Structural transformations and water associate interactions in poly-N-vinylcaprolactam-water system

Structural transformations and water associate interactions were studied in poly-N-vinylcaprolactam (PVCL)-H2O system by various methods (IR-spectrosc opy, quantum-chemical calculations, DSC and light microscopy). A number of features of PVCL macromolecules were first found: (i) the conformation type of a side seven-member ring deduced by quantum-chemical calculations is th e "chair"; (ii) the main chain of PVCL prepared by usual radical polymeriza tion has syndiotactic structure; (iii) the calculation of charge distributi on on a C=O oxygen atom in the analogue of PVCL chainlink gives the large e lectron density value being -0.362. The addition of water to PVCL changes g reatly glass transition temperature (T-g). The DSC method shows a lowering of T-g from 147 degrees (dry polymer) to -17 degrees divided by - 38 degree s at N (number of water molecules per unit) being 2.6 divided by 8.0. Cold crystallization and subsequent melting of ice-like units formed of water as sociates in the presence of PVCL macromolecules were displayed at N = 8 and 10, Crystallization under cooling happens only at the increased N (N > 10) , Sharp decrease of melting heat of ice-like units (Delta H-mt) from 225 to 48 J/g (334 J/g of ice in bulk water) occurs as N diminishes from 10 up to 8, PVCL macromolecules in aqueous solution are the strongest modifier of w ater associate structures bring affected by the polarization action of high polar amide C=O groups and by specific configurational and conformational structures of the polymer. (C) 1998 Elsevier Science Ltd. All rights reserv ed.