896
COMMUNICATION TO THE EDITOR
Vol. 65
COMMUNICATION TO THE EDITOR MEASUREMEXT OF T H E TACTICITY OF SYNDIOTACTIC POLY-(METHYL METHACRYLATE) BY T H E GEL MELTING POINT
Standard conditions therefore can be established so that the gel melting point becomes entirely a function of some element of tacticity of the syndiotactic poly-(methyl methacrylate). A single is0tactic poly- (methy1 met hacrylate) sample was used as the isotactic component of all Sir: Most of the quantitative methods for determin- gels. Gels were prepared with equal weights of ing the tacticity of stereoregular poly-(methyl various syndiotactic polymers in dimethylformmethacrylate) depend on nearest-neighbor inter- amide a t a total concentration of 5% by wt. The actions and, therefore, except in special cases,2 isotactic polymer4 was prepared by initiation with measure the fraction of monomer placements which phenylmagnesium bromide in toluene at 3 O , and may be in one tactic configuration or another. had M , = 130,000; the syndiotactic polymers6 This is the case with two of the more useful methods were prepared by free radical initiation at various thus far described, high-resolution n.m.r.2 and in- constant temperatures from -50” to +140°. The frared spectroscopy. 1,3,4 Since complete steric con- gel melting points were measured by determining trol of polymerization probably never is attained the temperature a t which the gel, contained in the with methyl methacrylate, it is also of importance tip of a 1-ml. pipet inserted into a snug-fitting testto learn the average length of the stereoregular se- tube, flowed readily from the tip. Some results are quences, and the distribution of these sequence given : Temp. of lengths. We report here a new method, specific to polymerization, OC. X 1CF Gel melting point, O C . poly-(methyl methacrylate), which we believe gives 8.0 92.7 -50 a relative measure of average syndiotactic sequence 87.5 -30 19.0 length. 0 11.5 76.5 This method is based on the observation that 60 25.1 60.0 when a solution of isotactic poly-(methyl methacryl140 5.7 43.5 ate) in a solvent such as dimethylformamide is Gornick‘j has applied the Flory theory of comixed with a solution of syndiotactic poly-(methyl polymer crystallization7 to partially t’actic systems, methacrylate) in the same solvent, a rigid continu- and concludes that for a polymer chain containing ous gel is formed rapidly. If this gel is heated, it blocks of crystallizable sequences the equilibrium will melt sharply to a clear solution. This gel melting point will be primarily dependent on the melting point is (1) reproducible to j = O . 5 O , (2) only lengths of the crystallizable blocks, and only secslightly affected by changes in the original polymer ondarily on the concentration of the blocks wit.hin concentration from about 1 to 9% by wt. or by the chain. We believe that the gel formation changes in the ratio of isotactic to syndiotactic described here involves a linearly ordered array of polymer from about 1:4 to 4:l by wt., (3) inde- short, stiff syndiotactic helical sequences with pendent of the moje of preparation of the isotactic longer isotactic helical sequences, and that t’he polymer if it has Mv > ca. 100,000, (4) only slightly “crystallite” dimensions, and hence melting points, affected by the molecula; weight of the syndio- depend mainly on the syndiotactic sequence lengths tactic polymer if it has Mv > ca. 50-100,000, ( 5 ) These gels give type I11 X-ray diffraction patterns’ markedly dependent on the temperature of polymeriza- which disappear a t very near the melting points of tion of the syndiotactic polymer. Both n.m.r. and the gels infrared spectroscopy have established that the frac\!-ARREN H. \VATANARE tion of syndiotactic placements increases with de- RESEARCH LABORATORIES CHARLES F. RYAN ROHM AND HAASCOMPAXY PAULC. FLEISCHER, JR. cwasing temperature of polymerization. BRISTOL, PENNSYLV.4NIA B. S.GARRETT @V
(1) T.G . I’ox, B. S. Garrett, W. E. Goode, S. Gratch. J. F. Kincaid. A . Spell and J. D. Stroupe, J . Am. Chem. Soc., 80, 1768 (1958). (2) F. A. Bovey and G. V. D. Tiera. J. Polymer Sci., 44, 173 (1980). (3) IT. Baumann, H. Schreiber and K. Tesamar, Eiiakromol. Chem.. 36, 81 (1959). (4) W. E. Goode. F. H. Owens, R. P. Fellrnann. W. €1. Snyder and J. 1;. Moore, J. Polymer Sci., 46, 317 (1960).
Received RIarch 10, 1961 (5)
T. G. Fox, W. E. Goode, S. Gratch, C . bf. €Iugget,t, ,l. F.
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m i d , .1. Spell, and J. fi. Stroupe, i b i d . , 31, 173 (1958). (6) F. Gornick. Ph.D. Thesis, University of Pennsylvania, June. 1959. (7) P. J. Flory, Trans. Faraday Soc.. 51, 8 B (1955),
