Synthesis of Chain-End Functionalized PP and Applications in Exfoliated PP/Clay Nanocomposites

This paper summarizes our research to the preparation of chain-end functionalized isotactic polypropylene (i-PP) having a terminal functional group, such as an OH and an NH₂. The chemistry involves metallocene-mediated propylene polymerization using the rac-Me₂Si[2-Me-4-Ph(Ind)]₂ZrCl₂/MAO complex in the presence of styrene derivatives (St-f) and hydrogen, which serve as the chain transfer agents. The molecular weight of the resulting i-PP polymers with terminal OH or NH₂ groups (i.e., PP-t-OH and PP-t-NH₂) are inversely proportional to the molar ratio of [St-f]/[propylene]. Despite the extremely low concentration of functional groups, the high molecular weight NH₃⁺-terminated PP (PP-t-NH₃⁺) exhibits a distinctive advantage over other functional PP polymers containing side chain functional groups or long functional blocks. The terminal hydrophilic NH₃⁺ cation, with good mobility and reactivity, effectively ion-exchanges the cations (Li⁺, Na⁺, etc.) located between the clay interlayers, and anchors the PP chain to the clay surfaces. On the other hand, the remaining rest of the unperturbed, end-tethered, high molecular weight PP tail exfoliates the clay layers. This exfoliated structure is maintained even after further mixing of the PP-bearing platelets with pure, neat PP polymers.     

Synthesis and Functionalization of Isotactic Poly(propylene) Containing Pendant Styrene Groups

Summary: Copolymerization of propylene and 1,4‐divinylbenzene was successfully performed by a MgCl₂‐supported TiCl₄ catalyst, yielding isotactic poly(propylene) (i‐PP) polymers containing a few pendant styrene groups. With a metalation reaction with butyllithium and a hydrochlorination reaction with dry hydrogen chloride, the pendant styrene groups were quantitatively transformed into benzyllithium and 1‐chloroethylbenzene groups, respectively, which allowed the synthesis of i‐PP‐based graft copolymers by living anionic and atom transfer radical (ATRP) polymerization mechanisms.

The incorporation of styrene pendant groups into isotactic poly(propylene) using a Zeigler–Natta catalyst gave functionalized polymers able to undergo living anionic and atom transfer radical (ATRP) polymerizations.     

Design and synthesis of structurally well-defined functional polypropylenes via transition metal-mediated olefin polymerization chemistry

Functionalization of polyolefins is an industrially important yet scientifically challenging research subject. This paper summarizes our recent effort to access structurally well-defined functional polypropylenes via transition metal-mediated olefin polymerization. In one approach, polypropylenes containing side chain functional groups of controlled concentrations were obtained by Ziegler-Natta-catalyzed copolymerization of propylene in combination with either living anionic or controlled radical polymerization of polar monomers. The copolymerization of propylene with 1,4-divinylbenzene using an isospecific MgCl₂-supported TiCl₄ catalyst yielded polypropylenes containing pendant styrene moieties. Both metalation reaction with n-butyllithium and hydrochlorination reaction with dry hydrogen chloride selectively and quantitatively occurred at the pendant reactive sites, generating polymeric benzyllithium and 1-chloroethylbenzene species. These species initiated living anionic polymerization of styrene (S) and atom transfer radical polymerization (in the presence of CuCl and pentamethyldiethylenetriamine) of methyl methacrylate (MMA), respectively, resulting in functional polypropylene graft copolymers (PP-g-PS and PP-g-PMMA) with controllable graft lengths. In another approach, chain end-functionalized polypropylenes containing a terminal OH-group with controlled molecular weights were directly prepared by propylene polymerization with a metallocene catalyst through a selective aluminum chain transfer reaction. Both approaches proved to be desirable polyolefin functionalization routes in terms of efficiency and polymer structure controllability.     

