Effects of reactive low‐profile additives on the properties of cured unsaturated polyester resins. II. Glass‐transition temperature and mechanical properties

The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)‐block‐poly(methyl methacrylate) (PVAc‐b‐PMMA) as low‐profile additives (LPAs) on the glass‐transition temperature and mechanical properties of low‐shrink unsaturated polyester resin (UP) were investigated by an integrated approach of determining static phase characteristics, reaction kinetics, cured sample morphology, and property measurements. The factors that, according to Takayanagi mechanical models, control the glass‐transition temperature in each phase region of the cured samples, as identified by both the thermally stimulated currents method and dynamic mechanical analysis, and the mechanical properties are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 867–878, 2006     

Effects of poly(vinyl acetate) and poly(vinyl chloride‐ co‐vinyl acetate) low‐profile additives on properties of cured unsaturated polyester resins. I. Volume shrinkage characteristics and internal pigmentability

Three series of self‐synthesized poly(vinyl acetate)‐based low‐profile additives (LPAs) with different chemical structures and molecular weights, including poly(vinyl acetate), poly(vinyl chloride‐co‐vinyl acetate), and poly(vinyl chloride‐co‐vinyl acetate‐co‐maleic anhydride), were studied. Their effects on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during cure were investigated. The experimental results were examined with an integrated approach involving measurements of the static phase characteristics of the ternary styrene/UP/LPA system, the reaction kinetics, the cured sample morphology, and microvoid formation by using differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. Based on the Takayanagi mechanical model, factors leading to both good volume shrinkage control and acceptable internal pigmentability for the molded parts were explored. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3336–3346, 2003     

Effects of chemical structure of polyurethane‐based low‐profile additives on the miscibility,curing behavior,volume shrinkage,glass transition temperatures,and mechanical properties for styrene/unsaturated polyester/low‐profile additive ternary systems. I: Miscibility,curing behavior,and volume shrinkage

The effects of chemical structure and molecular weight of three series of thermoplastic polyurethane‐based (PU) low‐profile additives (LPA) on the miscibility of styrene (ST)/unsaturated polyester (UP) resin/LPA ternary systems prior to reaction were investigated by using the Flory‐Huggins theory and group contribution methods. The reaction kinetics during the cure at 110°C and the cured sample morphology were also studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), respectively. The phase‐separation characteristics of ST/UP/LPA systems during the cure, as revealed by the cured‐sample morphology, and the DSC reaction‐rate profile, could be generally predicted by the calculated upper critical solution temperature for the uncured ST/UP/LPA systems. Finally, based on the measurements for volume change and microvoid formation, volume shrinkage characteristics for the cured ST/UP/LPA systems have been explored. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 543–557, 2000     

Effects of reactive low‐profile additives on the properties of cured unsaturated polyester resins. I. Volume shrinkage and internal pigmentability

The effects of reactive poly(methyl methacrylate) (PMMA) and poly(vinyl acetate)‐block‐PMMA as low‐profile additives (LPAs) on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing at 110°C were investigated. These reactive LPAs, which contained peroxide linkages in their backbones, were synthesized by suspension polymerization with polymeric peroxides as initiators. Depending on the LPA composition and molecular weight, the reactive LPAs led to a considerable volume reduction or even to a volume expansion after the curing of styrene (ST)/UP/LPA ternary systems; this was attributed mainly to the expansion effects of the LPAs on the ST‐crosslinked polyester microgel structures caused by the reduction in the cyclization reaction of the UP resin during curing as well as to the repulsive forces between the chain segments of UP and LPAs within the microgel structures. The experimental results were explained by an integrated approach of measurements for the static phase characteristics of the ST/UP/LPA system, reaction kinetics, cured sample morphology, and microvoid formation with differential scanning calorimetry, scanning electron microscopy, optical microscopy, and image analysis. With the aid of the Takayanagi mechanical model, the factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts were also explored. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 264–275, 2005     

Effects of chemical structure of polyurethane‐based low‐profile additives on the miscibility,curing behavior,volume shrinkage,glass transition temperatures,and mechanical properties for styrene/unsaturated polyester/low‐profile additive ternary systems. II: Glass transition temperatures and mechanical properties

