甲基丙烯酸甲酯高转化聚合动力学的研究

以金属膨胀计和差热扫描量热计法对甲基丙烯酸甲酯本体聚合的凝胶效应临界转化率和最终转化率与温度、引发剂种类和浓度等聚合条件的定量关系进行了探讨。进一步论证了均相理想聚合体系的最终转化率仅是温度系数。     

紫外光引发聚乙二醇二甲基丙烯酸酯的RAFT交联聚合研究

合成了S-1-十二烷基-S′-(α,α′-二甲基-α″-乙酸)三硫代碳酸酯(TTC),以此为链转移剂,采用光差动热分析仪(DPC)和动态力学分析(DMA)方法研究了室温条件下紫外光引发的聚乙二醇二甲基丙烯酸酯(PEGDMA)的可逆加成-断裂链转移(RAFT)自由基聚合行为.发现RAFT光聚合反应的反应速率小于常规自由基聚合,因为体系由扩散控制,反应中自加速趋势减缓.探讨了双键之间聚乙二醇链段长度对于聚合速率和最终转化率的影响.结果发现,随着中间聚乙二醇链段的增加,聚合速率先变小再变大,最终转化率缓慢变大.RAFT光交联产物的交联密度随中间链段长度的增加而下降,交联均匀性提高.     

丙烯酸酯/液晶复合体系的光聚合动力学

采用光差示扫描量热分析,研究了以2, 4, 6-三甲基苯甲酰基-二苯基氧化膦(TPO)为光引发剂、丙烯酸异辛酯(EHA)和三羟甲基丙烷三甲基丙烯酸酯(TMPTA)为单体、液晶为P0616A的丙烯酸酯/液晶复合体系在-40~80℃的光聚合动力学。研究表明：丙烯酸酯/液晶复合体系光聚合的自动加速现象非常显著,聚合反应速率和表观动力学常数在聚合过程中均存在最大值。随着反应温度的提高,体系的最终转化率、最大聚合反应速率(Rpmax)均明显提高,当反应温度高于20℃后,其增长均趋于平缓。随着体系中液晶含量的增加,体系的Rpmax呈下降趋势,体系的聚合反应转化率随时间的增长速率较慢,但是最终转化率差别不大,均接近80%。随着UV光强的增高,体系的Rpmax和最终转化率均明显提高, 体系的阈值光强约为4 mw/cm2。而随着体系平均官能度的增加,体系的Rpmax和最终转化率则呈下降的趋势。     

Temperature modulated DSC study of the kinetics of free radical isothermal network polymerization

Temperature modulated differential scanning calorimetry (TMDSC) is used to study the kinetics of the free radical isothermal polymerization of triethyleneglycol dimethacrylate (TEGDMA). Azo-bis-isobutironitrile was used as initiator. The polymerization’s temperature is lower than the final glass transition temperature of the polymer network. The measurement of the average heat flow released and the heat capacity during the reaction allows identifying the different stages of the reaction. The presence of double peaks in the heat flow is ascribed to the autoacceleration. The influence of temperature, measuring conditions and oxygen are described. Vitrification is detected by the drop in heat capacity. It occurs at increasing conversion rates for increasing temperatures. After vitrification, the diffusion-controlled reaction continues.     

Study of Kinetics of Dispersion Polymerization of Styrene in Organic Media

The kinetics of dispersion polymerization of styrene in alcohol/methyl or butyl cellosolve was investigated with dried-weigh methods. The reaction parameters, such as concentration of initiator, polymerization temperature, and solvent, play an important role in determine polymerization rate. It was found that polymerization rate increases with the reaction temperature. The apparent activation energy is of 42.2kJ/mole and 52.6kJ/mole for the initial polymerization stage and the stationary polymerization interval. The polymerization rate increases with the concentration of the initiator with approximately 0.67 order dependence at conversion about 5%. It was described that the relation of conversion with the Hansen Parameters of media in detail by analysis of solvent dispersion, polarity and hydrogen bonding contributions. More significant was the result that polymerization rate versus conversion curve consisted of 3 intervals (2 non-stationary and 1 stationary one). The plateau of polymerization rate was observed in the curve of polymerization rate vs. monomer conversion.     

Thermal behavior of amide substituted diacetylenes

Diacetylenes substituted with various amide groups were prepared and their solid-state polymerization behavior was studied. A calorimetric study of the isothermal polymerization of 1,6-diacetylamino-2,4-hexadiyne was performed in detail. This compound has an extremely high reactivity. The reaction proceeded very quickly and the ultimate conversion reached over 40% slightly above room temperature. The feature of the reaction resembles those observed in the solid-state polymerization of other diacetylene compounds, i.e., the reaction proceeds slowly in the initial stage, but the rate of reaction increases drastically at about 5% conversion to polymer. Quantitative conversion, however, was not attained at any temperature, and the reaction leveled off within 1.5 h. It is assumed that the reaction cannot continue owing to the distortions generated in the crystals during the polymerization process. The crystalline state of the polymer obtained was highly disordered.     

