二硫代酯对SiO2表面甲基丙烯酸甲酯可逆加成-断裂链转移聚合的影响

采用不同结构的可逆加成-断裂链转移聚合(RAFT)试剂,偶氮二异丁腈(AIBN)为引发剂,在乙烯基改性SiO2表面进行甲基丙烯酸甲酯接枝聚合。RAFT试剂的R基团和Z基团对接枝聚合的影响很大。R基团皆为苄基时,二硫代新戊酸苄酯调控SiO2表面甲基丙烯酸甲酯的接枝聚合速率较高;R基团皆为1-苯基乙基时,苯基二硫代乙酸-1-苯乙酯调控SiO2表面甲基丙烯酸甲酯的接枝聚合速率较大。Z基团皆为苯基时,二硫代苯甲酸叔丁酯调控SiO2表面甲基丙烯酸甲酯的接枝聚合速率较高。SiO2-PMMA接枝链末端二硫代酯基团,可进一步RAFT接枝聚苯乙烯。相同聚合条件下,二硫代苯甲酸苄酯调控SiO2-PMMA表面接枝聚苯乙烯的接枝率最高。     

不同双硫酯用量下RAFT自由基交联聚合体系的反应动力学及交联结构

考察了二硫代苯甲酸苄酯(BDB)用量对二甲基丙烯酸聚乙二醇酯/甲基丙烯酸聚乙二醇甲基醚酯可逆加成-断裂链转移(RAFT)自由基交联聚合动力学、凝胶行为和交联结构的影响.随BDB用量增加,增长自由基浓度降低,导致聚合速率不断下降.链自由基与休眠链的加成反应进入扩散控制后使得RAFT交联聚合出现自加速,随BDB用量增加自加...     

RATRP/RAFT活性自由基聚合现象的考察

以α-二硫代萘甲酸异丁腈酯(CPDN)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,CuCl2.2H2O为催化剂,2,2’-联二吡啶(bpy)为配体,对反向原子转移自由基聚合(RATRP)和可逆加成-断裂链转移自由基聚合(RAFT)的混合聚合体系进行了研究,得到了一系列末端带有双硫酯基团和-Cl的聚甲基丙烯酸甲酯均聚物。(1H-NMR)和(GPC)等测试结果表明,一锅法和两步法聚合体系均具有"活性"/可控聚合特征,其中两步法在反应初期分子量分布指数较一锅法宽,二者均存在短时间的诱导期。在混合聚合体系中,两种聚合机理共同起作用,使聚合体系具有"活性"聚合的特征。     

二甲基丙烯酸酯的RAFT交联聚合行为

将3种双硫酯链转移剂用于二甲基丙烯酸酯的可逆加成-断裂链转移(RAFT)交联聚合体系。使用差示扫描量热仪(DSC)和凝胶渗透色谱(GPC)研究了RAFT交联聚合行为和反应动力学;用动态力学分析方法(DMA)表征了交联聚合物结构。结果表明,二甲基丙烯酸酯的RAFT交联聚合前期具有"活性"聚合特征;交联聚合动力学受链转移剂种类及用量的影响;与通常自由基交联聚合物相比,RAFT交联聚合物具有更加均匀的交联网络。     

采用RAFT聚合方法制备丙烯酰胺类梯度共聚物

以N-异丙基丙烯酰胺(IPA)和N,N-二甲基丙烯酰胺(DMA)为反应单体,三硫代酯DMP为链转移剂,采用可逆加成-断裂链转移自由基聚合(RAFT)方法制备了结构可控、窄分布的均聚物PIPA、PDMA和系列共聚物PIPA-co- PDMA.由于单体DMA和IPA聚合速率的不同,得到了梯度型共聚物.     

