THE CRYSTALLIZATION OF COPOLYMERS

The crystallization of copolymers was studied with differential scanning calorimetry (DSC), and wide angle x-ray scattering (WAXS). The thermal behavior of vinylidene chloride -vinyl chloride (VDC-VC) copolymers and copolymer blends was observed as a function of overall composition, a drifting composition and composition distribution. For as received and solution precipitated VDC-VC copolymers the melting point (Tm) and heat of fusion ((DELTA)H(,f)) decreased as the fraction of comonomer (VC) in the copolymer increased. However, (DELTA)H(,f) values for the solution precipitated samples were lower than those for the as received materials of similar composition.;At each blend composition the solution blended materials crystallized faster and at higher temperatures during cooling than the physical blends did. This trend was also observed in the as received and solution precipitated VDC-VC copolymers. Increasing the melt temperature of the solution blended (or precipitated) samples caused the crystallization exotherms of these materials to more closely resemble those of the physical blends (or as received) samples. Apparently at temperatures just above Tm a higher degree of molecular orientation (nucleation) exists in the solution blended or precipitated materials.;Unit cell dimension of polyethylene single crystals brominated in suspension were monitored as a function of composition and thermal history. No change was observed in the cell dimensions of the as brominated materials until high bromine concentrations. Brominated crystals annealed above T(,c) exhibited increasing 'a' and 'b' dimensions of the unit cell at low Br concentrations. However at larger Br concentrations the cell dimensions decreased back towards those of the as brominated materials.;Finally samples recrystallized from the melt showed very large increases in the 'a' and 'b' dimensions of the cell as the Br content increased. A very large drop in (DELTA)H(,f) with greater levels of bromine for these samples support the view that comonomer units are incorporated into the crystal body for these materials after melt recrystallization.;For physical and solution blends of the VDC-VC copolymers small changes in Tm and (DELTA)H(,f) were observed over a limited composition range ((+OR-) 2% VDC). Little difference was observed in the melting behavior of blends containing identical overall compositions, but different composition distributions.