Kinetics of free-radical polymerization of p-vinylbenzyl methyl ether: Crosslinking by initiator free radicals

Kinetics of polymerization of p-vinylbenzyl methyl ether at low conversion either in bulk or in benzene have been found to be quite similar to those of the unsubstituted monomer styrene. Rates of polymerization initiated by peroxides or α,α′-azobisisobutyronitrile over the temperature range 50–70°C. have been found to be proportional to [Monomer][Initiator]^1/2 with an activation energy difference E_propagation – 1/2 E_termination ≈ 6 kcal./mole. Azo initiation leads to essentially unbranched poly(vinyl-benzyl methyl ether) even at very high conversions, whereas initiation of undiluted monomer by diacyl peroxides results in some crosslinking at high conversion. Use of biacetyl as a photoinitiator of polymerization over the temperature range 0–60°C. with either bulk monomer or monomer solutions in benzene has been found in each instance to yield crosslinked, insoluble polymers at low degrees of conversion. Benzene solutions of soluble polymer have been converted to high molecular weight branched polymers by free radicals generated by photolysis of biacetyl, and a substantial preference of methyl free radicals to abstract benzyl hydrogens of poly(p-vinylbenzyl methyl ether) rather than add to solvent benzene has been observed.     

二茂钛/锡/环氧化合物引发苯乙烯活性自由基聚合的研究

采用单茂钛CpTiCl3和二茂钛金属化合物(n-BuCp)2TiCl2,引发剂4-甲氧苯基缩水甘油基醚(I1),1,4-丁二醇二缩水甘油基醚(I2),4,4′-亚甲基二(N,N-二缩水甘油基苯胺)(I4)和苯基缩水甘油基醚甲醛共聚物(I5)及还原剂Sn组成引发体系,引发苯乙烯活性自由基聚合,合成线型和多臂聚合物.探讨了不同茂钛金属化合物、引发剂和还原剂对苯乙烯聚合的影响;并采用13C-NMR和GPC对聚苯乙烯的结构和性能进行了表征.结果表明所得聚合物是无规聚苯乙烯,聚合物分子量高,分子量分布窄.聚合行为属于活性自由基聚合.     

Stereospecific polymerization of benzyl vinyl ether by BF3·OEt2

Polymerization of benzyl vinyl ether was carried out by BF₃·OEt₂, and the effects of polymerization conditions on the stereoregularity of the polymer were studied by NMR analysis. The polymerization at ?78°C in toluene gave a highly isotactic polymer. The isotacticity of the polymer was independent of the catalyst concentration but increased with a decrease in the initial monomer concentration and decreased slightly on raising the reaction temperature. When the polymerizations were carried out in toluene—nitroethane mixtures, a gradual decrease in the isotacticity and a rapid decrease in the molecular weight of the polymer were observed with increasing nitroethane in the solvent. The molecular weight of the polymer was almost constant, regardless of the catalyst concentration, and increased with increasing initial monomer concentration and decreasing polymerization temperature. When the polymerization was performed in toluene at ?78°C with a small amount of water or benzyl alcohol, a linear relationship was found between the reciprocal DP of the polymer and water or benzylalcohol concentration. The mechanisms of the initiation reaction and the stereoregulation in the polymerization were also discussed.     

旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.     

Polymerization of allyl(vinyl phenyl) ethers and reactions of the resulting polymers

Solution polymerizations of allyl(o-vinyl phenyl)ether and allyl(p-vinyl phenyl)ether with cationic and radical initiators were investigated. Soluble polymers were formed in polymerizations with boron trifluoride etherate and with benzoyl peroxide. In polymerization with azobisisobutyronitrile the polymerization in dilute solution gave a soluble polymer, whereas that in concentrated solution gave a crosslinked, insoluble one. For informationon the polymerization behavior some infrared and ultraviolet spectroscopic investigations of the soluble polymers were made. From these results it appears that polymers with pendant allyl groups are formed in polymerization with boron trifluoride etherate at low temperature, and polymers containing pendant vinyl groups and allyl groups are obtained with the two types of radical initiator. Copolymerizations of these monomers with ethyl vinyl ether and styrene with the use of boron trifluoride etherate were sucessfully effected. Such reactions as Claisen rearrangement, crosslinking induced with radical initiators, and epoxidation with perbenzoic acid were examined for the polymers prepared in the polymerization with boron trifluoride etherate. Good results were obtained for the former two reactions. However, the latter was unsuccessful.     

