Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 141-148
141
I I. Symposium “ACS Award for Creative Invention Honoring Ralph Milkovich” 189th National Meeting of the American Chemical Society Miami Beach, Florida, April 28-May 3, 1985
Syntheses and Applications of Graft Copolymers from Poly( 1,I-diphenylethylene-co -divinylbenzene)s Kolchl Hatada, Tatsukl Kltayama, Shlgeru Sasakl, Yoshlo Okamoto, Ell1 Masuda, Yolchl Kobayashl, and Aklhlsa Nakajlma Department of Chemistty, Faculty of Engineering Science, Osaka Unlverslty, Toyonaka, Osaka 560, Japan
Hlroakl ArHome and Susumu Namba Department of Electrical Engineering, Faculty of Engineering Science, Osaka Unherslty, Toyonaka, Osaka 560, Japan
Anionic copolymerization of 1, ldiphenylethyleneand rn- and p divinylbenzenes gave soluble copolymers having pendant vinyl groups when an excess amount of 1,ldiphenylethylene over divinylbenzenes was used. The copolymers hardly formed cross-linked polymers, as compared with the homopolymers of divinylbenzenes, and were easlly converted to polymer anions by adding sec-butyllithlum in THF at -78 “C. The anions were reacted with several methacrylates or other vinyl monomers to give the graft copolymers with the corresponding polymer branches. The number of branches could be controlled by partially quenching the completely anionized copolymer with a certain amount of methanol before the addition of the monomers or by changing the amount of sec-butyllithium. Practical applications of the graft copolymers to polymeric emulsifier and negative electron-beam resist were examined.
Introduction Preparations of polymers of desired structure and molecular weight are the most interesting and important for pure and applied macromolecular science. Recently, much attention has been paid to the preparation of tailored graft copolymers using macromonomers. Polymers having reactive side groups such as vinyl groups can be used as the starting materials toward graft copolymers. Although divinylbenzene (DVB) has often been used as a crosslinking reagent, a few reports claim that DVB can afford soluble homopolymers under specific conditions. A linear poly(DVB) having a pendant vinyl group was prepared by anionic polymerization in the presence of diisopropylamine (Nitadori and Tsuruta, 1978). A different type of soluble poly(DVB) containing inner double bonds was prepared by cationic mechanism (Hasegawa and Higashimura, 1980). A short-time polymerization in tetrahydrofuran (THF) with alkyllithiums at -78 “C gave the soluble polymer of DVB (Hatada et al., 1983), but it easily formed an insoluble gel during storage. 1,l-Diphenylethylene (DPE) can copolymerize with styrene by anionic initiators to form an alternating copolymer (Yuki et d.,1964, 1967). Recently, we found that DPE copolymerized with m- and p-DVB’s in T H F with alkyllithium as initiator, and the pendant vinyl groups of the resultant copolymers reacted easily with sec-butyllithium (sec-C,HgLi) to give polymer anions (Hatada et al., 1983). The copolymers prepared in the presence of excess DPE over DVB had highly alternating character. The copolymers exhibited little tendency to form a gel and were easy to handle relative to the homopolymers of m0 196-4321I8611225-014 1$01.5010
and p-DVB’s, since most of the DVB units in the copolymers were flanked with bulky DPE units on both sides. The copolymers were converted into the polymer anions by the reaction with sec-C4HgLiin THF. The resulting polymer anions were reacted with vinyl monomers, mainly with methacrylates, to form graft copolymers. Since the reaction proceeded substantially in a “living” system, the molecular weights and the structures of the graft copolymers could be easily controlled. These results were reported briefly in the previous paper (Hatada et al., 1983). In this paper we will describe the graft copolymerization of vinyl monomers on the copolymer of DVB and DPE and some of the properties and practical applications of the graft copolymers. Experimental Procedures Materials. DPE was synthesized by dehydrating 1,ldiphenylethanol prepared from phenylmagnesium bromide and acetophenone (Kauffmann, 1906). The DPE was treated with n-C4HgLito remove a small amount of contaminants and distilled under reduced nitrogen pressure just before use. p-DVB and m-DVB were kindly supplied by Asahi Chemical Co. These were dried over calcium dihydride and distilled under high vacuum. The purities from gas chromatographic analysis were as follows: p-DVB para isomer 96.0, meta isomer 3.5, ethylvinylbenzene 0.5%; m-DVB meta isomer 93.4, para isomer 5.1, ethylvinylbenzene 1.5%. Triphenylmethyl methacrylate was prepared in diethyl ether from silver methacrylate and triphenylmethyl chloride (Adrova and Prokhorova, 1961)and 0 1986 American Chemical Society