叠氮端基聚N-异丙基丙烯酰胺的合成与表征

分别合成了端羧基三硫代酯链转移剂(CTA)和3-叠氮丙醇,并以此为反应物通过1,3-二环己基碳二亚胺/4-(二甲基氨基)吡啶催化合成得到带有叠氮端基链转移剂。采用可逆加成-断裂链转移自由基聚合(RAFT)N-异丙基丙烯酰胺(NIPAAm)得到叠氮端基聚(N-异丙基丙烯酰胺)(PNIPAAm)。核磁氢谱和红外分析表明,叠氮端基CTA反应转化完全,叠氮端基在聚合反应中稳定;聚合反应可控,GPC测定的分子量与理论分子量一致,聚合物分子量分布较窄(-Mw/-Mn<1.2)。     

RAFT法制备负载型CBS催化剂及其在苯乙酮不对称还原中的应用EI北大核心CSCD

以苯乙烯(St)与自制的功能性苯乙烯(FSt)为单体,双硫代苯甲酸枯基酯(CDB)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,通过可逆加成-断裂链转移(RAFT)聚合法合成了相对分子质量可控、窄分布的负载型CBS催化剂,并应用于苯乙酮的不对称还原中。利用红外光谱、高温凝胶色谱进行了表征。研究了FSt含量对催化剂前驱体相对分子质量(Mn)及其分布(PDI)的影响,以及RAFT法与传统自由基聚合法制备的催化剂催化效果的差异,并考察了CBS催化单元与二硫酯活性端基的相互影响。结果表明,随着FSt含量的增加,聚合物的Mn降低,其PDI先变大后保持在1.25左右;二硫酯活性端基不影响催化剂的活性;随着催化剂中FSt含量的增加,苯乙醇的对映体过量值(ee值)先迅速增大后维持在94%,产率达97.2%。     

碳纳米管表面的RAFT接枝共聚物

首先在碳纳米管表面接枝上可用做RAFT聚合的链转移剂——二硫代碳酸酯,然后用管壁接枝有二硫代碳酸酯的碳纳米管作为链转移剂引发甲基丙烯酸甲酯(MMA)和苯乙烯(St)进行可控的自由基共聚合反应,从而在碳纳米管的管壁接枝上MMA和St共聚物,通过接枝共聚极大地提高了碳纳米管在有机溶剂中的分散性能。并对接枝共聚物的结构进行了较详细的表征。     

RAFT法制备负载型CBS催化剂及其在苯乙酮不对称还原中的应用

以苯乙烯(St)与自制的功能性苯乙烯(FSt)为单体,双硫代苯甲酸枯基酯(CDB)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,通过可逆加成-断裂链转移(RAFT)聚合法合成了相对分子质量可控、窄分布的负载型CBS催化剂,并应用于苯乙酮的不对称还原中。利用红外光谱、高温凝胶色谱进行了表征。研究了FSt含量对催化剂前驱体相对分子质量(Mn)及其分布(PDI)的影响,以及RAFT法与传统自由基聚合法制备的催化剂催化效果的差异,并考察了CBS催化单元与二硫酯活性端基的相互影响。结果表明,随着FSt含量的增加,聚合物的Mn降低,其PDI先变大后保持在1.25左右;二硫酯活性端基不影响催化剂的活性;随着催化剂中FSt含量的增加,苯乙醇的对映体过量值(ee值)先迅速增大后维持在94%,产率达97.2%。     

二甲基丙烯酸酯的ATRP交联聚合及交联结构均匀性

使用动态力学分析方法(DMA)对二甲基丙烯酸酯常规自由基交联聚合(CRP)和原子转移自由基交联聚合(ATRP)产物的结构进行了分析。结果表明,ATRP交联聚合可以改善交联网络均匀性;随单体双键之间链段长度的增加,交联结构更加均匀。ATRP对交联结构均匀性的改善与其聚合机理有关,初级链的同步增长以及悬挂双键的均匀分布有利于抑制微凝胶的形成,获得均匀的交联结构。     

