Polymerization of N-(2,3,4,5,6-pentafluorophenyl)-maleimide

A novel fluorine-containing polymer, poly[N-(2,3,4,5,6-pentafluorophenyl)maleimide], was prepared by the anionic polymerization of N-(2,3,4,5,6-pentafluorophenyl)maleimide (PFPMI). Anionic polymerization with alkali metal tert-butoxides gave poly(PFPMI) in 14–32% yield. Phenyllithium and sec-butyllithium also afforded poly(PFPMI). No polymer was obtained with a radical initiator such as 2,2′-azoisobutyronitrile. The polymerization took place only via the vinylene group of PFPMI and no appreciable side-reaction occurred. The obtained poly(PFPMI) shows unimodal molecular weight distribution and begins to decompose at 325°C.     

Synthesis of comb‐like polystyrene with poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as macroinitiator

The copolymerization of N‐phenyl maleimide and p‐chloromethyl styrene via reversible addition–fragmentation chain transfer (RAFT) process with AIBN as initiator and 2‐(ethoxycarbonyl)prop‐2‐yl dithiobenzoate as RAFT agent produced copolymers with alternating structure, controlled molecular weights, and narrow molecular weight distributions. Using poly(N‐phenyl maleimide‐alt‐p‐chloromethyl styrene) as the macroinitiator for atom transfer radical polymerization of styrene in the presence of CuCl/2,2′‐bipyridine, well‐defined comb‐like polymers with one graft chain for every two monomer units of backbone polymer were obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2069–2075, 2006     

Oxidative coupling polymerization of 2,3‐dihydroxynaphthalene with dinuclear‐type copper(II) catalyst

The oxidative coupling polymerization of 2,3‐dihydroxynaphthalene with the novel dinuclear‐type copper(II) catalysts successfully produced poly(2,3‐dihydroxy‐1,4‐naphthylene). For example, the MeOH‐insoluble polymer with a number average molecular weight of 4.4 × 10³ from the polymerization using the complex of CuCl₂ and N,N′‐bis(2‐morpholinoethyl)‐p‐xylylenediamine ( p ‐ 1 ) at room temperature under an O₂ atmosphere followed by acetylation of the hydroxyl groups was obtained in 63% yield. The structures of the tetraamine ligands and the counter anion of the copper(II) salts significantly influenced the catalyst activity. The polymerization of 2,2′‐dimethoxy‐1,1′‐binaphthalene‐3,3′‐diol with the 2CuCl₂‐ p ‐ 1 catalyst, however, resulted in a lower yield. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1635–1640, 2005     

A kind of novel nonmetallocene catalysts for ethylene polymerization

A kind of novel bridged nonmetallocene catalysts was synthesized by the treatment of N,N‐imidazole and N,N‐phenylimidazole with n‐BuLi, and MCl₄ (M = Ti, Zr) in THF. Those catalysts were performed for ethylene polymerization after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M ratio, pressure of monomer, and concentration of catalysts on ethylene polymerization behaviors were investigated in detail. Those results revealed that the catalyst system was favorable for ethylene polymerization with high catalytic activity. The polymer was characterized by ¹³C NMR, WAXD, GPC, and DSC. The result confirmed that the obtained polyethylene featured broad molecular weight distribution around 20, linear structure, and relative low melting temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 33–37, 2008     

Indefinitely active aqueous cationic polymerizations,part I: Low cost,recyclable initiator systems

This article describes the first example of an aqueous cationic polymerization that utilizes a low cost, safe, and highly recyclable initiator system (phosphotungstic acid) that retains its activity indefinitely. Quantitative yields of low to medium molecular weight polymers of p-methoxystyrene and N-vinylcarbazole are obtained within minutes to hours. Polymerization is first order in both monomer and phosphotungstic acid. Negatively charged surfactants suppress polymerization; whereas, nonionic soaps increase the reaction rate and reduce both polymer molecular weight and polydispersity index. Herein, the discovery of a new form of aqueous cationic polymerization involving the condensation of the alcoholic derivative of p-methoxystyrene, 1-(4-methoxyphenyl)ethanol, is also disclosed.     