142
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
Table I. Cooolymerization of DPE and DVB with C2H6Li,C,D,Li, and CIHgLi in THFn coDolvmer no. 1
2 3 4' 58
fY
DVB rn-DVB rn-DVB rn-DVB p-DVB rn-DVB p-DVB
initiator CsH6Li CiDiLi n-C4HgLi n-C4HgLi n-C4HgLi n-C4HgLi
[monomer]/ [initiator] 375 375 1000 1000 86 97
temp, "C -78 -78 -20
-20 -78 -78
time 6h 6h 24 h 24 h 5 min 1 min
yield, % 6.0 5.6 52.5 34.0 98.1 97.9
DVB/DPE 1.38 1.39 1.19 1.43
M J 104 obsd calcdb 0.33d 0.37 0.34d 0.34 7.40e 8.23 4.02e 5.50 2.70e 1.12 1.57e 1.29
CH' 0.99 1.04
[DVB]o/[DPE]o = 0.5, [DVBl0 + [DPEIo = 1.0 mol/L. Reprinted with permission from Hatada et al. (1983). Copyright 1983 Springer-Verlag. Calculated from yield and composition of the copolymer and the amount of the initiator used. Number of terminal methine protons per polymer molecule. d,e Determined by VPO and GPC, respectively. f [p-DVB],/ [DPEIo = 0.3. BHornopolymerization of DVB. (I
recrystallized from hexane. Other vinyl monomers were obtained commercially, purified by distillation, dried over calcium dihydride, and then vacuum-distilled, THF was purified by refluxing over calcium dihydride and distilled twice over LiAlH4. The solvent thus purified was vacuum-distilled just before use. Organolithium compounds C2H5Li,C2D,Li, n-C4HgLi, and sec-C4HgLiwere synthesized from the corresponding alkyl chlorides and metallic lithium in heptane (Ziegler and Colonius, 1930), and the concentrations of the solutions were determined by titration with 2-butanol using 2,2'biquinoline as an indicator (Watson and Eastham, 1967; Ellison et al., 1972). Polymerizations and Graft Polymerizations. Copolymerization and graft copolymerization reactions were carried out in a glass ampoule under dry nitrogen. Nitrogen gas was dried by passing through the column packed with Molecular Sieves 4A colled at -78 "C. The polymerization reaction was terminated by adding a small amount of methanol, and the reaction mixture was poured into a large amount of methanol. The precipitated polymer was collected by filtration, washed several times with methanol, and dried under vacuum. Measurements. 'H and 13C NMR spectra of the polymers were measured on a JEOL JNM-MH-100 (CW) or a JEOL JNM-FX100 (FT) NMR spectrometer. 13C spin-lattice relaxation times were determined by inversion recovery method. The number-average molecular weight of the polymer was measured on a Hitachi 117 vapor pressure osmometer (VPO) in toluene at 60 "C. The molecular weight distribution was determined with a JASCO FLC-A10 GPC chromatograph equipped with Shodex GPC A-80M columns (50 cm X 2) with maximum porosity of 5 X lo7 and with a Shodex SE-11 refractive index detector. THF was used as an eluent. The chromatogram was calibrated against standard polystyrene samples. DSC and TG-DSC thermograms were obtained with Rigaku Denki calorimeters, Models 8001 SL/C and CN 8085 E l , respectively, at a heating rate of 10 "C/min and using an aluminum sample pan with lid. Emulsification. A known amount of the graft copolymer having PMMA branches was dissolved in acetonitrile, and then cyclohexane was added dropwise into the solution with shaking until the cyclohexane was not emulsified and separated out to form an immiscible phase. The concentration of the polymer was normalized to the total volume of the mixture just before the phase separation occurred. The experiments were carried out at different concentrations of the polymer to prepare the phase diagram. Similar experiments were performed for the poly(sodium methacrylate) grafted copolymer by using benzene-water mixtures. Lithographic Measurements. Graft copolymers containing vinyl double bonds were dissolved in toluene, and
Figure 1. Structure of poly(DPE-co-rn-DVB) prepared with C2H5Li.