Radiation-induced polymerization of glass-forming systems. II. Effect of temperature on the polymerization rate at higher conversion

The effect of temperature and conversion on the polymerization rate at higher conversion was investigated with regard to the γ-ray-induced polymerization of hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) in the supercooled phase. The polymerization rate changed from acceleration to depression at various conversions, depending on the polymerization temperature. It was found that T_v at which the viscosity of the system became ca. 10³ cpoise influenced the shape of the polymerization time–conversion curve. The experimentally obtained conversion reflection point in the polymerization time–conversion curve agreed with the conversion where the polymerization temperature is the same as the calculated T_v of the system. When the polymerization temperature was lower than T_v of the monomer, no acceleration of the polymerization occurred. When the polymerization temperature was higher than T_v of the polymer, no depression of the polymerization rate was observed. The effect of temperature on the saturated conversion (final conversion) was also examined in terms of T_g of the polymerization system. The experimentally obtained saturated conversion agreed with the conversion where the polymerization temperature is the same as the calculated T_g of the system.     

Four-center type photopolymerization in the solid state. II. Polymerization mechanism of 2,5-distyrylpyrazine

The polymerization mechanism of trans,trans-2,5-distyrylpyrazine (DSP) has been investigated and some crystal changes along with the polymerization process have been observed through polarizing microscope and x-ray diffraction pattern. Information has been obtained on the active species, polymerization reaction type, and other factors such as light intensity, reaction temperature, or crystalline state. The polymerization of DSP occurs only in the solid state by photoirradiation. Reduced viscosity increases gradually with the increase of conversion and increases sharply above 80% conversion. Polymerization rate increases with the increase of light intensity and temperature. On the other hand, reduced viscosity decreases with the increase of temperature but does not depend on light intensity within the range investigated. The polymer obtained at low conversion as well as at high conversion has high crystallinity, and the direction of polymer axes is simply related to that of monomer crystal. It was concluded that the four-center type polymerization of DSP proceeds topochemically by a photochemically induced stepwise mechanism.     

Poly(n-hexyl methacrylate) polymerization in three-component microemulsion stabilized by a cationic surfactant

The polymerization of n-hexyl methacrylate (n-HMA) in three-component microemulsion stabilized with dodecyltrimethylammonium bromide (DTAB) is reported as a function of monomer and initiator concentrations and temperature. The obtained latices were bluish, transparent, and translucent. Particle sizes and molar masses were on the order of 20 nm and 3 x 10(6) g/mol, respectively. In all cases, high reaction rates and final conversions of 98% were obtained. Polymerization temperature has a strong effect on reaction rate and conversion.     

Evidences of a hydrolysis process in the synthesis of N-vinylcaprolactam-based microgels

The hydrolysis process suffered by vinylcaprolactam (VCL) monomer during polymerization and the way of avoiding it is a matter of considerable interest when the final material is used in biomedical applications. In this work, in order to study the hydrolysis process in the synthesis of VCL-based microgels, VCL was polymerized by emulsion polymerization in batch and semi-batch reactors by using N,N′-methylenebisacrylamide (BA) as cross-linker and potassium persulfate (KPS) as initiator. Moreover, the partial conversion evolutions of VCL and BA were analyzed by ¹H NMR. The colloidal characterization was carried out by measuring the final average diameters as a function of temperature. The results showed that there were two competitive reactions (hydrolysis and propagation) in the polymerizations carried out in the absence of a buffer. However, VCL did not suffer hydrolysis by adding a buffer in the recipes. A new reliable method for the determination of the partial conversions was developed using the quantitative NMR method. The final cross-linked colloidal particles (microgel particles) obtained in the buffered reaction presented the conventional swelling de-swelling behavior corresponding to temperature sensitive microgels.     

Photocrosslinking of Silicones. Part 11. Radical Photopolymerization Under Oxygen-Silicone Acrylates as Model Systems

Abstract

Silicone acrylates were used as model systems for radical photo-polymerization under oxygen with commercial photoinitiators of the α-cleavage type. From calorimetric results, it is inferred that oxygen inhibits and terminates the chain process. The reaction rate, the final conversion, and the inhibition time of polymerization are proportional to the air pressure, to the intensity of the incident light, and to the quantum yield of the initiator photolysis. We show that the reaction starts if all oxygen is consumed in the silicone layer. Only oxygen which diffuses into the system determines the termination reaction. By means of the first Fickian diffusion law, it is demonstrated that the oxygen which diffuses into the silicone layer also determines the final conversion of double bonds in the system. However, in the absence of oxygen, the observed final conversion of double bonds is approximately 1. The high final conversion is combined with a high reaction rate.     

