Major Impact of Cyclic Chain Topology on the Tg-Confinement Effect of Supported Thin Films of Polystyrene
Major Impact of Cyclic Chain Topology on the Tg-Confinement Effect of Supported Thin Films of Polystyrene
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DOI：
10.1021/acs.macromol.5b02474
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发表时间：
2016-01
期刊：
影响因子：
5.5
通讯作者：
Lanhe Zhang;Ravinder Elupula;Scott M. Grayson;J. Torkelson
中科院分区：
文献类型：
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作者：
Lanhe Zhang;Ravinder Elupula;Scott M. Grayson;J. Torkelson
通过原子转移自由基聚合和“点击”化学合成了数均分子量（MW）为3.4和9.1 kg/mol的高纯度环状聚苯乙烯（c-PS）样品。通过差示扫描量热法测量的本体玻璃化转变温度（Tg）表现出弱得多的MW依赖c-PS相对于其线性前体和阴离子聚合的线性PS（A-PS）。使用椭圆偏振法和荧光光谱，主要的差异，观察到的Tg限制在C-PS膜支撑在硅衬底上的效果相比，A-PS。尽管对于支撑在二氧化硅上的A-PS通常观察到大的Tg随限制的降低，但在误差范围内，在Si/SiOx衬底上的c-PS/3.4k膜中观察到低至21 nm厚度的限制效应。虽然c-PS连接基团含有氮和氧原子，可能能够进行氢键，Tg是不变的限制c-PS/3.4k或略有减少c-PS/9.1k无论水平。
High purity cyclic PS (c-PS) samples with number-average molecular weight (MW) of 3.4 and 9.1 kg/mol were synthesized via atom transfer radical polymerization and “click” chemistry with narrow MW distribution. Bulk glass transition temperature (Tg) measured by differential scanning calorimetry exhibited a much weaker MW dependence for c-PS relative to its linear precursor and anionically polymerized linear PS (A-PS). Using ellipsometry and fluorescence spectroscopy, major differences were observed in the Tg-confinement effect in c-PS films supported on silicon substrates compared to A-PS. Whereas a large Tg reduction with confinement is commonly observed for A-PS supported on silica, within error, no confinement effect is seen in c-PS/3.4k films on Si/SiOx substrates down to 21 nm thickness. Although the c-PS linking group contains nitrogen and oxygen atoms potentially able to undergo hydrogen bonding, Tg is invariant with confinement for c-PS/3.4k or slightly reduced for c-PS/9.1k regardless of the level...