Equations are developed for the bulk free energy of fusion, melting temperature, crystal thickness, and nucleation rate of copolymer crystals containing an arbitrary concentration of comonomer units. These equations which represent advances over earlier ones are shown to be consistent with experimental data for copolymers of L-and DL-lactides and cis-and irons-isoprenes. Analysis of the lactide data confirms an earlier prediction that the crystal thickness should increase linearly with increasing small concentrations of the comonomer units for crystallizations carried out at the same temperature. Further, this linear dependence is shown to extend to crystals containing both equilibrium and nonequilibrium concentrations of the comonomer units. The nucleation rate equation is in agreement with the observed linear dependence of the logarithm of the growth rate on the comonomer concentration in isoprene copolymers. The following are consistent with the experimental data for the lactides: 461 °K, equilibrium melting temperature of the homopolymer; 403°K, equilibrium dissolution temperature in xylene; 1370 cal/mol of monomer (5730 J/mol) heat of fusion; 26.5 erg/cm2 (2.65 X 10~2 J/m2) surface free energy and 585 cal/ mol (2447 J/mol) comonomer defect energy. Directions for future research are suggested.

Dragline silk from the spider, Nephila clavipes, was characterized b y thermal analysis (TGA, DSC, DMA), computational modeling, scanning electron microscopy and by quasi-static as well as high rates of strain. Thermal stability to about 230°C was observed by TGA, two transitions by D M A , -75"C, representative of localized motion in the amorphous domain, and a main chain motion associated with partial melt at 210°C. Tensile tests indicated average initial modulus, ultimate tensile strength and ultimate tensile strain of 22 GPa, 1.1 GPa and 9%, respectively. The corresponding properties of the best fibers tested were 60 GPa, 2.9 GPa and 11 %, respectively. High strain rates (>50,000%/ see) indicated similar mechanical properties to the average values indicated above. Microscopy showed compressive and tensile strains to failure of 34%. Computational modeling yielded a cystal modulus of 200 GPa.

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The unit cell dimensions have been measured at temperatures between 93 and 333 K for linear polyethylene samples with long periods of 385, 220, and 99 Å. The angular positions of 6 x-ray diffraction lines were obtained at 5–10 K intervals with a powder diffractometer and the positions corrected for beam penetration so as to agree with powder camera results obtained with more lines at 296 and 155 K. At lower temperatures, the cell dimensions are nearly independent of long period, but at higher temperatures, the basal area of the cell appears to vary linearly with the reciprocal of the long period. The value of the slope increases with temperature and at 293 K is nearly the same for sets of data obtained with a number of different molecular weight distributions, crystallization and annealing conditions as well as for n-paraffins. The specific volume data for all three polymer samples can be represented between 133 and 333 K with a standard deviation of 2.6×10−4 cm3 g−1 by the equation V=0.8341(1055.5−T)/(931.7−T)+(0.12−1.6×10−3T+7.8×10−6T2)/l2in which V is in cm3 g−1, T is °K and l2 is the long period expressed in angstroms. It is concluded that the interaction of the molecules at the surface of the crystal is not as important as the length of the molecular stems between the folds in affecting the dimensions at higher temperatures. The stems probably alter the dimensions through their effect on the thermal energy. The dependence of crystal specific volume on crystal size is estimated to reduce the heat of fusion of small crystals by about 2% in the normal range of long period. Neglecting this in analyzing melting-temperature-lamella-thickness data can lead to errors of the order of 3% in the surface free energy and 0.3 K in the equilibrium melting temperature. The variation of crystal specific volume accounts for about 5% of the variation of macroscopic specific volume and constant pressure specific heat with long period.