/,2) We have been studying on synthesis of several types of silicon-containing polymers and investigating their characteristics. For example, polystyrene possessing doubly trimethylsilyl groups in each repeating unit, poly[4{bis(trimethylsilyl)methyl}styrene] (PBSMS), shows fairly high oxygen permselectivity among vinyl polymers.(i) Based on this characteristic of PBSMS, we are preparing high performance artificial lung via copolymerization of B SMS with 2-hydroxyethyl methacrylate. (4) The same polymer can be applicable as a resist material due to the high dry etching resistance of the organosilicon moiety. PBSMS shows negatively-working electron-beam resist with high resolution parameter.(5)

© 2000 American Chemical Society

In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

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Our alternating polymer, poly(silamine), which consists of alternating 3,3dimethyl-3-silapentamethylene and N,N'-diethylethylenediamine units in the main chain,(d) shows phase transition phenomena in aqueous media.(7) Because of suitable hydrophilic and hydrophobic balances in the main chain, the polymer is soluble in neutral water at lower pH. With increasing temperature or pH, the solution becomes turbid due to the deprotonation from amino group in the main chain. It should be noted that the rubber elasticity of the polymer drastically changes with the phase transition. Actually, the glass transition temperatures of poly(silamine) with and without protonation were +80 and -80 °C.(£) Such a remarkable change in the glass transition temperature was due to the freezing of molecular motion by the anion binding to the repeating silicon atoms along with protonation of amino groups in the main chain. Thus, the character of silicon segment in the polymer influences the characteristics of the base polymer molecule. In this paper, we describe another new silicon-containing polymer, poly(siloxyethylene glycol), which consists of alternating oligoether and oligosiloxane linkage in the main chain.(9) The synthesis, characterizations, characteristics in aqueous media are summarized. The applications for an electronbeam resist (70) and a ion conducting polymer are also described. Experimental Section Materials: Commercial THF (Wako) was purified in the following way. After THF was pre-dried with K O H for several days, reflux was carried out over lithium aluminum hydride for 5h, followed by distillation. The fraction at 68 °C was collected and stored under Ar atmosphere. 01igo(ethylene glycol)s were dried at 110 °C for 2 d in vacuo. Diethylamine (Wako), dichlorodimethylsilane (Shinetsu Chemical Co. Ltd.), 1,3-dichlorotetramethyldisiloxane (Shin-etsu Chemical Co. Ltd.) and dichlorodivinylsilane (Shin-etsu Chemical Co. Ltd.) were used as received. Bis(diethylamino)dimethylsilane (DAS), l,3-bis(diethylamino)tetramethyldisiloxane (DADS) and bis(diethylamino)divinylsilane (DADVS) were prepared by the reaction of diethylamine with the corresponding dichrolosilanes.(77) The boiling points of DAS, DADS and D A D V S were 30 - 31 °C /1 mmHg and 79 °C / 3 mmHg and 63.5 64.5 °C / 2mmHg, respectively. Other materials were used as received. Polymer Synthesis: A typical polymerization was performed in a 100-mL roundbottomed flask with a 3-way stopcock. After 6.19 g of O E G (Mn = 300) (20.6 mmol) was weighed into the flask, the inside of the reactor was degassed sufficiently and filled with Ar gas. 20 mL of THF and 4.17 g of DAS (20.6 mmol)" were then added to the flask via syringe and allowed to react for 24 h at 60 °C. After THF and liberated diethylamine were removed by evaporation in vacuo, the obtained polymer was analyzed by GPC. The ' H N M R of the obtained polymer was recorded after the sample was purified by GPC fractionation. Hydrolytic Stability Test: The stability of P S E G against hydrolysis in aqueous media was estimated as follows: A polymer sample was dissolved in phosphate buffer (1.5 wt.%; pH = 7.0; I = 0.05) at 4 °C. Every few hours, an aliquot of the solution was subjected to measurement of its turbidity after the sample was heated above the


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LCST. The turbidity was monitored as a normalized attenuance using the following equation. Normalized Attenuance = log(I / I ) / log(I / I R

st

R

smin

)

where, I and I denote the intensities of reference (phosphate buffer) and sample after t hours reaction, respectively. I represents the minimum intensity of the sample during the experiment. R

st


smin

Resist Processing: For the photo irradiation examination, a THF solution of the polymer sample was prepared with 20 wt.% concentration. Tetramethylmethanetetra(3-mercaptopropyonate) (4TP-5) (1.34 mmol) and benzoinmethylether (BME) (0.21 mmol) were added to the T H F solution of the polymer as follows: [-CH=CH ] : [-SH] : [BME] = 1 : 0.2 : 0.04. The prepared solution was spin-coated at 3000 r.p.m. for 30 s on a silicon wafer surface. The thickness of the resist fdm thus obtained was about 1pm, and it was irradiated with a 500W high pressure mercury lamp (USHIO INC.) equipped with a heat cut filter (HA-30 type, Kenko). A dose that ranged from 15 to 3240 mJ/cm was employed. In an E B exposure examination, a THF solution of PVSE300 (10 wt.%) was spincoated at the same conditions on a Si wafer surface. The thickness of the PVSE300 film thus obtained was 0.7 - 0.9 pm, and E B was exposed using a JEOL JSM-5200 scanning electron microscope (SEM) equipped with a Tokyo Technology L & S Pattern Generator LSPG1-1S at several probe currents (3, 10 and 100 pA) and accelerating voltages (2, 5, 10 and 20 kV). A dose that ranged from 0.01 - 44 uC/cm was employed. The PVSE300 film on the Si wafer was developed by soaking in cold water (4 °C) for 2 or 10 minutes after the photo irradiation and E B exposure. The remaining film thickness was measured with a Tencor A L P H A STEP 300. The sensitivity and resolution parameter were calculated from the sensitivity characteristic curve as D g and y value. The D g value denotes the exposure dose for a remaining thickness of 50 % of the initial thickness.(i2,75) The y value was calculated from the following equation. 2

