带有端烷烃链的超支化聚酯的受限结晶及动态黏弹行为

以三羟甲基丙烷(TMP)为核,二羟甲基丙酸(DMPA)为支化单体,通过熔融缩聚法合成了第3代端羟基脂肪族超支化聚酯,并用十八酸对其进行端基改性,采用广角X射线衍射(WAXD)、示差扫描量热分析(DSC)及红外光谱(FTIR)研究了不同端基改性程度的超支化聚酯的结晶熔融行为及端烷烃链的构象和堆积结构随温度的变化,采用旋转流变仪研究了端烷烃链对脂肪族超支化聚酯熔体动态黏弹行为的影响.结果表明,这类改性超支化聚酯的结晶归因于长链端烷烃的有序排列,改性程度越高,衍射峰强度越大.受限结晶的端烷烃链在升温后并不能完全转变为无序的结构状态,改性超支化聚酯在"熔点"以上仍有部分有序结构存在.超支化聚酯的线性黏弹区随着端基改性程度的增大而逐渐变短,超支化聚酯的弹性逐渐增大,剪切变稀越明显.动态流变测试中所出现的现象与改性超支化聚酯中端烷烃链的受限密切相关.

Confined Crystallization and Dynamic Viscoelastic Behavior of Hyperbranched Polyesters with Alkyl-terminated Branches

The third generation of hydroxyl-terminated aliphatic hyperbranched polyesters were end-capped with stearic acids,in which the polyesters were prepared using 1,1,1-trimethanol propane (TMP) as the core and 2,2-bis(hydroxymethyl)propionic acid (DMPA) as the branched monomer.The crystallization,melting behavior,temperature-induced variation of the conformational behavior and the packing structure of alkyl-terminated chains of the hyperbranched polyesters with different degrees of modification were investigated by wide angle X-ray diffraction (WAXD),differential scanning calorimeter (DSC) and Fourier transform infrared spectroscopy (FTIR).The influence of the terminal alkyl chains on the dynamic viscoelastic behavior of the modified hyperbranched polyesters was studied by rotational rheometer.The results showed that the crystallization of these modified hyperbranched polyesters could be attributed to ordered arrangement of the long-chain end alkanes,and the terminal alkyl chains tended to pack into hexagonal form.With the increase of degree of modification,the diffraction intensity strengthened.Double melting peaks were found in DSC heating curve.The lower melting peak was corresponding to the fusion of the imperfect crystals formed by confined terminal alkyl chains,and the higher melting peak was ascribed to the melting of the relatively well-developed crystals formed by slightly confined terminal alkyl chains.FTIR analysis conducted at different temperatures revealed that,accompanying the melting of the terminal alkyl chains crystallization,the conformation of the terminal alkyl chains of the modified hyperbranched polyesters showed no obvious transition.Upon the melting temperature,the terminal alkyl chains under confined crystallization did not emerge as completely disordered state.These hyperbranched polyesters melts might be arranged in a somewhat ordered state.With the improvement of the degree of modification,the onset of nonlinear viscoelastic region occurred at lower strains for these modified hyperbranched polyesters,and the elasticity of these modified hyperbranched polyesters increased gradually,with the phenomenon of shear-thinning behavior becoming more obvious.These phenomena,appeared in the dynamic rheological experiments,were closely related to the confined terminal alkyl chains of the modified hyperbranched polyesters.