梯度共聚物接枝纳米粒子的合成及其力学性能

Synthesis and Mechanical Properties of Gradient Copolymer Grafted Nanoparticles

通过RAFT聚合制备了3种不同序列(无规、嵌段及梯度)的丙烯酸正丁酯(BA)/甲基丙烯酸甲酯(MMA)二元共聚物(PBA-r-PMMA、PBA-b-PMMA、PBA-g-PMMA),以及2种含可交联侧链的聚甲基丙烯酸酰氧基丙基三乙氧基硅烷(PTEPM)的三元共聚物PTEPM-b-(PBA-g-PMMA)和PTEPM-b-(PBA-r-PMMA),三元共聚物中PBA/PMMA分别为无规和梯度结构.这5个共聚物中PBA/PMMA段具有相近的分子量和组分比.三元共聚物通过共组装及交联后得到球状的共聚物接枝纳米粒子NP-(PBA-g-PMMA)和NP-g-(PBA-r-PMMA).DSC结果表明NP-(PBA-g-PMMA)和PBA-g-PMMA具有较宽的玻璃化转变温度区间(~130℃),证明成功合成了梯度共聚物和接枝梯度共聚物的纳米粒子.通过DMA测试和变温拉伸测试发现,在升温过程中梯度结构二元共聚物及其对应的纳米复合材料力学性能呈现渐进式变化,而无规或嵌段对应物力学性能呈现突变,原因是前者具有较宽的玻璃化转变过程.由于无机内核的作用,NP-(PBA-g-PMMA)和NP-(PBA-r-PMMA)表现出更高的力学强度和模量,但断裂伸长率下降.

Three copolymers(random,block and gradient copolymers)(PBA-r-PMMA,PBA-b-PMMA,PBA-g-PMMA)with different MMA/BA sequences and two terpolymers were prepared by RAFT polymerization.Their molecular weights and molar ratios of PMMA/PBA for the terpolymers were almost the same as those of the first three copolymers.Spherical nanoparticles NP-(PBA-g-PMMA)and NP-(PBA-r-PMMA)were obtained by co-assembly and crosslinking of the two terpolymers.The glass transition behaviors for these five materials were characterized using DSC.The results showed that NP-(PBA-g-PMMA)and PBA-g-PMMA had a wide temperature ranges of glass transition(~130℃),which confirmed that the nanoparticles of grafted gradient copolymer and gradient copolymer were successfully synthesized.The five materials were further characterized using the DMA analysis and the tensile testing at different temperatures.The results showed that more and more chain segments gradually changed from plastic to rubber during the heating process for NP-(PBA-g-PMMA)and PBA-g-PMMA,and their mechanical properties showed a gradual change rather than the sudden change of random or block copolymer,due to the wide T_(g)of gradient copolymers.At high temperatures,the mechanical properties of gradient copolymer were better than those of random copolymer.For NP-(PBA-g-PMMA)and NP-(PBA-r-PMMA),they showed a similar situation due to the properties of the grafted copolymers,but their strengths and moduli were higher than those of the corresponding pure copolymers,and their elongations at break were lower,which could be ascribed to the reinforcing effect of inorganic cores.