468 J. K. STILLE A N D L. D. GOTTEK
freeze-evacuate-thaw cycles at liquid nitrogen temperature. The tube was placed in a Parr bomb (which also contained dimethylformamide to equalize internal and external pressures) and heated at 150" for 4 hr. The tube was then opened and the solution was poured into rapidly stirred methanol. The precipitated material was filtered and then dried in wcuo at 212" for 12 hr to afford 0.379 g (86.1%) of yellowish brown polymer, 17 = 0.58 (0.300 g/lOO ml of dimethylformamideat 30").
Muctwnolecuks
Anal. Calcd for Cl5HL2N2: C, 81.82; H, 5.48; N, 12.73. Found: C,81.31; H,5.83; N, 12.58. Poly(1-phenyl-3-p-phenylenepyrazole) (12). The polymerization of 2-phenyl-5-(4'-ethynyl)phenyltetrazole was carried out as described for 2-phenyl-5-(4'-vinyl)phenyltetrazole to provide 0.387 g (88.6%) of light brown polymer, 17 = 0.75 (0.300 si100 ml of dimethylformamideat 30'). A d . Calcd for CI5HlON2:C, 82.56; H, 4.58; N, 12.84. Found: C,82.67; H,4.70; N, 12.03.
Free-Radical Polymerization of 2-Phenyl-5-( 4'-viny1)phenyltetrazole. Reactivity Ratios and Q and e Values J. K. Stille and L. D. Gotter' Depurrment of' Chemistrj , Uniwrsify of l o w , low!u Ciry, lo!-va 52240. Receiced Muy 26, 1969
ABSTRACT: The monomer, 2-phenyl-5-(4'-vinyl)phenyltetrazole(l),has been homopolymerized and copolymerized with styrene, vinylidene chloride, methyl methacrylate, and acrylonitrile by free-radical initiation. Elemental analyses data have been used to calculate reactivity ratios and Q and e values for the tetrazoylstyrene monomer. Thermal cross-linking of the tetrazoylstyrene-acrylonitrile copolymer has been accomplished by the 1,3-dipolarcycloaddition reaction of the nitrilimine dipole across the nitrile dipolarophile. The tetrazoylstyrene monomer is similar to styrene in terms of reactivity in copolymerization ( Q = 0.75, e = 0.6).
I
n many polymer systems, a controlled degree of
cross-linking subsequent to the polymer forming reaction is desirable, particularly when the cross-linking renders the polymer insoluble and provides memory with respect to dimensional stability without providing brittleness. A monomer which can serve as a potential cross-linking agent in vinyl polymerization systems is of particular significance when selective and controlled cross-linking can be accomplished in one of the final steps in the conversion of polymer t o product. The monomer, 2-phenyl-5-(4 '-viny1)phenyltetrazole (1) synthesized for use in 1,3-dipolar cycloaddition polymerizations,* has the potential of undergoing vinyl addition copolymerization and subsequently reacting with suitable dipolarophiles in the polymer chain formed to a f o r d a cross-linked polymer by thermal treatment. The purpose of this investigation was to homopolymerize 1 and t o copolymerize it with a series of vinyl monomers including one containing a dipolarophile which would be present after the free-radical polymerization had occurred.
Discussion The free-radical homopolymerization reactions of 1 in a benzene solvent with azodiisobutyronitrile as a n initiator provided poly 4-[5 '-(2'-phenyltetrazoy1)lstyrene] (2) in 68% yield. The polymer was very similar to styrene in solubility and color and possessed a n intrinsic viscosity of 0.80 (0.300 si100 ml of dimethylformamide at 30"). Since monomer 1 could be ex( I ) Lubrizol Fellow, 1968-1969. (2) J . I1-5-(4’-vinyl)phenyltetrazole St, 1 ene 0.770(3.10) 0.609 (2.46) 0.387 ( 1 ,56) 0.999 (4.03) 0.250 ( 1 . O l )
60
(SEE
FIGUREY
4, 7. 10, A N D 13)
0.179 ( I .72) 0.519 (4.99) 0.636(6.11) 0.112(1.08) 0.948 ( 9 . IO)
7--
Time. min 1 40 180
175 130 250
Convn. 6.63 9.99 6.25 9.80 6.76
Anal..
a?h----.
C
N
73.99 77.45 79.91 73.35 84.64
20.05 16.24 13.21 21.21 8.79
a Solvent. 6 ml of benzene; initiator, 4 mg of azodiisobut~ronitrile. ii The values reported are averages of duplicate determinations.
