ENTHALPY OF FUSION OF LINEAR POLYETHYLENE
ENTHALPY OF FUSION OF LINEAR POLYETHYLENE
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DOI：
10.1021/j100847a060
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发表时间：
1968-01-01
影响因子：
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通讯作者：
GOPALAN, M
中科院分区：
文献类型：
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作者：
MANDELKERN, L;ALLOU, AL;GOPALAN, M
测定了在各种控制条件下结晶的线性聚乙烯分子量组分的熔化焓。对于在本体中结晶的样品，熔化焓非常依赖于分子量。对于一个给定的结晶程序，有一个单调减少，在这个数量与增加分子量，以便观察到一个广泛的值。熔融焓和密度测量计算的结晶度的比较表明，一个非常好的协议的样品从来没有低于初始结晶温度冷却。然而，对于随后冷却至室温的样品，焓测量给出的结晶度值低于密度值。这一结果归因于冷却时形成的小尺寸微晶和界面焓的相关贡献。与上述结果相反，稀溶液形成的晶体的熔化焓与分子量无关，仅取决于晶粒尺寸。从实验数据计算的界面焓和熵的晶体，讨论了不同的形态模型，已提出。
The enthalpy of fusion of molecular weight fractions of linear polyethylene, crystallized under a variety of controlled conditions, has been measured. For samples crystallized in the bulk, the enthalpy of fusion is very dependent on the molecular weight. For a given crystallization procedure, there is a monotonic decrease in this quantity with increasing molecular weight, so that a wide range of values are observed. A comparison of the degree of crystallinity calculated from enthalpy of fusion and density measurements indicates a very good agreement for samples which are never cooled belowthe initial crystallization temperature. However, for samples which are subsequently cooled to room temperature, the enthalpy measurements give lower values for the degree of crystallinity than does the density. This result is attributed to the small-size crystallites which form on cooling and the associated contribution from the interfacial enthalpy. In contrastto the above results, the enthalpy of fusion of crystals formed from dilute solution is independent of molecular weight anddepends only on the crystallite size. The interfacial enthalpy and entropy of such crystals, calculated from the experimental data, are discussed in terms of different morphological models that have been proposed.