Radical and anionic homopolymerization of maleimide and N-n-butylmaleimide

The rate of homopolymerization of maleimide has been measured in dimethylformamide solution at 60°C. in the presence of azobisisobutyronitrile; it has been compared to that of N-n-butylmaleimide. The overall rates of polymerization are equal to R_p = k[M]^1.1–1.2 [In]^0.8 for maleimide, and R_p = k'[M] [In]^0.5 for the N-substituted imide. The difference of behavior has been interpreted on the basis of an intramolecular tautomery of the terminal group of the maleimide growing chain and the formation of a resonance-stabilized succinimidyl radical. The relative ease of polymerization of these monomers and of maleic anhydride has been discussed. In the presence of sodium tert-butoxide at 20°C. in dimethylformamide solutions, maleimide polymerizes with hydrogen isomerization. The percentage of N-substituted isomerized units was evaluated at 70–75% by measurement of the rate of hydrolysis in 0.005N sodium hydroxide and comparison with succinimide and N-butylsuccinimide. N-n-butylmaleimide undergoes ring opening together with anionic polymerization in the presence of sodium tert-butoxide at 20°C. and butyllithium at -40°C. Unlike the radical-initiated polymerization, it was impossible to obtain anionic copolymers of maleimide and N-butylmaleimide with acrylonitrile and methyl methacrylate.     

Cyclopolycondensations. VI. Fully aromatic polybenzoxazinones from aromatic poly(amic acids)

New high temperature aromatic polybenzoxazinones of high molecular weight have been prepared by the cyclopolycondensation of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic dicarboxylic acid halides (II). The low temperature solution polymerization techniques afforded poly(amic acid) (III) of high molecular weight in the first step. An open-chain precursor subsequently underwent thermal cyclodehydration along the polymer chain at 200–350°C. in the second step, to give in quantitative yield a fully aromatic polybenzoxazinone (IV) of outstanding heat stability both in nitrogen and in air. The poly(amic acid) is soluble in N-methyl-2-pyrrolidone, and tough, transparent films can be cast from solution. Insoluble aromatic polybenzoxazinone films which possess excellent oxidative and thermal stability were obtained by the heat treatment of the polyamic acid. A detailed account of polymerization conditions in the low temperature solution polymerization of polybenzoxazinones is given, and the reaction mechanisms of cyclopolycondensation of poly(amic acids) and the formation of polybenzoxazinones are discussed.     

Transetherification polycondensation: The roles of the catalyst,monomer structure,and polymerization conditions

A detailed study of the novel melt transetherification polycondensation process, which was recently developed in our laboratory, is presented. The efficacy of different catalysts, such as p‐toluenesulfonic acid (PTSA), camphorsulfonic acid, and their pyridinium salts, was examined. The pyridinium salts, especially pyridinium camphorsulfonate (PCS), outperformed PTSA both in terms of the polymer molecular weights (the polydispersity) and the extent of discoloration of the polymer. The evolution of the molecular weight with the polymerization time was monitored with two different catalysts, PTSA and PCS, and these studies demonstrated that, while PTSA yielded polymers with a broad molecular weight distribution, the use of PCS curtailed possible side reactions that led to this broadening. Model reactions suggested that one possible reason for this broadening could be the formation of macrocyclics facilitated by an ether–ether exchange reaction, which was shown to occur much more rapidly when PTSA was used. A further interesting and rather unprecedented feature, which became apparent while the effect of the acid–catalyst concentration was being examined, was the dual role played by the acid, which acted both beneficially as a catalyst and detrimentally, defunctionalizing the chain end and terminating polymer growth. This conclusion was based on the observed decrease in the molecular weight of the polymer at very high catalyst concentrations, which suggested that there existed an optimum catalyst concentration at which a balance was struck between the molecular weight of the polymer formed and the polymerization time. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 102–111, 2004     

Polymerization initiated by an electron donor–acceptor complex. Part IV. Kinetic study of polymerization of methyl methacrylate initiated by the charge-transfer complex consisting of poly-2-vinylpyridine and liquid sulfur dioxide

