SYNTHESIS AND CHARACTERIZATION OF POLY(1,ll-DODECADIYNE) AND RELATED POLYMERS

Introduction

Over the last decade the solid-state diacetylene polymerization reaction (Fig. 1) first characterized by Wegner (1) has been shown to occur in a wide variety of monomers. It was also shown that some polyurethanes (2) and various other polymers (3) containing diynes at regular intervals undergo a crosslinking through the same diacetylene reaction mechanism. The ability of a diacetylene compound to polymerize is dependent on packing in the solid state, which is in turn dependent on the side groups R and R’ in Figure 1. It has been dem- onstrated that simple hydrocarbon side chains pack in a favorable manner that allows the polymerization to proceed (4). In accordance with this behavior a polymer was designed in our laboratory containing hydrocarbon segments and diacetylene (or diyne) groups in series. Upon exposure to ultraviolet (UV) or 7 rays (or by thermal annealing or with high pressure), these polymers in some cases were observed to undergo crosslinking through the reaction of the diacetylene groups, resulting in a regular or woven two-dimensional network of chains.

R-C NC-R. c I// C /

\ R--6

ACETYLENIC CUMULENIC POLYMER POLYMER

MONOMER

Fig. 1. Diacetylene reaction scheme.

Synthesis

Monomers of 1,l 1-dodecadiyne, 1,9-decadiyne, and 1 ,honadiyne were oxidatively coupled using a copper-pyridine catalyst (5,6). Pyridine (14 mi), ethanol (14 ml), and cupric chloride (10 g) were added to a three-necked flask. After dissolution, the monomer was added (0.025 mole) and the result- ing mixture was stirred and heated in the presence of air at 75°C. After 4 hr the temperature was increased and the reaction mixture was refluxed for an additional hour. After acidification with an aqueous HCl solution, the poly- mer was extracted with chloroform and washed several times with water. The chloroform was removed at reduced pressure and at room temperature. The

Journal of Polymer Science: Polymer Letters Edition, Vol. 19, 227-233 (1981) 0 1981 John Wiley & Sons, Inc. CCC 0360-6384/81/0SO227-07$01.00

228 POLYMER LETTERS EDITION

A 6

Fig. 2. Reactive model of polymers containing even numbers of methylene groups.

polymers were typically light brown in color and slightly rubbery, possibly due to small amounts of acetylene trimerization (7) or light crosslinking through the diacetylene group. It was found that this could be kept to a min- imum by reacting at lower temperatures.

Results and Discussion

Because the dodecadiyne, decadiyne, and nonadiyne polymers contain 8,6, and 5 CH, groups, respectively, per repeat, they will be referred to subsequent- ly as 8,6, or 5 polymer. Upon exposure to UV, the 5 and 8 polymers turn deep blue in color at the surface. This is presumably due to the reaction of the diyne groups through the normal diacetylene mechanism resulting in cross- linking of the polymer. Samples of the 5 and 8 polymer could be highly crosslinked through exposure to y radiation (20 mrad), rendering them brittle and completely insoluble. The 6 polymer did not turn blue under W or y irradiation, indicating an unfavorable packing relation between diynes in the crystal structure which prevents systematic diacetylene polymerization.

The crosslinking reaction is shown schematically in Figure 2. For polymers with an even number of CH2 groups, two structures are possible if the zigzags of the hydrocarbon segments are assumed to be coplanar [Figs. 2(A) and 31. The structure represented in Figure 2 is the more likely because of the larger chain extension. A layer line spacing of about 12 A is observed by x-ray dif- fraction of the oriented 8 polymer [Fig. 5(A)]. This also indicates a structure more similar to that in Figure 2, which has a theoretical repeat distance of 14.5 A compared to 27 A for that of the structure in Figure 3.

The predicted structure for polymers with an odd number of CH2 groups is

POLYMER LETTERS EDITION 229

Fig. 3. Nonreactive model of polymers containing even numbers of methyl- ene groups.

A .

Fig. 4. Structure and reaction model for polymers containing odd numbers of methylene groups.

slightly different and is shown for the 5 polymer in Figure 4. Diffraction of the oriented 5 polymer results in a layer line spacing of about 23 A, which

230 POLYMER LETTERS EDITION

(B) Fig. 5. (A) X-ray diffraction of uncrosslinked oriented polydodecadiyne.

(B) X-ray diffraction of crosslinked oriented polydodecadiyne.

agrees well with the predicted value of 21.5 A calculated from the model in Figure 4.