Metallocene-mediated synthesis of chain-end functionalized polypropylene and application in PP/clay nanocomposites

This paper summarizes our research in the preparation of chain end functionalized isotactic polypropylene (PP) having a terminal functional group, such as Cl, OH, and NH₂. The chemistry involves metallocene-mediated propylene polymerization using rac-Me₂Si[2-Me-4-Ph(Ind)]₂ZrCl₂/MAO complex in the presence of styrene derivatives (St-f) and hydrogen, which serve as the chain transfer agents. The molecular weight of the resulting PP polymers with a terminal Cl, OH and NH₂ group (i.e., PP-t-Cl, PP-t-OH and PP-t-NH₂) are inversely proportional to the molar ratio of [St-f]/[propylene]. Despite the extremely low concentration of functional group, the high molecular weight chain end functionalized PP-t-OH and exhibit a distinctive advantage over other functional PP polymers containing side chain functional groups or long functional blocks. The terminal hydrophilic OH and cations, with good mobility and reactivity, effectively hydrogen bond and ion-exchange the cations (Li⁺, Na⁺, etc.) located between the clay interlayers, respectively. Such interactions anchor the PP chain to the clay surfaces. On the other hand, the remaining rest of the unperturbed end-tethered high molecular weight PP tail exfoliates the clay layers. This exfoliated structure is maintained even after further mixing of the PP-bearing platelets with pure neat PP polymers.     

A new synthetic route to borane‐terminated isotactic polypropylenes via styrene/hydrogen consecutive chain transfer reaction

This paper discusses a new process of preparing borane‐terminated isotactic polypropylenes (i‐PPs) via in situ chain transfer reaction, which avoids the use of B‐H‐containing chain transfer agent and thus can be carried out with Al‐activated metallocene catalyst under mild reaction conditions. The chemistry centers on a consecutive chain transfer reaction, first to a trialkylborane‐containing styrene derivative, 4‐[B‐(n‐butylene)‐9‐BBN]styrene (B‐styrene), then to hydrogen in the isoselective polymerization of propylene catalyzed by rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ZrCl₂/MAO. The borane‐terminated i‐PP thus obtained keeps the desired properties of a polymeric alkyl‐9‐BBN reagent and was used to initiate radical polymerization of methyl methacrylate (MMA) to prepare i‐PP‐b‐PMMA diblock copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 539–548, 2006     

机理转移法合成聚丁二烯-b-聚(甲基丙烯酸N,N-二甲氨基乙酯)两亲性嵌段共聚物

将活性负离子聚合与原子转移自由基聚合(ATRP)技术相结合,运用机理转移法制备了一种两亲性材料聚丁二烯-b-聚(甲基丙烯酸N,N-二甲氨基乙酯)(PB-b-PDMAEMA)嵌段共聚物.首先通过负离子聚合方法设计合成聚丁二烯,用环氧丙烷封端,2-溴异丁酰溴作酯化剂,合成具有活性端基溴的聚丁二烯大分子引发剂(PB-B r),再用其引发亲水性单体DMAEMA进行原子转移自由基聚合,聚合动力学证实了该聚合反应具有典型的活性/可控自由基聚合的特征.通过差示扫描量热法(DSC)研究嵌段共聚物的微相分离行为.制备的大分子引发剂及两亲性嵌段共聚物经凝胶色谱、红外和核磁表征证实了预定的结构.     

含氟丙烯酸酯与苯乙烯共聚物的RAFT合成及表征

通过可逆加成-断链链转移(RAFT)溶液聚合,以三硫代碳酸酯为RAFT试剂,偶氮二异丁腈(AIBN)为引发剂,1,4-二氧六环为溶剂,制备甲基丙烯酸(2,2,2-三氟)乙酯(TFEMA)和苯乙烯(St)共聚物.详细研究了不同引发剂的用量、RAFT试剂与引发剂摩尔比以及聚合温度等实验条件对聚合反应过程的影响.通过GPC、FTIR测试共聚物的分子量、分子量分布和分子结构,并用静态接触角仪和AFM分别表征聚合物膜的接触角、表面能及膜的表面形貌.     