Simulation of conversion profiles and temperature distributions within dimethacrylate thick material during photopolymerization

Photoinitiated polymerization of multifunctional monomers is an usual method to prepare highly crosslinked networks which have a wide variety of applications. This method leads to high reaction rates and the resulting exothermic effect of this reaction can be the cause of defects in the final material. The heterogeneities alter greatly the physical properties of ultimate products, particularly the optical ones, what causes problems in the design of thick and optically perfect materials. The knowledge of the conversion profile and the temperature distribution within the material during the photopolymerization is useful for the process optimization. Unfortunately, these parameters cannot be measured during the process. Thus, we decided to simulate them. Firstly, the necessary parameters (like conversion and reaction rate) were measured on thin material in isothermal conditions by photocalorimetry. Secondly, these kinetic data were used in a computational calculation to obtain the conversion profile and the temperature distribution within dimethacrylate thick material. The calculated temperature and conversion-time curves are in good agreement with the experimental curves determined under the same conditions.     

Tailor‐made poly(ethyl acrylate) by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of ethyl acrylate (EA) was carried out using different initiators, CuBr or CuCl as catalyst in combination with different ligands e.g., 2,2′‐bipyridine (bpy) and N,N,N′,N″N″‐pentamethyl diethylenetriamine (PMDETA). Use of PMDETA as ligand resulted in faster polymerization rate (95% conversion in 15 min) than those using bipyridine (～58% conversion in 10.5 h). This is due to the lower reduction potential of copper‐amine than that of copper‐bpy complex, resulting in higher rates of activation of dormant halides. Use of ethylene carbonate as solvent lead to faster polymerization rate and better control in polymerization when compared with p‐xylene as solvent. The reaction temperature had a positive effect on polymerization rate and the optimum reaction temperature was found to be 90 °C. An apparent enthalpy of activation of ～85 kJ/mol was determined for the ATRP of ethyl acrylate, corresponding to an enthalpy of equilibrium of ～64 kJ/mol. By judicious choice of the reaction parameters it was possible to tailor the end group of the final polymer. MALDI‐TOF‐MS analysis and the chain extension experiment of poly(ethyl acrylate) (PEA) prepared using bpy as ligand showed the presence of ? Br as the end group. On the contrary, when PMDETA was used as the ligand, the mass spectra analysis showed hydrogen terminated polymer as the major species towards the end of polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1661–1669, 2007     

Photoinitiated polymerization of methacrylates comprising phenyl moieties

Investigation of photopolymerization kinetics of 4-(4-methacryloyloxyphenyl)-butan-2-one (1) in comparison with 2-phenoxyethyl methacrylate (2) and phenyl methacrylate (3) using a UV-LED emitting at 395 nm shows significantly faster polymerization of 1 compared to both 2 and 3 at 40°C. Vitrification affects photopolymerization kinetics of all methacrylates under investigation. Interestingly, quantitative final conversion is observed during photoinitiated polymerization of 1 and 2 whereas 3 shows limited conversion at about 80%. Furthermore, higher degree of polymerization is obtained by photoinitiated polymerization of 1 compared to 2 and 3. This shows that the 3-oxobutyl substituent at the phenyl ring of 1 significantly affects both polymerization kinetics and final conversion of the photoinitiated polymerization. Moreover, an additional higher molecular weight fraction is observed in case of polymerization of 1 at 85°C that is above the glass transition temperature of the polymer formed during photoinitiated polymerization. As a thermal polymerization at 85°C in the absence of light results in a high molecular weight polymer as well, an additional thermal process may be discussed as reason for the higher molecular weight polymer fraction in case of the photopolymer made at 85°C.     

TEMPO存在下丙二腈对苯乙烯聚合的加速作用研究

在少量丙二腈存在下,苯乙烯在稳定自由基TEMPO作用下的聚合速率显著增加,分子量分布较窄,且随转化率增大而增大,具有活性聚合特征.丙二腈与TEMPO的摩尔比在4:1时加速效果较好,在125℃下聚合1h转化率可达到70%,分子量可达到105,且反应温度降低到110℃.¹HNMR分析表明,丙二腈在反应中起催化剂作用,通过削弱碳氮键可以提高转化速度,还可明显降低聚合温度.     

