| Popis: |
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 60°C, yielding highly functionalized carbon-chain polymers of general structure (CH2CH2C(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 (M¯w/M¯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 360°C, while poly(2a–d) and poly(4) are stable up to 200°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 TGG¯ TGG¯ 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 180°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 140°C, but only oligomers (X¯n < 5) were obtained after long reaction times. An alternative synthetic strategy to synthesize the desired poly(1,1-difunctionalized tetramethylene)s (CH2CH2CH2C(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 25°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. |
