Mechanical properties of films prepared from model high‐glass‐transition‐temperature/low‐glass‐transition‐temperature latex blends

The mechanical properties of films prepared from model high‐glass‐transition‐temperature (T_g)/low‐T_g latex blends were investigated with tensile testing and dynamic mechanical analysis. Polystyrene (PS; carboxylated and noncarboxylated) and poly(n‐butyl methacrylate‐co‐n‐butyl acrylate) [P(BMA/BA); noncarboxylated] were used as the model high‐T_g and low‐T_g latexes, respectively. Carboxyl groups were incorporated into the PS latex particles to alter their surface properties. It was found that the presence of carboxyl groups on the high‐T_g latex particles enhanced the Young's moduli and the yield strength of the PS/P(BMA/BA) latex blend films but did not influence ultimate properties, such as the stress at break and maximum elongation. These phenomena could be explained by the maximum packing density of the PS latex particles, the particle–particle interfacial adhesion, and the formation of a “glassy” interphase. The dynamic mechanical properties of the latex blend films were also investigated in terms of the carboxyl group coverage on the PS latex particles; these results confirmed that the carboxyl groups significantly influenced the modulus through the mechanism of a glassy interphase formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2788–2801, 2002     

Effect of polymer latexes with varied glass transition temperature on cement hydration

Influence of styrene‐acrylate latexes with varied glass transition temperature (T_g) on cement hydration was studied and the mechanism was analyzed. Results show that polymer latexes with varied T_g retard cement hydration to different extents. Specifically, low T_g polymer shows stronger retardation effect than the high T_g polymer. Despite similar surface charges, colloidal particles with lower T_g exhibit higher affinity to surface of cement grains than the high T_g polymer, indicated by the higher adsorption amount and denser covering layer. The low T_g polymer experiences particle packing, deforming, and film forming processes along with the consumption of water during cement hydration, which eventually produces a covering layer of polymer surrounding cement grains. However, for the high T_g polymer, film forming process is absent. Consequently, the higher adsorption amount and the film‐formation process along with cement hydration are the two reasons for the stronger retardation effect of the low T_g polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45264.     

Does morphology stick? Tailored particle morphologies by swelling polymerization process

Structured dispersion particles suitable for pressure sensitive adhesives (PSA) were synthesized via swelling polymerization technique (EP 359562). Particles consisting of poly(n‐butyl acrylate) copolymerized with different types of carboxylic acids were used as seeds. The final particles were synthesized by swelling polymerization process, using 6 wt % styrene or 6 wt % methyl methacylate. The resulting particle morphology was analyzed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). From previous works (Coll Surf A 2001, 183–185, 725–737; J Appl Polym Sci 2004, 91, 2610–2623) where two‐step emulsion polymerization was used on similar particles, it is expected that the particle morphology is affected by the polarity of the monomer used for swelling polymerization because of the phase compatibility (thermodynamic parameter). In this work, the seed particles used were always of a glass transition temperature (T_g) below polymerization temperature. The diffusion of the growing polymer chains from the swelling polymerization is therefore mainly affected by their own T_g and the influence of the carboxy groups on the chain length of the entering radicals (kinetic parameter). The different morphologies of the single particles are discussed qualitatively. The effects of reaction parameters are compared with the results given in the previous work. The structure of the corresponding dispersion films was characterized using AFM. Correlations to macroscopic properties such as the cohesive strength and peel adhesion to different substrates are discussed. The results are also compared with the application properties of the corresponding unmodified particles, statistical copolymers, and to blends with small sized PMMA or PS particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1444–1455, 2006     

Photon transmission method for studying film formation from polstyrene latexes with different molecular weights