The effects of three series of thermoplastic polyurethane‐based (PU) low‐profile additives (LPA) with different chemical structures and molecular weights on the glass transition temperatures and mechanical properties for thermoset polymer blends made from styrene (ST), unsaturated polyester (UP), and LPA have been investigated by an integrated approach of static phase characteristics‐cured sample morphology‐reaction conversion‐property measurements. The three series of PU used were made from 2,4‐tolylene di‐isocyanate (2,4‐TDI) and varied diols, namely polycaprolactone diol (PCL), poly(diethylene adipate) diol (PDEA), and poly(propylene glycol) diol (PPG), respectively, while the two UP resins employed were synthesized from maleic anhydride (MA) and 1,2‐propylene glycol (PG) with and without modification by phthalic anhydride (PA). Based on the Takayanagi mechanical models, factors that control the glass transition temperature in each phase region of cured samples, as identified by the method of thermally stimulated currents (TSC), and mechanical properties will be discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 558–568, 2000     

Effects of poly(vinyl acetate) and poly(vinyl chloride‐co‐vinyl acetate) low‐profile additives on properties of cured unsaturated polyester resins. II. glass‐transition temperatures and mechanical properties

Three series of self‐synthesized poly(vinyl acetate)‐based low‐profile additives (LPAs), including poly(vinyl acetate), poly(vinyl chloride‐co‐vinyl acetate), and poly(vinyl chloride‐co‐vinyl acetate‐co‐maleic anhydride), with different chemical structures and molecular weights were studied. Their effects on the glass‐transition temperatures and mechanical properties for thermoset polymer blends made from styrene, unsaturated polyester, and LPAs were investigated by an integrated approach of the static phase characteristics, cured sample morphology, reaction kinetics, and property measurements. Based on Takayanagi mechanical models, the factors that control the glass‐transition temperature in each phase region of the cured samples and the mechanical properties are discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3347–3357, 2003     

Effect of the addition of depolymerised ethylene vinyl acetate on the mechanical,thermal, chemical and shrinkage properties of cured unsaturated polyester resins

Unsaturated polyester resins (UPRs) are versatile compounds. However, their major drawback is the high shrinkage exhibited on curing. An attempt was made to reduce the shrinkage of UPRs without affecting other properties. In the present study a commonly used iso‐reactive UPR was modified by the addition of ethylene–vinyl acetate (EVA; subjected to controlled depolymerisation to obtain samples of various molecular weights), and was cured at room temperature. The peak exotherm temperature and gel time were both observed to decrease with an increase in EVA content. The composition incorporating 0.5% of depolymerised EVA1 (highest degree of branching) showed maximum improvement in tensile and flexural properties with the heat deflection temperature and impact properties remaining almost unaffected. A uniform dispersion for the UPR containing 0.5% of EVA1 was observed. Addition of EVA reduced the percentage shrinkage in the modified matrix. Incorporation of depolymerised EVA can be an attractive option for the reduction of shrinkage in UPRs. The advantage of using depolymerised EVA is that generated waste EVA can be depolymerised and reused for this application making it cost effective. Copyright © 2010 Society of Chemical Industry     

Effects of poly(methyl methacrylate)‐based low‐profile additives on the properties of cured unsaturated polyester resins. II. Volume shrinkage characteristics and internal pigmentability

The effects of three series of self‐synthesized poly(methyl methacrylate) (PMMA)‐based low‐profile additives (LPAs), including PMMA, poly(methyl methacrylate‐co‐butyl acrylate), and poly(methyl methacrylate‐co‐butyl acrylate‐co‐maleic anhydride) with different chemical structures and MWs on the volume shrinkage characteristics and internal pigmentability for low‐shrink unsaturated polyester (UP) resins during curing were investigated by an integrated approach of static phase characteristics of the ternary styrene (ST)/UP/LPA system, reaction kinetics, cured‐sample morphology, microvoid formation, and property measurements. The relative volume fraction of microvoids generated during the cure was controlled by the stiffness of the UP resin used, the compatibility of the uncured ST/UP/LPA systems, and the glass‐transition temperature of the LPAs used. On the basis of the Takayanagi mechanical model, the LPA mechanism on volume shrinkage control, which accounted for phase separation and microvoid formation, and factors leading to both a good volume shrinkage control and acceptable internal pigmentability for the molded parts are discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3388–3397, 2004     

Effect of 2,2‐dimethyl malonate on the volume shrinkage control of the CaCO3/unsaturated polyester resin composites

