Curing kinetics and glass‐transition temperature of hexamethylene diisocyanate‐based polyurethane

The curing process of hexamethylene diisocyanate‐based polyurethane has been monitored by applying FTIR and DSC methods. A general relationship between glass‐transition temperature (T_g) and conversion of curing process has been obtained. This suggests that the reaction path and the relative reaction rates are independent of the curing temperature. The reaction kinetics of the system is analyzed using the T_g data converted to the conversion of the curing process. A set of experimental data and one theoretical model of T_g versus chemical conversion are presented to prove the assumption where a direct one‐to‐one relationship between the T_g (as measured) and the chemical conversion is obtained. Apparent activation energies (E_a) obtained by applying three different methods suggest good agreement. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2213–2220, 2000     

Prediction of polyimide materials with high glass‐transition temperatures

The prediction of chemical structures that possess higher glass‐transition temperatures (T_g's) is crucial for designing polyimides. Because of a lack of suitable parameters, several estimation methods cannot be used for this purpose. In this study, therefore, we used molecular dynamic simulation with the DREIDING II force field to predict T_g's for polyimides. Simulated results indicated a good agreement with experimental observations. A barrier analysis of the bridging bonds between moieties along the main‐chain backbone showed a correlation between T_g and the barrier height. This proved to be helpful in a preliminary selection before the molecular dynamic simulation for accelerating the process of research and development on new polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2243–2251, 2001     

Nonisothermal cold crystallization behavior and kinetics of polylactide/clay nanocomposites

The nonisothermal cold crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) was studied using differential scanning calorimetry, polarized optical microscope, X‐ray diffractometer, dynamic mechanical thermal analysis, and Fourier transform infrared spectrometer. The results show that both the cold crystallization temperature (T_cc) and melting point (T_m) of PLA matrix decreases monotonously with increasing of clay loadings, accompanied by the decreasing degree of crystallinity (X_c%) at the low heating rates (≤5 °C/min). However, the X_c% of PLACNs presents a remarkable increase at the high heating rate of 10 °C/min in contrast to that of neat PLA. The crystallization kinetics was then analyzed by the Avrami, Jezioney, Ozawa, Mo, Kissinger and Lauritzen–Hoffman kinetic models. It can be concluded that at the low heating rate, the cold crystallization of both the neat PLA and nanocomposites proceeds by regime III kinetics. The nucleation effect of clay promote the crystallization to some extent, while the impeding effect of clay results in the decrease of crystallization rate with increasing of clay loadings. At the high heating rate of 10 °C/min, crystallization proceeds mainly by regime II kinetics. Thus, the formation of much more incomplete crystals in the PLACNs with high clay loadings due to the dominant multiple nucleations mechanism in regime II, may have primary contribution to the lower crystallization kinetics, also as a result to the higher degree of crystallinity and lower melting point in contrast to that of neat PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1100–1113, 2007     

Sub‐glass‐transition temperature interface formation between an immiscible glass rubber pair

We used neutron reflectivity to measure the interfacial width in the immiscible system polystyrene/poly(n‐butyl methacrylate) (PS/PnBMA). Measurements were made on the same samples at temperatures ranging from below the glass‐transition temperature (T_g) of PS to slightly above. We observed significant broadening of the interface at temperatures below the T_g of PS, indicating chain mobility below the bulk T_g value. The interfacial width exhibited a plateau at a value of 20 Å in the temperature range of 365 K < T < 377 K. A control experiment involving hydrogenated and deuterated PS films (hPS/dPS) showed no such broadening over the same temperature region. The results are consistent with a reduction of the T_g of PS in the interfacial region of ～20 K. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2664–2670, 2001     

