梳状高分子烷基侧链构象和堆积结构的红外光谱研究

以正十九烷和两种接枝烷基链的梳状高分子N-十八烷基聚乙烯亚胺(PEI18C)、N-十八烷基聚对苯甲酰胺(PBA18C)为研究对象,利用红外光谱对处于受限和自由状态的烷基链的构象和堆积结构随温度的变化进行了对比研究.结果表明,处于受限和自由状态的烷基链的构象排列和堆积结构及其转变行为不同,且受限于柔性PEI主链和刚性PBA主链的烷基链也不相同.从主链刚性的角度,探讨了影响烷基侧链构象和堆积结构的原因.

Transition Investigation on the Conformation and Packing Structures of Alkyl Sid e Chains in Comblike Polymers with FT-IR Spectroscopy

The temperature-induced variation of the conformational behavior and the packing structure of alkyl chains in n-nonadecane,N-octadecylated polyethyleneimine(PEI18C) and N-octadecylated poly(p-benzamide)(PBA18C) were investigated with FT-IR spectroscopy and other techniques.The main aim is to in-depth understand the specific aggregation structure of alkyl side chains in the comblike polymers.N-alkylation reactions on polyethyleneimine(PEI) and poly(pbenzamide)(PBA) backbone were carried out in homogenous solutions composed of octadecyl bromide and polymer substrate.According to the results of nuclear magnetic resonance(NMR) and elemental analysis measurements,the N-substitution degree was obtained,i.e.47% for PEI18C and 97% for PBA18C,respectively.The relative intensity of the conformation bands of methylene group at 1463 cm~(-1) and 1470 cm~(-1) was utilized to investigate the conformation transition behavior of PEI18C and nonadecane in the heating process.The results indicated that the octadecyl chains of PEI18C exhibited different conformation transition process compared with those of nonadecane.The variation of the rocking bands of methylene groups implied that the ordered packing structure of the octadecyl chains in PEI18C had much more slower transition velocity and complicated variation process than those of pure nonadecane.Based on the differences among the above mentioned IR spectral bands of PEI18C,PBA18C and nonadecane,the ordered degree of the conformation and the packing structure of the alkyl chains were compared.The alkyl side chains of PEI18C and PBA18C were found to pack into aggregation structure with different ordered degree,originating from the confinement and rigidity difference of the main chain.After melting,unlike nonadecane,the alkyl chains of PEI18C and PBA18C can not get into totally random amorphous state.The above results reveal that the conformational changes,packing structure of CH_2 groups and their phase transition behavior in the confined and non-confined state are obviously different in all the above three cases,which might be attributed to the different mobility of alkyl side chains under the aforementioned confinement condition.Moreover,the different main-chain structural characteristic i.e.flexibility or rigidity,also has extensive influence on the conformational changes and packing structure of alkyl groups grafted on the PEI and PBA backbone.The main reason can be ascribed to the different conformation adjustment ability of the PEI and PBA backbones.