Preparation of poly(styrene‐co‐isobornyl methacrylate) beads having controlled glass transition temperature by suspension polymerization

The styrene (St) and isobornyl methacrylate (IBMA) random copolymer beads with controlled glass transition temperature (T_g), in the range of 105–158°C, were successfully prepared by suspension polymerization. The influence of the ratios of IBMA in monomer feeds on the copolymerization yields, the molecular weights and molecular weight distributions of the produced copolymers, the copolymer compositions and the T_gs of these copolymers was investigated systematically. The monomer reactivity ratios were r₁ (St) = 0.57 and r₂ (IBMA) = 0.20 with benzyl peroxide as initiator at 90°C, respectively. As the mass fraction of IBMA in monomer feeds was about 40 wt %, it was observed that the monomer conversion could be up to 90 wt %. The fractions of IBMA unit in copolymers were in the range of 35–40 wt % and T_gs of the corresponding copolymers were in the range of 119.6–128°C while the monomer conversion increased from 0 to greater than 90 wt %. In addition, the effects of other factors, such as the dispersants, polymerization time and the initiator concentration on the copolymerization were also discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Substituent effect on the glass transition temperature of polyoxetanes

Summary The effect of the substituents on the glass transition temperature is analyzed for a series of polyoxetanes, with alkyl substituents in position 3. The results show a regular increase of that parameter with the Van der Waals volume of the linear substituents, although a departure from this trend seems to be observed for poly(3,3-dibutyloxetane), presumably because of the effect of internal plasticization. On the other hand, the increase of T_g for poly(3-terbutyloxetane) is specially high, as usual for branched substituents. The behaviour of the glass transition temperature along the series has been analyzed in terms of interand intramolecular interactions, concluding that the latter factor is the dominant contribution in determining the T_g in this group of polymers.     

The effect of synthesis condition on physical properties of epoxy‐containing microcapsules

The physical properties of microcapsules are largely influenced by the synthesis conditions such as weight ratio of core/shell material, agitation rate, reaction time, and different emulsifier. Different synthesis condition would lead to different property. It is an important issue for application in composites that require self‐healing microcapsules possessing rough surface morphology, less adhesion, less core material permeability, appropriate diameter and core content, and adequate shell thickness. The properties of microcapsules influenced by the synthesis conditions were investigated systematically in this article. According to orthographic factorial design, the most influencing factor on microcapsule's yield, core material, average shell thickness and average diameter, are concluded, respectively. The synthesis parameters when the epoxy‐containing microcapsules exhibit the optimum properties are concluded: 1.4 : 1 for the weight ratio of core/shell material, 250 rpm for the agitation rate, 3 h for the reaction time and 1.5% content for the emulsifier DBS. The chemical structure of resultant microcapsules is confirmed by FT‐IR, and core material of microcapsule exhibits reactivity through DSC measurement. Subsequently, the microcapsules are characterized by SEM, OM, and contact angle experiment so as to provide parameters of microcapsule's physical properties for making binary self‐healing materials. As a result, the resultant microcapsules are suitable for fabricating self‐healing materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The effect of disperse dyes on the glass transition temperature of polymers

The lowering of the glass transition temperature (T_g) of a polymer produced by the incorporating various concentrations of azo disperse dyes has been investigated, and the effects of the structure and concentrations of the dyes were examined. The T_g values were lowered with increasing dye concentrations in the polymer, and the lowering of T_g produced by the dyes was influenced not only by the molecular structure of the dyes but also the dye-polymer interactions.     

The effect of confinement in nanoporous polymers on the glass transition temperature

The glass transition temperature (T_g) of nanoporous polyetherimide (PEI) and PEI thin films was investigated. The T_g decreased from its bulk value in both of these confined systems. Monte Carlo simulations were performed to calculate the nearest neighbor pore-to-pore distances in the nanoporous PEI. A quantitative analogy between the nanoporous PEI and PEI thin films is proposed through an equivalence of nearest neighbor pore-to-pore distances and thin film thickness. The effect of confinement is believed to be due to the interface regions, which possess higher chain mobility than the bulk. When these high mobility interface regions are sufficiently close together, the excess mobility at the interface region affects the dynamics of the system by restraining percolation of the slow domains resulting in the observed decrease in T_g.     

