Kinetic study on the poly(methyl methacrylate) seeded soapless emulsion polymerization of styrene. III. Seeds with crosslinking

In this work, a seeded soapless emulsion polymerization was carried out with crosslinking (XL) poly(methyl methacrylate) (PMMA) as seeds, styrene as monomer, and potassium persulfate (K₂S₂O₈) as initiator to synthesize the PMMA XL–PS composite latex, which we knew as the latex interpenetrating polymer network (IPN). The morphology of the latex IPN was observed by transmission electron microscopy (TEM). It showed a core–shell structure. The kinetic data from the early stages of the reaction of seeded soapless emulsion polymerization showed that the square root of polymer yield (W_p)^1/2 was proportional to the reaction time. The reaction rate decreased with the increase of crosslinking density of PMMA seeds. The core–shell model proposed in our previous work^1–2 was modified to predict the conversion of polymerization over the entire course of the synthesis of PMMA (XL)–PS composite latex. Our modified core–shell kinetic model fitted well with the experimental data. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:425–438, 1997     

Kinetics studies of two-stage soapless emulsion polymerization of butyl acrylate and methyl methacrylate

In this work, butyl acrylate (BA) and methyl methacrylate (MMA) were used as monomers and K₂S₂O₈ was used as the initiator to study the kinetics of two-stage soapless emulsion polymerization. The first stage of the reaction was to synthesize polyBA (PBA) seeds, and the second stage of the reaction was a seeded polymerization of MMA. The results showed that an increase of initiator concentration would increase the rate of polymerization and the number of polymer particles, but would decrease the size of the polymer particles and the weight-average molecular weight of the polymers. On the other hand, a decrease of the weight ratio of BA/MMA caused a decrease in the reaction rate and the weight-average molecular weight of the polymers in the second stage of the reaction. The morphology of emulsion particles was observed from transmission election microscopy (TEM). The polymer particles were very uniform in size and showed coreshell morphology with PBA as a core and poly MMA (PMMA) as a shell. © 1994 John Wiley & Sons, Inc.     

Study on the synthesis of poly(methyl methacrylate)–poly(methacrylic acid) composite latex and their humidity sensitive properties

The composite latex particles of poly(methyl methacrylate)–poly(methacrylic acid) [poly(MMA–MAA)] were synthesized through either soapless seeded emulsion polymerization or a soapless emulsion copolymerization technique. The reaction kinetics, morphology, and size of latex particles, composition, glass transition temperature (T_g), and molecular weight of polymer products were studied under different experimental conditions. Moreover, this work also focused on the humidity‐sensitive properties of the polymer films fabricated by melting under the temperature of 200°C and followed by chemical modification with aqueous solution of NaOH. It is confirmed that there exists both an optimum ratio of hydrophilic to hydrophobic monomers and the initial structure of the latex particle to provide the humidity‐sensitive polyelectrolyte film with excellent water resistivity and good sensitivity to humidity. Besides, little hysteresis and quick response were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 47–57, 1999     

Polymer latex containing carboxylic acid functional groups. I. Synthesis of polymer latex from MMA and AA

The polymer latex of poly(MMA‐AA) was synthesized using two techniques: soapless seeded emulsion polymerization, and the soapless emulsion copolymerization technique. The reaction kinetics, morphology, composition, and size of latex particles, as well as the structure using thin‐layer chromatographic separation techniques, glass transition temperature (T_g), and molecular weight of polymer products, were studied under different experimental conditions. The reaction of the hydrophilic AA monomer took place in two places—on or in the latex particles, and in the water phase. Therefore, the polymer latex, whose size is very small and uniform, dispersed uniformly all over the PAA continuous phase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3111–3120, 1999     

Morphologies of polybutylacrylate/poly(styrene‐co‐methyl methacrylate) latex prepared by starved emulsion polymerization Part I. Thermodynamics equilibrium morphology