Isothermal crystallization kinetics of chain‐extended PET

The crystallization behavior of a commercial chain‐extended PET (foam grade) was evaluated and compared to that of bottle‐grade PET. Cold and melt isothermal crystallization were analyzed by using the Avrami' model. The foam grade PET showed a slower crystallization kinetic compared to the bottle‐grade PET. The Hoffman‐Lauritzen analysis showed that the energetic barriers to nucleation and molecular mobility were higher for the chain‐extended PET. This resulted in a lower nucleation rate in both cold and melt crystallization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1966–1972, 2005     

Spatially heterogeneous dynamics in thermoset resins below the glass‐transition temperature

A photobleaching technique was used to measure the rotational dynamics of rubrene dispersed in thermoset resins. The matrices were polymerized from mixtures of two monomers with five different compositions. At temperatures below the glass‐transition temperature, probe rotational correlation times were shorter and showed a much weaker temperature dependence than those observed in glassy homopolymers. The probe correlation functions became increasingly nonexponential as the amount of the minor component in the matrix increased, presumably because a more heterogeneous set of environments resulted. Dynamics in the single‐component sample were quite homogeneous at room temperature. In contrast to homopolymer systems, a bimodal distribution of local relaxation times developed with the addition of the second component. At a given polymer composition, this bimodal distribution changed shape with temperature in a reversible manner. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2232–2239, 2000     

Effect of benzenesulfonamide plasticizers on the glass‐transition temperature of semicrystalline polydodecamide

The effect of various benzenesulfonamide (BSA) plasticizers on the amorphous phase of semicrystalline polydodecamide (PA‐12) has been investigated. MonoBSAs appear as efficient glass‐transition temperature (T_g) depressors because of their miscibility with the host polyamide (PA), low glass transition, and small molecule size. PA‐12's T_g shifts from 50 to about 0 °C at 20 mol % of the most efficient molecules. Comparatively, the more bulky bisBSAs appear to induce less important absolute T_g decreases (30 K at 20 mol %), although these appear as more important when considering the polymer T_g to plasticizer T_g difference. This unexpected observation could be ascribed to both the amide‐sulfonamide interactions and the sterically generated disorder within the polyamide because of the plasticizer molecule's size. Phase‐separation behavior of BSA plasticizers within the host PA has also been investigated. Crystalline phenyl‐SO₂NH₂, for instance, dephased beyond 20 mol % in PA‐12, forming distinct 1–2 micrometer wide crystalline domains as a result of its high propensity to crystallize upon cooling from the melt. By contrast, slow crystallizing N,N‐dimethylBSA, which lacks any specific interaction for PA‐12, remained nevertheless dispersed at a molecular level (metastable state, no phase separation) when vitrification of the host PA‐12 amorphous phase occurred on cooling. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2208–2218, 2002     

Synthesis and characterization of silica‐graft‐polystyrene hybrid nanoparticles: Effect of constraint on the glass‐transition temperature of spherical polymer brushes

The effect of the chain constraint on the glass‐transition temperature of polystyrene (pS) was studied in the context of polymer tethering to curved surfaces. The synthesis and characterization of silica‐graft‐polystyrene (SiO₂‐g‐pS) hybrid nanoparticles is reported. Silica nanoparticles possessing covalently bound pS chains were prepared by the atom transfer radical polymerization of styrene from functionalized colloidal surfaces. These hybrid nanoparticles serve as interesting examples of spherical polymer brushes, as a high density of grafted pS was achieved on the inorganic colloid. The confirmation of a brushlike extension of immobilized chains in a good solvent was obtained with dynamic light scattering in toluene of SiO₂‐g‐pS colloids possessing various molar masses of tethered pS. The solid‐state morphology of SiO₂‐g‐pS ultrathin films was assessed with transmission electron microscopy, and this confirmed that the silica colloids were well‐dispersed in a matrix of the tethered polymer. Differential scanning calorimetry was used to study the effects of tethering and chain immobilization on the glass‐transition temperature of pS. The measured glass‐transition temperature of annealed bulk films of the hybrid nanoparticles was elevated with respect to the value for pure bulk pS. The enhancements ranged from 13 to 2 K for SiO₂‐g‐pS brushes possessing tethered pS with number‐average molecular weights of 5230 and 32,670 g/mol, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2667–2676, 2002     