Absorption of trioctyl trimellitate into mass‐polymerization and suspension‐polymerization poly(vinyl chloride)

Poly(vinyl chloride) (PVC) slush powder has been widely used; we prepared it by dry blending. We found that the absorption of plasticizer by the PVC resins was the most important factor in the dry‐blending process and, further, that different types of PVC resin had different absorption rates. This results of this study provide new information about the relationship of absorption to PVC and other parameters. Haake rheomix testing and the quantity of plasticizers absorbed by the PVC resins were used to characterize the absorption process. Suspension‐polymerization poly(vinyl chloride) (SPVC) and mass‐polymerization poly(vinyl chloride) (MPVC) in different sizes were used for the test. The results showed that the MPVC absorbed the plasticizer more quickly than SPVC, especially at a higher temperature. However, for the same PVC resin type, the absorbing speeds were nearly independent of particle size. The studies that used a scanning electric microscope and specific surface area revealed that the morphology of the two types of particles was different. The surfaces of the individual particles of SPVC were smoother than those of MPVC. There was a “skin” covering the SPVC particles, whereas with the MPVC particles, the primary polymer was exposed directly on the surface. This difference in morphology was shown to be a significant factor in the different rates of absorption of the plasticizers for the different PVC resins. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2369–2374, 2004     

Modification of porous suspension‐PVC particles by stabilizer‐free aqueous dispersion polymerization of absorbed monomers

The modification of porous PVC particles by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within the PVC particles is presented. The modifying crosslinked polymers are polystyrene (PS) crosslinked with DVB (divinyl benzene), polymethyl methacrylate (PMMA) crosslinked with ethylene glycol dimethacrylate (EGDMA), and styrene‐MMA copolymer crosslinked with DVB. The modified PVC particles characterization includes polymerization yield, non‐extractables, ¹³C solid‐state CPMAS NMR, porosity measurements and also morphology and dynamic mechanical behavior (DMTA). The levels of nonextractable fractions found and ¹³C solid‐state CPMAS NMR results are indicative of low chemical interaction in the semi‐IPN PVC particles. Particle porosity levels and SEM observations indicate that styrene and MMA mainly polymerize within the PVC particles' bulk and just small amounts in the pores. MMA polymerization in the PVC pores is as crusts covering the PVC pore surfaces, whereas styrene polymerization in the PVC pores is by filling the pores. Dynamic mechanical studies show that tanδ and the storage modulus curves are influenced by the incorporation of PS and XPS but not by the incorporation of PMMA and XPMMA.     

Curing of epoxy systems at sub‐glass transition temperature

Three epoxy‐amine thermoset systems were cured at a low ambient temperature. Evolution of the reaction kinetics and molecular structure during cure at the sub‐glass transition temperature was followed by DSC and chemorheology experiments. The effect of vitrification and the reaction exotherm on curing and final mechanical properties of the epoxy thermosets was determined. Thermomechanical properties of the low‐temperature cured systems depend on the reaction kinetics and volume of the reaction mixture. Curing of the fast‐reacting system in a large volume (12‐mm thick layer) resulted in the material with T_g exceeding the cure temperature by 70–80°C because of an exothermal temperature rise. However, the reaction in a too large volume (50‐mm layer) led to thermal degradation of the network. In contrast, thin layers (1.5 mm) were severely undercured. Well‐cured epoxy thermosets could be prepared at sub‐T_g temperatures by optimizing reaction conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3669–3676, 2006     

Surface modification of jute yarn by photografting of low‐glass transition temperature monomers

Jute yarns were grafted with three types of vinyl monomers of different functionalities such as methyl acrylate (MA), ethyl acrylate (EA), and 2‐hydroxyethyl acrylate (HEA) with ultraviolet radiation. The graft copolymerization reaction between the cellulose of the jute fibers and the monomer and the chemical environment of the treated fibers were confirmed by Fourier transform infrared spectroscopy. The reduction of OH groups and increment of >C?O groups in treated jute yarns were observed. DSC studies showed that the treated jute fibers were more thermally stable compared to the untreated one. The surface topography of the yarns was analyzed by an environmental scanning electron microscope. Different parameters, such as concentration of monomers and irradiation time, were optimized with the extent of mechanical properties such as tensile strength and elongation at break of the jute yarn. MA, EA, and HEA produced enhanced tensile strengths of 87, 78, and 85%, respectively. The monomers MA, EA, and HEA showed improved elongations at break of 118, 91, and 76%, respectively. The water uptake of treated and untreated jute yarns were studied. The maximum water uptake was observed of the grafted sample compared to the untreated jute yarn. The effects of additives such as urea on mechanical properties were also studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 993–1000, 2003     

