Atom transfer radical bulk polymerization of methyl methacrylate under microwave irradiation

Microwave irradiation (MI) was applied to the atom transfer radical bulk polymerization of methyl methacrylate. The influence of the amount of the refluxing solvent used for controlling the polymerization temperature, irradiation power, irradiation time, and initiator concentration on the conversion, molecular weight, and molecular weight distribution of the polymers was studied with a benzyl chloride/cuprous chloride/2,2′‐bipyridyl initiation system and compared with the corresponding conventional heating (CH) process. In comparison with CH, the results can be summarized as follows. The polymerization rate for reaching 70% conversion increased 2.6–5.1 times under an irradiation power of 270–630 W. The apparent increasing rate constant was much larger than that with CH and increased with the irradiation power. MI produced a higher polymerization rate and conversion even if the concentration of the initiation system was very low (initial monomer concentration/initial initiator concentration = 200:0.33 mol/mol) and the polydispersity index (DI) was narrower; however, CH yielded almost no polymers. MI promoted the activities of the catalyst and monomer, and its initiation efficiency was higher than that with CH and increased with the irradiation power. MI obviously played an important role in promoting the polymerization rate of atom transfer radical polymerization (ATRP). MI reduced the concentration of the initiation system and perhaps made ATRP controlled (cf. uncontrolled ATRP with CH); at the same time, it made the DI values of the polymers narrower. In comparison with the initiation efficiencies found with benzyl bromide and 2,2′‐azobisisobutyronitrile used as initiators, the initiation efficiency with p‐toluene sulfonyl chloride used as an initiator was higher; moreover, DI was much narrower (1.17), and the polymerization rate was greater. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1787–1793, 2003     

Controlled/‘living’ radical polymerization of methyl methacrylate with p-TsCl/CuBr/BPY initiating system under microwave irradiation

Atom-transfer radical polymerization of methyl methacrylate under microwave irradiation (MI) using p-TsCl/CuBr/BPY as the initiating system was successfully carried out. The polymerization of methyl methacrylate under MI shows linear first-order rate plots, a linear increase in the number-average molecular weight with conversion and low polydispersities, 1.1 < M_w/M_n < 1.3. The influence of polymerization time, temperature and monomer/initiator ratio on the conversion, molecular weight and polymer distribution were studied using the MI process, and compared with that obtained by the corresponding conventional heating (CH) process. The MI process not only increases the rate of polymerization, but also narrows the polydispersity index of polymers. The apparent rate constant, , under MI is 6–8 times higher than that under CH with an identical initiating system and polymerization temperature. The effect of MI on the stereoregularity and T_g of PMMA were investigated by ¹³C NMR spectroscopy and DSC, respectively. Copyright © 2004 Society of Chemical Industry     

Microwave-assisted controlled copolymerization of styrene and acrylonitrile catalyzed by FeCl<Subscript>3</Subscript>/isophthalic acid

The copolymer of styrene-co-acrylonitrile (SAN) was synthesized by the atom transfer radical polymerization (ATRP) using FeCl₃-isophthalic acid (IA)/2,2′-azobis(isobutyronitrile) catalyst system under microwave irradiation (MI). Compared with conventional heating (CH), the copolymerization rate was accelerated under MI, and the conversion of monomer rapidly achieved 30% in 38 min for MI relative to 8% for CH under other same conditions. The kinetics results indicated that RATRP of St/AN is a ‘living’/controlled polymerization, corresponding to a linear increase of molecular weights with the increasing of monomer conversion and a relatively narrow polydispersities index (PDI < 1.25) when the conversion is beyond 30%. The resultant SAN was characterized by FT–IR, NMR, and GPC.     

Atom transfer radical polymerization of methyl methacrylate with low concentration of initiating system under microwave irradiation

Homogeneous atom transfer radical polymerization of methyl methacrylate (MMA) under microwave irradiation (MI) with low concentration of initiating system [ethyl 2-bromobutyrate (EBB)/CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA)] was successfully carried out in N,N-dimethylformamide (DMF) at 69 °C. Plots of ln ([M]₀/[M]) vs. time and molecular weight evolution vs. conversion showed a linear dependence. A 27.3% conversion for a polymer with number-average molecular weight (M_n) of 57,280 and a polydispersity index (PDI) of 1.19, was obtained under MI (360 W) with the ratio of [MMA]₀/[EBB]₀/[CuCl]₀/[PMDETA]₀=2400/1/2/2 in only 150 min; but 963 min was needed under conventional heating (CH) process to reach a 26.0 % conversion (M_n=63,990 and PDI=1.14) under identical polymerization conditions, indicating a significant enhancement of the polymerization rate under MI.     

