PGMA-b-PS二嵌段共聚物的RAFT/细乳液合成及表征

以2-(十二烷基三硫代碳酸酯)-2-甲基丙烯酸为链转移剂,利用RAFT/细乳液联合技术合成了相对分子质量分布较窄(PDI=1.53)的大分子链转移剂聚甲基丙烯酸缩水甘油酯。再以该大分子为可逆加成-断裂链转移(RAFT)试剂,通过连续加料的方式加入苯乙烯后进一步引发聚合,得到PGMA-b-PS二嵌段共聚物。采用GPC、FT-IR、1H-NMR、DSC等方法对聚合产物进行了表征。结果表明:合成的聚合物为线型二嵌段共聚物,相对分子质量分布为1.87,该聚合过程具有活性/可控特征。DSC测得二嵌段共聚物具有2个玻璃化转变温度(Tg),分别为77.33℃和98.30℃。此外,还考察了单体加料顺序对聚合过程的影响。     

反应介质对催化链转移聚合反应的影响探究

采用催化链转移聚合法制备得到了端基带双键的聚甲基丙烯酸甲酯(PMMA)大分子单体,通过红外吸收光谱(FT-IR)、核磁共振氢谱(1HNMR)对大分子单体的结构进行了表征,并用凝胶渗透色谱法(GPC)测定了大分子单体的分子量及分子量分布;首次利用碘值法测定了大分子单体的双键含量。实验过程中考察了反应介质及其含量对大分子单体的分子量的影响,结果表明由于催化链转移剂与反应溶剂的络合作用,大分子单体的数均分子量随溶剂含量的增加而变大。     

不同反应条件对星形聚(N-异丙基丙烯酰胺)制备的影响

采用可逆加成裂解链转移自由基聚合法(RAFT),以四羟基卟啉为核制备RAFT链转移剂,以N-异丙基丙烯酰胺为单体合成四臂星形聚(N-异丙基丙烯酰胺)。通过红外光谱仪、核磁共振氢谱仪对聚合物的结构进行表征,结果表明,已成功地合成出星形聚(N-异丙基丙烯酰胺)。同时,聚合物的相对分子质量随反应时间的延长和单体浓度的增大而不断增长,呈现出“活性-可控”聚合特征。     

超高相对分子质量聚(甲基)丙烯酸酯的制备及应用

介绍了制备超高相对分子质量聚(甲基)丙烯酸酯的常用方法,如等离子体引发自由基聚合、单电子转移-衰减链转移自由基聚合、反向原子转移自由基聚合、可逆加成-断裂链转移聚合、高压原子转移自由基聚合、金属催化活性自由基聚合等,分析了单体含量、催化剂种类和用量、引发剂种类和含量、反应温度、反应时间、反应压力等对合成超高相对分子质量聚(甲基)丙烯酸酯的影响,介绍了其良好的机械强度和透光性能以及其应用情况。认为超高相对分子质量聚(甲基)丙烯酸甲酯其韧性不足,极大地限制了其适用范围,如果将其与纳米材料复合改性将可以弥补这个缺点。复合改性的超高相对分子质量聚(甲基)丙烯酸甲酯将在有机玻璃及包覆材料等领域中具有非常广泛的应用前景。     

高单体浓度下超低相对分子质量PAM的水溶液聚合

为合成高浓度水溶性胶黏剂,在高单体浓度下(40%),以过硫酸铵为引发剂,异丙醇为链转移剂,采用水溶液聚合法合成了超低相对分子质量聚丙烯酰胺。探讨了反应温度、链转移剂、引发剂等因素对聚合物相对分子质量的影响。EDTA能消除微量金属离子对相对分子质量波动的影响。在反应温度为80~90℃,引发剂浓度2~15×10-3mol/L,链转移剂浓度1~2.5mol/L时,所合成的聚丙烯酰胺相对分子质量为1.8~4.3×104。     

聚丙烯酰胺的合成及性能

以丙烯酰胺(AM)为单体,(NH_4)_2S_2O_8,NaHSO_3为氧化还原引发体系,采用水溶液聚合法制备聚丙烯酰胺(PAM)。研究了PAM的结构、性能和相对分子质量,同时考察了反应温度及单体、引发剂和链转移剂的质量分数对聚合反应转化率及PAM相对分子质量的影响。傅里叶变换红外光谱谱图中998 cm~(-1)处C=C双键的伸缩振动吸收峰消失以及在X射线衍射谱图中衍射角为20°～23°出现PAM特征弥散衍射峰,表明AM聚合生成了PAM。PAM热分解分3个阶段进行,其玻璃化转变温度随相对分子质量增大而升高。提高反应温度、增大引发剂和单体质量分数都可以提高单体转化率。升高反应温度、降低单体质量分数、增加引发剂和链转移剂质量分数均可以降低PAM的相对分子质量。     