Atom transfer radical polymerization of sodium2‐acrylamido‐2‐methylpropanesulfonate

The first example of well‐controlled atom transfer radical polymerization (ATRP) of a permanently charged anionic acrylamide monomer is reported. ATRP of sodium 2‐acrylamido‐2‐methylpropanesulfonate (NaAMPS) was achieved with ethyl 2‐chloropropionate (ECP) as an initiator and the CuCl/CuCl₂/tris(2‐dimethylaminoethyl)amine (Me₆TREN) catalytic system. The polymerizations were carried out in 50:50 (v/v) N,N‐dimethylformamide (DMF)/water mixtures at 20 °C. Linear first‐order kinetic plots up to a 92% conversion for a target degree of polymerization of 50 were obtained with [ECP]/[CuCl]/[CuCl₂]/[Me₆TREN] = 1:1:1:2 and [AMPS] = 1 M. The molecular weight increased linearly with the conversion in good agreement with the theoretical values, and the polydispersities decreased with increasing conversion, reaching a lower limit of 1.11. The living character of the polymerization was confirmed by chain‐extension experiments. Block copolymers with N,N‐dimethylacrylamide and N‐isopropylacrylamide were also prepared. The use of a DMF/water mixed solvent should make possible the synthesis of new amphiphilic ionic block copolymers without the use of protecting group chemistry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4446–4454, 2005     

Synthesis of ethylene/propylene elastomers containing a terminal reactive group: The combination of metallocene catalysis and control chain transfer reaction

This article discusses a chemical route to prepare new ethylene/propylene copolymers (EP) containing a terminal reactive group, such as ?‐CH₃ and OH. The chemistry involves metallocene‐mediated ethylene/propylene copolymerization in the presence of a consecutive chain transfer agent—a mixture of hydrogen and styrene derivatives carrying a CH₃ (p‐MS) or a silane‐protected OH (St‐OSi). The major challenge is to find suitable reaction conditions that can simultaneously carry out effective ethylene/propylene copolymerization and incorporation of the styrenic molecule (St‐f) at the polymer chain end, in other words, altering the St‐f incorporation mode from copolymerization to chain transfer. A systematic study was conducted to examine several metallocene catalyst systems and reaction conditions. Both [(C₅Me₄)SiMe₂N(^t‐Bu)]TiCl₂ and rac‐Et(Ind)₂ZrCl₂, under certain H₂ pressures, were found to be suitable catalyst systems to perform the combined task. A broad range of St‐f terminated EP copolymers (EP‐t‐p‐MS and EP‐t‐St‐OH), with various compositions and molecular weights, have been prepared with polymer molecular weight inversely proportional to the molar ratio of [St‐f]/[monomer]. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1858–1872, 2005     

Kinetics and stereochemical control of propylene polymerization initiated by ethylene bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane catalyst

The kinetics and sterochemical control of propylene polymerization initiated by rac-ethylene bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane ( 1 /MAO) and by rac-ethylene bis (1-indenyl) zirconium dichloride/MAO ( 2 /MAO) were investigated. The polymerization activities increase monotonically with temperature corresponding to an overall activation energy of 10.6 kcal mol^?1. This is accompanied, however, by reduction of stereochemical control as reflected in the amount of the polypropylene (PP) soluble in low boiling solvent. At a temperature of 30°C and higher, polymerization initiated by 1 /MAO produced no PP insoluble in refluxing n-heptane. Tritium radiolabeling showed that at [Al]/[Zr] ≥ 3500 and 30°C, two-thirds of 1 becomes catalytically active. There are at least two kinds of active species formed in about equal amounts; one has more stereoselectivity, 10–20 times greater rate constant of propagation, and a factor of 5–15 faster chain transfer to MAO than the second kind of Active species. This is also true at low [Al]/[Zr] of 350, except that the total amount of the two active species corresponds to only 13% of the [ 1 ]. Replacement of MAO with trimethyl aluminum resulted in the decrease of stereoselectivity and loss of catalytic activity proportional to the amount of replacement. A comparison was made with the polymers obtained with 2 /MAO.     