Shrinkage is critical to the unsaturated polyester resin (UPR) composite materials. Shrinkage influences the surface appearance, thus leading to warpage, internal cracks, and depression on the surface of the composite materials' products. Some studies and technologies have been conducted to controll the shrinkage. In this study, we presented 2,2‐dimethyl malonate as an anti‐shrinkage agent, which was different from the previous thermoplastic macromolecular agents. The shrinkage level of the CaCO₃/UPR matrix dropped to zero with 12% 2,2‐dimethyl malonate by mass of UPR. The bending strength of CaCO₃/UPR matrix with 2,2‐dimethyl malonate was also higher than that with the same adding amount of commercial thermoplastic agents at the low‐shrinkage level (below 0.25%) and the micro‐shrinkage level (below 0.08%). A reaction including two stages was proposed on the supporting of DSC and FTIR investigations. From the analysis results, we deduced that the first stage of the reaction was the esterification between 2,2‐dimethyl malonate and UPR, which did not occur in the UPR containing general thermoplastic anti‐shrinkage agent, and the second stage was restraining the cross polymerization of UPR, same to the reaction processes of general macromolecular anti‐shrinkage agents. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microgelation of unsaturated polyester resins in the presence of poly(vinyl acetate) by static and dynamic light scattering

The partially cured unsaturated polyester (UPE)/styrene resins with various degrees of conversion lower than gel conversion blended with PVAc and 2‐fluorotoluene solvent were investigated using both static and dynamic light scattering (SLS and DLS). The solvent (i.e., 2‐fluorotoluene) is isorefractive with PVAc; thus, one sees only primary and partially cured UPEs in light‐scattering experiments. DLS was used to follow the variations of primary UPE and UPE microgel particle sizes, and SLS was used to follow the variations of UPE molecular weight, second virial coefficient (A₂), anisosymmetry (ρ_v), and differential index refraction (dn/dC) with degree of UPE conversion and PVAc concentration. The experimental data showed that, at a fixed degree of UPE/styrene conversion, increasing PVAc concentration in the UPE/styrene system caused decreases in dn/dC, A₂, ρ_v, and particle sizes of UPE microgels. These results suggest that mixing PVAc into UPE/styrene resins causes an increase in the compactness of UPE coils and favors intramolecular UPE/styrene cyclization in the early stage of curing. Thus A₂, ρ_v, and particle sizes of microgels decreased with increasing PVAc concentration. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1439–1449, 2001     

Synthesis and reactive features of a terpolymer: Poly(N‐vinyl‐2‐pyrrolidone‐co‐vinyl acetate‐co‐glycidyl methacrylate)

A polyvinyl pyrrolidone terpolymer system is described that can be chemically cross‐linked at moderate, 70–100°C, temperatures. The system has significant potential for development of durable long‐lasting pyrrolidone coatings in a wide range of applications, particularly in water filtration membrane construction where leaching is an unresolved, serious problem. The synthesis of the terpolymer, poly(N‐vinyl‐2‐pyrrolidone‐co‐vinyl acetate‐co‐glycidyl methacrylate), by free radical polymerization is described. The reactive features of this terpolymer are presented in the context of acidic anhydride curing. In a polar aprotic solvent, the terpolymer is reacted with poly(methyl vinyl ether‐co‐maleic acid) and cured thermally. Key aspects of the terpolymer synthesis and the acid anhydride cross‐linking reaction using DSC, rheology, FTIR, and a small molecule model system to study the cross‐linking chemistry are presented. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of free volume fraction,inter/intramolecular energy ratio,and chain segment density on the Gibbs-DiMarzio theory of the glass transition

Based upon computer analysis, the Gibbs-DiMarzio (G-DM) theory is evaluated for the case of (a) constant V₀ and (b) constant r where V₀ is the fractional free volume at T_g and r is the ratio of the hole (E₀) to the flex (ε) energy. For each respective case, results are presented in a reduced variables format that indicate the extent to which r and V₀ vary at the transition temperature as a function of the reciprocal degree of polymerization (P^?1). To further account for chemical differences that exist among polymers, an index (n) is introduced that ultimately incorporates the effective number average of chain atom segments (x?) per P?. Using these reduced variables plots, the effects of V₀, r, and n are compared with the T_g data for four well-documented polymers. Although the theory adequately describes the PMMA, PS, and PVC data, for PαMS the fit is doubtful. The analysis demonstrates that, in order to maintain V₀ within the range of 0.015–0.045, r must remain within approximately 1.0–1.1. Moreover, under conditions of either constant V₀ or r, other more flexible polymers require that $\text{n?10}$.     