己内酯改性聚醚合成聚羧酸及其性能研究

采用甲基烯丙基聚氧乙烯醚与己内酯反应制得的大分子单体与丙烯酸共聚,合成侧链疏水改性的聚羧酸减水剂。研究了温度、催化剂、酸醚比、链转移剂和己内酯个数对聚羧酸性能的影响。合适的条件为:n(丙烯酸)∶n(大单体)=3.5∶1,链转移剂3%,催化剂20 mg/kg,温度45℃,己内酯个数2。合成的聚羧酸具有良好的稳泡效果,混凝土含气量适中,和易性得到明显改善,后期强度不受影响。     

甲基丙烯酸甲酯的RAFT聚合研究

在链转移剂(CTA)二硫代苯甲酸异丙苯酯(CDB)、二硫代苯甲酸异丁氰酯(CPDB)和S,S′-二(α,α′-二甲基-α″-乙酸)-三硫代碳酸酯(CMP)的存在下,以甲基丙烯酸甲酯(MMA)为单体,采用可逆加成-断裂链转移(RAFT)聚合法合成聚甲基丙烯酸甲酯(PMMA)。研究了引发剂的用量、链转移剂与引发剂的物质的量比以及链转移剂的性质对聚合过程的影响。结果表明,对于三种CTA而言,偶氮二异丁腈(AIBN)用量为0.2%时聚合效果均最好;CTA的用量决定了聚合物的聚合度,减小CTA与AIBN的物质的量比可以得到相对分子质量较大的聚合物;在m(AIBN)∶m(MMA)=0.2%,n(CTA)∶n(AIBN)=4∶1时,三种CTA中CDB对此聚合过程的可控性最佳(相对分子质量分布指数为1.16),CPDB聚合得到的产物产率最高(86.5%),CMP聚合得到的产物数均相对分子质量最大(Mn=14 767g/mol)。     

自由基聚合制备甲基丙烯酸甲酯-苯乙烯嵌段共聚物

以偶氮二异丁腈为引发剂,乙二硫醇（EDT）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）,继而以HS-PMMA作为大分子链转移剂进行苯乙烯的自由基聚合,采用普通自由基聚合方法合成了结构可以设计的嵌段共聚物。     

聚苯乙烯为规整侧链的支化SIS的设计及合成

以苯乙烯和对乙烯基苄氯(VBC)为原料,采用负离子聚合法合成含苯乙烯基末端的聚苯乙烯大分子单体,并以正丁基锂(BuLi)为引发剂,四氢呋喃(THF)为调节剂,环己烷为溶剂进行异戊二烯与大分子单体的负离子共聚合,用一锅法制备出侧链规整的支化结构苯乙烯-异戊二烯-苯乙烯(SIS)嵌段聚合物。通过核磁共振和凝胶渗透色谱等对聚苯乙烯大分子单体和支化SIS结构进行了表征,利用旋转流变仪对支化SIS进行了流变性能表征。结果表明,利用上述聚合方法成功合成了相对分子质量3000～5000的聚苯乙烯大分子单体;使用聚苯乙烯大分子单体制备出相对分子质量为10万～14万,分子量分布为1.1～1.2的支化结构SIS,并且其流体黏度明显低于相同相对分子质量及结合苯乙烯线型结构的SIS。     

High‐conversion catalytic chain transfer polymerization of methyl methacrylate

In this work the effects of conversion on the apparent catalyst activity in the catalytic chain transfer polymerization of methyl methacrylate are reported. Several mechanisms are discussed that may explain the experimental observations. The discussion is supported with computer simulations using Predici software. It is shown that the experimental decrease in weight average molecular weight with conversion is smaller than the decrease obtained in simulations. The most likely cause for this discrepancy is slow catalyst deactivation. The half‐life of CoBF under the reported conditions was determined to be about 10 h. Furthermore, the effect of acetic acid (HAc) and benzoyl peroxide (BPO) on the evolution of the molecular weight distribution is investigated. Both HAc and BPO enhance catalyst deactivation. For HAc, catalyst deactivation scales with the square root of its concentration. BPO‐ enhanced deactivation depends linearly on its concentration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1375–1388, 2004     

Preparation of polytetrahydrofuran monomethacrylate macromonomers by cationic ring‐opening polymerization of tetrahydrofuran