RATRP of MMA in AIBN/FeC1<Subscript>3</Subscript>/PPh<Subscript>3</Subscript> initiation system under microwave irradiation

Summary Reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) under microwave irradiation (MI), using azobisisobutyronitrile (AIBN) /FeC1₃/triphenylphosphine (PPh₃) as the initiating system, was successfully carried out in N, N-dimethylformamide (DMF) at 69°C. Plots of In ([MI₀/[M]) vs. time and molecular weight evolution vs. conversion showed a linear dependence. A polymer for reaching 82% conversion, with molecular weight (M_n) 34,000 and polydispersity index (PDI) 1.37, was obtained under MI (90U') with the ratio of [MMA]₀/[AIBN]₀/[FeCl₃]₀/[PPh₃]₀ = 1600/2/4/8 in only 60 min; while 840 min was required under conventional heating (CH) process for reaching 82 % conversion (M_n = 48,000 and PDI = 1.31) at identical polymerization conditions, indicating a significant enhancement of the polymerization rates and apparent initiator efficiencies under MI. Received: 2 September 2002/Revised version: 3 October 2002/Accepted: 10 December 2002 Correspondence to Xiulin Zhu     

Polymerization of diisopropyl fumarate under microwave irradiation

Diisopropyl fumarate (DiPF), a representative monomer of dialkyl fumarates, was polymerized by microwave irradiation at three different powers (140, 210, and 280 W), using a domestic microwave oven. The nature and concentration of initiators [2,2′‐azobisisobutyronitrile (AIBN) and benzoyl peroxide (BP)], power and energy of microwave irradiation on the conversion, weight average molecular weight (M_w), and polydispersity index (M_w/M_n) were analyzed. The results indicate that the microwave conditions have a significant nonthermal effect in enhancing the polymerization rate of DiPF. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3785–3791, 2007     

Emulsion polymerization of styrene under pulsed microwave irradiation

We performed the emulsion polymerization of styrene successfully with potassium persulfate (KPS) as an initiator and sodium dodecylsulfonate as an emulsifier under high‐power pulsed microwave irradiation (PMI). We investigated the effects of the temperature, the concentration of initiator, and various parameters of PMI (i.e., irradiation power, duty cycle, irradiation energy, and pulse width) on the polymerization. The results indicated that PMI, compared to conventional heating (CH), caused a significant increase in the decomposition rate of KPS (2.4 times higher than that under CH at about 70°C) and in the amount of particles (5 times higher than that under CH); consequently, the polymerization rate was effectively enhanced. For initiator concentrations of 0.10 and 0.20 wt %, the enhancement of the polymerization rate under PMI was 129 and 38% greater, respectively, than that under CH. The glass‐transition temperature and the regularity composition of the polymers under PMI and CH showed no difference, which indicated that PMI had little effect on the physical properties and microstructure of the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 28–35, 2003     

微波辅助法合成高分子量聚丙烯酰胺

以丙烯酰胺(AM)为单体,水为溶剂,过硫酸铵(APS)和偶氮二异丁基脒盐酸盐(AIBA)为复合引发体系,采用微波辅助法制备聚丙烯酰胺(PAM)。研究了微波辐照功率、辐照时间、单体浓度、引发剂用量对聚丙烯酰胺分子量和单体残留率的影响,采用红外光谱(FT-IR)表征了聚合物产物结构,最后考察了剪切作用对PAM性能的影响。结果表明:采用微波辅助法制备的PAM反应时间短、能耗低、分子量高、单体残留率低;当微波功率为100 W,辐照时间为8 min,单体浓度为25%,引发剂用量为0.05%时产物分子量可达1050×104,并且单体残余量低;PAM的降解随着剪切时间的延长和剪切速度的加快而加快。     

乙酸乙烯酯的微波加热聚合

对乙酸乙烯酯甲醇溶液在微波加热条件下的聚合反应进行了研究,讨论了微波聚合条件、引发剂浓度、溶剂浓度和种类对聚合产物的转化率和分子量的影响。聚合物可以在较短时间内获得。且在同样的实验条件下,用不同的溶剂获得的聚合物的分子量不同。     

Microwave‐irradiated ring‐opening polymerization of D,L‐lactide under atmosphere

Poly(D ,L ‐lactide) (PDLLA) was synthesized by microwave‐irradiated ring‐opening polymerization catalyzed by stannous octoate (Sn(Oct)₂) under atmosphere. The effects of heating medium, monomer purity, catalyst concentration, microwave irradiation time, and vacuum level were discussed. Under the appropriate conditions such as carborundum (SiC) as heating‐medium, 0.15% catalyst, lactide with purity above 99.9%, 450 W microwave power, 30 min irradiation time, and atmosphere, PDLLA with a viscosity–average molecular weight (M_η) over 2.0 × 10⁵ and a yield over 85% was obtained. The dismission of vacuum to ring‐opening polymerization of D ,L ‐lactide (DLLA) under microwave irradiation simplified the process greatly. The temperature under microwave irradiation and conventional heating was compared. The largely enhanced ring‐opening polymerization rate of DLLA under microwave irradiation was the coeffect of thermal effects and microwave effects. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2244–2247, 2006     

