基于甲壳型液晶高分子的刚-柔型二嵌段共聚物的层状相:链伸展行为的研究

研究了一系列以聚己内酯(PCL)为柔性链段、甲壳型液晶高分子聚{2,5-二(4-甲氧基苯基)氧羰基]苯乙烯}(PMPCS)为刚性链段的刚-柔型二嵌段共聚物(PCL-b-PMPCS)的微相分离结构.小角X射线散射(SAXS)和广角X射线衍射(WAXD)实验结果表明,当PMPCS为无定形态时,PCL-b-PMPCS的微相分离行为与柔-柔型二嵌段共聚物相似,其相形态主要取决于两段的体积分数.随温度升高,PMPCS链段采取伸展的棒状构象,形成六方柱状向列相(ΦHN),会诱导体系的微相分离结构出现"有序-有序"或"无序-有序"转变,使得在很宽的PMPCS体积分数(fPMPCS:40%~80%)内样品均呈现层状微相分离结构.我们对在200oC得到的层状相SAXS数据进行了一维相关函数分析,详细考察了层状相中PMPCS及PCL相区的厚度(LPMPCS、LPCL)与相应链段聚合度(NPMPCS、NPCL)的关系.对PMPCS相区,发现LPMPCS=0.2NPMPCS(nm).因棒状PMPCS链段与层的法线方向平行,该线性关系表明PCL-b-PMPCS的层状相为"单层近晶A相"结构,LPMPCS即为棒状PMPCS链段的长度,可通过控制PMPCS的聚合度予以精确控制.对PCL相区,则LPCL与NPCL近似有标度关系LPCL~NPCL0.85,说明处于熔融态的PCL链段受迫强烈伸展.进一步分析WAXD实验数据并计算每根PMPCS链段在层状相中的界面面积(S/X)可知,随NPMPS增大,PMPCS链段的液晶度从~20%增至~55%,S/X则从~2.4nm2增至~2.7 nm2.与此相应,PCL链段的伸展程度会略有降低,说明LPCL有较弱的NPMPCS依赖性.另一方面,LPCL与S/X的乘积与NPCL满足线性关系LPCL(S/X)=0.21NPCL(nm3),斜率即为PCL重复单元的体积.

Lamellar Phase of Rod-Coil Diblock Copolymer Based on Mesogen-jacketed Liquid Crystalline Polymer: A Study of Chain Stretching

We have studied the microphase phase separation behavior of a series of rod-coil diblock copolymers with poly(2,5-bis4-methoxyphenyl]oxycarbonyl)styrene) (PMPCS) as the rod and poly(e-caprolactone) (PCL) as the coil.PMPCS is a typical mesogen-jacketed liquid crystalline polymer,of which the hexatic columnar nematic (ΦHN) phase can develop from the amorphous state upon heating irreversibly once the chain conformation becomes extended.It is found that the PCL-b-PMPCS samples with amorphous PMPCS behave similar to the coil-coil diblock copolymer,with the microphase separated morphology mainly determined by the volume fraction of PMPCS (fPMPCS).At the temperature above the glass transition temperature of PMPCS (～ 116 C),the transition from amorphous phase to ΦHN phase of PMPCS blocks occurs.This induces the "order-order" and/or "disorder-order" transition of the phase morphology,resulting in the lamellar morphology existing in a wide range of fPMPCs from 40％ to 80％.In this case,PCL-b-PMPCS presents the typical feature of rod-coil diblock copolymer.Using one-dimensional correlation function to analyze the small-angle X-ray scattering data measured at 200 ℃,we obtained the thicknesse of PMPCS and PCL domain (LPMPCs and LPCL) in the lamellar structures.A linear relationship is identified,LPMPCs =0.2NPMPCs (nm),with NPMPCs as the degree of polymerization of PMPCS block.As the chain axis of PMPCS block is parallel to the normal of the lamellae,we conclude that the diblocks form a "single-layer smectic A" lamellar phase,and more importantly,LPMPCs is the extended chain length of PMPCS block,which can be well controlled by polymerization.For PCL block,a scaling of LpCL ～～ NPCL0.85 (NPCL is the degree of polymerization of PCL block) is observed,indicating that the molten PCL block is highly stretched.We further estimated the interracial area per rod-like PMPCS (S/X) in the lamellar phase,which is always smaller than the cross section area of PMPCS rod in the ΦHN phase.Combining with the liquid crystallinity of samples measured by wide-angle X-ray diffraction,we consider that the variation of S/X reflects that,near the PMPCS/PCL interface,the PMPCS segments are not packed in ΦHN phase.This is mainly due to the strong segregation between the molten PCL and the liquid crystalline PMPCS which can cause the PMPCS blocks to be further stretched.For a fixed NpCL,the smaller S/Xis,the larger LPCL is.However,a linear relationship of LPCL(S/X) =0.21NPCL (ntm3) can be realized,wherein the value of slope is the volume of PCL repeating unit.