A kinetic study has been made of the polymerization of methyl methacrylate (MMA) initiated by a charge-transfer complex of poly-2-vinylpyridine (electron donor) and liquid sulfur dioxide (acceptor) in the presence of carbon tetrachloride. It is concluded that the polymerization proceeds through free-radical intermediates, as with the pyridine-liquid sulfur dioxide complex system. The association constants K of acceptor and polymer electron donors which range widely in their molecular weight were determined spectrophotometrically, and it has been found that both K and overall rate of polymerization R_p of MMA decrease with increasing molecular weight of polymer donor; contrary to this, molecular weight of PMMA formed increases with increasing molecular weight of the polymer donor. Other kinetic behaviors was essentially the same as in the pyridine–liquid sulfur dioxide system, i.e., R_p is proportional to the square root of the concentration of the complex and to the 3/2-order of the monomer concentration; R_p is clearly sensitive to the carbon tetrachloride concentration at low concentration of carbon tetrachloride, but for a higher concentration it is practically independent of the carbon tetrachloride concentration. It has been deduced from a kinetic mechanism for the initiation that a primary radical may be produced from the reduction of carbon tetrachloride by an associated complex consisting of liquid sulfur dioxide–polymer donor and the monomer.     

Palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodide,aromatic bis(boronic acid propanediol ester), and norbornadiene: A new route for poly(p‐phenylene vinylene)

A novel synthetic method for soluble precursor polymers of poly(p‐phenylene vinylene) (PPV) derivatives by the palladium‐catalyzed three‐component coupling polycondensation of aromatic diiodides, aromatic bis(boronic acid) derivatives, and norbornadiene is described. For example, the polymerization of 1,4‐diiodo‐2,5‐dioctyloxybenzene, benzene‐1,4‐bis(boronic acid propanediol ester), and norbornadiene at 100 °C for 3 days provided a polymer consisting of the three monomer units in a 97% yield (number‐average molecular weight = 3100, weight‐average molecular weight/number‐average molecular weight = 1.37). A derivative of PPV was produced smoothly by the retro Diels–Alder reaction of the polymer both in a dodecyloxybenzene solution and in a film at 200 °C in vacuo. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3403–3410, 2005     

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by ¹³C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon-bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.     

The synthesis and solution properties of some rigid-chain,water-soluble polymers: Poly[N,N′-(sulfo-phenylene)phthalamide]s and poly[N,N′-(sulfo-p-phenylene)pyromellitimide]

Poly[N,N′-(sulfo-phenylene)phthalamid]es and poly[N,N′-(sulfo-p-phenylene)pyromellitimide] were prepared in water-soluble form and were found to have unique solution properties, similar in some respects to xanthan. The polymer most investigated, poly[N,N′-(sulfo-p-phenylene)terephthalamide] (PPT-S), is produced as the dimethylacetamide (DMAC) salt by the solution polymerization of 2,5-diaminobenzenesulfonic acid with terephthaloyl chloride in DMAC containing LiCl. The isolated polymer requires heating in water to dissolve; the resulting cooled solutions are viscous or gels at concentrations as low as 0.4%. They are highly birefringent, exhibit circular dichroism properties, and are viscosity-sensitive to salt. Solutions of this polymer mixed with those of guar or hydroxyethyl cellulose give significantly enhanced viscosity. The polymer is relatively low molecular weight, ca. 5000 estimated from viscosity data. Some meta and para isomeric analogs of PPT-S were prepared; these polymers have similar properties except they are more soluble in water, and higher concentrations are required to obtain significant viscosity. Poly[N,N′-(sulfo-p-phenylene) pyromellitimide] (PIM-S) was prepared similarly from 2,5-diaminobenzenesulfonic acid and pyromellitic dianhydride. Its aqueous solution properties are similar to those of PPT-S. It appears that these relatively low-molecular-weight rigid-chain polymers associate in water to form a network that results in viscous solutions at low concentrations.     

Synthesis of α‐maleimide‐ω‐dienyl heterotelechelic poly(methyl methacrylate) and its cyclization by the intramolecular Diels–Alder reaction

The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α‐maleimide‐ω‐dienyl end‐groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3‐tert‐butyldimethylsilyloxypropyl‐1‐lithium and 5‐bromo‐1,3‐pentadiene as the initiator and terminator, respectively, to synthesize α‐hydroxy‐ω‐dienyl‐PMMA. The introduction of the maleimide group to the α chain end by the reaction of the sodium salt of the polymer with N‐(3‐chloromethylphenyl)‐maleimide or N‐(3‐bromomethylphenyl)‐maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon carbon double bond of the maleimide group. When 4,4′‐bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α‐maleimide‐ω‐dienyl‐PMMA was obtained in a good yield. Ring closure by the intramolecular Diels–Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 237–246, 2000     