Study of Solution Polymerization of Styrene in the Presence of Poly(ethylene glycol)-RAFT Agents Possessing Benzoyl Xanthate Derivatives

In this work, Macro-Reversible addition fragmentation termination (RAFT) agents based on poly(ethylene glycol) (PEG) possessing different molecular weights and bearing benzoyl xanthate moieties were synthesized by the reaction of PEG potassium xanthate salts with benzoyl chloride, 4-methyl benzoyl chloride and 4-chloro benzoyl chloride. Controlled free radical polymerization of the styrene were carried out in the presence of these macro-RAFT agents using 2,2′-azobisizsobutyronitrile (AIBN) as an initiator to yield PS-b-PEG-b-PS block copolymers. The linear kinetic plot ln [M]_o/[M] vs. polymerization time indicated that was first order with reference to monomer concentration. The block copolymerization possessed controlled/living character. The controlled character of the RAFT polymerization of the styrene was confirmed by the formation of narrow polydispersity of the polymers, linear increases in the molecular weight with polymerization time and molecular weight of the products that agreed well with theoretical values. Polymers having relatively narrow molecular weight distributions and predetermined number average molecular weights were obtained by the RAFT polymerization of the styrene. However, molecular weights of the polymers deviated from the theoretical values when low molecular weight RAFT agents are used. The results indicate that PEG benzoyl xanthate RAFT agents can more efficiently control the polymerization comparing methyl or chlorobenzoyl derivatives. The block copolymers were characterized by spectroscopic and GPC methods.     

(n-BuCp)_2TiCl_2/Sn/I_s引发合成梳形羟基功能化无规聚苯乙烯及聚合物结构与性能的研究

采用茂金属化合物(n-BuCp)2TiCl2,还原剂(Sn),引发剂苯基缩水甘油基醚甲醛共聚物(Is)组成的催化体系引发苯乙烯活性自由基聚合,合成梳形羟基功能化无规聚苯乙烯.考察了聚合温度、聚合时间及引发剂与单体的比例对苯乙烯聚合的影响.当聚合温度在65～95℃范围内,随着聚合温度的升高,聚合物的分子量及单体转化率增加;在一定温度下,聚合物的分子量与单体转化率之间存在线性增长关系,且聚合物的分子量分布较窄(Mw/Mn=1.6～1.9).采用GPC,WAXD,13C(1H)-NMR对聚合物(沸丁酮可溶级分)的结构与性能进行了表征.GPC结果证明(n-BuCp)2TiCl2/Sn/Is引发苯乙烯聚合为活性聚合;13C-NMR和WAXD结果说明聚苯乙烯链段为无规结构;1H-NMR结果表明聚合物分子链中含有羟基,并根据其结果计算出聚合物分子的臂数为4,与引发剂Is的环氧基团数相等.这些结果证明了其聚合机理是经环氧基团开环后形成的自由基引发苯乙烯自由基聚合.     

Ionic polymerization of p-vinylbenzyl methyl ether

Ionic polymerizations of vinylbenzyl methyl ether initiated by either carbanions or Lewis acids has been found to lead to crosslinked polymers. By comparative studies of strong carbanionic bases and Lewis acids with benzyl ethers, it has been possible to define details of mechanisms which in conjunction with cationic or anionic propagation lead to crosslinks. The α-hydrogens of benzyl ethers have been found to be sufficiently acidic to terminate anionic polymerization of styrene and displacement of alkoxide anion from the benzyl ether linkage by nucelophilic polymer anions is proposed as a mechanism leading to branching and eventual crosslinking in anionic polymerization of vinylbenzyl methyl ether. Cationic polymerization of vinylbenzyl methyl ether is quite complex. In addition to propagation, chain transfer, and spontaneous termination of cation chain carriers, there is evidence for complex formation between Lewis acid initiator and the benzyl ether substituent. A slow decomposition of ether–Lewis acid complexes produces benzylcarbonium ions which alkylate aromatic rings of polymer and thereby crosslink the polymer. Benzyl ether has been found to be an effective chain terminator for cationic styrene polymerization.     