Heterogeneous latexes were prepared by a semicontinuous seeded emulsion polymerization process under monomer starved conditions at 80 °C using potassium persulfate as the initiator and sodium dodecyl sulfate as the emulsifier. Poly(butyl acrylate) latexes were used as seeds. The second‐stage polymer was poly(styrene‐co‐methyl methacrylate). By varying the amounts of methyl methacrylate (MMA) in the second‐stage copolymer, the polarity of the copolymer phase could be controlled. Phase separation towards the thermodynamic equilibrium morphology was accelerated either by ageing the composite latex at 80 °C or by adding a chain‐transfer agent during polymerization. The morphologies of the latex particles were examined by transmission electron microscopy (TEM). The morphology distributions of latex particles were described by a statistical method. It was found that the latex particles displayed different equilibrium morphologies depending on the composition of the second‐stage copolymers. This series of equilibrium morphologies of [poly(butyl acrylate)/poly(styrene‐co‐methyl methacrylate)] (PBA/P(St‐co‐MMA)) system provides experimental verification for quantitative simulation. Under limiting conditions, the equilibrium morphologies of PBA/P(St‐co‐MMA) were predicted according to the minimum surface free energy change principle. The particle morphology observed by TEM was in good agreement with the predictions of the thermodynamic model. Therefore, the morphology theory for homopolymer/homopolymer composite systems was extended to homopolymer/copolymer systems. © 2002 Society of Chemical Industry     

聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子的制备

由种子乳液聚合法制备了聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子。以过硫酸钾(KPS)为引发剂,辛基酚聚氧乙烯醚(OP-10)为乳化剂,合成了聚苯乙烯(PS)种子核;连续滴加甲基丙烯酸甲酯(MMA),在核表面富集MMA,制备了粒径范围在0.16~0.67μm的核-壳粒子;当单体苯乙烯与甲基丙烯酸甲酯(St/MMA)的比为30∶70(质量比)时,所得粒径在0.18μm,粒径分布为0.012。差示扫描量热(DSC)研究显示,复合粒子的玻璃化转变温度(Tg)为97.2℃,峰形单一,表现出良好的热性能。     

Effects of compatibilizing agents in poly(n-butyl acrylate)/poly(methyl methacrylate) composite latexes

Graft copolymers with poly(n-butyl acrylate) (PBA) backbones and poly(methyl methacrylate) (PMMA) macromonomer side chains are used as compatibilizing agents for PBA/PMMA composite latexes. The composite latexes are prepared by seeded emulsion polymerization of methyl methacrylate (MMA) in the presence of PBA particles. Graft copolymers were already incorporated into the PBA particles prior to using these particles as seed via miniemulsion (co)polymerization of n-butyl acrylate (BA) in the presence of the macromonomers. Comparison between size averages of composite and seed particles indicates no secondary nucleation of MMA during seeded emulsion polymerization. Transmission electron microscopy (TEM) observations of composite particles show the dependence of particle morphologies with the amount of macromonomer (i.e., mole ratio of macromonomer to BA and molecular weight of macromonomer) in seed latex. The more uniform coverage with the higher amount of macromonomer suggests that graft copolymers decrease the interfacial tension between core and shell layers in the composite particles. Dynamic mechanical analysis of composite latex films indicates the existence of an interphase region between PBA and PMMA. The dynamic mechanical properties of these films are related to the morphology of the composite particles, the arrangement of phases in the films, and the volume of the interphase polymer. © 1997 John Wiley & Sons, Inc.     

聚丙烯酸酯无皂核壳乳液聚合反应的研究

采用无乳液聚合技术，合成了PBA／PMMA核壳结构的复合乳液，研究齐聚物用量及配比、温度，DDM对齐聚物聚合反应速率的影响，以及引发剂浓度，齐聚物浓度等因素对核壳乳液聚合速率的影响。     

Photo‐Induced atom transfer radical polymerization with nanosized α‐Fe2O3 as photoinitiator

Photo‐induced atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was achieved in poly(ethylene glycol)‐400 with nanosized α‐Fe₂O₃ as photoinitiator. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in conjunction with ethyl 2‐bromoisobutyrate (EBiB) as ATRP initiator and FeCl₃·6H₂O/Triphenylphosphine (PPh₃) as complex catalyst. The photo‐induced polymerization of MMA proceeded in a controlled/living fashion. The polymerization followed first‐order kinetics. The obtained PMMA had moderately controlled number‐average molecular weights in accordance with the theoretical number‐average molecular weights, as well as narrow molecular weight distributions (M_w/M_n). In addition, the polymerization could be well controlled by periodic light‐on–off processes. The resulting PMMA was characterized by ¹H nuclear magnetic resonance and gel permeation chromatography. The brominated PMMA was used further as macroinitiator in the chain‐extension with MMA to verify the living nature of photo‐induced ATRP of MMA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42389.     

