D,L-丙交酯聚合方法改进

以辛酸亚锡为催化剂,十二醇为引发剂,经D,L-丙交酯的开环聚合反应合成聚(D,L-乳酸)(PDLLA),产率为60%,分子量分布(PDI)为1.2,并分别通过核磁共振氢谱(1H NMR)和凝胶渗透色谱(GPC)对其结构和分子量进行表征。此方法不仅缩短了反应时间,而且简化了实验流程,提高了实验效率。由于反应过程是本体聚合,无反应溶剂参与,因此对产物的后处理更加简便。     

聚D,L-乳酸的合成及表征

以D，L－乳酸为单体，辛酸亚锡为催化剂，乳酸先缩聚合解聚制备了D，L－丙交酯，并以丙交酯为单体开环本体聚合制备了聚乳酸。用IR、^1H－NMR对丙交酯及聚乳酸的结构加以证实；用TG、DSC测定了聚乳酸的热分解温度和玻璃化温度。测试结果表明，环状丙交酯在辛酸亚锡催化剂作用下发生了开环反应，所得聚合物的热分解温度为233．9℃，玻璃化温度为54．4℃。     

减压气流法合成D,L-丙交酯

以质量分数85%的D,L-乳酸为原料,采用先常压除水,然后加入辛酸亚锡催化剂,减压除水,通氮气将生成的丙交酯蒸出的工艺路线,减少了原料损失,提高了产率。使用循环水真空泵代替油泵,低真空度条件下成功得到了丙交酯,降低了设备成本。然后对比了乙酸乙酯和乙醇作为溶剂对粗产品的提纯,发现无水乙醇的结晶效果好于乙酸乙酯。最后用核磁、红外等对纯化后的丙交酯进行了表征。     

L-丙交酯的制备与聚合研究

首先以L-乳酸为原料，合成了L-丙交酯。考察了解聚温度对L-丙交酯产率的影响。结果表明，当解聚温度超过235℃时，丙交酯的构型发生变化，所得产物为现．丙交酯；然后以辛酸亚锡为催化剂，以开环聚合的方法合成了聚L-乳酸，研究了催化剂的用量、聚合时间、聚合温度对聚L-乳酸摩尔质量的影响。     

L-丙交酯的合成研究

L丙-交酯产率偏低是制约聚-L-乳酸大规模应用的关键因素之一,寻找合理的催化剂是其中的关键技术。分别采用氧化锌(ZnO)、辛酸亚锡[Sn(Oct)2]、氧化锌/辛酸亚锡[ZnO/Sn(Oct)2]、三氧化二铝/辛酸亚锡[A l2O3/Sn(Oct)2]催化剂合成L-丙交酯。实验结果表明,催化剂的种类和用量对L-丙交酯的收率有显著的影响。以A l2O3/Sn(Oct)2为催化剂,用量为反应物总质量的2.03%时催化效果较好,能使L-丙交酯的收率高达70.5%。     

聚D,L-丙交酯合成方法研究

以辛酸亚锡为催化剂,研究开发了环境友好材料聚D,L-丙交酯(PDLLA)的合成方法。探讨了单体丙交酯纯度、催化剂辛酸亚锡用量、反应时间、反应温度及真空度对聚合物相对分子质量的影响。实验结果表明,重结晶4次后的丙交酯作为单体,在辛酸亚锡摩尔分数为0.1%—0.18%,真空度0.098 MPa,聚合温度150—160℃下聚合6—8 h可获得粘均相对分子质量Mη大于20×104的聚D,L-丙交酯。分别采用FTIR和1H-NMR对产物的结构进行了表征。     

乳酸合成中间体丙交酯工艺的研究

以乳酸为原料合成中间体丙交醋,通过正交试验探讨了温度、时间、催化剂对反应的影响并确定了最佳的工艺条件：在100g乳酸中加入0．5gSnCl2·2H2O、0．75g对甲苯磺酸,在150℃下反应4h并在反应后期加入30mL正辛醇可照丙交醋收率达到43．3％。     

