Polyvinyl alcohol crystal structure

The mixed crystal formation in ethylene/vinyl alcohol copolymers was previously quoted 3). The examination of the X-ray data shows a different structure from both that of polyethylene and of polyvinyl-alcohol. The repeat along the chain axis is 2.5 A, indicating a planar... 

Crystal structure of polyvinyl alcohol. Nature (Lond.) 161, 929—930 (1948). 

Rather recently, we have studied the solid-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],and amylose [31] with solid-state high-resolution X3C NMR with supplementary use of other methods, such as X-ray diffraction and IR spectroscopy. Through these studies, the high resolution solid-state X3C NMR has proved very powerful for elucidating the solid-state structure of polymers in order of molecules, that is, in terms of molecular chain conformation and dynamics, not only on the crystalline component but also on the noncrystalline components via the chemical shift and magnetic relaxation. In this chapter we will review briefly these studies, focusing particular attention on the molecular chain conformation and dynamics in the crystalline-amorphous interfacial region. 

Rather recently, we have studied the soUd-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],andamylose [31] with solid-state high-resolution NMR with supplementary use of other methods, such as X-ray dif-... 

In the comparison of BC and the BC-PVA composite, the crystallinity of BC in the composite was decreased by 50%. By immersing wet BC pellicles in polyvinyl alcohol [PVA] solution, PVA could penetrate the BC network structure and filled the pores. Acetal linkages were formed in the BC-PVA composites by a cross-linking reaction, which made PVA insoluble in water. However, the crystal destruction was observed after the cross-linking [84]. 

FIGURE 4.9 Crystal structure models of polyvinyl alcohol (6-projection) (a) Bunn (b) Sakurada. Broken lines represent hydrogen bonds. 

Bunn CW (1948) Crystal structure of polyvinyl alcohoL Nature 161 929... 

The examination of the appearance or otherwise of OH absorption bands from single crystals examined in polarised radiation has also been employed in the determination of structures — as, for example, in the study of the bonded OH groups in polyvinyl alcohol [65] and in carbohydrates [46]. As in the case of free OH groups, deuteration is often of considerable assistance in identifying OH groups and in studying bonding effects, and it has been employed for this purpose by Rowen and Plyler [66], Sheppard [116], Sutherland [125] and many others. 

Differential scanning calorimetry and Fourier transform infrared spectroscopy techniques were used to study the structure of water molecules in polyvinyl alcohol and polyethylene grafted acrylate hydrophilic polymers. Varying amounts of water were added to test samples and the samples conditioned to the sorption equilibrium state in sealed containers for 24 hours prior to evaluation. It was concluded that below a threshold water content, depending on the polymers physical and chemical stmcture, water molecules absorbed in hydrophilic polymer cannot form ice crystals in the polymer matrix. Above this threshold content, the water crystallises but below zero. It was also demonstrated that the absorbed water in hydrophilic polymers develops differing hydrogen bonds in the first and second hydration layers. It was concluded that the potential influence of these intermolecular interactions should therefore be taken into account whenever a polymer is used with a solvent. 25 refs. 

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