Morphological studies in thermally initiated emulsion (co)polymerization without conventional initiators

Poly(methyl methacrylate‐co‐styrene) composite latices were prepared by thermally initiated seed emulsion (co)polymerization of styrene (ST), methyl methacrylate (MMA), or ST and MMA employing a PST or PMMA seed in the absence of conventional initiators. The changes of particle morphology, observed by transmission electron microscopy (TEM), were investigated by varying seed particle component, the weight ratio of monomer to seed polymer, monomer composition, and employing preswelling of the seed particles. The size distribution of polymer particles obtained from thermally initiated emulsion (co)polymerization was improved by employing the seed process. Hemisphere‐like, sandwich‐like, core‐shell, and inverted core‐shell particle morphologies were observed depending upon the polymerization conditions. The preswelling of seed particles did not affect the morphology of final particles. The particle morphologies, obtained from the thermal process, were compared with those obtained from conventional seed emulsion polymerization. The incorporation of an initiator fragment SO to polymer chain ends seemed to allow the PST chains to gain some hydrophilicity. From the observation of particle morphology, the hydrophilicity of involved polymers were in the following order: PMMA with ionic (? SO) chain ends > PMMA with no ionic ends > PST with ionic ends > 60% MMA P(MMA‐co‐ST) with no polar ends > 40% MMA P(MMA‐co‐ST) with no polar ends > PST with no polar ends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1737–1748, 2002; DOI 10.1002/app.10581     

Kinetics of emulsifier–free emulsion polymerization of methyl methacrylate

The influences of polymerization temperature, initiator and monomer concentrations, ionic strength of the aqueous phase, as well as ethylene glycol dimethacrylate (EGDM) co-monomer, on the kinetics of the emulsifier-free emulsion polymerization of methyl methacrylate (MMA) and on the properties of the resulting poly(methyl methacrylate) (PMMA) lattices were studied. The polymerizations were carried out using potassium persulfate (KPS) as the initiator. Monodisperse PMMA lattices with particle diameters varying between 0.14–0.37 μm and polymer molecular weights of the order 0.4 × 10⁶ to 1.2 × 10⁶ g/mol were prepared. The initial rate of polymerization increases with increasing temperature, KPS-MMA mole ratio, EGDM content, or with decreasing ionic strength of the aqueous phase. It was shown that the bead size can be limited by reducing the monomer concentration or by using the cross-linking agent EGDM. The ionic strength of the aqueous phase has a dominant effect on final particle diameter and polymer molecular weight. The uniformity of the latex particles increases as the temperature increases or as the initiator concentration decreases. The experimental results can be reasonably interpreted by the homogeneous nucleation mechanism of the emulsifier-free emulsion polymerization of MMA. © 1996 John Wiley & Sons, Inc.     

苯乙烯-甲基丙烯酸甲酯悬浮-乳液耦合聚合动力学

采用苯乙烯(St)悬浮聚合过程滴加甲基丙烯酸甲酯(MMA)乳液聚合组分,进行悬浮-乳液耦合聚合(SECP), 制备大粒径聚苯乙烯-聚甲基丙烯酸甲酯(PS-PMMA)复合粒子.采用¹H NMR分析方法,讨论了SECP动力学特征.St的SECP聚合速率和转化率与悬浮聚合一致;MMA聚合速率决定于乳胶粒子聚合速度和凝并在悬浮粒子表面的速度,聚合速率比常规乳液聚合速率低.由于凝并在悬浮粒子表面的PMMA乳胶粒子不再有乳液聚合特征,MMA在SECP中转化率低于同条件常规乳液聚合.分别得到乳化剂和引发剂浓度与SECP和普通乳液聚合恒速段聚合速率的关系.     