聚D,L-丙交酯的常压微波辐射合成

研究了常压下微波辐射开环聚合制备聚D,L-丙交酯(PDLLA)。考察了单体纯度、微波辐射时间、催化剂用量和体系真空度对聚合反应的影响。采用气相色谱(GC)测定丙交酯纯度;FTIR和1H-NMR表征产物结构;GPC测定分子量分布。实验结果表明:重结晶4次后的丙交酯,在催化剂辛酸亚锡用量为0.15%,常压下经微波辐射30min,可获得分子量为21.87×104的PDLLA。反应时间与传统法相比大大缩短。与传统合成法的不同还表现为,随丙交酯纯度的提高,最佳聚合时间延长;体系真空度对反应无影响。GPC结果表明聚合产物的分子量分布较窄。     

丙交酯开环聚合催化体系的研究进展

介绍了丙交酯开环聚合的三种反应机理:阴离子型开环聚合、阳离子型开环聚合和配位-插入开环聚合。根据其反应机理,催化剂可分为:质子酸型催化体系、路易斯酸型催化体系、碱金属催化体系、金属有机化合物催化体系、氧化物催化体系、稀土化合物催化体系及其他催化体系。此文阐述了这7种催化体系的不同特点,对其催化性能进行了比较。     

聚d,l-乳酸的合成

本文分别以氧化锌、氯化亚锡和辛酸亚锡为催化剂，采用两部法合成了聚d,l-乳酸。用化学滴定法和粘度法测定了产物相对分子质量，并以红外光谱和DSC对产物进行了表征。结果表明所得到为无定形聚乳酸，Tg为53．3℃。     

催化链转移聚合法制备聚对甲基苯乙烯大分子单体

首次以钴Ⅱ肟氟化硼配合物(CoBF)催化剂、2,2′-偶氮二异丁腈(AIBN)为引发剂,由催化链转移聚合法制备聚对甲基苯乙烯大分子单体(poly(p-Methylstyrene)),考察不同CoBF的用量对相对分子质量的影响。结果表明:随着CoBF用量的增加,聚对甲基苯乙烯大分子单体的相对分子质量逐渐减小。另外,还采用了基于重均聚合度(DPw)的Mayo方程,计算出催化剂表观链转移常数(ct)为365.6。     

Surface grafting of poly(pentafluorostyrene) on the iron and iron oxide particles via reversible addition fragmentation chain transfer (RAFT) polymerization

A surface grafting technique is reported for synthesis of poly(pentafluorostyrene) via reversible addition fragmentation chain transfer onto iron (iron oxide) particles. 4‐Methoxydithiobenzoate is used for the RAFT chain transfer agent. The molecular weight, surface morphology, thickness, thermal properties, and monomer conversion of the grafted polymer are reported. The grafted poly(pentafluorostyrene)–iron particles show a higher thermal transition temperature compared to the nongrafted polymer because it is speculated that the covalent bond between the polymer backbone and the surface of the iron particles restricts the molecular mobility. The monomer conversion increases in proportion to the amount of chain transfer agent (CTA) concentration at early polymerization time. The grafted poly(pentafluorostyrene) shows a “hairy” like polymer architecture with fibril thickness in the range of 80 to 100 nm. A thin coating is expected to maintain the magnetic saturation properties of iron particles. To the best of our knowledge, this is the first time that poly(pentafluorostyrene) has been grafted onto the iron particles utilizing RAFT and 4‐methoxydithiobenzoate as a CTA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44898.     

