丙烯酸甲酯共聚单体对聚甲基丙烯酸甲酯物理老化行为的影响

Effect of Methyl Acrylate Comonomer on Physical Aging Behaviors of Poly(methyl methacrylate)

通过差示扫描量热法(DSC)研究了聚甲基丙烯酸甲酯(PMMA)和甲基丙烯酸甲酯(MMA)-丙烯酸甲酯(MA)共聚物(P(MMA-co-MA))在40、60、80℃的物理老化行为。结果表明:二者的老化速率βH都随老化温度的升高而增大。通过计算得出,PMMA改变局部构象所需的自由能大于P(MMA-co-MA),并且参与到构象松弛的分子链段尺寸小于P(MMA-co-MA),这是由于在共聚物中丙烯酸甲酯链段的加入影响了临近甲基丙烯酸甲酯链段的运动能力。因此,在较低温度下PMMA的老化速率远小于P(MMA-co-MA)。但随着老化温度升高,参与到构象重排的分子链段逐渐增加,并且MMA链段的运动能力也有了很大提高,这时少量MA链段对分子链段整体运动能力的影响变得不再明显,PMMA与P(MMA-co-MA)的老化速率趋于相同。

The physical aging behaviors of poly（methyl methacrylate） （PMMA） and poly （methyl methacrylate- co-methyl acrylate） P（MMA-co-MA） at 40 °C ,60 °C and 80 °C were investigated by DSC. The results show that： the aging rate,H） of PMMA and P（MMA-co-MA） increases with the improvement of temperature. By calculating, PMMA need higher activation energy to change the local chain conformation and the scale of local cooperative motion is smaller than that of P（MMA-co-MA）. It is because the existence of MA segments can affect the adjacent MMA segments to enhance their mobility. Therefore, at low annealing temperature, the relaxation rate of PMMA is quite lower than that of P（MMA-co-MA）. However, higher temperature results in higher segmental mobility and more segments participate in the conformations rearrangement. Relaxation at such scale would eliminate the loci of the smaller rearrangement caused by MA comonomer. Therefore, the relaxation rates of PMMA and P（MMA-co-MA） are basically the same.