Investigation on the homogeneity of PMMA gels synthesized via RAFT polymerization
Investigation on the homogeneity of PMMA gels synthesized via RAFT polymerization
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DOI：
10.1016/j.polymer.2014.12.035
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发表时间：
2015-02
期刊：
影响因子：
4.6
通讯作者：
R. Scherf;L. Müller;D. Grosch;E. Hübner;W. Oppermann
中科院分区：
文献类型：
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作者：
R. Scherf;L. Müller;D. Grosch;E. Hübner;W. Oppermann
通过RAFT聚合合成的PMMA凝胶和通过自由基聚合（FRP）制成的相应凝胶的特征在于宏观上通过确定剪切模量和溶胀比，微观上通过动态光散射（DLS）特别强调不均匀性。在γ-丁内酯浓度为13 ~ 20wt%（15 ~ 22.5vol%）时，RAFT聚合的交联效率明显低于相应的FRP。这意味着在RAFT聚合中，更多的交联被浪费在网络缺陷中。使用由DLS确定的总系综平均散射强度的静态分数作为不均匀性的度量。随着RAFT剂用量的增加，以及从FRP聚合到RAFT聚合时，该量减少。然而，由于有效网络密度同时下降，聚合机理对均匀性的影响只是一个明显的。当基于具有相同有效网络密度的系统进行比较时，RAFT凝胶并不比FRP凝胶更均匀。相反，用高含量的RAFT试剂制备的RAFT凝胶看起来比用较低含量的RAFT试剂或通过FRP制备的那些凝胶稍不均匀，条件是比较具有相同模量的凝胶。
PMMA gels synthesized by RAFT polymerization and corresponding gels made by free radical polymerization (FRP) were characterized macroscopically by determining the shear moduli and the swelling ratios, and microscopically by dynamic light scattering (DLS) with particular emphasis on inhomogeneity. The gels were prepared in the solventγ-butyrolactone at concentrations ranging from 13 to 20 wt% (15–22.5 vol%).The cross-linking efficiency attained in RAFT polymerizations was significantly smaller than that obtained in corresponding FRPs. This means that in RAFT polymerizations more cross-links were wasted in network imperfections. The static fraction of the total ensemble-averaged scattering intensity determined by DLS was used as a measure of inhomogeneity. This quantity decreased with rising amount of RAFT agent and when going from FRP to RAFT polymerization. However, since the effective network density decreased concurrently, the influence of the polymerization mechanism on homogeneity is just an apparent one. The RAFT gels are not more homogeneous than the FRP gels when the comparison is based on systems having the same effective network density. On the contrary, RAFT gels prepared with a high content of RAFT agent appear slightly less homogeneous than those made with a lower content of RAFT agent or via FRP, provided gels having identical moduli are compared.