膦亚胺半茂钛催化体系合成无规聚丙烯弹性体的研究

采用2种膦亚胺半茂化合物[(t-Bu)_3P=N]CpTiCl_2(PT1)和[(t-Bu)_3P=N]CpTiMe_2(PT2)为主催化剂,分别以甲基铝氧烷(MAO)或[Ph_3C][B(C_6F_5)_4]为助催化剂用于丙烯聚合研究.详细考察了不同n(Al)/n(Ti)、反应温度、反应压力、反应时间等因素对丙烯聚合活性、分子量与分子量分布及其分子结构的影响.还与典型的(rac-[En(IndH_4)_2]ZrCl_2)(1),CpTiCl_3(2)及Cp_2TiCl_2(3)催化剂的催化效果进行了比较.凝胶渗透色谱(GPC)、核磁共振氢谱与碳谱(1H/13C-NMR)、示差扫描量热分析(DSC)和红外(FTIR)分析结果表明:这2种催化剂催化丙烯聚合的活性可高达3.25×10~6g聚合物/molTi×h,重均分子量高达4.4×10~5,分子量分布2.0.降低温度及升高反应压力和延长反应时间都能使聚丙烯分子量增加.观察到聚合初期产物分子量随聚合时间线性增大.在-100~200oC范围内没有观察到熔融峰出现,但在-3.7~-2.6oC区间可以观察到有玻璃化转变温度出现.序列结构分析表明,所生成的聚丙烯为无规结构,但二元组r(62.28%)高于m(37.72%),意味着聚合过程中有间规聚合倾向.[mr/(2mm+mr)]+[mr/(2rr+mr)]=1.04的计算结果进一步说明,由此类催化剂体系催化丙烯聚合生成的产物立体结构序列分布服从伯努利统计模型,聚合主要以1,2-插入方式为主,同时含有少量2,1-插入.     

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene,propylene homopolymerizations,and their copolymerization

A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)₂ZrCl₂/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C^*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C^*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C^*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C^*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C^*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (k_p) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 867–875     

活性正离子聚合制备聚(异丁烯-b-α-甲基苯乙烯)嵌段共聚物

以2-氯-2,4,4-三甲基戊烷(TMPCl)/TiCl4/质子捕捉剂(DtBP)为引发剂体系,引发异丁烯聚合,随后加入1,1-二(4-甲基苯基)乙烯作为封端剂稳定末端碳正离子,再引入四异丙醇钛(Ti(OiPr)4),降低Lewis酸性,继续引发α-甲基苯乙烯聚合,实现活性正离子聚合制备聚(异丁烯-b-α-甲基苯乙烯)嵌段共聚物.考察了α-甲基苯乙烯聚合时间对单体转化率、产物的dn/dc值、分子量及其分布的影响以及四异丙醇钛对聚合速率的影响.并通过体积排斥色谱法/紫外检测器/示差折光指数/多角激光光散射、1H-NMR以及DSC以对产物进行表征.实验结果表明,嵌段共聚物分子量分布窄(MWD≤1.2),单体转化率与分子量呈线性关系,聚合速率对单体浓度呈一级动力学关系,具有活性聚合的特征.Ti(OiPr)4能有效稳定活性中心,降低聚合速率.聚(异丁烯-b-α-甲基苯乙烯)嵌段共聚物的DSC测试发现明显的两个Tg,表明存在微相分离结构.     

Catalytic synthesis of styryl‐capped isotactic polypropylenes

Bis‐styrenic molecules, 1,4‐divinylbenzene (DVB) and 1,2‐bis(4‐vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H₂) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac‐dimethylsilylbis(2‐methyl‐4‐phenylindenyl)zirconium dichloride, I ) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl‐capped isotactic polypropylenes (i‐PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H₂ or BVPE/H₂ caused a copolymerization‐like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H₂ or BVPE/H₂, which gave the styryl‐terminated polymer chain alongside a metal‐hydride active species. It was confirmed that the chain reinsertion occurred in a regio‐irregular 1,2‐fashion, which contrasted with a normal 2,1‐insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal‐hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl‐terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non‐conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709–3713, 2010     

Group 4 Metallocene Catalysts with Hapto‐Flexible Cyclopentadienyl‐Aryl Ligand

Catalytic precursors Ti(IV) and Zr(IV) complexes bearing cyclopentadienyl and substituted cyclopentadienyl anionic ligands, bonded to phenyl or substituted phenyl through an isopropylidene bridge have been utilized in the polymerization of propene and styrene and in ethylene‐styrene copolymerization. In the presence of trichloro[(1,2,3,4,5‐η)‐1‐(1‐methyl‐1‐phenylethyl)‐2,4‐cyclopentadien‐1‐yl]titanium (LTiCl₃) we have obtained either partially isotactic (chain‐end type) or atactic poly‐(propylene), and either atactic or syndiotactic polystyrene depending on the reaction temperature. [1‐Methyl‐1‐naphthylethyl‐2‐inden‐1‐yl]titanium(IV) behaves like (LTiCl₃) in styrene polymerization, while it affords metal‐controlled partially isotactic poly(propylene), as well as the corresponding zirconium compounds. The experimental data are tentatively explained by the temperature dependence of coordination of the bridged aryl group of the ligand.     