悬浮聚合法制取不同分子量级别的聚甲基丙烯酸甲酯

采用粉状MgCO3 作为分散剂 ,悬浮聚合制取了分子量从 2 4× 10 4 ～ 2 5 4× 10 4 的聚甲基丙烯酸甲酯。考察了温度、引发剂种类和浓度、分子量调节剂、转化率对聚合物分子量的影响规律 ,用粘度法测量了聚合物聚甲基丙烯酸甲酯 (PMMA)的分子量。结果表明 :温度的升高、引发剂浓度的增大、分子量调节剂的加入都会导致分子量的减小 ,随着转化率的提高 ,聚合物的分子量增大。在同等条件下 ,引发剂过氧化苯甲酰 (BPO)聚合所得的分子量较偶氮二异丁腈 (AIBN)高。通过实验 ,得到了满足作者需求的分子量 (96× 10 4 ～ 10 0× 10 4 )的聚合物的聚合条件为 :分散剂MgCO3 用量 1% ,单体∶水相 =1∶2 5 (质量比 ) ,引发剂BPO浓度 0 5 % ,反应温度 70℃ ,反应时间 3h。     

Microwave assisted synthesis of high molecular weight polyvinylsilazane via RAFT process

The microwave-assisted synthesis of high molecular weight polyvinylsilazane (H-PVSZ) leads to a narrow molecular weight distribution at accelerated polymerization rates under controlled/living polymerization, while retaining the excellent controllability offered by reversible addition fragmentation chain transfer (RAFT) polymerization in a thermal reaction process. Under microwave irradiation, higher molecular weight H-PVSZ (6250 vs. 4370) was obtained with higher conversion (86.7 vs. 30.1%) than under conventional heating through a simple 3 h reaction of vinylcyclicsilazane with a molecular weight of 314 in the presence of dithiocarbamate derivatives (RAFT agent) and 2,2′-azobis-isobutyronitrile (AIBN, thermal initiator). H-PVSZ with a well-controlled high molecular weight is useful for synthesizing inorganic-organic diblock copolymer polyvinylsilazane-block-polystyrene (PVSZ-b-PS) with a higher molecular weight and lower polydispersity than by conventional heating of the PVSZ-derived product.     

高分子表面活性剂存在下超声辐照引发苯乙烯乳液聚合的研究

采用高分子表面活性剂(CMC-A9)和十二烷基硫酸钠(SDS)做乳化剂,用超声辐照乳液聚合方法制备了相对分子质量高(>106)的寡链聚苯乙烯纳米粒子。研究结果表明,在适当的反应条件下,CMC-A9的加入使反应速率大大提高,反应60min单体转化率能达到85%,制得直径30～60nm的聚苯乙烯胶乳粒子,乳胶粒子中含平均分子链数为3～20。CMC-A9或SDS质量浓度提高,能降低乳胶粒径和乳胶中所含的平均分子链数,增加聚合物相对分子质量。超声波输出功率对乳胶粒径影响不大。     

Microwave accelerated synthesis and characterization of poly(acrylamide)

Poly(acrylamide) (PAM) was efficiently synthesized under microwave (MW) irradiation using catalytic amount of potassium persulfate. The synthesis does not require any inert atmosphere and could be accomplished in very short time. Microwave power, exposure time, concentration of persulfate, and concentration of the acrylamide were varied to optimize the polymerization in terms of the % conversion (%C). The maximum %C that could be achieved was in 98.5%. The average molecular weight of the synthesized PAM samples ranged from 4.11 × 10⁴ to 1.30 × 10⁵, depending upon the MW power used for their synthesis. The representative PAM was characterized by Fourier transform‐infrared, SEM, and X‐ray diffraction studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3702–3707, 2007     

Evolution to similarity solutions for polymerization and depolymerization with microwave radiation

The kinetics of polymerization and depolymerization are critical in understanding the stability and characterization of polymers. The kinetics of simultaneous polymerization and degradation of poly(methyl methacrylate) have been investigated by varying the initiator concentration and monomer concentration under the influence of microwave energy. Microwave radiation initially polymerizes the monomer, then degrades the resulting polymer and the polymer attains an equilibrium molecular weight distribution with a polydispersity of two. To understand more fully the kinetics, the molecular weight distribution (MWD) is represented as a gamma distribution; the random degradation rate coefficient is assumed to vary linearly with molecular weight and the polymerization rate coefficient is assumed to be independent of molecular weight. The change of the MWD with time is studied by continuous distribution kinetics; the solutions obtained depict the change of the average molecular weight, polydispersity and the gamma distribution parameters with time. Experimental data indicate that reaction rates are enhanced by microwave radiation and the MWD approaches a similarity solution within 10 min for all the investigated cases. The model satisfactorily predicts the change of the MWD with time. © 2001 Society of Chemical Industry     