Synthesis of poly(benzyl glutamate‐b‐styrene) rod‐coil block copolymers by dual initiation in one pot

We have developed a metal free synthetic pathway to homopolypeptide rod‐coil block copolymers. The concept was proven for the synthesis of poly(benzyl‐L ‐glutamate‐b‐styrene). A dual initiator containing a primary amine and a nitroxide group was used in a macroinitiation approach with high initiation efficiency. Good control over the molecular weight in the ring opening polymerization of benzyl‐L ‐glutamate N‐carboxyanhydride was obtained in DMF at 0 °C yielding poly(benzyl‐L ‐glutamates) with low polydispersities around 1.1. The almost quantitative incorporation of the dual initiator was confirmed by MALDI‐ToF analysis. Macroinitiation of styrene by nitroxide‐mediated controlled radical polymerization yielded the block copolymer with high structural control. The diblock structure was confirmed by molecular weight increase upon macroinitiation by size exclusion chromatography and retention time comparison with homopolymers using gradient polymer elution chromatography. Both polymerizations were also successfully conducted in one pot without intermediate isolation owing to the high compatibility of both polymerization techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3068–3077, 2008     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure

A styrene‐based monomer having a five‐membered cyclic dithiocarbonate structure, 4‐vinylbenzyl 1,3‐oxathiolane‐2‐thione‐5‐ylmethyl ether (VBTE), was synthesized from 4‐vinylbenzyl glycidyl ether (VBGE) and carbon disulfide in the presence of lithium bromide in 86% yield. Radical polymerization of VBTE in dimethyl sulfoxide by 2,2′‐azobisisobutyronitrile was carried out at 60 °C to afford the corresponding the polymer, polyVBTE, in 64% yield. PolyVBTE with number‐averaged molecular weight higher than 31,000 was obtained. The glass transition temperature (T_g) and 5 wt % decomposition temperature (T_d5) of the polyVBTE were evaluated to be 66 and 264 °C under nitrogen atmosphere by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBTE repeating unit could also be obtained via polymer reaction, that is, a lithium bromide‐catalyzed addition of carbon disulfide to a polyVBGE prepared from a radical polymerization of VBGE. Copolymerization of VBTE and styrene with various compositions efficiently gave copolymers of VBTE and styrene. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Photopolymerization of methyl methacrylate with the use of iodine monobromide as photoinitiator

Iodine monobromide easily induces photopolymerization of methyl methacrylate (MMA) at 40°C under visible light. Initiator exponent and monomer exponent values were found to be 0.5 and 2, respectively, at low initiator concentrations, while the corresponding values at high initiator concentration conditions were zero and 3. The chain transfer constant of IBr at 40°C was found to be 13.0. Kinetic and other data indicate a radical polymerization mechanism involving complexation of monomer molecules with iodine monobromide prior to radical generation, and termination is believed to take place biomolecularly at low IBr concentrations and unimolecularly, involving reaction with the initiator, at high IBr concentrations (initiator termination).     

Synthesis and radical polymerization of styrene‐based monomer having a five‐membered cyclic carbonate structure