A photon‐transmission method was used to probe the evolution of transparency during film formation from polystyrene (PS) particles with different molecular weights. The latex films were formed at room temperature from the PS particles having two different average molecular weights and annealed at elevated temperatures in various time intervals above the glass transition (T_g). Onset temperatures (T_H) at given times (τ_H) for the optical clarity of films formed from low (LM) and high molecular (HM) weight PS particles were used to calculate the healing activation energies for the minor chains and found to be 22.0 ± 0.5 and 27.0 ± 0.6 kcal/mol, respectively. The increase in the transmitted photon intensity, I_tr, above the T_H was attributed to increase in the number of interfaces that disappeared. The Prager–Tirrell (PT) model was employed to interpret the increase in crossing density at the junction surface. The backbone activation energies (ΔE) were measured and found to be 127.8 ± 2.5 kcal/mol for a diffusing polymer chain across the junction surface for LM and HM latex films. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 866–874, 2000     

Heterogeneous latices as binders in porous particle structures

Heterogeneous carboxylated styrene-butadiene (S/Bu) latices were prepared by a two-stage polymerization process, using three seeds of polystyrene with different molecular weights. The second-stage polymer was a copolymer with a fixed S/Bu-ratio of 1 and a methacrylic acid (MAA) content of either 1 or 10 wt %. It has been found that the morphology of the films made from these latices influenced the modulus in the rubbery region of these films. The heterogeneous latices were used as binders in porous structures based on micron-sized kaolin particles. Such structures are typically employed as paper coatings. Polyester substrates were coated with aqueous suspensions containing the kaolin particles and the heterogeneous latex. The coatings were dried at room temperature, which corresponds to the rubbery region of the latex films. It was found that a higher modulus (which is determined here by the morphology of the latex film) in the rubbery region of the films was associated with coating layers with higher porosity, greater light scattering ability, and higher coating gloss. This is interpreted as being the result of a retarded shrinkage of the coating layers during the drying of these structures due to the increase in modulus of the latex films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 661–670, 1997     

Effect of vinylidene chloride content on film-formation property of vinylidene chloride-methyl acrylate copolymer latex

Minimum film-formation temperature (MFFT) of vinylidene chloride (VDC)-methyl acrylate (MA) copolymer latexes prepared by batch emulsion polymerization with various compositions from 20 to 97 wt % of VDC were measured. For latexes with VDC content below 90 wt %, MFFT was similar to polymer T_g. As VDC content increased beyond 90 wt %, the MFFT curve plotted against VDC content rose sharply, in contrast with the T_g curve that descended smoothly. Measurements of infrared absorption of latexes in the dispersed state, and X-ray diffraction and infrared absorption of lyophilized polymers were conducted on 40 : 60, 80 : 20, and 95 : 5 VDC-MA specimens. These observations indicated that only 95 : 5 VDC-MA specimens were highly crystalline. It was therefore believed that film-formation property of latex with high VDC content was significantly affected by polymer crystallinity of particles in the dispersed state. Morphology and oxygen gas transmission rate of heat-treated and non-heat-treated coatings of 95 : 5 VDC-MA latex were investigated. Heat treatment of coatings beyond the temperature at which crystalline polymer began to melt induced effective particle coalescence, resulting in reduced oxygen gas transmission rate. This supported our belief that film-formation property of VDC-MA latex with high VDC content was significantly affected by polymer crystallinity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 565–572, 1998     

Plasticizer diffusion as the rate-determining step in dry blending of poly(vinyl chloride)

Differential thermal analysis has been used to examine the process of dry blending of plasticizer and PVC. The rate of transformation of the glass transition from that of the polymer initially in the cold mix to the glass transition of the blend (blend T_g) has been examined at various temperatures from room temperature to above the polymer T_g. The dependence on temperature of this rate of transformation of the observed T_g is similar to the temperature dependence of the diffusion of plasticizer into PVC. It is concluded that diffusion of plasticizer into polymer particles is the rate-determining step in the dry blending of PVC. It also appears that a single mechanism of diffusion is involved both below and above the glass transition of the polymer.     