the solutions were spun onto a silicon substrate. The thickness of the resist films was about 0.3 pm. The coated wafer was exposed to a 20-kV electron beam by using a JEOL JBX-5B electron-beam exposure system. The exposed films were developed by using pentyl acetate and subsequently rinsed with 2-propanol. Results and Discussion Anionic Copolymerization of DPE with m - and p-DVB's. Copolymerizations of DPE and m- and pDVB's were carried out at an initial monomer ratio of m-DVBIDPE = 0.5 or p-DVB/DPE = 0.3 with alkyllithiums in THF at -78 OC (Hatada et al., 1983). The results are shown in Table I together with the results of homopolymerizations of m- and p-DVB's. Soluble homopolymers of m- and p-DVB's could be obtained only in the polymerization for a limited short reaction time, but the prolonged reaction time caused gel formation. All the copolymerizations gave soluble copolymers. In 'H NMR spectra of all the copolymers, there appeared the signals of phenyl protons and methine and methylene protons of pendant vinyl groups at 7.0, 6.0, and 5.8-5.2 ppm, respectively. The low molecular weight copolymer prepared with C2H5Li(Table I, no. 1) showed signals around 0-1 ppm due to initiator fragments (C2H5-), which was not observed in the spectrum of the copolymer prepared with C2D5Li(Table I, no. 2) or of the copolymer of high molecular weight (Table I, no. 3). The low molecular weight copolymer also exhibited a broad singlet at about 3.0 ppm due to the terminal methine proton (-C!H2C(C6H5),H). This singlet had one-fifth the intensity of that of the signal due to the initiator fragment and disappared upon termination with CD30D. The number of terminal methine protons per copolymer molecule was calculated to be about unity from the measurement of the intensity and the molecular weight. The molecular weights determined by vapor pressure osmometry (VPO) agreed well with those calculated from the yields and compositions of the copolymers and the initiator concentrations (Table I, no. 1, and no. 2). These results indicate that the copolymer obtained had linear structures, as shown in Figure 1, and the attack of the propagating anion onto the pendant vinyl bond hardly occurred during the reaction. As mentioned above, almost all the copolymer molecules end with a DPE unit; that is, the propagating anion mostly exists as a highly bulky DPE anion, and the pendant vinyl group is blocked sterically by the phenyl groups of DPE units on both sides (Figure 2). This is the reason the propagating anion does
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25,
No. 2, 1986 143
Figure 2. Propagating anion scarcely attacks the vinyl group of different polymer chains. Polyh-DVB)
lo6
lo4 MWlPStl
lo5
Figure 4. Change in GPC curve of poly(DPE-co-rn-DVB)(Table I,
PolylDPE-co-m-DVB)
no. 3) during preservationunder air in the dark at room temperature.
*qeq
b q . 9 q-+ s-Bu-CHp-CHLi
PolylDPE-c~-rn-DVBl
100
200
300
s-Bu-CHz-CHLi
400
Temperature ("C)
Figure 3. DSC thermograms of poly(DVB)'s (Table I, no. 5 and no. 6) and poly(DPE-co-DVB)'s (Table I, no. 3 and no. 4).
not attack the pendant vinyl groups of other copolymer molecules. Monomer reactivity ratios were determined for the copolymerizations of DPE (Ml) with rn-DVB (M,) and p DVB (M3)in THF by n-C4H&i at -20 and -78 "C. In all the cases, rl (kll/k12) was 0, indicating that the copolymers do not have DPE-DPE sequence. Other reactivity ratios = 1.2 (-20 and -78 "C); and were as follows: r2 (k22/k21) r3 (k33/k31)= 2.5 (-20 "C) and 2.8 (-78 "C). Copolymers of highly alternating structure were obtained in the presence of excess DPE over DVB's, and these can be used as starting materials for various types of functional polymers and graft copolymers. Figure 3 illustrates the DSC curves of poly(rn-DVB) (Table I, no. 5), poly@-DVB) (Table I, no. 6), poly(DPEco-rn-DVB) (Table I, no. 3), and poly(DPE-co-p-DVB) (Table I, no. 4). The homopolymers of rn- and p-DVB's exhibited exothermic peaks around 160 "C probably due to oxidation and cross-linking. However, the copolymers did not show any peaks around this temperature region, indicating the absence of the homopolymers of DVB's and higher thermal stability of the vinyl groups in the copolymer. Figure 4 shows the change in molecular weight distribution of poly(DPE-co-m-DVB) (Table I, no. 3) during preservation at room temperature in the dark under atmospheric pressure. The GPC chromatogram of the sample stored for 30 days was almost the same as that of the copolymer preserved for 1 day after preparation. After 5 months, a small shoulder appeared at the higher molecular weight side of the chromatogram. The molecular weight for this shoulder was estimated to be 2 to 3 times as large as that of the original copolymer, though the sample was still soluble in organic solvents. When the copolymer was preserved in a refrigerator, no change in the chromatogram was observed even after 5 months. The result confirms easy handling and high stability of the copolymer. Grafting Reaction of the Copolymer. Preparation of the graft copolymer from poly(DPE-co-rn-DVB) is illustrated in Figure 5. The copolymer was reacted with an equimolar amount of sec-C4H9Li to the pendant vinyl groups a t -78 "C in THF. Upon the addition of sec-
M
MsOH __.
