Nachweis von Verzweigungen in Polyacrylnitril mit der ¹³C‐NMR‐Spektroskopie

Abstract

Die NMR-Spektren von radikalisch und anionisch polymerisiertem Acrylnitril weisen auf strukturelle Unterschiede hin. In anionisch hergestellten Proben sind Kurzkettenvcrzweigungen an den a-Kohlenstoffatomen nachweisbar. Verzweigungsgrad und Lange der unverzweigten kurzen Ketten konnen rnit dieser Methode bestimmt werden. OBnapyincenue pa3eemenenuQ 8 nosuaEpwonumpune &emoao& W -H M P -c n e l~m p o c~o n u uHMP-CneKTpbI o 6 p a 3 u o~ ~OJIHaKpMJIOHHTpHJIa, nOJIyYeHHbIX pZl@KaJIbHblM H aHUOHHbIM UHHqHHpOBaHHeM, Bbl-KBJIKIOT CTPJ' KTYPHbIe paaJIHYHJX. B aHHOHHO ElHMQHHPOBaHHbIX 0 6 p a s~a x 0611apyme~~d KOpOTKOqeIIHLJe pas-BeTBJIeHHK y a-C-aTOMOB. OnIlCaHHbIfi MeTOA nO3BOJIfieT 0npe~eJIHl.b CTeneHb pa3BeTBJIeHHH I1 AJIHHY Hepa3BeT-BneHHblX KOPOTKHX 4enefi. Detection of branching in polyacrylonitrile by 13C-NMR-spectroscopyNMR-spectra of radically and anionically polymerized acrylonitrile indicate structural differences of the polymers obtained. Anionically polymerized samples have short chain branchings a t the a-carbon atoms of the acrylonitrile monomer units. Branching degree and length of the nonbranched short chains can be determined by this method.

Polymerization of acrylonitrile catalyzed by single yttrium tris(2,6‐di‐tert‐butyl‐4‐methyl phenolate)

“…The peak around 2.7 ppm with very little intensity might be attributed to H a and H b in branched and/or cyclized structures proposed by Verneker et al (Schemes and ) 17. It can also be seen from Fig 4 that, in addition to three peaks of the C a (32.1 ppm), C b 26.8 ppm) and C c (119.5 ppm) atoms,18 there is an additional peak around 14.0 ppm with very little intensity that may be attributed to C d atoms in the branched structure as suggested by Scheller and Kamide (Scheme ) 19. 20 The results indicate that there is a small amount branched and/or cyclized structure in the PAN obtained in n ‐hexane and THF mixture.…”

“…(Fig 6). 19, 20 Yellow colouration of PAN might come from the branched and cyclized structure. The above results suggest that a highly branched and/or cyclized structure in PAN is obtained in DMF, which leads to the formation of lower molecular weight polymers ( M w < 10 000).…”

Co(acac)2‐Mediated Radical Polymerization of Acrylonitrile: Control Over Molecular Weights and Copolymerization With Methyl Methacrylate

“…As determined by 13 C NMR, all polymers prepared displayed an atactic linear structure with no discernible branching (Figure 3). 29, 30 Thus, only the signals for the nitrile carbon at δ = 120, of the methane‐carbon at δ = 32.5 and of the methylene carbon at δ = 27.5 are visible. The signal splitting is attribute to the coexisting mm , mr, and rr triads and to the mmm , mmr , mrr and rrr tetrads (ratio 1:2:1 and 1:3:3:1, respectively).…”

Polymerization of acrylonitrile with magnesiumdialkyls. Reaction conditions and stereospecificity

“…Longer side chains obtain independently on the chain length terminal cyanomethyl chemical shifts at 14.4 ppm with normal line width. The last but one cyanomethylene group of a side chain consisting of three monomer units is expected at 28.2 ppm [9]. The amount of this kind of branches does not exceed 1% of all branches.…”

“…It is well known that under certain reaction conditions side reactions occur during the acrylonitrile polymerization, resulting in branchings. First indisputable evidence of short chain branches in polyacrylonitrile was given by 13C NMR investigations [9]. Because short chain branches influence significantly the polymer properties, we used both the branching degree and the tacticity from NMR spectra to characterize the products.…”