Synthesis and characterization of highly functionalized carbon-chain polymers
Abstract (Summary)This project involves the design, synthesis and characterization of a new class of carbon-chain polymers with substituents on every third and every fourth carbon along the backbone. 1,1-Dicyanocyclopropane 1 , alkyl 1-cyanocyclopropanecarboxylates 2a-d and 1-phenylcyclopropanecarbonitrile 4 undergo ring-opening polymerization in the presence of thiophenolate anions at 60Ã?Â°C, yielding highly functionalized carbon-chain polymers of general structure (CH2 CH2 C(XY)) n . Monomer 1 is highly reactive, while 2a-d show intermediate reactivity between 1 and 4 . GPC analysis indicated poly(2a-d ) had narrow molecular weight distributions (MÃ?Â¯w /MÃ?Â¯n < 1.17). Due to the poor solubility of poly(1 ) and poly( 4 ), their molecular weights could not be measured. Thermogravimetric analysis (TGA) shows that poly(1 ) is highly stable up to 360Ã?Â°C, while poly(2a-d ) and poly(4 ) are stable up to 200Ã?Â°C. X-ray analysis indicated that the polymers are all semi-crystalline, with melting temperatures above their decomposition temperatures. A detailed study of the crystal structure of poly(diethyl-1,1-cyclopropanecarboxylate) poly(3b ) indicated that the conformation of the backbone is close to a TGGÃ?Â¯ TGGÃ?Â¯ structure. Similar attempts to ring-open polymerize dialkyl-1,1-cyclobutanedicarboxylates 5a-c and ethyl 1-cyanocyclobutanecarboxylate 6 using thiophenolate anions at temperatures ranging from 140 to 180Ã?Â°C were unsuccessful. For these reactions, the thiophenolate preferentially attacks the carbon on the ester substituent (Krapcho reaction) and not the ring-carbons. 1,1-Dicyanocyclobutane 8 ring-opens in the presence of potassium or sodium thiophenolate at 140Ã?Â°C, but only oligomers (XÃ?Â¯n < 5) were obtained after long reaction times. An alternative synthetic strategy to synthesize the desired poly(1,1-difunctionalized tetramethylene)s (CH2 CH2 CH2 C(XY))n was attempted via the anionic polymerization of ethyl 2-cyano-2,4-pentadienoate 9 and diethyl 2-propeny-lidene malonate 10 . NMR and IR analysis of samples (initiated with piperidine in benzene at 25Ã?Â°C) indicated that the microstructure of poly(9 ) consisted only of 1,4-addition units, but for poly(10 ), a mixture of 3,4- (66%), 1,4- (17%) and 1,2 (17%) units are obtained. Subsequent hydrogenation of a sample of poly(9 ) with only a 1,4-microstructure using diimide as a hydrogenation agent. The results indicated up to 80% hydrogenation was achieved. This strategy, although not direct, provides a feasible method to achieving our target carbon-chain polymers with substituents on every fourth carbon.
School Location:USA - Massachusetts
Source Type:Master's Thesis
Date of Publication:01/01/2001