+
partially quenching
I
r-Bu-CH2-CH2 s-Bu-CH2CHLi
\
S-BU-CH2-CH2
\
s-Bu-CH2-CHiM$
Figure 5. Grafting reaction by partially quenching method. C4HgLi,the solution colored deep red immediately, due
to the formation of the polymer anion. A certain amount of methanol was then added to the solution to partially quench the anion. Changing the amount of methanol controls the number of branches in the graft copolymer to be formed. Finally, a monomer was added to the resulting solution to form a graft copolymer. Degree of polymerization (DP) of the branch can be controlled by changing the amounts of monomer and anion. The polymer anion was quenched by methanol without adding a monomer, and the resultant polymer was studied by 13CNMR spectroscopy (Figure 6 0 . The signals due to vinyl methylene and methine carbons, which would appear at 112.4 and 137.3 ppm, respectively (cf. Figure 6B), disappeared completely in the spectrum. The polymer anion was also reacted with an excess amount of chlorotrimethylsilane. Gas chromatographic analysis of the reaction mixture indicated that there existed no 2-trimethylsilylbutane, which would be the reaction product of the chlorosilane and the remaining sec-C4HgLi. Therefore, the grafting method shown in Figure 5 is suitable for preparing the graft copolymers containing the desired amount of branches with desired DP without formation of homopolymers. If the amount of sec-C4H&i is less than that of the vinyl group of the copolymer, a partially anionized polymer containing unreacted vinyl groups is obtained (Figure 7). The copolymer of DPE and m-DVB was reacted with a half-molar amount of sec-C,H&i to that of the vinyl group in the copolymer in THF at -78 "C for 5 min, and the resulting polymer anion was quenched with methanol. The 13C NMR spectrum of the resultant polymer showed the vinyl carbon signals, the intensities of which corresponded to 50% of the vinyl group in the original copolymer. The results indicate that the reaction between the vinyl group and sec-C4H9Liwas almost completed within 5 min and that the remaining vinyl group was not attacked by the polymer anion. The method can afford the graft copolymers containing pendant vinyl groups, which will be
144
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Table 11. Grafting Reaction of Methacrylates with Poly(DPE-co-m-DVB) in T H F at -78 OC" graft copolymer methacrylate ~ ~ 1 0 4 no. ester group mmol time, h grafted ester, % GPC calcd 1 CH3 2.83 1 66 16.2' 15.5 12 97 38.9 72.9 2 CH3 18.8 3 CH3d 2.83 0.33 26' 4 C2H5d 2.40 6 63 13.3 14.6 5 C2H5 4.81 6 49e 95 10.1 15.4 6 C4H9 1.76 24 C4HSd 1.76 24 86' 95 12.41 15.4 8 t-C,Hs 1.76 12 51 9.8 12.1 9 t-C4Hgd 1.76 12 10 C(CdG3 3.01 21 90' 11 MAg 3.33 24 12 8.2 10.2
DP of branchb 12.4 135 9.5 11.3
I
11.5 1.3
2.6
" T H F 60 mL, backbone copolymer (m-DVBIDPE = 1.19, M,,= 74000 (Table I, no. 3)) 0.2 g. Eighty percent of polymer anion was quenched by methanol before the addition of methacrylate monomer. Reprinted with permission from Hatada et al. (1983). Copyright 1983 Springer-Verlag. bEstimated from the amounts of grafted monomer and the anion. ' M , , measured by VPO was 12.2 X lo4. dThe grafting reaction was carried out without partially quenching the polymer anion. 'The graft copolymer obtained was insoluble in usual organic solvents. f M , measured by VPO was 13.3 X lo4. #Methyl acrylate.
M
8
-CH~-C-CHZ-CH-CH~-C-CH~-
CH-
09 00 CH2'
H
S-BU-CH$H-tM+,
Figure 7. Preparation of the graft copolymer containing vinyl group.