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     

The effect of molding time and temperature on the modulus and glass transition of phenolics

The effects of molding time and temperature on the dynamic mechanical behavior of a novolak phenolic molding compound were measured using the DuPont Dynamic Mechanical Analyzer. Large differences were found in the modulus-temperature response over the range of curing times (10 to 1800 s.) and temperatures (132 to 218°C) employed. Glass transition temperatures increased well beyond cure temperatures at long cure times. In the asmolded condition, samples cured at lower temperature had higher room temperature modulus than those cured at higher temperatures, and the lower modulus corresponded to lower density. Postbaking by steps up to 232°C increased the glass transition above 280°C, and also served to normalize the modulus differences found in as-molded samples.     

The effect of benzenesulfonamide plasticizers on the glass transition temperature of an amorphous aliphatic polyamide

The plasticizing effect of benzenesulfonamides (BSAs) on an amorphous aliphatic polyamide (AAPA) has been studied using dynamic mechanical analysis of copper‐supported spin‐coated mixtures. It follows that N‐(n‐butyl)BSA (BBSA), an amorphous liquid hydrogen bonding BSA, is fully miscible with AAPA because their mixtures are characterized by a single glass transition (T_g) throughout the compositional range. The T_g–composition dependence, however, is not linear because experimental results suggest a 20 K fall in T_g occurring around 0.65 BBSA units per amide unit, which coincides with the system shifting from a polymer‐like to a liquid‐like glass‐forming material. When considering a crystallizable hydrogen‐bonding plasticizer such as ethylBSA (EBSA), AAPA/EBSA mixtures become fully crystalline at a 1.3 EBSA unit per amide group. Nevertheless, melting point depression together with the single T_g observed throughout the compositional range on quenched (and therefore amorphous) samples confirms the miscibility of AAPA chains with the plasticizer. N,N‐DialkylBSAs, which lack the sulfonamide proton and therefore the possibility of hydrogen bonding with amide groups, quickly phase separate from AAPA, the glass transition of the latter staying mainly unaffected apart from a small (9 K) decrease at 10–15 mol% plasticizer. © 2001 Society of Chemical Industry     

粉末涂料的玻璃化温度

重点讨论了粉末涂料玻璃化温度、玻璃化转变理论,并对玻璃化温度与粉末涂料稳定性、熔融黏度、热应力、分子量、化学结构和聚合物的关系做了全面的阐述。     

The glass transition temperature of star-shaped polystyrenes

The glass transition temperatures of linear and four- and six-branched regular star polystyrenes are measured by penetration, differential scanning calorimetry, and a density gradient technique. The results of the three methods show that the glass transition temperature depends on the concentration of chain ends in the polymer sample. An attempt is made to assess the influence of the presence of the branch point on the glass transition temperature using a series of four-branched polystyrenes containing varying amounts of isoprene near the branch point. However, any effect of the central branch point on the glass transition temperature is obscured by plastification of polystyrene by polyisoprene.     

碳纳米管对液体石蜡微胶囊性能影响的探究

以液体石蜡为囊芯,三聚氰胺-甲醛树脂作壳材,碳纳米管为改性剂,采用原位聚合法制备碳纳米管/石蜡相变储能微胶囊。研究了碳纳米管对于微胶囊相变储能材料的粒径分布、包覆率、机械强度、密封性的影响。结果表明,随着碳纳米管量增加,囊芯所占比例逐渐减小,包覆率逐渐降低;当添加MNCNTs-OH量为0.0,1.7%,3.3%,6.7%时,破损率分别为22.3%,15.9%,14.7%,17.6%,且比未添加MNCNTs-OH的相变微胶囊重量释放速率慢,说明MNCNTs-OH不仅能够降低胶囊破损率,改善了胶囊壁材的韧性与强度,而且提高相变微胶囊的密封性。     

碳纳米管对液体石蜡微胶囊性能影响的探究

以液体石蜡为囊芯,三聚氰胺-甲醛树脂作壳材,碳纳米管为改性剂,采用原位聚合法制备碳纳米管/石蜡相变储能微胶囊。研究了碳纳米管对于微胶囊相变储能材料的粒径分布、包覆率、机械强度、密封性的影响。结果表明,随着碳纳米管量增加,囊芯所占比例逐渐减小,包覆率逐渐降低;当添加MNCNTs-OH量为0.0,1.7%,3.3%,6.7%时,破损率分别为22.3%,15.9%,14.7%,17.6%,且比未添加MNCNTs-OH的相变微胶囊重量释放速率慢,说明MNCNTs-OH不仅能够降低胶囊破损率,改善了胶囊壁材的韧性与强度,而且提高相变微胶囊的密封性。     