A variety of poly(m-benzamide)s with low polydispersities from inductive effect-assisted chain-growth polycondensation

Chain-growth polycondensation of 3-(alkylamino)benzoic acid alkyl esters 1 was investigated for obtaining poly(m-benzamide)s with defined molecular weights and low polydispersities. Polymerization conditions were first studied to find that ethyl 3-(octylamino)benzoate ( 1b ) polymerized in a chain polymerization manner in the presence of lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base and phenyl 4-methylbenzoate ( 2b ) as an initiator in THF at 0 °C. The molecular weight of the polymer was controlled by the feed ratio of monomer to initiator. The polymerization of 1c – i with a variety of N-alkyl groups was then carried out under the established conditions to yield well-defined poly(m-benzamide)s, which showed higher solubility than those of the corresponding poly(p-benzamide)s. Furthermore, the 4-octyloxybenzyl group on the amide nitrogen in poly 1i was removed by treatment with trifluoroacetic acid (TFA) to give N-unsubstituted poly(m-benzamide) (poly 1j ) with a low polydispersity, which is soluble in DMAc and DMSO, contrary to the para-substituted counterpart. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4990–5003, 2006     

Solution polymerization of polybenzimidazole

Polybenzimidazoles (PBI) are an important class of heterocyclic polymers that exhibit high thermal and oxidative stabilities. The two dominant polymerization methods used for the synthesis of PBI are the melt/solid polymerization route and solution polymerization using polyphosphoric acid as the solvent. Both methods have been widely used to produce high‐molecular weight PBI, but also highlight the obvious absence of a practical organic solution‐based method of polymerization. This current work explores the synthesis of high‐molecular weight meta‐PBI in N,N‐dimethyl acetamide (DMAc). Initially, model compound studies examined the reactivity of small molecules with various chemical functionalities that could be used to produce 2‐phenyl‐benzimidazole in high yield with minimal side reactions. ¹H NMR and FTIR studies indicated that benzimidazoles could be efficiently synthesized in DMAc by reaction of an o‐diamine and the bisulfite adduct of an aromatic aldehyde. Polymerizations were conducted at various polymer concentrations (2‐26 wt % polymer) using difunctional monomers to optimize reaction conditions in DMAc which resulted in the preparation of high‐molecular weight m‐PBI (inherent viscosities up to 1.3 dL g^?1). TGA and DSC confirmed that m‐PBI produced via this route has comparable properties to that of commercial m‐PBI. This method is advantageous in that it not only allows for high‐polymer concentrations of m‐PBI to be synthesized directly and efficiently, but can be applied to the synthesis of many PBI derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1795–1802     

Polymerization and copolymerization of trioxane: Factors influencing molecular weight and end groups

In bulk polymerization and copolymerization of trioxane with ethylene oxide, it has been shown that p-chlorophenyldiazonium hexafluorophosphate is a superior catalyst as compared to boron trifluoride dibutyl etherate (BF₃ · Bu₂O). Polymers and copolymers of significantly higher molecular weight have been obtained. The higher molecular weight has been attributed primarily to less inherent chain transfer during propagation, which in turn can be attributed to the superior gegenion PF₆^?. The polymerization proceeds via a clear period followed by sudden solidification. Faster polymerization and higher molecular weight polymers have been observed for homopolymerization than for copolymerization. The polymer yield obtained after solidification is determined by both rate of polymerization and rate of crystallization of polymers. These rates, in turn, are dependent on the catalyst concentration. The molecular weight is determined both by polymer yield and extent of inherent chain transfer. In the range of monomer to catalyst mole ration [M]/[C] = (0.5–20) × 10⁴ investigated, it has been found that in the higher range, the polymer yield is independent of the catalyst concentration and the extent of inherent chain transfer is inversely proportional to the half power of catalyst concentration: [M]/[C] = (0.5–8) × 10⁴ for homopolymerization and (0.5–3) × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. In the lower range, the yield decreases with catalyst concentration and the extent of inherent chain transfer is inversely proportional to higher power of catalyst concentration. The dependence of molecular weight of polymers on catalyst concentration has been shown to be a complex one. The molecular weight goes through a maximum as the catalyst concentration is decreased. The maximum molecular weights have been obtained at [M]/[C] ≈ 8 × 10⁴ for homopolymerization and ～3 × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. Prior to reaching maximum the molecular weight is inversely proportional to the half power of catalyst concentration indicating it is primarily controlled by inherent chain transfer. Upon further decrease of catalyst, molecular weight decreases as a result of both a decrease in polymer yield and an increase in inherent chain transfer. In copolymerization of trioxane and ethylene oxide, it has been ascertained that methylene chloride exhibits a favorable solvating effect. Although higher inherent chain transfer takes place in copolymerization than in homopolymerization, the extent of chain transfer is independent of ethylene oxide concentration. The difference in polymer yield and molecular weight a t different ethylene oxide concentrations is attributed primarily to the difference in k_p/k_t ratio. It also has been demonstrated that end capping of polymer chains can be accomplished by the use of a chain transfer agent—methylal.     