150
100
50
0 ppm
Figure 6. 13CNMR spectra of poly(DPE-co-rn-DVB) (Table I, no. 3) (A) and the copolymers after the reaction with sec-C4H&i of 50% (B) and of equimolar (C) amounts of vinyl group in the original copolymer (CDC13, 60 "C, 25 MHz).
usable in, for example, negative type electron-beam resists (cf. Figure 15). Graft copolymers having polymethacrylate or polyacrylate branches were prepared in THF at -78 "C by the method shown in Figure 5. The results are shown in Table 11. The copolymer of DPE and n-DVB (Table I, no. 3) was reacted with sec-C,H,Li of equimolar amount to the pendant vinyl group in T H F at -78 "C for 1 h, and 80% of the polymer anion formed was deactivated by adding methanol. The resulting partially quenched polymer anion was then reacted with various methacrylates to form graft copolymers. The deep-red color of the anion disappeared upon the addition of the methacrylates. When MMA was used as the monomer, the graft copolymer formed was completely insoluble in acetonitrile (Table 11, no. l),which dissolves the homopolymer of MMA. The GPC curve of
the graft copolymer shifted to the higher molecular weight side compared with that of the original copolymer and did not show any peak ascribed to the latter polymer. The results indicate that the graft copolymer did not contain the original copolymer or the homopolymer of MMA. When a long chain of MMA was grafted (Table 11, no. 21, the resulting graft copolymer was dissolved in acetonitrile at 60 "C. The graft copolymer may be solubilized in the solvent, owing to the long branches of PMMA. The reason for the large difference between the observed and calculated molecular weights is probably due to the difference in molecular shapes in solution between the graft copolymer containing long branches and polystyrene used as a standard for GPC. Number-average molecular weight (M,) of some graft copolymers having short branches in Table I1 was measured both by GPC and by VPO. The values were roughly equal to each other (Table 11, no. 1 and no. 8). Strictly speaking, however, Mn's obtained by GPC measurement should be different between linear and branched polymers of the same molecular weight. The study on this point is now under way using graft copolymers of well-defined structure, which are prepared by the present method. When MMA monomer was added to the polyanion solution without partially deactivating the anion, the graft copolymer formed was not soluble in any organic solvent (Table 11, no. 3). Similar insolubility occurred in the case of poly(ethy1 methacrylate) (PEMA) or poly(buty1 methacrylate) (PBuMA) grafted copolymer (Table 11, no. 5 and
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
145
Table 111. '*C Spin-Lattice Relaxation Times of PMMA-Grafted Poly(DPE-co-m-DVB)" Measured i n CDCIJ (20 w t % ) a t 60 OC TI,ms PMMA branch c=o >C< a-CH3 densityb DPc S H -CH2- (r) OCH, H S H S 0.5 0.5 0.2
10 100 100
1870 1860 2270
59 54 68
1700 1700 1820
720 690 820
"Backbone copolymer, m-DVBIDPE = 1.19, M n= 74000 (Table I, no. 3). rn-DVB units]. cDegree of polymerization of branch.
970 920 1230
850
97 98
810 910
82 68 91
130
[Amount of PMMA-grafted m-DVB units]/[amount of total
1. s - B u L i
Poly(DPE-co-in-DVB)
OCH3 O\H
CHC13 II
a-CH3
Isotactic PMMA graft c h a i n (
I:H:S=92:7:1)
,
CH3
s - B U- C H2-'C Hf C H2- $
-Ifn
c=o
0- Na' Figure 8. Conversion of poly(triphenylmethy1methacrylate)-grafted copolymer (Table 11, no. 10) to the graft copolymer having a highly isotactic PMMA branch or the water-soluble graft copolymer containing a poly(sodium methacrylate) branch.
no. 7). This may be due to the cross-linking through the attack of the PMMA, PEMA, or PBuMA anion on the carbonyl group in the PMMA, PEMA, or PBuMA branches since the graft copolymer prepared under similar conditions using tert-butyl methacrylate (t-BuMA) (Table 11, no. 9) was completely soluble in chloroform and THF. Carbonyl attack by the initiator occurs more largely in the polymerization with n-C4H9Liof MMA than in that of t-BuMA (Hatada et al., 1979,1982). Cross-linking by the association of the PMMA branches, like stereocomplex formation, could be another possible explanation. However, the DP of PMMA branches in the insoluble polymer seem to be too small to associate each other. The graft copolymers with the branches of various polymethacrylates and poly(methy1 acrylate) were prepared in a similar manner (Table 11). The N M R and GPC analyses indicated the formation of graft copolymers. When poly(triphenylmethy1 methacrylate) (PTrMA) was grafted (Table 11, no lo), the copolymer obtained was insoluble, owing to the insolubility of PTrMA branches. The polymer became soluble when the branches were converted to PMMA branches by hydrolysis followed by methylation with dimmethane (Figure 8). The tacticity of the branches was highly isotactic, while that of other polymethacrylate branches was syndiotactic or atactic. When the copolymer containing poly(methacry1ic acid) graft was neutralized with sodium hydroxide, a watersoluble graft copolymer having poly(s0dium methacrylate) branches was obtained. The copolymer could be used as a polymeric emulsifier as described later. Properties of Some Graft Copolymer. 1. NMR Spectroscopy of PMMA Graft Copolymer. Figure 9 shows 'H NMR spectra of the graft copolymer, in which
in CDC$ 30
40 M 60 Temperature ("C)
70
Figure 10. Temperature dependence of half-height width of methoxy proton signal in the 'H NMR spectra of PMMA-grafted poly(DPE-co-rn-DVB) (Table 11, no. 2).