环硅氧烷负离子乳液聚合中活性中心浓度的变化规律

以八甲基环四硅氧烷(D4)为单体,十二烷基二甲基苄基氢氧化铵(BDAH)为乳化剂兼催化剂,进行环硅氧烷负离子乳液聚合,采用凝胶色谱(GPC)测定聚合产物的转化率及分子量.在此基础上,分析基元反应,提出活性中心生成机理,并应用环硅氧烷开环聚合普适动力学模型计算乳液聚合平衡之前的活性中心浓度变化规律.结果发现,聚合温度较低时,活性中心浓度随时间逐渐增加,最终恒定;聚合温度较高时,活性中心浓度随时间仅单调递增.结果与机理相符.     

A one-component photoinitiator based on 4-methylbenzophenone and morpholine

4-Benzoylbenzyl-3-morpholinopropanoate was synthesized, characterized and used as a one-component photoinitiator of Type II. Real-time near-IR spectroscopy was used to study the kinetics of conversion of double bonds of monomers vs. irradiation time. In this initiator, the radicals could be generated through hydrogen abstraction based on intermolecular reaction. Light intensity, concentration of initiator, and the functionality of acrylates affected the polymerization rate and the final monomer conversion.     

丙烯腈与衣康酸在DMSO/H_2O中的聚合及聚合物性能表征

采用丙烯腈 (AN)与衣康酸 (IA)为共聚单体 ,以偶氮二异丁腈为引发剂在混合介质二甲基亚砜 水(DMSO H2 O)中自由基沉淀共聚合 ,合成了高分子量的聚丙烯腈 .通过正交设计方法研究了聚合反应条件 ,如反应温度、单体浓度、混合介质DMSO H2 O配比等对聚合反应的转化率的影响 ,还重点探讨了混合介质DMSO H2 O配比对转化率和粘均分子量的影响 .采用DSC ,TG ,IR等手段研究了PAN均聚物及 (PAN co IA)的结构与性能 .研究结果表明 ,增加反应温度 ,降低单体浓度 ,降低喂料AN IA配比中IA的含量 ,均有利于提高聚合反应的转化率 .AN与IA共聚反应的转化率随着反应介质中DMSO含量的增加而降低 ,同时聚合物的粘均分子量也降低 .对于喂料AN IA配比中IA含量相同的P(AN co IA)共聚物 ,高分子量P(AN co IA)共聚物比常规低分子量的放热峰起始温度低 ,放热峰宽     

三元无皂乳液共聚合动力学及其模型的研究

以苯乙烯（ Ｓｔ） 和甲基丙烯酸甲酯（ Ｍ Ｍ Ａ） 为主单体,以丙烯酸（ Ａ Ａ） 为功能单体进行了无皂乳液批量共聚合．考察了功能单体浓度、引发剂过硫酸铵（ Ａ Ｐ Ｓ） 浓度及聚合温度对其动力学行为的影响．建立了转化率 时间关系曲线的模型函数——— Ｇａｍ ｍａ 积分函数,用它拟合了转化率 时间关系曲线,获得了聚合过程的重要特征参数,如平均成核速率（ Ｎ Ｖ） ,聚合最大速率（ Ｍ Ｖ） 和平稳期平均聚合速率（ Ａ Ｖ） 及成核结束和聚合进入完成期对应的转化率．同时对聚合速率与以上各聚合参数的关系数据进行了非线性拟合,得到了它们之间的关系式．研究发现拟合误差很小,成核结束时转化率在１５ ％ 以内,成核及聚合速率均随以上参数增大而增大,引发剂过硫酸铵在聚合过程中起决定作用．     

Suspended Emulsion Copolymerization of Acrylonitrile with Methyl Acrylate: Effects of Reaction Parameters on the Polymerization

Acrylonitrile/methyl acrylate copolymers were synthesized by suspended emulsion polymerization with water as dispersed phase and monomers as continuous phase, potassium peroxydisulphate (KPS) as initiator, Span-80 as emulsifier, and poly(vinyl alcohol) (PVA) as suspending agent. Effects of reaction parameters such as water/monomer mass ratio, concentration of initiator, polymerization temperature and agitation rate on polymerization conversion and the particle size distribution of acrylonitrile/methyl acrylate copolymers were studied. It was found that polymerization conversion increased with an increase of water/monomer mass ratio, concentration of initiator and polymerization temperature, while the agitation rate had no significant effect on the polymerization conversion. Particle size distribution became narrower with an increase of water/monomer mass ratio and agitation rate. Under the same initiator concentration and polymerization temperature, particle size distribution became wider along with polymerization time. The differential scanning calorimetry (DSC) results indicated that the peak temperature of the copolymers decreased with increasing MA content.