Similarities and differences of epoxide, aldehyde and peroxide initiators for Cp2TiCl-catalyzed styrene living radical polymerizations

Cp₂TiCl is the first example of a single electron transfer (SET) agent that both provides initiating radicals from three different types of functionalities (i.e. radical ring opening of epoxides and reduction of aldehydes and peroxides) and doubles as mediator for the living radical polymerization of styrene (St) by reversibly endcapping the growing polymer chains. An initiator (I) comparison was performed using 1,4-butanediol diglycidyl ether (BDE), benzaldehyde (BA) and benzoyl peroxide (BPO) as models. The investigation of the effect of reaction variables was carried out over a wide range of experimental conditions ([Cp₂TiCl₂]/[I] = 0.5/1-4/1; [Zn]/[Cp₂TiCl₂] = 0.5/1-3/1, [St]/[I] = 50/1-400/1 and T = 60-130 °C) to reveal living polymerization features such as a linear dependence of molecular weight on conversion and narrow molecular weight distribution (M_w/M_n) for each initiator class. However, progressively lower polydispersities and larger initiator efficiencies are obtained with increasing the [Cp₂TiCl₂]/[I] and [Zn]/[Cp₂TiCl₂] ratios and with decreasing temperature. Accordingly, optimum conditions correspond to [St]/[I]/[Cp₂TiCl₂]/[Zn] = [50-200]/[1]/[2-3]/[4-6] at 70-90 °C. By contrast to peroxides, aldehydes and the more reactive epoxides provide alcohol end groups useful in block or graft copolymers synthesis.     

Anionic heterogeneous polymerization of methacrylonitrile by n-butyllithium

The anionic heterogeneous polymerization of methacrylonitrile by butyllithium in petroleum ether was investigated. The polymerization was of the “living” type, as seen from the linear dependence of the molecular weights on [MAN]/[BuLi]. This behavior was further supported by block polymerization experiments in which the monomer was added in two portions and the molecular weights obtained were directly proportional to the total monomer concentration. The initiator efficiency was low, and initiator consumption was only about 2%. This fact, together with the results of the block polymerizations showed that there was preferential addition of monomer to the growing chain ends rather than to the initiator. The molecular weights were independent of the rate of monomer addition. This as well as the “living” behavior of the polymerization of methacrylonitrile on a wide range of monomer and catalyst concentrations and the absence of chain transfer to monomer was essentially different from that of the similar heterogeneous polymerization of acrylonitrile by butyllithium previously investigated. This is due to the absence of an α-acidic hydrogen in methacrylonitrile.     

Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

The influence of MgR₂ and AlR₃ additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s-Bu₂Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4- to 1,2- chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R₃Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.     

Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups

Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.     

A NOVEL AND SIMPLE METHOD OF PREPARATION OF POLY(STYRENE-B-2-VINYLPYRIDINE) BLOCK COPOLYMER OF NARROW MOLECULAR WEIGHT DISTRIBUTION: LIVING ANIONIC POLYMERIZATION FOLLOWED BY MECHANISM TRANSFER TO CONTROLLED/“LIVING” RADICAL POLYMERIZATION (ATRP)

A novel and simple method of preparation of a block copolymer of styrene and 2-vinylpyridine with narrow molecular weight distribution is reported. The novelty lies in the transformation of the polymerization mechanism from living anionic to controlled/“living” radical polymerization (ATRP). Thus, anionic polymerization of styrene is carried out in benzene using sec-butyllithium as the initiator followed by termination with ethylene oxide to prepare hydroxy-terminated polystyrene (PS-OH). PS-OH is converted to chloride-terminated polystyrene (PS-Cl) by a displacement reaction involving thionyl chloride and pyridine in benzene. PS-Cl is used to initiate the heterogeneous ATRP of 2-vinylpyridine in p-xylene with CuCl/2,2′-bipyridine system. The polymers synthesized are characterized by gel permeation chromatography (GPC), thin layer chromatography (TLC), IR and proton NMR spectroscopies.