After crosslinking the samples, diffraction patterns from the 8 polymer samples were relatively unchanged [Figs. 5(A) and (B)] . Although the layer line spacing is expected to shorten slightly, the orientation in the samples was not good enough to achieve the required accuracy in measurement. Qualita- tively, the relative intensities also do not appear to change after crosslinking due to the low degree of atomic movement upon reaction.

cant changes in intensities and a decrease in layer line spacing from 23 to about 10 layer line in which case the spacing is a quite reasonable 20 A.

Diffraction of the crosslinked 5 polymer samples, however, did show signifi-

[Figs. 6(A) and (B)] . This is probably the result of a weak first

POLYMER LETTERS EDITION 23 1

(B) Fig. 6. (A) X-ray diffraction of uncrosslinked oriented polynonadiyne. (B)

X-ray diffraction of crosslinked oriented polynonadiyne.

The relative conductivity of thin films of the 8 polymer was measured using a specially prepared lock-and-key device (8) (donated to us by Professor S . Senturia, Electrical Engineering, M.I.T.). A lock-and-key device is essentially two long parallel aluminum electrodes sandwiched into a small area on a glass plate and enables low conductivities to be measured at reasonably low voltages. Thin films of the 8 polymer were made by first preparing a dilute solution of it in chloroform. A few drops of this solution were placed on the surface of water and allowed to expand over the surface. After solvent evaporation, the thin film (about 5 pm) which remained was deposited on the lock and key by dipping the lock-and-key device down through the water surface.

The uncrosslinked films exhibited initial currents of lo-' A which decayed on the order of days to lo-' A (at 60 V dc). This remained unchanged upon

232 POLYMER LETTERS EDITION

'*+a t J I

Fig. 7. Doping apparatus containing lock-and-key device.

illumination or doping the film with iodine (Fig. 7). Crosslinked samples ex- hibited similar initial behavior. The crosslinked samples also exhibited no photoconduction but did increase 2.5 orders of magnitude in conductivity when doped with iodine. The current decreased to its original value (ca. 10-11 A), however, after the removal of the iodine.

Conclusion

Polymers containing hydrocarbon chain segments and diyne groups at regu- lar intervals can be made and successfully crosslinked in some cases. The crosslinking of the polymer which results in a regular woven network of hydro- carbon and conjugated backbones renders the material completely insoluble. The occurrence of a crystal phase transition in the reaction involving the poly- mer with six CH2 units between diacetylene units is a definite indication of high conversion in the crystalline regions. Recent preliminary solid-state magic angle NMR studies of these materials indicate high conversions in the crystal- line regions and negligible systematic crosslinking in the amorphous regions. This will be reported on in more detail in a future article.

The increase in conductivity of the crosslinked material upon doping with iodine demonstrates the nature of the system. It is possible that other dopants may increase conduction to higher values and would result in a useful semicon- ducting polymer. These polymers would be advantageous in that they are very tractable in their uncrosslinked state and therefore easily used for any given application.

POLYMER LETTERS EDITION 233

Summary

Polymers of the general type --+(CH2),-CEC-CSfj7 have been prepared (n = 5,6,8). Two of these polymers (n = 5,8) undergo a systematic crosslink- ing reaction to produce polydiacetylenes when exposed to UV or higherenergy radiation. These two-dimensional structures have been examined by x-ray dif- fraction techniques and preliminary structures have been proposed. Doping of films of these crosslinked structures with iodine results in a 2.5 order increase in electrical conductivity.

Acknowledgment

The support of this work by Office of Naval Research Contract NOOO14-77- C-0213 is gratefully acknowledged.

References

(1) G. Wegner, Z. Natuforsch., 24b, 824 (1969). (2) G. Wegner, Makromol. Chem., 134, 219 (1970). (3) A. Hay, D. Bolon, K. Leimar, and R. Clark, J. Polym. Sci. Polym.

Lett. Ed., 8 ,97 (1970). A. Hay, US. Pat. 3,300,456 (Cl. 260-88.2) (January 24, 1967).

(4) G. Arndt, Doctoral Dissertation, University of Mainz, West Germany, 1975.

(5) I. Campbell and G. Eglinton, Org. Synth., 45,39. (6 ) I . Campbell and A. Galbraith, J. Am. Chem. SOC., 182, 889 (1959). (7) H. Jabloner, Hercules, Wilmington, Delaware, personal communication. (8) S. Senturia, “Fabrication and Evaluation of Polymers for use in Early

Warning Fire-Alarm Devices,” NASA CR-I34764 (1975). David Day Jerome B. Lando

Department of Macromolecular Science Case Institute of Technology Case Western Reserve University Cleveland, Ohio 44106

Received November 24, 1980 Accepted January 23, 1981