Polytetrahydrofuran monomethacrylate (MA‐PTHF) macromonomer was prepared by cationic ring‐opening polymerization(CROP) of tetrahydrofuran (THF) using boron trifloride etherate (BF₃ · OEt₂) as initiator and epichlorohydrin (ECH) as promoter. Two kinds of transfer agents were used: methacrylic acid (represented as TA1), and a mixture of methacrylic acid and sodium methacrylate (represented as TA2). The effects of polymerization conditions on molecular weight and molecular weight distribution of macromonomers were studied in this article, when the composition of reactants was kept constant. Under the same conditions, the molecular weight of macromonomer using TA2 is lower than that using TA1, which indicates that TA2 is more active than TA1. The molecular weight of MA‐PTHF macromonomer varies with the polymerization time before transfer agents were added (T1), but molecular weight distribution remains constant. When T1 is limited in 30 min, the apparent number‐average molecular weight of MA‐PTHF increases significantly with the increase of T1, and ranges from 5000 to 18,000. Hence, the molecular weight of MA‐PTHF macromonomer can be controlled by varying T1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 810–815, 2000     

New chain transfer agents for free radical polymerizations

The palmitoyl ester of N-hydroxypyridine-2-thione displayed useful chain transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations. 4-Methyl-3-palmitoyloxythiazol-2(3H)-thione had good chain transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (chain transfer constant C_x ～1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate. Addition-fragmentation pathways are postulated for chain transfer.     

Efficient molecular weight control of bacterially synthesized polyesters by alcohol supplementation

The bacterial plastic poly(3‐hydroxybutyrate) (PHB) has many practical applications but its commercial potential is presently limited, partly due to the challenge of achieving appropriate mechanical performance characteristics. One method of tailoring the physical properties of the polymer is to control its molecular weight, which can be achieved by the addition of chain transfer agents such as poly(ethylene glycol) (PEG) to the culture medium during production. For the first time, PEG has been compared directly with alternative chain transfer agents, all of which contain at least one hydroxyl group. Methanol, ethanol and isopropanol all reduced the molecular weight of PHB produced by transgenic Escherichia coli by the same amount as PEG (～60%). PEG‐treated cultures grew to lower density and produced less PHB than control or alcohol‐treated cultures. Glycerol and sodium acetate were also tested, but only reduced the molecular weight by 15–24%. Naturally occurring short chain alcohols such as methanol and ethanol are a superior choice of chain transfer agent than the currently preferred PEG, as they achieve the same effect with reduced toxicity and are substantially less expensive. © 2013 Society of Chemical Industry     

接枝型水性聚合物分散剂的催化链转移聚合制备及其炭黑分散能力研究

应用催化链转移聚合技术合成末端带有可聚合双键的大分子单体,然后大分子单体进一步与主链单体共聚制备接枝聚合物,并通过定量酸性水解得到支链亲水、主链疏水的两亲接枝聚合物。同时系统研究了该聚合物的主链与侧链的分子量大小、主链锚定基团种类与浓度等因素对其在水性体系中炭黑分散能力的影响,为分散剂的结构优化奠定基础;所优选结构的分散剂其炭黑分散能力与进口分散剂Disperbyk-190相当。     

P2VP-b-PS-b-PI三嵌段共聚物的RAFT合成及表征

以S-十二烷基-S’-(α,α’-二甲基-α’’-乙酸)-三硫代碳酸酯(DDMAT)为链转移剂,通过可逆加成-断裂链转移自由基聚合(RAFT)方法制备了窄分布的聚2-乙烯基吡啶。再以该聚合物为大分子链转移剂,引发苯乙烯的RAFT聚合,得到聚2-乙烯基吡啶-b-聚苯乙烯(P2VP-b-PS)的两嵌段共聚物。以P2VP-b-PS为RAFT试剂,合成聚2-乙烯基吡啶-b-聚苯乙烯-b-聚异戊二烯(P2VP-b-PS-b-PI)的三嵌段共聚物。运用1H NMR、IR和凝胶渗透色谱(GPC)等技术对产物的结构和分子量及分子量分布进行表征,采用原子力显微镜(AFM)观察三嵌段共聚物薄膜的微相分离结构。结果表明,所得三嵌段共聚物P2VP72-b-PS136-b-PI300分子量分布较窄(PDI=1.69),合成过程具有活性/可控聚合特征,聚合物薄膜经溶剂退火处理后出现了明显的微观相分离结构。     

低分子量AN/AA共聚物的制备

以过硫酸钾—亚硫酸氢钠的氧化还原体系为引发剂,采用水相沉淀聚合法制备了AN/AA共聚物,用不同链转移剂控制共聚物的分子量。研究了反应时间、引发剂含量、链转移剂含量对聚合物转化率以及聚合物分子量的影响。结果表明,选用N,N-二乙基羟胺为链转移剂,其用量为5%,反应时间为2 h时,共聚物分子量最小,控制在15000左右。     

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.     

链转移剂存在下PVC分子量的调节规律

本文考察了转化率、聚合温度和链转移剂对聚氯乙烯平均分子量的影响,并建立了分子量调节模型,定义了一拟链转移常数.这一模型可用于预测加有链转移剂时的聚氯乙烯平均分子量.