Incorporation of silver/carbon nanoparticles into poly(methyl methacrylate) via in situ miniemulsion polymerization and its influence on the glass‐transition temperature

Silver/carbon nanoparticles (9 nm) were incorporated, as reinforcements, into a matrix of poly(methyl methacrylate) via in situ miniemulsion polymerization. It was found by differential scanning calorimetry that the glass‐transition temperature of the poly(methyl methacrylate) showed an improvement of 14 °C with only 0.5 wt % nanoparticles in comparison with a pure poly(methyl methacrylate) control, which was also obtained by miniemulsion polymerization under the same conditions. This increase was related to a polymer chain mobility restriction due to a combination of bound plastic and joint plastic shell effects at the interphase and the surrounding regions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 511–518, 2007.     

Nonlinear characteristics of the quantitative relationship between the glass‐transition temperature and the structure of homopolymers

Fuzzy set theory was used to study the relationship between the glass‐transition temperature (T_g) and structure of homopolymers. The method can map the relationship and give the T_g for 235 polymers with a standard deviation of 8 K (the confidence bound was 90%). The entropy of the fuzziness was used to quantitatively describe the interactions among groups. The method was used to predict the T_g of 10 polymers not included in the 235 polymers, with a standard deviation of 9 K (the confidence bound was 90%). The study demonstrates again that fuzzy set theory can be effectively used to investigate the quantitative structure–property relationship of polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2164–2169, 2002     

Enhancing the glass‐transition temperature of polyimide copolymers containing 2,2′‐bipyridine units by the coordination of nickel malenonitriledithiolate

Polyimide copolymers containing 2,2′‐bipyridine were synthesized and characterized. The glass‐transition temperatures (T_g's) of the polymers ranged from 260 to 300 °C. In contrast to most known organic chromophore‐containing polyimides, the polyimide copolymers in this study showed elevated T_g's (270–320 °C) after coordination with nickel malenonitriledithiolate inorganic chromophores. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 498–503, 2000     

Poly(vinylamine) complexes with f‐block salts from the lanthanide series that exhibit significant glass‐transition temperature enhancement

Six f‐block salts from the lanthanide series form complexes with poly(vinyl amine) and increase the glass‐transition temperature of the polymer. Results for poly(vinylamine) complexes with EuCl₃(H₂O)₆ and TbCl₃(H₂O)₆ surpass those for d⁷ cobalt complexes that were studied previously. The glass‐transition temperature increases by 49 °C per mol % Eu³⁺ and 50 °C per mol % Tb³⁺, up to 2 mol % of the f‐block cations. At 5 mol % Eu³⁺, T_g is slightly higher than 250 °C with no visual evidence of thermal degradation of either component in the complex. This corresponds to a T_g enhancement of almost 200 °C with respect to the undiluted polymer. The increases in T_g for these lanthanide complexes with poly(vinylamine) obey the following trend: up to 2 mol % of the f‐block cation. With the exception of Gd(CH₃COO)₃, which contains different anionic ligands than all of the other trichlorides, this trend correlates inversely with the highest dehydration/dehydrochlorination temperature of each undiluted lanthanide salt, as measured via calorimetry above the melting point and verified by thermogravimetry. Waters of hydration and amino sidegroups undergo ligand substitution in the coordination sphere of the lanthanides. Since lanthanide cations are classified as hard acids, it is not unreasonable that they form complexes with the nitrogen lone pair in the amino sidegroup of the polymer, which is classified as a hard base. Micro‐clustering of several amino side groups reduces chain mobility significantly in the vicinity of each metal center, produces coordination crosslinks, and increases T_g. Complementary solution studies reveal that hydrogels form with swelling ratios between 20 and 50 at Eu³⁺ mole fractions between 0.01 and 0.05 with respect to poly(vinylamine). Infrared spectroscopic observations suggest that the amino nitrogen lone pair in poly(vinylamine) interacts with these lanthanide metal centers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1931–1938, 2000     

