ABSTRACT:The molecular and crystal structures of aliphatic polyurethane series -[O-(CH2)m-OCONH-(CH2)6-NHCO-]p-with m=2-6, have been studied by X0 ray diffraction methods. Two types of molecular structures have been found. The one (m=3, 5 and type II of m=2) is similiar to the model proposed for r-phase of polyamides, where the hydrogen bonding requirements between adjacent chains are satisfied by tilting the urethane group planes approximately 30° with respect to the fiber axis causing a shortening of the fiber identity periods. The other (m=4, 6 and type I of m=2) is similar to the a-phase of polyamides, where the molecular chains have planar zigzag conformation. These structures are well confirmed by the comparison of the observed and calculated intensities of X-ray diffraction spots. 4, 6-polyurethane (Perlon U) has an X-ray diffraction pattern similiar to that of the unsubstituted polyamides. The chain repeat distance (fiber period) was found to be 19.1 A by Zahn and Kohler\ which is in accordance with that predicted for a fully extended planar zigzag chain. The similarity in the X-ray data between polyamides and polyurethanes suggests that the latter has a conformation of side-by-side zigzag chains with hydrogen bondings between neighbouring chains. This view was pointed out by Borchert2, who proposed the two-molecule unit cell, a=4.95 A, b(fiber axis)=l9.2 A, c=S.69 A, a=90°, ~= 60.2°, and r=170-176°. Zahn and Winter 3 reported the four-molecule unit cell, a=9.55 A,

The crystal structures of polyurethanes with the formula H 0 (m = 4,6) have been determined by X-ray diffraction analysis. Poly(tetramethylene 0 p trimethylene dicarbamate) (4,3-polyurethane) crystallizes in the triclinic space group with a= 5.06A, b= 5.04A, c(fiber axis)= 30.IOA, a= 1!2°, /3= 113°, andy= 1!0°. Poly(hexamethylene trimethylene dicarbamate) (6,3-polyurethane) crystallizes in the triclinic space group PIe !, with a= 5.04A, b= 5.04A, c= 34.65 A. a= Ill 0 , /3= Ill 0 , andy= Ill 0 • By conformational analysis, we attempted to find structure models that would satisfy the condition of full intermolecular hydrogen bonding. These models were then refined by three dimendional Fourier synthesis to the R values of 0.225 for 4,3-and 0.207 for 6,3-polyurethane. The molecules of both polymers are linked two dimensionally by C = 0 • • • hydrogen bonds. These polymers are the same in structure except for their fiber periods which differ in the length of two methylene groups of the glycols. The hydrogen bonding patterns of these polyurethanes differ from those of other polyurethanes. KEY WORDS Linear Polyurethane I X-Ray Diffraction Poly(tetramethylene trimethylene dicarbamate) I Poly(hexamethylene trimethylene dicarbamate) I Conformational Analysis I Hydrogen Bonding I Fourier Synthesis I Linear polyurethanes consisting of aliphatic diisocyanates and glycols are expressed by the general formula crystal X-ray diffraction analysis. 2 The bond lengths and angles of these compounds are considered to be appliceable to m,n-polyurethanes.

Morphological changes of poly(ethylene terephthalate) (PET) film during degradation in an aqueous ethylamine solution at room temperature were examined using photomicrographies. Sample films used in this study were prepared by stretching and annealing the melt quenched amorphous PET film, as shown schematically in Fig. 1.The more crystalline and highly oriented the specimen is, the lower is the rate of the weight loss during the aminolysis (Fig. 2-4). This indicate that ethylamine selectively etches the amorphous PET chains.In the case of non-crystalline film (Fig. 5), the etching pattern was sensitive to the chain orientation anisotropy. For the crystalline films (Fig. 6-8), the etching pattern mainly occurs perpendicularly to the draw direction in accordance with the formation of folded-chain crystals during annealing.The changes of weight loss and of the melting behavior are in accordance with the results from the microscopy.

A study was made of the morphological changes of crystalline fine texture that occurred when poly(ethylene terephthalate) films were degraded in aqueous ethylamine at room temperature. Earlier works proposed that photomicrographies applied to the investigation of the etching patterns were sensitive technique to detect the differences of orientation anisotropy and amounts of crystallinity for PET films which had different mechanical and thermal history. In the present work X-ray measurements were used to deduce the information on the occurring of the various etching patterns based on the structural changes of the crystallite orientation, the size of crystallite, the long period spacing and the distributions of the size of laminar domains by the degradation of films.

No abstract