20% of the m-DVB units were attached to PMMA branches having an average DP of 135 (Table 11, no. 2). In CDC13 solution, the polymer showed an 'H NMR spectrum similar to that of syndiotactic PMMA, but no signals in the aromatic region. This means that the mobility of the backbone chain of this graft copolymer is much lower than that of PMMA branches. The NMR signals of the branches were much broader in acetonitrile-d3 (CD3CN) than in chloroform-d. This suggests that the graft copolymer is forced to be solubilized in acetonitrile owing to the long branches of PMMA. The half-height widths of the methoxy proton signal of the graft copolymer observed in CDC13and CD3CN were plotted against temperature (Figure 10). The peak width of the spectrum measured in CDC13 was small and independent of temperature. The width observed in CD3CN increased with decreasing temperatures, especially below 40 "C, at which
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Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986
YH2 FH3 CH3-C-COO-C-CH3 CH3
1
FH2 CH3-C-COOH
i
+
CH2'C.
CH3 CH3
Figure 12. Thermal degradation of tert-butyl ester in poly(tBuMA)-grafted copolymer.
c
10
0.5
i 100
300
200
Temperature
400 (
500
' 0 6W
Cl
& 0.05
Figure 11. T G D S C thermogram of poly(t-BuMA)-grafted copolymer (Table 11, no. 9). 0
Table IV. Thermal Decomposition of Poly( tert -butyl methacrylate)-Grafted Copolymera t-BuMA 1st decomp 2nd decomp units, wt % temp, "C loss, wt % temp, "C loss, wt % 364 72.4 49.0 255 24.5 363 74.5 34.7 250 19.4 By thermal gravimetry.
temperature the solution became cloudy or turbid; that is, the precipitation of the polymer occurred. In Table 111, 13C spin-lattice relaxation times for the PMMA branches in some graft copolyers are shown. The PMMA side chains of DP = 10 and 100 showed similar Tl's when the densities of side chains were the same. Here, the density means the ratio of the amount of DVB units grafted with PMMA to that of total DVB units. When the density decreased from 0.5 to 0.2, the Tl's were increased. The results indicate that the mobility of the side chain is greatly affected by the density or crowdedness of the side chains but very slightly by the length of the chain. 2. Thermal Decomposition of Poly( tert -butyl methacrylate) Graft Copolymer. Thermal properties of some graft copolymers were examined by DSC. Most of them showed one exothermic peak above 340 "C due to decomposition. However, poly(t-BuMA)-grafted copolymer showed two exothermic peaks at about 250 and 360 "C, as shown in Figure 11. Weight loss was monitored by thermal gravimetric (TG) analysis. Table IV summarizes the results of TG-DSC analyses for two graft copolymers with different contents of t-BuMA units. The weight loss at the first decomposition was nearly proportional to the amount of t-BuMA units contained in the graft copolymer. Homopolymer of t-BuMA decomposes thermally to yield poly(methacry1ic acid) and 2-methylpropene (Grant and Grassie, 1960; Grassie et al., 1981). The same mechanism may be applicable to the poly(tBuMA) branches in the graft copolymer, as shown in Figure 12. The weight loss at the first decomposition amounted to 5045% of the weight of t-BuMA units in the samples, while the weight fraction of tert-butyl groups in the monomeric unit was 40%. This probably means that some scission of the main chain of poly(t-BuMA) graft occurred simultaneously. In any case, the thermal decomposition of the graft copolymer will be another method for the preparation of the graft copolymer having poly(methacrylic acid) branches.
20
40 60 Cyclohexane (wt%)
80
100
Figure 13. Phase diagram in emulsification of the cyclohexaneacetonitrile mixtures with PMMA-grafted copolymers: (A) PMMA branch density, 0.5; (B)PMMA branch density, 0.2. Backbone copolymer, no. 3 in Table I.
10
c
0
20
40
60
80
1W
Benzene (wt%)
Figure 14. Phase diagram in emulsification of the benzene-water mixture with poly(scdium methacrylate)-grafted copolymer derived from poly(triphenylmethy1 methacrylate)-grafted copolymer (Table 11, no. 10) (cf. Figure 8).