Preparation and structure control of hollow polymer particles: Influence of seeded emulsion polymerization and alkalization treatment process

Hollow polymer latex particles containing a hydrophilic core were prepared by seeded emulsion polymerization with MAA/BA/MMA/St as comonomers, followed by stepwise alkalization treatment with ammonia. The size and morphology of composite latex particles was determined by TEM. The effects of the seeded emulsion polymerization conditions and alkalization treatment on the size and hollow structure of latex were investigated. The results showed that the optimum content of crosslinking agent in the shell polymers was about 0.5–1.0 wt %, emulsifier was about 0.8–1.1 wt %, and the core/shell weight ratio was 1/7. To obtain uniform hollow latex particles with large size, the starved feeding technique should be adopted in seeded emulsion polymerization, and the neutralization temperature should equal to the T_g of the shell polymer. Then, the obtained polymer particles under this condition had an excellent hollow structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure–property behavior of gamma‐irradiated poly(styrene) and poly(methyl methacrylate) miscible blends

Polymer blends based on various ratios of polystyrene (PS) and polymethyl methacrylate (PMMA) were exposed to different doses of gamma radiation up to 25 Mrad. The structure–property behavior of the polymer blends before and after they had been irradiated was investigated by DSC, TGA, and FTIR spectroscopy. The DSC scans of the glass transition temperature (T_g) of the different polymer blends showed that the T_g was greatly decreased by increasing the ratio of the PMMA component in the polymer blends. Moreover, the T_g of PS/PMMA blends was found to decrease with increasing irradiation dose. The depression in T_g was noticeable in the case of blends rich in PMMA component. The TGA thermograms showed that the thermal stability of the unirradiated polymer blends decreases with increasing the ratios of PMMA component. Also, it was found that the presence of PS polymer in the blends affords protection against gamma radiation degradation and improves their thermal stability. However, exposing the polymer blends to high doses of gamma radiation caused oxidative degradation to PMMA components and decreased the thermal stability. The investigation of the kinetic parameters of the thermal decomposition reaction confirm the results of thermal stability. The FTIR analysis of the gamma‐irradiated polymer blend films gives further support to the TGA data. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 509–520, 1999     

Preparation and characterization of stable and high solid content St/BA emulsifier-free latexes in the presence of AMPS

Stable and high solid content (about 50 wt%) St/BA emulsifier-free latexes were successfully synthesized using emulsifier-free emulsion polymerization with the addition of a small amount of reactive emulsifier AMPS. Properties of the latexes, such as the average particle diameter and its distribution, the morphology of latex particles, and stability were investigated. Physical properties of the latex films, i.e., glass transition temperature (T _g), water resistance, and solvent resistance were investigated as well. The size of latex particles is 400–600 nm in diameter, which is larger than that prepared by conventional emulsion polymerization. And the particle size distribution is narrow and uniform. It was found that the diameter of the latex particles decreases with the increasing content of the initiator KPS and the reactive emulsifier AMPS. Compared with the film prepared by conventional emulsion polymerization, water resistant and solvent resistant of the films prepared by emulsifier-free emulsion polymerization are improved greatly.     

Miscibility evolution of polycarbonate/polystyrene blends during compounding

The miscibility evolution of polycarbonate/polystyrene (PC/PS) blends during the compounding process in three blending methods of industrial relevance, namely melt blending, remelt blending in a twin‐screw extruder and third melt blending in an injection molding machine, was investigated by measuring their glass transition temperatures (T_g) and their specific heat increment (ΔC_p). Differential scanning calorimetry (DSC) was used to examine nine blend compositions. Shifts in glass transition temperature (T_g) of the two phases in melt‐mixed PC/PS blends suggest partial miscibility of one polymer in the other. The observed solubility strongly depends on blend composition and blending method. The T_g measurements showed maximum mutual solubility around 50/50 composition. The miscibility of PC/PS blended after the third stage (melt injection molding) was higher than that after the first stages (melt extrusion) and the second stages (remelt extrusion).     