Brittle–ductile transition in high‐density polyethylene/glass‐bead blends: Effects of interparticle distance and temperature

The toughness of high‐density polyethylene (HDPE)/glass‐bead blends containing various glass‐bead contents as a function of temperature was studied. The toughness of the blends was determined from the notch Izod impact test. A sharp brittle–ductile transition was observed in impact strength–interparticle distance (ID) curves at various temperatures. The brittle–ductile transition of HDPE/glass‐bead blends occurred either with reduced ID or with increased temperature. The results indicated that the brittle–ductile‐transition temperature dropped markedly with increasing glass‐bead content. Moreover, the correlation between the critical interparticle distance (ID_c) and temperature was obtained. Similar to the ID_c of polymer blends with elastomers, the ID_c nonlinearly increased with increasing temperature. However, this was the first observation of the variation of the ID_c with temperature for polymer blends with rigid particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1855–1859, 2001     

Mechanical and flame‐retardant properties of biodegradable polylactide composites with hyperbranched silicon‐containing polymer

A hyperbranched polymer (HBP‐B2) containing siloxane chains was synthesized via bulk polymerization of diepoxide with a primary amine in the presence of monoepoxide. The weight‐average molecular weight of the prepared polymers was approximately 9200. Composites of polylactide (PLA) with aluminum trihydroxide (ATH) and the HBP‐B2 were prepared via direct melt compounding using a brabender. The test results showed that the LOI could be raised to 34% for the PLA composite with 25 wt% ATH and 5% HBP‐B2. The surface thermal profile of the composite during UL94 V test was further captured by an infrared camera, which was helpful to understand the flame‐retardant properties of the different samples. A V‐0 rating could be achieved by adding ATH and HBP‐B2 to the PLA matrix. Incorporation of HBP‐B2 as a plasticizer could increase the impact strength of a PLA blend or composite. For example, an addition of 10 wt% of HBP and 20 wt% ATH increased the elongation at break from 5% for neat PLA to 155% for the PLA composite.     

Effects of filler size and heat treatment on the crystallization behavior of glass bead‐filled polypropylene

The effects of glass bead (GB) size and annealing temperature on the formation of β‐crystals of glass bead‐filled polypropylene (PP) are studied in this articles. Differential scanning calorimetry (DSC) measurements indicated that the amount of β‐form in PP crystals was a function of the glass bead content and size. For a fixed glass bead content, it was found that the smaller the diameter of the glass bead, the higher was the content of β‐crystals formed in the PP. On the other hand, wide‐angle X‐ray diffraction (WAXD) measurements revealed that the annealing temperature was also a major factor that affected the crystallization behavior of glass bead‐filled PP. It seemed that the blends with different glass bead contents had their own optimal annealing temperatures for β‐crystal formation. As an example, when the glass bead content was 48 wt %, the optimal annealing temperature for β‐crystal formation was about 108 °C, whereas it shifted to 100 °C for 14 wt % glass bead‐filled polypropylene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 306–313, 2005     

Influence of matrix glass transition temperature on the memory effect of polymer‐dispersed liquid crystals

In this article, macroinitiators with different glass transition temperature (T_g) were synthesized by reversible additional‐fragmental chain transfer polymerization, and used to prepare polymer‐dispersed liquid crystals (PDLCs) with methyl acrylate. The memory effect of these PDLCs was investigated. The results showed that remarkable memory effect exhibit only in PDLCs with high and low T_g block chain. The possible mechanism responsible for the behavior is sketched. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 729–732, 2010     

Effect of chain structure on the glass transition temperature and viscoelastic property of cis‐1,4‐polybutadiene via molecular simulation