PMMA/PAN核-壳粒子制备工艺研究

加入适量的引发剂,通过无皂乳液聚合,以聚甲基丙烯酸甲酯( PMMA)核体为种子乳液,制备了PMMA/PAN核-壳乳液.实验中分别对引发剂量、丙稀腈( AN)滴加量对PMMA/PAN壳层厚度及其粒径和粒径分布的影响进行了较详细的研究,确定了种子乳液聚合法制备PMMA/PAN核-壳结构聚合物粒子的实验方法及条件.通过激光粒度仪、扫描电镜和透射电镜对核-壳粒子的形态结构进行了表征,证明了PMMA/PAN复合粒子的核-壳结构.     

Preparation of polystyrene/poly(methyl methacrylate) core‐shell composite particles by suspension‐emulsion combined polymerization

Suspension‐emulsion combined polymerization process, in which methyl methacrylate (MMA) emulsion polymerization constituents (EPC) were drop wise added to styrene (St) suspension polymerization system, was applied to prepare polystyrene/poly(methyl methacrylate) (PS/PMMA) composite particles. The influences of the feeding condition and the composition of EPC on the particle feature of the resulting composite polymer particles were investigated. It was found that PS/PMMA core‐shell composite particles with a narrow particle size distribution and a great size would be formed when the EPC was added at the viscous energy dominated particle formation stage of St suspension polymerization with a suitable feeding rate, whereas St‐MMA copolymer particles or PS/PMMA composite particles with imperfect core‐shell structure would be formed when the EPC was added at the earlier or later stage of St suspension polymerization, respectively. It was also showed that the EPC composition affected the composite particles formation process. The individual latex particles would exist in the final product when the concentrations of MMA monomer, sodium dodecyl sulfate emulsifier, and potassium persulfate initiator were great in the EPC. Considering the feature of St suspension polymerization and the morphology of PS/PMMA composite particles, the formation mechanism of PS/PMMA particles with core‐shell structure was proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology,thermal property,and mechanical property of core–shell latex polymers. I. Effect of heating and pressuring on PBA/PS linear composite polymer

In this work, butyl acrylate and styrene were used as monomers in the first stage and second stage of polymerization, respectively, and potassium persulfate (K₂S₂O₈) was used as the initiator to synthesize the poly(butyl acrylate)–polystyrene (PBA/PS) composite latex by the method of two-stage soapless emulsion polymerization. The morphology of the latex particles was observed by transmission electron microscopy (TEM), which showed that the composite latex particles had a core–shell structure. The particle-size distribution of the composite latex was very uniform. A thin layer of a PBA-graft-PS copolymer was formed in between the core (PBA) and shell (PS) regions, which thus increased the compatibility between the PBA and PS phases. The process of heating and pressuring influenced the morphology, mechanical properties, and thermal properties of the PBA/PS composite polymer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 13–23, 1998     

About morphology in ethylene-propylene(-diene) copolymers-based latexes

Coatings and engineering plastics often require high impact strength. This property can be achieved with tougheners. For the present paper, core-shell impact modifiers were synthesized using ethylene-propylene copolymers (EPM), ethylene-propylene-diene copolymers (EPDM) or a mixture of both types (EP(D)M) as core material, as well as poly(methyl methacrylate) (PMMA) as shell material.EP(D)M-based polymers were dispersed in water using an Ultra-Turrax^® and a high pressure homogenizer. The prepared artificial latexes were used, either without further treatment or after crosslinking, as seed latexes in the emulsion polymerization of methyl methacrylate (MMA). The free radical seeded emulsion polymerization of MMA was investigated in the presence of an oil-soluble initiator, i.e. cumene hydroperoxide (CHP), combined with a redox system, i.e. sodium formaldehyde sulfoxylate hydrate (SFS), disodium salt of ethylenediamine tetra-acetic acid (EDTA), iron (II) sulfate heptahydrate (FeSO₄). This initiation system promotes polymerization of MMA near the surface of the seed particles, partially suppressing homogeneous secondary nucleation and polymerization in the aqueous phase.Kinetic and thermodynamic considerations were used to predict the particle morphology. The monomer type, the monomer-to-rubber ratio, the monomer feed type, and crosslinking of the seed latex particles were investigated, to optimize the polymerization kinetics and the properties of the resulting dispersions. The particle morphology was determined by cryo-transmission electron microscopy (cryo-TEM). Monomer-flooded conditions led to the formation of inverted core-shell particles, whereas starved-feed MMA or MMA/styrene mixtures gave rise to partially engulfed structures, i.e. snowman-like. Crosslinking of the EP(D)M seed particles was found to be required to provide the desired core-shell structures.Finally, the obtained core-shell structured particles were used to toughen a PMMA matrix. The tensile properties of the modified PMMA matrix were investigated. The micro-morphology of modified PMMA was studied by scanning electron microscopy (SEM). Tensile tests as well as TEM and SEM analyses demonstrated that the main mechanism of deformation operating in the EP(D)M-toughened PMMA matrix is shear yielding, accompanied by debonding and cavitation processes.     