Synthesis of porous supports containing N‐(p‐hydroxyphenyl)‐ or N‐(3‐4‐dihydroxybenzyl) maleimide‐anchored titanates and application as catalysts for transesterification and epoxidation reactions

N‐(p‐acetoxyphenyl)maleimide and N‐(piperonyl)maleimide were polymerized in suspension to give macroporous supports. After deprotection of the p‐acetoxyphenyl and of the piperonyl groups, resins with pendant p‐hydroxyphenyl and catechol units were obtained. These results illustrate a very easy and convenient way to synthesize phenol and catechol containing supports. Polymer‐supported transesterification and epoxidation catalysts were obtained by immobilization of Ti(OiPr)₄ and TiCl₄. These catalysts were efficient for both reactions and could be recycled several times although some titanium leaching (≤ 20%) was observed in each case. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2879–2886, 2000     

Pyrolysis of poly(vinyl chloride)

A pyrolysis–gas chromatography–mass spectrometric technique has been developed to study the thermal degradation of poly(vinyl chlorides) polymerized at different temperatures. Hydrogen chloride and benzene evolution during successive stages of pyrolysis have been quantitatively determined and correlated to the tacticity and molecular weight of the polymer. It was found that lowering the temperature of polymerization and molecular weight depresses benzene evolution and increases char weight but does not affect the HCl yield. It is suggested that the syndiotactic trans microstructure favored at low temperature of polymerization yields polyenes which cannot cyclize to form benzene. As the molecular weight decreases, the increase in number of vinyl chain ends facilitates pyrolytic crosslinking and char formation.     

Poly(3-hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis,characterization, and properties

The spontaneous polymer formed from 3-hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water-soluble, atactic, poly(3-hydroxyoxetane) (PHO) of high crystallinity with ? OCH₂CH(OH)CH₂OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water-soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i-Bu₃Al–0.7 H₂O cationic catalyst followed by hydrolysis. Two ¹H-NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an ¹H-NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water-insoluble fraction with T_m = 223°C. The low molecular weight PHO prepared previously by the base-catalyzed, rearrangement polymerization of glycidol is highly branched.     

Anionic polymerization of N-substituted maleimide. II. Polymerization of N-ethylmaleimide

Anionic polymerization of N-ethylmaleimide (N-EMI) was carried out with potassium t-butoxide, lithium t-butoxide, n-butyllithium, and ethylmagnesium bromide as initiators in THF and in toluene. An almost quantitative yield of poly(N-EMI) was obtained with potassium t-butoxide as initiator in THF in a wide range of polymerization temperatures. Initiators possessing lithium as counter cation produced poly(N-EMI) in slightly lower yields and ethylmagnesium bromide gave the polymer only in less than 35% yield in THF. As a polymerization reaction solvent, THF was preferable for the polymerization of N-EMI compared with toluene with respect to polymer yields. Poly(N-EMI) obtained with anionic initiators exerted unimodal molecular weight distribution. From ¹H- and ¹³C-NMR spectra of poly(N-EMI) anionic polymerization of N-EMI with potassium t-butoxide was revealed to proceed at carbon–carbon double bond. t-Butoxide system was found to have a “living” polymerization character, i.e., the observed average degree of polymerization was in good agreement with the one calculated from the initial molar ratio of N-EMI/initiator and the yield of polymer.