二甲基丙烯酸酯原子转移自由基聚合行为和交联结构

通过差示扫描量热法研究了二甲基丙烯酸酯原子转移自由基(ATRP)交联聚合的反应动力学,用平衡溶胀法跟踪了交联结构的形成和发展。结果表明,二甲基丙烯酸酯ATRP的聚合速率比通常自由基聚合慢得多,不出现明显的自加速效应,交联网络结构更疏松。单体双键之间的链段长度对其ATRP交联聚合行为和交联结构有较大影响,随链段长度增加,聚合反应速率放慢,双键的转化率下降,交联网络结构更加均匀和疏松。     

Rheological Investigation of Thermal-Induced Gelation of Polyacrylonitrile Solutions

In this article, thermal-induced gelation of polyacrylonitrile (PAN) solutions in dimethylformamide was studied through rheological measurements. The entangled and non-entangled states were delimited for an overlap parameter of macromolecular coils of 2.7. In temperature sweep experiments, two types of gelation processes were identified for PAN entangled solutions at: (1) a reversible gelation in the region of low temperatures (below 15°C) due to the formation of a crosslinked structure with a small region of order that dissolves completely in an excess of solvent, and (2) an irreversible gelation at high temperatures (above 60°C) and this gel is insoluble in an excess of solvent, due to the formation of a chemical three-dimensional network. Physical PAN gels with good elastic properties were also obtained by the freezing and thawing method. The gel properties depend on the thermal history of the solution (freezing time, aging time, and aging temperature), its composition (concentration and molar mass of the polymer), and gelation conditions (freezing rate). The gelation was attributed to the formation of junction zones via an aggregation process between a certain number of chain segments due to attractive dipole–dipole interactions.     

Monitoring the thermal gelation of cellulose ethers in situ using attenuated total reflectance fourier transform infrared spectroscopy

In this work attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used to probe the thermal gelation behavior of aqueous solutions of hydroxypropyl methylcellulose (HPMC), specifically thermal gelation and accompanying precipitation. Cloud point measurements are usually evaluated through turbidity in dilute solutions but the method cannot readily be applied to more concentrated or highly viscous solutions. From the ATR-FTIR data, intensity changes of the nu(CO) band marked the onset of gelation and information about the temperature of gelation and the effect of the gel structure on the water hydrogen bonding network was elucidated. Changes in the relative intensities of bands associated with the methoxyl groups and hydrogen-bond-forming secondary alcohol groups indicated that hydrophobic polymer chain interactions were involved in the gelation process. The dominance of inter-molecular H bonding over intra-molecular H bonding within the cellulose ether in solution was also observed. The ATR-FTIR data was in good agreement with measurements of turbidity conducted on the same systems. The work indicates significant potential for the use of ATR-FTIR for the investigation of gelation and cloud point measurements in viscous cellulosic formulations.     

杂萘联苯聚醚砜酮类材料成膜动力学研究(Ⅱ)凝胶介质对 PPESK凝胶动力学的影响

以杂萘联苯聚醚砜酮(PPESK)/NMP为聚膜液体系,进行了成膜过程凝胶动力学研究;浊点实验表明,随着醇类物质碳原子数目的增多,相图的二相区变小,凝胶过程所需的非溶剂量增多.还考察了不同凝胶浴对PPESK/NMP体系凝胶速度的影响.结果表明,使絮凝值增大的非溶剂,凝胶过程中所需的非溶剂量增多,凝胶速度降低.凝胶浴中加入溶剂使铸膜液和凝胶浴的化学势差降低,使非溶剂和溶剂的传质速度下降,凝胶速度减小.当NMP浓度为80%时,膜结构由指状转变为海绵状结构.     