Application of Graft Copolymers to Practical Use. 1. Polymeric Emulsifier. The copolymers of DPE and m-DVB grafted with PMMA emulsified cyclohexaneacetonitrile mixtures similarly to block copolymers of styrene and MMA (Periard and Riess, 1973). Figure 13 shows the emulsifying behaviors of the graft copolymers for cyclohexane-acetonitrile mixtures. The graft copolymers having PMMA branches (DP = 100) of two different graft densities were used. On the left-hand side area of the curves the mixture existed in an emulsion. The graft copolymer of a larger graft density emulsified the mixture more effectively. Addition of 0.05-2.0 wt % of the copolymer greatly stabilized the emulsion of the mixture. The copolymer grafted with poly(sodium methacrylate) derived from the copolymer grafted with poly(tripheny1methyl methacrylate) (cf. Figure 8) emulsified benzenewater mixtures very effectively, as shown in Figure 14. 2. Negative Electron-Beam Resist of Graft Copolymer Containing Vinyl Group. The copolymers of DPE and p - and rn-DVB's as well as homopolymers of DVB's acted as a negative resist. Poly(p-DVB) showed a high sensitivity, Do C/cm2, but a lower y-value.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 2, 1986 147 Table V. Electron-Beam Exposure Characteristics” of Graft Copolymers of Poly(DPE-co-DVB) backbone copolymer poly(DPE-co-pDVB)d
none
.-
$E 1
“ J
6 6L 0
R+MMA)~
poly(DPE-co-mDVB)O
0
01 0.2 0.5 1.0 Exposed charge density (uC/cd)
Figure 15. Electron-beam exposure characteristics of poly(DPEco-p-DVB) grafted with PMMA branches (l:rn:n= 0.400.57:0.03, k = 20) (cf. Table V).
y-Value is defined as a slope of the exposure-characteristics curve at 0 0 . 5 (cf. Figure 15). Dois the minimum dose for gel formation, and is the dose at which 50% of the f i i thickness has been retained after development. The sensitivity of the copolymer of DPE and p-DVB (Table I, no. 4) as a negative resist (Do= 0.29 X lo4 C/cm2) was lower than that of poly@-DVB),but the y-value and storability were improved, as compared with the homopolymer. A defect of this resists was the poor adhesiveness on the silicon wafer, probably because the copolymer is nonpolar while the surface of silicon wafer is polar. This was fairly improved by grafting polar polymers such as polymethacrylates or polyacrylates. The graft copolymer containing pendant vinyl groups was prepared from poly(DPE-co-pDVB) by the procedure shown in Figure 7. Five or ten mole percent of the pendant vinyl groups were reacted with sec-C4HgLi,and the resulting polymer anion was used as an initiator for polymerizing MMA, methyl acrylate (MA), or acrylonitrile (AN) to form a graft copolymer. Electron-beam exposure characteristics for the typical graft copolymer containing PMMA branches are shown in Figure 15. Sensitivities and y-values for the graft copolymers having different amounts of side chains of PMMA are shown in Table V. The highest sensitivity and y-value were obtained for the graft copolymer having PMMA branches with the density of 0.05 and the DP of 20. Further increase in the amount of PMMA or in DP decreased the sensitivity and y-value. The graft copolymers with poly(methy1 acrylate) (PMA) and polyacrylonitrile (PAN) branches also functioned as negative resists of high sensitivity. The results indicate that grafting of a small amount of polar monomers improves the adhesiveness of the polymer on the silicon substrate to give rise to higher sensitivity and y-value. The copolymer of DPE with rn-DVB (Table I, no. 3) also acted as negative electron-beam resist (Do= 0.5 X lo4 C/cm2). Several graft copolymers were synthesized by anionizing 5 mol 90of the vinyl group in the copolymer with sec-C4HgLifollowed by the reaction with MMA. In this case, grafting of MMA to the copolymer decreased the sensitivity, in contrast to the case of poly(DPE-co-p-DVB), while the y-value increased up to 2.9 (Table V). 2- (Na-Dimethylamino)ethyl methacrylate (DMAEMA) was grafted onto the poly(DPE-co-rn-DVB)as a more polar branch than the PMMA branch. As seen in Table V, sensitivity of the graft copolymer increased extremely with increasing DP of poly(DMAEMA) branch. Because the homopolymer of DMAEMA acted as a negative resist t o the electron beam (Hatada et al., unpublished), in contrast
graft chain D0/10*, densityb DPc C/cm2 0.29
PMMA PMMA PMMA PMMA PMA PAN none
0.05 0.05 0.05 0.10 0.05 0.05
40 20 4 5
PMMA PMMA PMMA PDMAEMA PDMAEMA PDMAEMA
0.05 0.05 0.05 0.05 0.05 0.05
3 8 17 5 6 12
5 20
0.05 0.08 0.94 0.50 0.05 0.07 0.50 0.62 1.50 1.50 0.11 0.07 0.02
y
2.0 2.9 2.3 1.7 2.4
1.1 2.9 2.9 0.8 0.8 0.8
Acceleration voltage 20 kV, developer pentyl acetate, rinse 2propanol. [Amount of grafted DVB units] / [amount of total DVB units]. cDegree of polymerization of branch. dp-DVB/DPE = 1.43, M,, = 40200 (Table I, no. 4). ‘m-DVB/DPE = 1.19, M , = 74000 (Table I, no. 3).