A styrene‐based monomer having a five‐membered cyclic carbonate structure, 4‐vinylbenzyl 2,5‐dioxoran‐3‐ylmethyl ether (VBCE), was prepared by lithium bromide‐catalyzed addition of carbon dioxide to 4‐vinylbenxyl glycidyl ether (VBGE). Radical polymerization of the obtained VBCE was carried out using 2,2′‐azobisisobutyronitrile as an initiator. PolyVBCE with number‐averaged molecular weight higher than 13,800 was obtained by a solution polymerization in N,N‐dimethylformamide, N,N‐dimethylacetamide, dimethyl sulfoxide, and methyl ethyl ketone. The glass transition temperature and 5 wt % decomposition temperature of the polyVBCE were determined to be 52 and 305 °C by differential scanning calorimetry and thermal gravimetry analysis, respectively. It was confirmed that a polymer consisting of the same VBCE repeating unit can be also obtained via chemical modification of polyVBGE, that is, a lithium‐bromide‐catalyzed addition of carbon dioxide to a polyVBGE prepared from a radical polymerization of VBGE. Further copolymerization of VBCE with styrene gave the corresponding copolymer in a high yield. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymerization of methylmethacrylate with cetyl benzyl dimethyl ammonium chloride and benzoyl peroxide as redox initiator system

Polymerization of methylmethacrylate was studied using benzoyl peroxide and cetyl benzyl dimethyl ammonium chloride (CBDAC) combination as the redox initiator at 40°. Equilibrium complexation between the redox components precedes the radical generation process, and the complex acts as the actual initiating species. Initiator exponent was 0.5 under various conditions of homogeneous polymerization. Kinetics of polymerization in diluted systems were variable in respect of order with respect to monomer depending on the nature of the solvent or additive. DMF, acetonitrile and pyridine produced rate enhancing effects through actively influencing the initiation step; cyclohexanone, acetone, chloroform, methanol and benzene behaved as (normal) inert diluents, while formamide and acetamide produced retardation. Termination of polymerization occurred exclusively bimolecularly. As a redox component, the quaternary chloride salt, CBDAC behaved somewhat differently from quaternary bromide salts cetyl trimethyl ammonium bromide and cetyl pyridinium bromide.     

Photopolymerization of methyl methacrylate with the use of iodine as the photoinitiator

Kinetics of photopolymerization of MMA at 40°C with the use of iodine as the photoinitiator was studied. At low range of iodine concentration (< 0.0004M), the rate of polymerization was proportional to square root of iodine concentration and the monomer exponent was 2.5, while at a higher range of iodine concentration, (0.0005–0.002M) the initiator exponent and monomer exponent were zero and 3.6–3.8 (i.e., close to 4), respectively. The chain-transfer constant of iodine at 40°C was found to be 6.0. Polymerization was found to be largely inhibited in the presence of relatively high concentrations of iodine (> 0.005M) and also in presence of hydroquinone. Kinetic and other data indicate a radical mechanism of polymerization involving complexation of monomer molecules with iodine prior to radical generation, and termination is believed to take place bimolecularly at low iodine concentrations and unimolecularly, involving reaction with iodine, at high iodine concentrations (initiator termination).     

Atom Transfer Radical Polymerization of Styrene Using Multifunctional Iniferter Reagents as Initiators

Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (M_w/M_n ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and ¹H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group.     

Evaluation of polymerization rate by chain length dependence on polymer–polymer termination and primary radical termination in radical polymerization

In order to analyze the polymerization rate at high initiation rate and/or low monomer concentration, the rate equations are derived by a rate formulated previously for polymer–polymer termination and another rate for primary radical termination, which is formulated here (both rates depend on chain length of polymer radical). Such equations would be applicable to the kinetic data in the polymerizations of styrene and methyl methacrylate. This shows that the assumption that both rates are independent of chain length overestimates the rate of primary radical termination.     

Porphyrin derivatives act as vinylene monomers in TEMPO‐mediated radical copolymerization with styrene

