Sanchez Isaac C, DiMarzio Edmund A
Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234.
J Res Natl Bur Stand A Phys Chem. 1972 May-Jun;76A(3):213-223. doi: 10.6028/jres.076A.026.
A nonequilibrium (kinetic) theory of polymer molecular weight (MW) fractionation is formulated and applied to binary and multicomponent polyethylenes crystallized from unstirred xylene solutions. High MW components crystallize more readily than do low MW components. This fractionation effect is enhanced as the crystallization temperature is raised. At low crystallization temperatures (high undercoolings) the polymer tends to fractionate according to the volume fraction distribution of its MW components and thus, the number average MW of the crystal that is formed is approximately equal to the weight average MW of the polymer in solution. It is shown that MW fractionation does not depend on the details of nucleation. but rather on the rates for post-nucleation crystal growth. The effects of MW polydispersity on crystalline properties is considered and in particular it is shown that polydispersity tends to mask the intrinsic dependence of crystal thickness on MW. The variables which govern and influence fractionation are also discussed.
提出了一种聚合物分子量（MW）分级的非平衡（动力学）理论，并将其应用于从不搅拌的二甲苯溶液中结晶的二元和多组分聚乙烯。高分子量组分比低分子量组分更容易结晶。随着结晶温度的升高，这种分级效应会增强。在低结晶温度（高过冷度）下，聚合物倾向于根据其分子量组分的体积分数分布进行分级，因此，形成的晶体的数均分子量大约等于溶液中聚合物的重均分子量。结果表明，分子量分级并不取决于成核的细节，而是取决于成核后晶体生长的速率。考虑了分子量多分散性对晶体性能的影响，特别是表明多分散性倾向于掩盖晶体厚度对分子量的内在依赖性。还讨论了控制和影响分级的变量。