Synthesis of a water-soluble chain transfer agent and its application in gel dispersions

Pre-crosslinked gel particles, colloidal dispersion gels, and polymer microspheres are often used as profile-controlling and flooding agents to displace residual crude oil from formations. The preparation process of these profile-controlling and flooding agents is complicated. In order to simplify the preparation steps, a water-soluble chain transfer (RAFT) agent, S,S′-bis(2-propionic acid) trithiocarbonate (PATTC), was synthesized, and then, hydrogel dispersions were prepared by one-pot RAFT polymerization. The structure of PATTC was confirmed by infrared spectroscopy and nuclear magnetic resonance. The effects of reaction conditions on the viscosity and viscosity-average molecular weight of hydrogel dispersions were explored, the rheology, viscoelasticity, particle size, temperature responsiveness, and salinity responsiveness of hydrogel dispersions were measured, and the seepage properties of hydrogel dispersions in porous medium were analyzed. The results show that at higher shear rates, the polyacrylamide gel dispersions exhibited Newtonian fluid characteristics. Viscoelasticity tests further confirmed that the polyacrylamide gel dispersions were successfully synthesized. The particle size of the hydrogel dispersions is 1–75 μm, its viscosity is less affected by temperature and salinity, and its residual resistance coefficient is higher than that of the polyacrylamide solution under similar apparent viscosity.     

丙交酯及聚乳酸的合成条件研究

以D, L-乳酸为单体、氧化锌为催化剂,使乳酸先缩聚后解聚制备了D, L-丙交酯;再以辛酸亚锡为催化剂,使丙交酯单体开环本体聚合制备了聚乳酸.考察了乳酸脱水温度、氧化锌用量对丙交酯收率的影响;考察了聚合温度、辛酸亚锡用量对聚乳酸相对分子质量的影响;用红外光谱(IR)、核磁共振光谱( 1H-NMR)对丙交酯及聚乳酸的结构进行了表征.结果表明,乳酸在130℃、氧化锌质量分数为1.3%时,仅用3h就可制得丙交酯,且其收率大于24%;丙交酯聚合时,当n(单体)/n(辛酸亚锡)＝ 5000、聚合温度在160℃时,常压聚合5h即可得到粘均分子质量为6.3×104的聚乳酸;IR、 1H-NMR测试结果表明环状丙交酯在辛酸亚锡催化剂作用下发生了开环反应.聚乳酸在氢氧化钠水溶液中降解实验表明,聚乳酸具有很好的降解性,在碱溶液中降解速度较快.     

Modeling analysis of chain transfer in reversible addition‐fragmentation chain transfer polymerization

The validity of simplifying the reversible addition‐fragmentation chain transfer (RAFT) polymerization as a degenerative chain transfer process was verified in this work. The simplified chain transfer mechanism enabled the direct modeling investigation of chain transfer coefficient in the RAFT polymerization. It also gave the analytical expressions for concentration, chain length, and polydispersity of various chain species. The comparison between the simulations based on chain transfer mechanism and those from general RAFT mechanism showed that this simplified mechanism can accurately predict RAFT polymerization in the absence of side reactions to adduct radicals other than fragmentation. However, significant errors are introduced at high conversion when side reactions to adduct are present. The chain transfer coefficient of RAFT agent is the key factor in RAFT polymerization. The polydispersity is more sensitive to chain transfer coefficient at low conversion. At high conversion, however, the polydispersity is mainly determined by termination, which can be controlled by RAFT agent concentration and the selection of initiator. At last, an analytical equation is derived to directly estimate chain transfer coefficient of RAFT agent from the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Reversible addition–fragmentation chain transfer polymerization of styrene with benzoimidazole dithiocarbamate as a reversible addition–fragmentation chain transfer agent

Two novel dithiocarbamates [2‐Y‐benzoimidazole‐1‐carbodithioic acid benzyl esters: Y = methyl (1b) or phenyl (1c)] were synthesized and successfully used in the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene in bulk with thermal initiation. The effects of the temperatures and concentration ratios of the styrene and RAFT agents on the polymerization were investigated. The results showed that the polymerization of styrene could be well controlled in the presence of 1b or 1c. The linear relationships between ln([M]₀/[M]) and the polymerization time (where [M]₀ is the initial monomer concentration and [M] is the monomer concentration) indicated that the polymerizations were first‐order reactions with respect to the monomer concentration. The molecular weights increased linearly with the monomer conversion and were close to the theoretical values. The molecular weight distributions [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] were very narrow from 5.3% conversion up to 94% conversion (M_w/M_n < 1.3). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 560–564, 2006