Modeling of diffusion‐controlled reactions in free radical solution and bulk polymerization: Model validation by DSC experiments

In this work, a detailed experimental study of diffusion‐controlled reactions in free radical polymerization by using differential scanning calorimetry (DSC) was carried out. The systems studied include the methyl methacrylate bulk polymerization as well as the solution and the bulk polymerization of vinyl acetate at a wide range of experimental conditions including initial initiator concentration, reaction temperature, and type and amount of solvent. The conversion data obtained by DSC was successfully simulated by using a mathematical model based on sound principles such as the free volume theory. The estimated parameters, by fitting predictions of this model to conversion data obtained by DSC were found to be in close agreement with the reported parameters in the literature, thus validating both the experimental and theoretical methods used in this work. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of the compatibilization of linear low‐density polyethylene‐g‐acrylic acid on the morphology and mechanical properties of poly(butylene terephthalate)/linear low‐density polyethylene blends

A poly(butylene terephthalate) (PBT)/linear low‐density polyethylene (LLDPE) alloy was prepared with a reactive extrusion method. For improved compatibility of the blending system, LLDPE grafted with acrylic acid (LLDPE‐g‐AA) by radiation was adopted in place of plain LLDPE. The toughness and extensibility of the PBT/LLDPE‐g‐AA blends, as characterized by the impact strengths and elongations at break, were much improved in comparison with the toughness and extensibility of the PBT/LLDPE blends at the same compositions. However, there was not much difference in their tensile (or flexural) strengths and moduli. Scanning electron microscopy photographs showed that the domains of PBT/LLDPE‐g‐AA were much smaller and their dispersions were more homogeneous than the domains and dispersions of the PBT/LLDPE blends. Compared with the related values of the PBT/LLDPE blends, the contents and melting temperatures of the usual spherulites of PBT in PBT/LLDPE‐g‐AA decreased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1059–1066, 2002; DOI 10.1002/app.10399     

Study of heat shrinkability of crosslinked low‐density polyethylene/poly(ethylene vinyl acetate) blends

In this study, the heat‐shrinkage property in polymer was induced by first compounding low‐density polyethylene/poly(ethylene vinyl acetate) (LDPE/EVA) blends with various amounts of peroxide in a twin‐screw extruder at about 130°C. The resulting granules were molded to shape and chemically crosslinked by compression molding. A process of heating–stretching–cooling was then performed on the samples while on a tensile machine. Shrinkability and effective parameters were also investigated using thermal mechanical analysis. The results showed that the gel fraction was higher for the sample of higher EVA content with the same amount of dicumyl peroxide (DCP). A decrease in the melting point and heat of fusion (ΔH_f), as determined from DSC, was observed with an increase in the DCP content. Studies on the heat shrinkability of the samples showed that samples stretched above the melting point had a higher shrinkage temperature than those stretched around the crystal transition temperature. The results showed that by increasing the peroxide content, the shrinkage temperature was decreased. These could be attributed to the formation of new spherulites as well as changes in the amount and the size of crystals. Furthermore, in samples elongated at 120°C (above the melting point), the rate of stretching had no effect on the shrinkage temperature. The results showed that the extent of strain had no effect on the temperature of shrinkage, but rather on the ultimate shrinkage value. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1389–1395, 2004     

Rheological and curing behavior of reactive blending. II. Natural rubber‐g‐poly(methyl methacrylate)–cassava starch

Graft copolymers of natural rubber (NR) and methyl methacrylate (MMA) were prepared using cumene hydroperoxide and tetraethylene pentamine as redox initiators via the semibatch emulsion polymerization technique. Various molar percentage ratios of NR/MMA were studied in the grafting reaction (i.e., 95/5, 90/10, 80/20, 70/30, and 60/40). The graft copolymer with a 70/30 molar ratio was selected and used to prepare rubber blends with cassava starch. The starch was used at levels of 0, 20, 40, and 60 phr. Another set of rubber blends was prepared for comparison purposes. The NR‐g‐poly(MMA) (PMMA, 75 phr) was blended with 25 phr of NR air dried sheets (ADS) and a given level of the cassava starch. We found that the Mooney viscosity, shear stress, and shear viscosity increased with an increasing concentration of cassava starch. This may be attributed to the chemical interactions between the polar groups of the NR‐g‐PMMA and the cassava starch. The blends were later compounded using a compounding formulation according to ASTM D 3184‐89. A similar short delay onset of vulcanization (i.e., approximately 1 min) was observed for the whole set of compounds under study. However, different curing characteristics were observed for the blends of NR‐g‐PMMA–cassava starch and NR‐g‐PMMA–ADS–cassava starch. The NR‐g‐PMMA–cassava starch compounds exhibited two‐stage curing characteristics. The curing curve had a slight reversion at a testing time of approximately 8 min. The shear modulus then abruptly increased with an increasing testing time in the range of 20–60 min. The curing curves for NR‐g‐PMMA–ADS–cassava starch blends exhibited a single curing stage with a shear modulus that increased slightly with the testing time was increased from 20 to 60 min. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1453–1463, 2003     

