用多官能链转移剂通过普通自由基聚合制备两亲性杂臂星形聚合物

以偶氮二异丁腈为引发剂,四(3-巯基丙酸季戊四醇四酯)(PETMP)为链转移剂进行甲基丙烯酸甲酯(MMA)的自由基聚合,得到了含有残余巯基的聚甲基丙烯酸甲酯大分子链转移剂(HS-PMMA).然后,以HS-PMMA作为大分子链转移剂进行甲基丙烯酸叔丁酯(tBMA)的自由基聚合,合成了杂臂星形聚合物.最后,将所得杂臂星形聚合物的PtBMA链段水解得到了两亲性杂臂星形聚合物.

SYNTHESIS OF AMPHIPHILIC HETEROARM STAR-SHAPED POLYMER BY THE USE OF POLYFUNCTIONAL CHAIN-TRANSFER AGENT via CONVENTIONAL FREE RADICAL POLYMERIZATION

Amphiphilic heteroarm star-shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in three steps.Firstly,conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was carried out at 70℃ in toluene in the presence of polyfunctional chain transfer agent,pentaerythritol-tetrakis (3-mercaptopropinate) (PETMP),with [MMA]_0∶[PETMP]_0∶[AIBN]_0 to be 262.5∶4∶1 and [MMA]_0=5 mol/L.After polymerized for 2 h,the monomer conversion reached 43.61%,and HS-PMMA with number-average molecular weight to be 4000 determined by gel permeation chromatography (GPC) and polydispersity index 1.37 was obtained.The ~1H-NMR spectrum of HS-PMMA confirmed that there were two unreacted thiol groups still existed at the center of PMMA chain.Secondly,the HS-PMMA obtained above was used as macro-chain-transfer agent for free radical polymerization of tert-butyl methacrylate (tBMA).The polymerization of tBMA was carried out at 72℃ in toluene with [tBMA]_0:[HS-PMMA]_0:[AIBN]_0 to be 655∶5∶1 and [tBMA]_0=1.57 mol/L.With the increase of tBMA conversion,the number-average molecular weights of the crude products shifted to higher molecular weight direction.Furthermore,their molecular weight distribution curves were unimodal through out the polymerization process.When tBMA conversion reached 70.00%,its number-average molecular weight increased from 4000 of HS-PMMA to 10600.Its ~1H-NMR spectrum showed that the residual thiol groups of the obtained heteroarm polymer decreased from 2.0 of the HS-PMMA to 0.4.That is to say,on average,the heteroarm polymer had two PMMA arms and 1.6 PtBMA arms.Finally,cleavage of the tert-butyl ester groups was achieved by treating the heteroarm star-shaped polymers in dichloromethane with trifluoroacetic acid at room temperature for 6 days.The ~1H-NMR spectrum of hydrolyzed product showed that the tert-butyl protons of the PtBMA disappeared completely,indicating that the PtBMA chains had been successfully transformed into poly(methylacrylic acid) (PMAA) chains.The self-assembly behavior of the amphiphilic heteroarm star-shaped polymer in 1% KOH were investigated.Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize the sizes and size distributions of the aggregates of the hydrolyzed product.TEM showed that the amphiphilic heteroarm star-shaped polymer aggregates took spherical shape and that its diameter was about 50～100 nm.DLS results showed that the average particle diameter was 273.6 nm and the diameter distribution index was 0.114.