Molecular origin of the foam structure in model linear and comb polystyrenes: II. Volume expansion ratio
Molecular origin of the foam structure in model linear and comb polystyrenes: II. Volume expansion ratio
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DOI：
10.1016/j.polymer.2020.122354
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发表时间：
2020-04
期刊：
影响因子：
4.6
通讯作者：
M. Abbasi;Lorenz Faust;M. Wilhelm
中科院分区：
文献类型：
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作者：
M. Abbasi;Lorenz Faust;M. Wilhelm
研究了阴离子合成的线状和梳状无规聚苯乙烯（PS）的分子结构对泡沫性能的影响，包括泡沫孔大小、孔密度和体积膨胀比。梳子- ps的主链分子量相同，Mw,bb≈290 kg/mol，Zbb≈20个缠结，分支分子量相同，Mw,br≈44 kg/mol，Zbr≈3个缠结，但分支数不同，3≤Nbr≤190。用co2对纯化良好的线状聚苯乙烯和梳状聚苯乙烯分批发泡，池密度分别约为109和4 × 109cell/cm3，表明LCB对池密度无明显影响，而线状聚苯乙烯中少量残留杂质使池密度降至~108cell/cm3。对于具有相同纠缠主干的梳子- ps系列，Mw,bb≈290 kg/mol，Zbb≈20个缠结，分支相似，Mw,br≈44 kg/mol，Zbr≈3个缠结，但分支数不同，3≤Nbr≤190，随着密集接枝梳子构象的thenbr增加到120，可获得的最高V.E.R.逐渐增加，接近co22溶解度给出的理论极限。随着瓶刷结构的进一步增加，nbr190降低了泡沫的V.E.R.。从流变学的角度来看，该最佳nbr与梳子- ps有关，梳子- ps在单轴拉伸时应变硬化系数最大（SHF≈200），同时在零剪切粘度时最小（η0）。该梳- ps系列的最优nbr = 120对应于两个相邻分支点之间的平均间距约为zs≈0.2纠缠。
The effect of the molecular architecture of a series of anionically synthesized linear and comb atactic polystyrenes (PS) on their foam properties including cell size, cell density, and volume expansion ratio (V.E.R.) was investigated. The comb-PS had the same molecular weight of the backbone,Mw,bb≈ 290 kg/mol,Zbb≈ 20 entanglements, and branches,Mw,br≈ 44 kg/mol,Zbr≈ 3 entanglements, but different numbers of branches, 3 ≤Nbr≤ 190. Batch foaming of well-purified linear and comb-PS using CO2resulted in cell densities about 109and 4 × 109cell/cm3, respectively, which shows that LCB has no distinct effect on the cell density, whereas a small amount of residual impurity in linear PS reduced the cell density to ~108cell/cm3. For a comb-PS series with the same entangled backbone,Mw,bb≈ 290 kg/mol,Zbb≈ 20 entanglements, and similar branches,Mw,br≈ 44 kg/mol,Zbr≈ 3 entanglements, but different numbers of branches, 3 ≤Nbr≤ 190, an increase in theNbrto 120 with densely grafted comb conformation gradually increased the highest achievable V.E.R. close to a theoretical limit given by the CO2solubility. The further increase ofNbrto 190 with a bottlebrush conformation reduced the V.E.R. of the foam. From a rheological point of view, this optimumNbrwas related to a comb-PS which showed the maximum strain hardening factor (SHF ≈ 200) in uniaxial extension, and simultaneously the minimum in the zero shear viscosity,η0. The optimumNbr= 120 for this comb-PS series corresponds to an average spacing distance between two neighbor branch points of aboutZs≈ 0.2 entanglements.