In this work, by adopting the united atom model of cis‐1,4‐poly(butadiene) (PB), we systemically investigate the effect of the chain structure on the glass transition temperature (T_g) and the viscoelastic property of PB system. First, we analyze the atom translational mobility, bond reorientation dynamics, torsional dynamics, conformational transition rate, and dynamic heterogeneity of the PB chains with different chain structures in detail by determining the corresponding T_g. In addition, our results clearly indicate that with the decrease of the amount of the free end atoms of PB via the end‐linking method, the mobility of the PB chains quickly decreases. As a result, the T_g of the PB chains gradually increases. Depending on the chain structure and the calculation method, the T_g of the PB chains varies from 154 to 240 K. In addition, the temperature dependence of the dynamic properties has different Arrhenius behaviors above and below T_g. The calculated activation energy varies from 7.37 to 16.37 KJ/mol for different chain structures above T_g, which can be compared with those for other polymers. In addition, through the end‐linking approach the strong interaction between the PB chains improves the storage modulus G′ and the loss modulus . Meanwhile, the immobility of the free end atoms effectively reduces the friction loss of the chains under the shear field, which is reflected by the low loss factor . In summary, this work can further help to understand the effect of the chain structure on the dynamic properties of the PB chains. Meanwhile, it provides an effective approach to reduce the energy loss during the dynamic periodic deformation, which can cut the fuel consumption via the end‐linking method. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1005–1016     

Investigation of the relationship of the glass‐transition temperature and the polymer structure by fuzzy set theory

Fuzzy set theory can be used to study the relationship between the glass‐transition temperature (T_g) and structure of polymers. We used the method to map this relationship and obtained T_g's for 241 polymers with a standard deviation of 20 K (the confidence bound was 90%). We also used the method to predict T_g's for 15 polymers with a standard deviation of 67 K (the confidence bound was 90%). This study demonstrates that fuzzy set theory can be effectively used for determining the quantitative structure–property relationship of polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 454–459, 2002; DOI 10.1002/polb.10105     

Effects of water on epoxy cure kinetics and glass transition temperature utilizing molecular dynamics simulations

Effects of water on epoxy cure kinetics are investigated. Experimental tests show that absorbed water in an uncured bisphenol‐F/diethyl‐toluene‐diamine epoxy system causes an increase in cure rate at low degrees of cure and a decrease in cure rate at high degrees of cure. Molecular simulations of the same epoxy system indicate that the initial increase in cure rate is due to an increase in molecular self‐diffusion of the epoxy molecules in the presence of water. Effects of water on the glass transition temperature (T_g) of the crosslinked thermoset are also studied. Both experiments and simulations show that water decreases T_g. Both types of results indicate that T_g effects are small below 1% water by weight, but that T_g depression occurs much quickly with increasing water content above 1%. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1150–1159     

Miscibility and crystallization behavior of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) and methoxy poly(ethylene glycol) blends

Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHB‐HHx) and methoxy poly(ethylene glycol) (MPEG) blends were prepared using melt blending. The single glass transition temperature, T_g, between the T_gs of the two components and the negative χ value indicated that PHB‐HHx and MPEG formed miscible blends over the range of compositions studied. The Gordon–Taylor equation proved that there was an interaction between PHB‐HHx and MPEG in their blends. FTIR supported the presence of hydrogen bonding between the hydroxyl group of MPEG and the carbonyl group of PHB‐HHx. The spherulitic morphology and isothermal crystallization behavior of the miscible PHB‐HHx/MPEG blends were investigated at two crystallization temperatures (70 and 40 °C). At 70 °C, melting MPEG acted as a noncrystalline diluent that reduced the crystallization rate of the blends, while insoluble MPEG particles acted as a nucleating agent at 40 °C, enhancing the crystallization rate of the blends. However, no interspherulitic phase separation was observed at the two crystallization temperatures. The constant value of the Avrami exponent demonstrated that MPEG did not affect the three‐dimensional spherulitic growth mechanism of PHB‐HHx crystals in the blends, although the MPEG phase, such as the melting state or insoluble state, influenced the crystallization rate of the blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2852–2863, 2006