In this article, we offer clear evidence for the radical copolymerizability of porphyrin rings in 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)‐mediated radical copolymerizations with styrene. The radical copolymerizations of styrene with 5,10,15,20‐tetrakis(pentafluorophenyl)porphyrin (H₂TFPP) was conducted using 1‐phenyl‐1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethane as an initiator. The refractive index (RI) traces for the size‐exclusion chromatography of the resulting copolymers were unimodal with narrow molecular weight distributions. The RI traces shifted toward higher molecular weight regions as the polymerization progressed, and the number‐average molecular weights were close to those calculated on the basis of the feed compositions and monomer conversions. These features were in good agreement with a TEMPO‐mediated mechanism. The traces recorded by the ultraviolet‐visible (UV‐vis) detector (430 nm) were identical to those obtained by the RI detector, indicating a statistical copolymerization of styrene with H₂TFPP. This also indicated that H₂TFPP acted as a monomer and not as a terminator or a chain‐transfer agent under the conditions used. A benzyl radical addition to H₂TFPP was conducted as a model reaction for the copolymerization using tributyltin hydride as a chain‐transfer agent, affording a reduced porphyrin, 2‐benzyl‐5,10,15,20‐tetrakis(pentafluorophenyl)chlorin 1 , via radical addition to the β‐pyrrole position. The UV‐vis spectrum of 1 was fairly similar to that of poly(styrene‐co‐H₂TFPP), indicating that H₂TFPP polymerized at its β‐pyrrole position in the TEMPO‐mediated radical polymerization. TEMPO‐mediated radical copolymerizations of styrene with several porphyrin derivatives were also demonstrated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Kinetics and mechanism of emulsion polymerization initiated by oil-soluble initiators. II. Kinetic behavior of styrene emulsion polymerization initiated by 2,2′-azoisobutyronitrile

In order to clarify the general kinetic behavior of emulsion polymerization initiated by oilsoluble initiators, the emulsion polymerization of styrene initiated by 2,2′-azoisobutyronitrile was as a typical example, investigated thoroughly. The variations of the polymerization rate and the number of polymer particles produced with changes in emulsifier (sodium lauryl sulfate), initiator, and monomer concentrations initially charged and the reaction temperature were determined. It is shown from these experimental results that the kinetic behavior of this emulsion polymerization system is quite similar to that of styrene emulsion polymerization initiated by the water-soluble initiator, potassium persulfate despite the difference in the principal loci of radical production in both systems.     

PMMA-containing ITX Residues and its Initiation for Synthesizing PMMA-b-PSt Copolymer

In virtue of the reversible coupling and cleaving mechanism involved isopropylthioxanthone (ITX), a precursor of poly(methyl methacrylate) ended with ITX residues (PMMA-ITXH) was firstly synthesized through the photopolymerization of methyl methacrylate (MMA) initiated by a binary system of ITX and ethyl-p-dimethyl amino benzoate (EDAB), and secondly, applying this precursor as a macroinitiator, block copolymer of poly(methyl methacrylate) and polystyrene (PMMA-b-PSt) was produced through a thermal activated radical polymerization of styrene (St) at a temperature above 80°C. The content of incorporation of the reduced ITX groups in the precursor was estimated by UV-vis spectrum analysis and the results indicated that it was greatly influenced by the ITX concentration in system. The presence of EDAB could promote the polymerization and result in high monomer conversions and low molecular weight of polymers with wide distributions, but had no evident effect on the incorporation of reduced ITX moieties in polymer. Furthermore, more monomer supplied in system was advantageous for the production of high molecular weight of polymers and provided apparently low content of reduced ITX residues in polymer. Using a selected precursor of PMMA-ITXH with a moderate level of reduced ITX residues, molecular weight and its distribution, the bulk polymerization of St was initiated. FTIR spectrum analysis and GPC measurement confirmed the formation of block copolymer of PMMA-b-PSt.     

Kinetics of two-phase bulk polymerization. II. The influence of dissolved polymer

The effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high-precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions increased with the amount of dissolved polybutadiene and with its molecular weight and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Surprisingly, analogous rate reductions were observed when polystyrene were substituted for the polybutadienes, except that at high polystyrene concentrations, the expected autoacceleration was observed. These rate reductions showed no correlation with the viscosity of the reaction mass, nor did the dissolved polymer affect initiator efficiency. At a given level of a particular dissolved polybutadiene, rate reductions were diminished by increasing levels of each initiator, and by adding a chain-transfer agent. Good quantitative agreement was obtained with the number-average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain-transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated by North and Reed whereby the dissolved polymer makes the reaction mass a “poorer” solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.