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006     

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     

The effect of solid content on latex coalescence and film formation: Steady-state energy transfer study with fluorescence labeled polymers

The steady-state fluorescence technique was used to examine the healing and interdiffusion of polymer molecules as a function of solid content during annealing of latex films above the glass transition (T_g). Films were prepared from a mixture of naphthalene (N)- and pyrene (P)-labeled poly(methy methacrylate) (PMMA) latex particles. Above T_g, interdiffusion of polymer chains was observed by detecting the steady-state energy transfer from excited naphthalene to pyrene molecules. Various latex films with different latex content were used to measure the critical occupation percent for the reliable steady-state fluorescence measurements. Diffusion activation energies in these latex films were measured and found to be around 30 kcal/mol, which was attributed to the backbone motion of PMMA chains. © 1996 John Wiley & Sons, Inc.     

How the infrared radiation affects the film formation process from latexes?

In this study, the effect of the infrared radiative heating (IRH) was investigated on the film formation from composites of polystyrene (PS) latex particles and poly vinyl alcohol (PVA). The films were prepared as a pure PS and a mixture of PS and PVA particles at equal compositions at room temperature and they were annealed at elevated temperatures above the glass transition temperature (T_g) of PS for 10 min by using IRH technique. Identical experiments were performed by using standard convectional heating technique in oven as comparison. It was shown that the activation energy for the film formation from PS latex particles decreased considerably in IRH annealing technique. Photon transmission (PT) and steady state fluorescence (SSF) techniques were used to monitor the film formation process at each sintering step. Minimum film formation temperature, T_o, and healing temperature, T_h, were determined by the data obtained from the SSF and the PT measurements for each heating processes. The film formation was modeled as a void closure and as an interdiffusion stage below and above T_h, respectively. Scanning electron microscopy (SEM) was used to examine the variation in morphological structure of annealed composite films. It was observed that IRH heating causes more homogenous and more flat film surface than films annealed in the oven. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43289.     

Dynamic mechanical properties of UV-curable polyurethane acrylate with various reactive diluents

UV-curable polyurethane acrylate (PUA) based on polycaprolactone and m-tetramethylxylene diisocyanate were considered with different acrylate monomers as reactive diluents: ethylhexylacrylate, hexanediol diacrylate, and isobornyl acrylate. The effect of the chemical structure and functionality of the reactive diluent (33 wt %) on their thermal and mechanical properties were investigated. The synthetized PUA networks are homogeneous from a thermodynamical point of view. The initial glass transition temperature (T_g) and the functionality of the reactive diluent do not affect the onset value of the glass transition temperature of the network. Nevertheless, the main mechanical relaxation, denoted α, associated with the glass transition temperature becomes broader as the T_g of the homopolymer of the considered reactive diluent becomes higher than the T_g of the PU soft segments. The increase of the amount of the diacrylate monomer leads to an increase in the equilibrium and storage moduli in the rubbery state and to a decrease in the amplitude of the α relaxation. © 1996 John Wiley & Sons, Inc.     

Influence of seed polymer molecular weight on polymerization kinetics and particle morphology of structured styrene–butadiene latexes

Heterogeneous film‐forming latexes were prepared using two‐stage, seeded emulsion polymerization. The polymerization was performed in a calorimetric reactor with a control unit that monitored the reaction rate and controlled the charging rate of the monomers. Three types of styrene seed latexes were prepared at 70°C. The first was an unmodified polystyrene (PS) latex. The second had the molecular weight lowered by the use of carbon tetrachloride (CCl₄) as a chain‐transfer agent, added at the start of the polymerization. For the third one, divinylbenzene (DVB) was used as a comonomer. DVB was added under starved conditions near the end of the polymerization to achieve crosslinked particle shells and to introduce double bonds as possible grafting sites. The second polymerization step was performed at 80°C as a batch operation in a 200‐mL calorimeter reactor. The second‐stage polymer was poly(styrene‐co‐butadiene‐co‐methacrylic acid) (S/B/MAA). A fixed S/B ratio was used together with varying small amounts of MAA. Particle morphology and particle‐size distributions were examined after the second stage using TEM after staining with osmium tetroxide. The particle morphology was found to depend on both the seed composition and the amount of MAA used in the second stage. Molecular weight and crosslinking of the DVB‐containing seed influenced the internal particle viscosity, which gave differences in the polymerization rate and the particle morphology. Crosslinking of the second‐stage polymer decreased the monomer concentration in the particles, which could be detected as a change in the slope the pressure/conversion curve. This phenomenon was used to indicate the critical conversion for crosslinking of the second‐stage polymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 297–311, 2000     