大分子链转移剂活性对聚合物分散液晶电光性能的影响

采用可逆加成-断裂链转移(RAFT)、引发转移终止(Iniferter)、反向原子转移自由基聚合(RATRP)等活性自由基聚合方法,合成了分子量相近而带有不同端基的大分子链转移剂。通过紫外光聚合诱导相分离法制备聚合物分散液晶(PDLC)膜。通过研究大分子链转移剂光引发活性,发现采用RAFT聚合制备的大分子链转移剂具有较高的光活性,带有Iniferter活性基团的大分子链转移剂光活性很低。对不同大分子链转移剂制备的PDLC膜的电光性能进行比较,发现采用RAFT法合成的具有高光活性的大分子链转移剂能够使PDLC膜具有较高的开态透光率和较低的驱动电压。加入大分子链转移剂会导致PDLC记忆效应升高。     

RAFT聚合制备丙烯酰胺-N-乙烯基吡咯烷酮嵌段共聚物及其水解物与性能表征

以S,S-二(α,α′-二甲基-α″-丙烯酸)三硫代碳酸酯(BDATC)为链转移剂,甲基丙烯酰胺(MAM)为第一单体,通过可逆加成断裂链转移聚合(RAFT)法合成出链转移剂(PMAM-CTA),以N-乙烯基吡咯烷酮(NVP)作为第二单体合成PAM-b-PNVP,再水解得到含有氨基和羧基的CO2分离固定载体膜材料N-乙烯基-γ-氨基丁酸钠-丙烯酸钠共聚物(VSA-SA)。通过FT-IR、1H-NMR、XRD和DSC对PMAM-CTA、PMAM-b-PNVP和VSA-SA进行表征,采用GPC测定分子量及分子量分布。研究发现,该聚合具有活性可控聚合的特征,聚合动力学呈一级线性关系,得到数均相对分子质量可控、相对分子质量分布(1.2～1.3)窄的聚合物。与自由基聚合产物相比,水解产物VSA-SA的结晶度减小,载体含量增加。     

聚合条件对丙烯酸丁酯反应动力学的影响

采用溶液聚合方法,通过改变聚合条件研究丙烯酸丁酯转化率随聚合时间变化的关系,考察其聚合反应动力学.改变引发剂过氧化苯甲酰(BPO)含量发现,BPO质量百分数提高聚合反应速率加快,单体转化率差别不大;提高温度有利于聚合速率的提高,但同时会导致单体最终转化率的降低;单体浓度越高,聚合速率越快,凝胶化现象明显;采用乙苯为溶剂...     

Poly(N-isopropylacrylamide) copolymer nanogels with thermogelling ability prepared by a single step of dispersion polymerization

The copolymer nanogels composed of two N-substituted acrylamides with different water solubility, N-isopropylacrylamide (NIPAM, water-soluble) and N-t-butylacrylamide (TBAM, water-insoluble), were prepared by free-radical polymerization in the presence of sodium dodecyl sulfate (SDS) as a dispersant and found to exhibit thermogelling ability at very low concentrations. To investigate the structure of the P(NIPAM-TBAM) nanogel and its formation mechanism in dispersion polymerization, we prepared the nanogels by changing the conditioning time, which is the time between the addition of SDS to the monomer solution and the start of polymerization, and compared the thermogelling properties of the resultant nanogels. As the conditioning time increased, (i) the hydrodynamic diameter of the nanogel decreased, (ii) the sol–gel and gel-syneresis transition temperatures of the nanogel dispersion decreased, and (iii) the storage moduli of the nanogel dispersion in a gel state increased. These results indicate that the P(NIPAM-TBAM) nanogel has a block-like structure composed of the TBAM-rich brushes and the NIPAM-rich core with three-dimensional polymer network, and that the TBAM ratio in the brushes increases with an increase in the conditioning time. It should be noted that the critical gelation concentration of the P(NIPAM-TBAM) nanogel dispersion was very low (～1.3 wt%), compared with other thermogelling polymers reported in literatures. This low gelation concentration can be attributed to the gel structure of the nanogel core because the NIPAM-rich core can retain water inside even when the TBAM-rich brushes are dehydrated and crosslink with each other to induce gelation of the system.