Crystallization kinetics of thermosetting polymer blends of poly(ε‐caprolactone) and unsaturated polyester resin

A study has been made of the isothermal crystallization kinetics of poly(ε‐caprolactone) (PCL) in partially miscible crosslinked polyester resin (PER)/PCL blends by using differential scanning calorimetry (DSC). For comparison, miscible blends of PCL with uncured polyester resin, i.e., oligoester resin (OER), were also investigated. The overall crystallization rate of PCL remarkably decreased with the addition of amorphous component, OER or PER. The kinetic rate constant K_n decreased sharply for both the OER/PCL blends and the crosslinked PER/PCL blends with decreasing PCL concentration. The mechanism of nucleation and geometry of the growing PCL crystals was not remarkably affected by the incorporation of OER, but changed considerably with the addition of PER. However, the overall crystallization rate of PCL in the crosslinked PER/PCL blends was much higher compared with the corresponding uncured OER/PCL blends, which is attributable to the phase‐separated structure and the reduced miscibility in the crosslinked blends. According to the nucleation and growth theories, the nucleation process was considered to be the rate controlling step in the crystallization. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 322–327, 1999     

The synthesis of PHA‐g‐(PTHF‐b‐PMMA) multiblock/graft copolymers by combination of cationic and radical polymerization

A new and promising method for the diversification of microbial polyesters based on chemical modifications is introduced. Poly(3‐hydroxy alkanoate)‐g‐(poly(tetrahydrofuran)‐b‐poly(methyl methacrylate)) (PHA‐g‐(PTHF‐b‐PMMA)) multigraft copolymers were synthesized by the combination of cationic and free radical polymerization. PHA‐g‐PTHF graft copolymer was obtained by the cationic polymerization of THF initiated by the carbonium cations generated from the chlorinated PHAs, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHx) in the presence of AgSbF₆. Therefore, PHA‐g‐PTHF graft copolymers with hydroxyl ends were produced. In the presence of Ce⁺⁴ salt, these hydroxyl ends of the graft copolymer can initiate the redox polymerization of MMA to obtain PHA‐g‐(PTHF‐b‐PMMA) multigraft copolymer. Polymers obtained were purified by fractional precipitation. In this manner, their γ‐values (volume ratio of nonsolvent to the solvent) were also determined. Their molecular weights were determined by GPC technique. The structures were elucidated using ¹H‐NMR and FTIR spectroscopy. Thermal analyses of the products were carried out using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Unsaturated 2‐oxazoline end capping of liquid crystalline polyester by reactive processing and in a solution

End capping of liquid crystalline poly(ethylene terephthalate‐co‐oxybenzoate) with a bifunctional 2‐oxazoline derivative, 2‐(4‐allyloxyphenyl)‐2‐oxazoline, has been performed in melt under the condition of reactive processing and in a solution. The reaction in melt is very fast and, despite some modifier evaporation, it is completed in 2 min at 230°C. The product is a polyester containing unsaturated end groups bonded via esteramide linkage. The presence of unsaturation was proved by ¹³C‐NMR spectroscopy. An increase in temperature and prolongation of the processing time gives raise to thermal‐induced reactions on the unsaturated end groups, resulting in an increase of the glass transition temperature. Depending on the processing temperature decomposition, propagation and crosslinking occur in different extent and influence polymer properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1047–1053, 1999     

Studies on the properties and structure of electron‐beam crosslinked low‐density polyethylene/poly[ethylene‐co‐(vinyl acetate)] blends

Blends of low‐density polyethylene (LDPE) and poly[ethylene‐co‐(vinyl acetate)] (PEVA), crosslinked by electron‐beam (EB) radiation, formed separate crystalline lattices with a homogeneous amorphous phase. The crystallinity of the EB‐exposed samples slightly decreased, as verified by a slight reduction in the densities and melting heats and temperatures of the samples. The results obtained from both gel content and hot set tests showed that the degree of crosslinking in the amorphous regions was dependent on the dose and blend composition. The molecular weights between the crosslinks, measured from creep data, showed that an increasing PEVA content resulted in tighter network structures, thus supporting the idea that the crosslinking density at a given irradiation dose depends on the amorphous portions of the polymers. Addition of trimethylolpropane trimethacrylate as a radiation sensitizer enhanced the gel content of the neat polyethylene significantly, while the addition of an antioxidant showed the reverse effect. A significant improvement in the tensile strength of the neat PEVA samples was obtained upon EB radiation up to 210 kGy. The irradiated LDPE/PEVA blends showed improved tensile strength and elongation at break when compared to LDPE. Copyright © 2004 Society of Chemical Industry