Three‐dimensional thermorheological behavior of isotactic polypropylene across glass transition temperature

The aim of this work was to determine the three‐dimensional thermorheological behavior of isotactic polypropylene (i‐PP) in the region of its glass transition temperature (T_g) by a master curve. The i‐PP is a widespread polymer with a T_g ～ 0°C. Dynamic mechanical analysis (DMA) at varying frequencies and temperatures and bulk tests at varying temperatures and times are carried out to obtain the relaxation spectra. Traditionally, the combination of time and temperature is done for thermorheological simple material by the creation of a master curve based on the Arrhenius or William–Landel–Ferry (WLF) equation. This investigation shows that these equations do not fit the behavior across the glass transition of i‐PP. Instead, a new arc tangent function is derived. Additionally, it can be shown that the shifting factors differ from shear to bulk load. Therefore, the mode of mechanical stress seems to have an influence on the thermorheological behavior. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 877–880, 2004     

The glass transition temperature of filled polymers and its effect on their physical properties

The glass transition temperature, dynamic shear moduli, and bulk viscosities of Phenoxy PKHH (a thermoplastic polymer made from bisphenol-A and epichlorohydrin) filled with glass beads and Attapulgite clay were investigated. The glass temperature of the polymer increased with increasing filler concentration and with increasing specific surface area of the filler. The data were interpreted by assuming that interactions between filler particles and the polymer matrix reduce molecular mobility and flexibility of the polymer chains in the vicinity of the interfaces. From the measured moduli and the viscosities of the filled and unfilled materials, the modulus reinforcement ratio in the glassy state and the relative viscosity in the viscous state were obtained as functions of the filler type and concentration. The relative modulus for the glass bead composite system follows the Kerner equation, while the clay-filled systems exhibit slightly greater reinforcement. The relative viscosities are strongly temperature dependent and do not follow conventional viscosity predictions for suspensions. It is suggested that the filler has a twofold effect on the viscosity of the composite materials; one is due to its mechanical presence and the other is due to modifications of part of the polymer matrix caused by interaction. Using the WLF equation to express all modifications of the matrix, one can isolate a purely mechanical contribution to the viscosity reinforcement. This mechanical part is approximately bounded by the theoretical predictions of Kerner,³² Mooney, ³⁶ and Brodnyan,⁴¹ for suspension viscosities.     

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer

Effect of glass transition temperature and saturation temperature on the solid‐state microcellular foaming of cyclic olefin copolymer (COC)—including CO₂ solubility, diffusivity, cell nucleation, and foam morphology—were investigated in this article. COCs of low T_g (78°C) and high T_g (158°C) were studied. Solubilities are 20–50% higher in high T_g COC than in the low T_g COC across the saturation temperature range. Diffusivities are about 15% higher on average in high T_g COC for temperatures up to 50°C. A much faster increase of diffusivity beyond 50°C is observed in low T_g COC due to it being in the rubbery state. Under similar gas concentration, high T_g COC starts foaming at a higher temperature. And the foam density decreases faster in low T_g COC with foaming temperature. Also, high T_g COC foams show about two orders of magnitude higher cell nucleation density than the low T_g COC foams. The effect of saturation temperature on microcellular foaming can be viewed as the effect of CO₂ concentration. Nucleation density increases and cell size decreases exponentially with increasing CO₂ concentration. Uniform ultramicrocellular structure with an average cell size of 380 nm was created in high‐T_g COC. A novel hierarchical structure composed of microcells (2.5 μm) and nanocells (cell size 80 nm) on the cell wall was discovered in the very low‐density high‐T_g COC foams. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42226.     

The glass transition temperature of an epoxy resin and the effect of absorbed water

Summary The glass transition temperature, T_g, of a diamino-dipenyl methane (DDM, II) cured diglycidyl ether of bispenol-A epoxy resin (I, n=0) has been determined by proton NMR line width studies to be 410°K. In the presence of 2.5±0.1 w/o absorbed water T_g is reduced to 378°K. Such a large reduction of Tg by such a small amount of water requires specific interactions. It is postulated that segmental motion is increased as a result of the disruption of hydroxyl group hydrogen bonds by the absorbed water molecules.