Experimental Section Purification of Monomers. The comonomers styrene, vinylidene chloride, methyl methacrylate, and acrylonitrile along with the initiator azodiisobutyronitrile were commercially available reagent grade materials. The four comonomers were each distilled immediately before use. The initiator, azodiisobutyronitrile, was recrystallized from methanol and madme up as a stock solution, 4 mg/rnl in
as follows. A mixture of 0.770 g (3.10 mmol) of 2-phenyl5-(4’-vinyl)phenyltetrazole and 0.179 g (1.72 mmol) oJ styrene along with 5.0 ml of benzene and I .O ml of initiator solution was placed in a 20-ml polymerization tube. The contents of the tube were degassed by several freeze-thaw cycles at liquid nitrogen temperature and then sealed iti caciio. The tube was immersed in an oil bath at 60.0” and heated for 2 hr. After that time, the tube was removed
474 J. K. STILLE A N D L. D. GOTTER
Macrornol~~ciilrs
TABLE IV
SOLUTION COPOLYMERIZATION OF
2-PHENYL-5-(4'-VINYL)PHENYLTETRAZOLE A N D VINYLIDENE
---Charge,,&g (mmol)---2-Phenyl-5-(4'-vinyl)No.
(SEEFIGURES 5 , 8, 11,
AND
CHLORIDE AT 60'
14)
z
phenyltetrazole
Vinylidene chloride
Time, min
Convn,
0.788 (3.18) 0.373 (1.50) 0.304 (1.22) 0.192 (0.52)
0.274(2.83) 0.578 (5.97) 0 . 8 5 3 (8.80) 0.912 (9.41)
120
4.11
180
3.79 3.77 3.04
7 -
Anal., %*---
C
N
64.86 64.92 61.20 52.24
20.86 18.44 16.29 12.20
~
1 2 3 4
330 330
The values reported are averages of duplicate deter-
Solvent, 6 ml of benzene; initiator, 4 mg of azodiisobutyronitrile. minations. TABLE V
SOLUTION COPOLYMERIZATION OF
2-PHENYL-5-(4'-VlNYL)PHENYLTETRAZOLEA N D
METHYL METHACRYLATE A T 60"
(SEEFIGURES 7, 9, 12, AND 15) ~~
Charge,a g (mrno1)--2-Phenyl-5-(4'-vinyl)phenyltetrazole Methyl methacrylate
---Anal.,
7 -
No. 1
2 3 4 5
6
0.751 (3.03) 0.696 (2.80) 0.782 (3.15) 0.481 (1.94) 0.746 (3.00) 0.251 (1.01)
0.304 (3.04) 0.515 (5.15) 0.156 ( I .56) 0.600 (6.00) 0.418 (4.18) 0.906 (9.06)
Time, min
120
8.72 9.60 9.72 5.75 5.11
180
8.00
180
I80 180 150
Solvent, 6 ml of benzene; initiator, 4 mg of azodiisobutyronitrile. minations. Q
from the bath, immediately cooled to liquid nitrogen temperature, and opened. The contents of the tube were poured into 200 ml of rapidly stirred methanol. The precipitated white polymer was filtered, dried itz CUCLIO, and weighed. The polymer weighed 0.066 g which represents a 6.63 conversion. The polymer was dissolved in benzene, reprecipitated into methanol, filtered, and dried BI CUCLIO. The white polymer was dissolved in 3 ml of benzene and poured into a I-dram sample vial. The sample was frozen, lyophilized, and analyzed for carbon and nitrogen in duplicate (Tables 111-V).
z
Convn,
h
%b---
C
N
70.77 69.43 71.11 68,86 70.30 66.56
18.19 17.91 20.37 15.29 18.19 10.01
The values reported are averages of duplicate deter-
Pyrolysis of 2-Phenyl-5-(4 '-viny1)phenyltetrazole-Acr ylonitrile Copolymer (6). A solution of 0.250 g of copolymer 6 (30 mol 2 ) in 10 ml of 1,2,4-trichlorobenzene was heated 1 hr at the reflux temperature. A precipitate appeared immediately on heating the solution as the temperature rose above 160" and further precipitate was not formed after -20 min. The solution was cooled and the brown polymer was filtered and dried bz ccicim at 212" to give 0.235 g (98%) of product. The polymer was insoluble in formic acid, sulfuric acid, dimethylformamide, hexamethylphosphoramide, 1,2,4-trichIorobenzene, chlorobenzene, and benzene.