to most of the other polymethacrylates, cross-linking between the graft chains of poly(DMAEMA) must occur simultaneously with that between vinyl groups. The mechanism of cross-linking in poly(DMAEMA) chains is now under investigation. Acknowledgment We express our sincere thanks to Dr. I. Sohma of the Government Industrial Reserach Institute, Osaka, for the measurements of TG-DSC thermograms. Registry No. DPE, 530-48-3; rn-DVB, 108-57-6; p-DVB, 105-06-6; poly(rn-DVB) (homopolymer), 25989-96-2; poly(p-DVB) (homopolymer), 25989-95-1; (DPE).(rn-DVB) (copolymer), 92267-90-8; (DPE).(p-DVB) (copolymer), 92267-94-2; (DPE).(rnDVB).(methyl methacrylate) (copolymer), 92267-91-9; (DPE). (rn-DVB).(ethyl methacrylate) (copolymer), 92267-84-0; (DPE). (rn-DVB)-(butyl methacrylate) (copolymer), 92267-85-1; (DPE).(m-DVB).(tert-butyl methacrylate) (copolymer), 9226786-2; (DPE)-(rn-DVB)-(triphenylmethyl methacrylate) (copolymer), 98125-02-1; @ P E ) . ( m - D v B ) . ( m e t ~ ~(copolymer), ~~) 92267-89-5; (DPE)-(p-DVB)-(methylmethacrylate) (copolymer), 92267-83-9; (DPE).(p-DVB).(methyI acrylate) (copolymer), 99948-78-4; (DPE).(p-DVB).(acetonitrile) (copolymer), 99948-79-5; (DPE)-(p-DVB).(DMAEMA) (copolymer), 98613-67-3; cyclohexane, 110-82-7; acetonitrile, 75-05-8; benzene, 71-43-2.
Literature Cited Adrova, N. A.; Prokhorova, L. K. Vysokomol. Soedin. 1061, 3 , 1509. Ellison, R. A.; Griffin, R.; Kotsonis, F. N. J . Organomet. Chem. 1072, 3 6 , 209. Grant, D. H.; Grassie, N. Polymer 1060, 1 , 445. Grassie, N.; Johnston, A.; Scotney, A. Eur. Po/ym. J . 1081, 17, 589. Hasegawa, H.; Higashimura, T. Macromolecules 1080, 13, 1350. Hatada, K.; Kitayama, T.; Sugino, H.; Umemura, Y.; Furomoto, M.; Yuki, H. Polym. J . (Tokyo) 1070, 7 7 , 989. Hatada, K.; Ktayama, T.; Okahata, S.; Yuki, H. Po/ym. J . (Tokyo) 1082, 14, 971. Hatada, K.; Okamoto, Y.; Kitayama, T.; Sasaki, S. Polym. Bull. (Berlin) 1063, 4 , 228. Kauffmann, N. Z . Phys. Chem. Stoechlom. Verwandtschaftsl. 1006, 55, 547. Nltadori, Y.; Tsuruta, T. Makromol. Chem. 1978, 179, 2069. Perlard, J.; Rless, G. Eur. Polym. J . 1073, 9 , 687. Watson, C.; Eastham, J. F. J . Organomet. Chem. 1067, 9 , 165. Yuki, H.; Kosai, K.; Murahashi, S.; Hotta, J. J . Polym. Sci. Part B 1064, 82, 1121. Yuki, H.; Hotta, J.; Okamoto, Y.; Murahashi, S. Bull. Chem. SOC.Jpn. 1067, 4 0 . 2659. Ziegier, K.; Colonius, A. Justus Lleblgs Ann. Chem. 1030, 479, 135.
Received for review August 5, 1985 Revised manuscript received October 21, 1985 Accepted November 17, 1985