非极性混合介质中分散聚合法制备聚乙烯基吡咯烷酮

以乙烯基吡咯烷酮(NVP)为单体,环己烷的混合溶剂为分散介质,AIBN为引发剂,SEBS为分散剂,采用分散聚合的方法制备了分散性能好、粒径为1μm左右、热稳定性较好的聚乙烯基吡咯烷酮。考察了单体含量、引发剂用量、分散剂用量对分散聚合反应的影响。结果表明,转化率和分子量均随单体含量增加而增大,随引发剂的量的增大而减小;且在单体含量为30%、AIBN的用量为0.5%,分散剂用量为10%时,所合成的聚合物分子量最大。     

Microwave-assisted synthesis of tetrasubstituted aryl imidazole based polymers via cascade polycondensation process

Poly(Tetrasubstituted Aryl Imidazole)s (PTAIs), a new class of poly(heteroaromatic) polymers was prepared via a cascade polycondensation process, under microwave irradiation. These polymers were obtained by the tetrasubstituted aryl imidazole ring formation involving bis(aryl α-diketone)s, bis(arylaldehyde)s, mono(arylamine)s and ammonium acetate. The polymerization performed under microwave irradiation allowed to get high molecular weight PTAIs in very short reaction times. The chemical structure of these PTAIs was confirmed by NMR spectroscopy. Thermogravimetric analyses (TGA) showed a very good grade of thermal stability of these polymers. Glass transition temperatures (T_g) of PTAIs ranging from 155 °C to 265 °C were determined by Differential Scanning Calorimetry (DSC).     

Synthesis of syndiotacticity‐rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Vinyl pivalate (VPi) was suspension‐polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity‐rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2′‐azobis(2,4‐dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55°C by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number‐average degree of polymerization (P_n): 8200–10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94–98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P_n and conversion of 10,700–11,800 and 32–43% were obtained, respectively. The DB was lower and the P_n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 832–839, 2003     

Coumarin end-capped polystyrene by ATRP and photodimerization reaction

Summary New coumarin-end-capped polystyrenes have been prepared using functional initiators by atom-transfer radical polymerization (ATRP). In the first case, the photosensitive initiator, 7-chloroacetoxy-4-methyl-coumarin, was prepared. Then the styrene was initiated by 7-chloroacetoxy-4-methyl-coumarin in the presence of a CuBr/bipyridine. The functionalization of the polymers was nearly quantitative, the molecular weight and structure were well controlled by adjusting the monomer/initiator molar ratio, polymerization temperature and time. At high monomer conversion, the polydispersity index of polymer was about 1.40. These coumarin-end-capped polystyrenes underwent [2+2] cycloaddition reaction under UV irradiation in film state. After irradiation the molecular weight and polydispersity index of polystyrene both increased, but the maximum molecular weight was less than the double of original one. It means that the photodimerization reaction was not complete throughly in film state for the diffusion of coumarin groups was blocked by polymeric chain entanglement.     

Synthesis of new polyethers derived from isoidide under phase‐transfer catalysis: Reactivity and selectivity under microwaves and classical heating

Microwave irradiation was applied to the synthesis of polyethers from 1,8‐dibromo‐ and 1,8‐dimesyl‐octane under solid–liquid phase‐transfer catalytic conditions. To evaluate the influence of microwaves on the reaction rates and polyether properties, we carried out the polymerization reactions under similar conventional conditions (oil bath) with the same temperature profiles. First, the microwave‐assisted syntheses proceeded more rapidly in comparison with conventional heating, and the reaction time was reduced from 24 h to 30 min with higher yields of polyethers. Second, the structure of the polymers strictly depended on the activation mode. Under microwave conditions, the polyethers were characterized by higher molecular weights with better homogeneity. Third, the mechanism of chain termination was different under microwave and conventional conditions. The polyethers prepared with conventional heating possessed shorter chains with mainly hydroxylated ends, whereas under microwave irradiation, the polymer chains were longer with mainly ethylenic group ends. In fact, under microwave irradiation, ethylenic group ends were formed rather rapidly and set up a hindrance to further polymer growth. In contrast, under conventional conditions terminations were essentially constituted by hydroxyl functions; however, further polymerization was terminated as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1255–1266, 2003