Effect of acrylic acid on water-whitening resistance of polyacrylate latex films and its mechanism

Two groups of polyacrylate latexes with higher (21 ~ 35 °C) or lower (−33 ~ −43 °C) glass transition temperatures (T_g) were prepared by adjusting the monomer ratio of butyl acrylate (BA) and styrene (St), and the effect of acrylic acid (AA) on water-whitening resistance of these latex films was investigated. It was found that the water-whitening resistance of the two groups of latex films was different. With the increase of AA content, the water whitening resistance of the latex films with higher T_g continued to improve, while that of the latex films with lower T_g increased first and then decreased. A series of characterizations, such as light transmittance, water whitening, water absorption, static water contact angle, surface morphology, and optical microscope test of the latex film, and so forth, showed that the reason for this difference was that under higher AA content (≥5%), compared with the polyacrylate latex films with lower T_g, the latex films with higher T_g could reach the saturation state of water absorption quickly, and water in these latex films exhibited continuous and large area distribution, rather than formation of many so-called micro- or nano-scale water sacs that can scatter light as found in the latex films with lower T_g.     

Nonequilibrium particle morphology development in seeded emulsion polymerization. II. Influence of seed polymer Tg

Most structured latex particles are formed in the nonequilibrium state as a result of the reaction kinetics proceeding faster than the phase separation kinetics. Of the many factors controlling such morphologies, the polarity and glass transition temperature (T_g) of the seed polymer are important. In order to study the direct effect of the seed polymer T_g on morphology, we produced a series of poly(methyl methacrylate)/poly(methyl acrylate) seed copolymers having glass points between 52 and 98°C, and particle sizes between 320 and 390 nm. We then used styrene as a second‐stage monomer reacting in both the batch and semibatch process modes, and utilized reaction temperatures (T_r) between 50 and 70°C. Monomer feed rates were varied between flooded and starve‐fed conditions. The equilibrium morphology for these composite particles is an inverted core–shell structure, but all morphologies obtained in our experiments were nonequilibrium. Under monomer starved conditions only core–shell structures were formed when (T_r?T_g) < 0, but significant penetration of the polystyrene into the acrylic core occurs when (T_r?T_g) > 15°C. These results are reasonably well predicted using the “fractional penetration” model developed earlier. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 905–915, 2003     

Thermal and dynamic mechanical behavior of poly(vinyl chloride)/wood flour composites

Thermal and dynamic mechanical behaviors of wood plastic composites made of poly vinyl chloride (PVC) and surface treated, untreated wood flour were characterized by using differential scanning calorimetry and dynamic mechanical analysis. Glass transition temperature (T_g) of PVC was slightly increased by the addition of wood flour and by wood flour surface treatments. Heat capacity differences (ΔC_p) of composites before and after glass transition were markedly reduced. PVC/wood composites exhibited smaller tan δ peaks than PVC alone, suggesting that less energy was dissipated for coordinated movements and disentanglements of PVC polymer chains in the composites. The rubbery plateaus of storage modulus (E′) curves almost disappeared for PVC/wood composites in contrast to a well defined plateau range for pure PVC. It is proposed that wood flour particles act as “physical crosslinking points” or “pinning centers” inside the PVC matrix, resulting in the absence of the rubbery plateau and high E′ above T_g. The mobility of PVC chain segments were further retarded by the presence of surface modified wood flour. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008