2

2

50

50

50

1

,

y = [21og(Dg /Dg )]1

where Dg represents the minimum dose in which the cross-linking reaction is proceeded by E B . ( i ¥ ) 0 R I E Resistance: A polymer sample for the 0 RIE experiment was prepared in a similar way as stated above, viz., the film was exposed to an E B dose of 10 uC/cm at 100 pA, 20 k V followed by development in 4 °C water for 2 minutes. The plasma etching experiment was carried out in an oxygen atmosphere in a Model: BP-1, from the Samco International Research Corporation. The radio frequency (Rf) power and gas pressure were 100 W and 0.5 Torr, respectively. The etching time was varied from 5 to 60 minutes. The temperature of the substrate was maintained by heating the sample-plate at 40 °C during the etching. The thickness of the film was 2

2

2


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measured before and after etching using a A L P H A STEP 300. was plotted as the reducing fdm thickness versus etching time.

The etch rate curve

Ionic conductivity of P S E G gel: P S E G having pendent vinyl groups was mixed with tetrafunctional thiol, pentaerythritol tetrakis(2-mercaptopropionate) (4TP-5), and photoinitiator, 2,2-dimethoxy-2-phenylacetophenone (DMPA), in acetonitrile. Lithium perchlorate was dissolved to the mixture. The ratio for [Li] / [-0-] was in the range of 0.025 - 0.317. After the polymer was crosslinked by U V light (1.6 J/cm ), the obtained sample was dried for 48 h at ambient temperature. The obtained sample was cut to disk shape, the diameter of which was 13 mm. The disk was placed between two Pt electrodes and the conductivity was measured in thermoregulated cell from -20 to 100 °C.


2

Measurement: GPC measurements were performed on a Toso C C P E with a RI detector and TSK-Gel G M H 6 X 2 + G M H X L X 2 columns. The N M R spectra ( H: 399.65 MHz; C : 100.53 MHz) were determined on a JEOL EX400 spectrometer using CDC1 as a solvent at room temperature. Chemical shifts relative to CHC1 ( H: 8 = 7.26) were employed. Glass transition temperatures of the polymers were determined using a differential scanning calorimeter (DSC) (Mettler TA4000 system) at a heating rate of 20 °C/min from -170 °C to 200 °C. The turbidity of the polymer solution was recorded using Photorode Mettler DP 550. The absorption at 550 nm was monitored. ]

1 3

3

3

!

Results and Discussion Synthesis and characteristics of poly(siloxyethylene glycol) Synthesis and Characterization: In this study, PSEGs were synthesized by polycondensation reactions between O E G and a bi-functional silicon monomer (Scheme 2). There are several choices of leaving groups from silicon monomers. Especially, dichlorosilane is the most common organosilicon monomer for the reaction with hydroxyl groups. However, if dichlorosilane were employed to synthesize the PSEG, the main chain of the polymerized product should be decomposed by the liberated acid.(/5) Therefore, we employed a diethylamino group as a leaving group in the bi-functional silicon monomers. PSEG possessing vinyl groups as pendent, PVSE was also synthesized by a polycondensation reaction between O E G and bis(diethylamino)divinylsilane (DAVS) in the same way as that of P S E G (Scheme 2). The polycondensation reaction between O E G and diethylaminosilane derivatives proceeded smoothly, and no gel formation took place even in the case of D A V S which possesses vinyl groups as a side chain. Figure 1 shows the gel permeation chromatography (GPC) profiles of the representative polycondensation products; PSEG(l/7), PSEG(2/7) and PVSE(l/7), where the numbers in parenthesis (m/n) denote the number of Si atoms in siloxane and ethylene glycol units in O E G , respectively. The polymers thus obtained were viscous liquids, and the number average molecular weights of the products were in


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Scheme 1 "CH Si-O 3


£ H

•£CH CH 0i 2

2

3

m Poly(siloxyethylene glycol), PSEG(m/n)

'

'f

-£CH CH 03

-Si-O

2

2

j r

-

m Poly(divinylsiloxyethylene glycol), PVSE(m/n)

Scheme 2 CH " Et N—j-Si-O CH _ 3

CHq

3

S i — NEt CH

2

m-1

2

+

HO—[CH CH o3jp-H 2

2

9 3" H

Et NH

Si-O- - E C H C H 0 i ft* /—s

w

1

« CO OH

3

«4-1 Ο

V)

Poly(siloxyethylene glycol) for New Functionality Materials - ACS

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