Kinetics and mechanism of seeded dispersion polymerization

The kinetics and mechanism of seeded dispersion polymerization of methyl methacrylate (MMA) was studied by applying both micron and submicron PMMA seeds. Using a 1.7 μm PMMA seed (N_p = 1 × 10¹²/L) and a monomer polymer ratio (M/P) of 28/1, secondary nucleation was found to occur and the number of new particles exceeded that produced in a parallel ab initio dispersion polymerization. This was explained by the paradoxical initiator concentration effect seen in dispersion polymerizations where the number of particles decreases with increasing initiator concentration. In contrast, using 194 nm (N_p = 26 × 10¹²/L; M/P = 833/1) and 317 nm (N_p = 5.6 × 10¹²/L; M/P = 714/1) submicron seeds, it was found that the final particle number was similar to (or less in a few cases) the initial seed number over a relatively wide range of initiator concentrations. With increasing initiator concentration, the initial reaction rate increased but the maximum reaction rate decreased slightly. This was explained by increased radical termination particularly in unstable nuclei, leading to a reduced radical entry rate. The reaction rate was found to be moderately dependent on the number of seed particles, but was independent of the seed surface area. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of butyl acrylate/methyl methacrylate/glycidyl methacrylate latexes

The butyl acrylate (BA)/methyl methacrylate (MMA), and glycidyl methacrylate (GMA) composite copolymer latex was synthesized by seeded emulsion polymerization technique taking poly(methyl methacrylate) (PMMA) latex as the seed. Four series of experiments were carried out by varying the ratio of BA : MMA (w/w) (i.e. 3.1 : 1, 2.3 : 1, 1.8 : 1, and 1.5 : 1) and in each series GMA content was varied from 1 to 5% (w/w). The structural properties of the copolymer were analyzed by FTIR, ¹H‐, and ¹³C‐NMR. Morphological characterization was carried out using transmission electron microscopy (TEM). In all the experiments, monomer conversion was ～99% and final copolymer composition was similar to that of feed composition. The incorporation of GMA into the copolymer chain was confirmed by ¹³C‐NMR. The glass transition temperature (T_g) of the copolymer latex obtained from the differential scanning calorimetry (DSC) curve was comparable to the values calculated theoretically. With increase in GMA content, particles having core‐shell morphology were obtained, and there was a decrease in the particle size as we go from 2–5% (w/w) of GMA. The adhesive strength of the latexes was found to be dependent on the monomer composition. With increase in BA : MMA ratio, the tackiness of the film increased while with its decrease the hardness of the film increased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of environment-friendly acrylic latex laminating adhesives applied in plastic/plastic composite films

Acrylic latex laminating adhesives (ALLAs) were successfully prepared via a monomer-starved seeded semi-continuous emulsion polymerization with butyl acrylate (BA), methyl methacrylate (MMA), styrene (St), acrylamide (Am), and methacrylate glycidyl ether (GMA) as monomers. Impacts of GMA on the final latex, the dried latex films and the adhesive properties of ALLAs were investigated, respectively. The results indicated that the increase of GMA contents in the pre-emulsion feed has no apparent effect on the final latex average particle size and size distribution, while the gel contents, glass transition temperature (T_g) and water contact angle of the ALLAs gradually increased, and the molecular weight (M_n, M_w) obviously increased. Additionally, as the amount of GMA increased from 0 to 10?wt%, the maximum peel strength of the composite films reached 3.72 N/15mm with 5?wt% GMA contents. When heated to 65?°C, the peel strength of the composite films with 5?wt% of GMA can still maintain an acceptable peel strength (2.51 N/15mm) for application, showing excellent adhesive performance and heat resistance properties.