Dual entropic and enthalpic processes in the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions

In the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions, the process corresponding to the weakening of the hydrogen bond interaction with increasing temperature is dominant and occurs over the entire concentration region of solutions and over a broad temperature range from 30 to 41°C, giving rise to the energetic enthalpic effect during phase separation, while the conformational change, that is, collapse of the swollen polymer coils, occurs only in the swelling polymer solution when the water concentration is above 38.3 wt %, giving rise to the entropic effect during phase separation. In addition, the entropic process corresponding to the collapse of the polymer coils occurs in a much narrow theta temperature range from 35.5 to 37°C. If the solution is held at a constant temperature for a sufficiently long time, 90% collapse of the polymer coils occurs in only the 0.5 °C temperature region between 35.5 and 36°C. Accordingly, in the enthalpic process, the most dramatic blueshift of the νC‐O bond peak occurs in the temperature range between 35 and 41°C, while this blueshift is only approximately 2 cm^?1 in the temperature range from 30 to 35°C, prior to the collapse of the polymer coils due to the entropic effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 323–330     

Synthesis of poly(vinyl acetate)‐b‐polystyrene and poly(vinyl alcohol)‐b‐polystyrene copolymers by cobalt‐mediated radical polymerization

Well‐defined poly(vinyl acetate) macroinitiators, with the chains thus end‐capped by a cobalt complex, were synthesized by cobalt‐mediated radical polymerization and used to initiate styrene polymerization at 30 °C. Although the polymerization of the second block was not controlled, poly(vinyl acetate)‐b‐polystyrene copolymers were successfully prepared and converted into amphiphilic poly(vinyl alcohol)‐b‐polystyrene copolymers by the methanolysis of the ester functions of the poly(vinyl acetate) block. These poly(vinyl alcohol)‐b‐polystyrene copolymers self‐associated in water with the formation of nanocups, at least when the poly(vinyl alcohol) content was low enough. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 81–89, 2007     

High melting thermoplastic/epoxy resin blends: Influence of the curing reaction on the crystallization and melting behavior

The influence of the cure process and the resulting reaction‐induced phase separation (RIPS) on the crystallization and melting behavior of polyoxymethylene (POM) in epoxy resin diglycidylether of bisphenol A (DGEBA) blends has been studied at different cure temperatures (180 and 145 °C). The crystallization and melting behavior of POM was studied with DSC and the simultaneous blend morphology changes were studied using OM. At first, the influence of the epoxy monomer on the dynamically crystallized POM was investigated. Secondly, a cure temperature above the melting point of POM (T_cure = 180 °C) was applied for blends with curing agent to study the influence of resulting phase morphology types on the crystallization behavior of POM in the epoxy blends. Large differences between particle/matrix and phase‐inverted structures have been observed. Thirdly, the cure temperature was lowered below the melting temperature of POM, inducing isothermal crystallization prior to RIPS. As a consequence, a distinction was made between dynamically and isothermally crystallized POM. Concerning the dynamically crystallized material, a clear difference could be made between the material crystallized in the homogeneous sample and that crystallized in the phase‐separated structures. The isothermally crystallized POM was to a large extent influenced by the conversion degree of the epoxy resin. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2456–2469, 2007     

Dynamic mechanical properties of two copolymers of styrene and n-hexyl methacrylate

The storage (J′) and loss (J″) shear compliances have been measured for two random copolymers of styrene and n-hexyl methacrylate with styrene contents of 18% and 30% (by weight) in the frequency range 45–4400 Hz and the temperature range 31–107°C. The data at different temperatures were combined by the method of reduced variables, and the WLF coefficients were calculated from the temperature shift factors by the method of Pierson and Kovacs. The data were compared with earlier data for the two homopolymers. The thermal expansion coefficient of the fractional free volume, and the free volume at the glass transition temperature, varied monotonically with composition, but the fractional free volume at a reference temperature of 100°C appeared to pass through a maximum as a function of concentration. Comparison of isothermal plots of J′ at 100°C, plots of the relaxation spectrum at 100°C, the monomer friction coefficient and its temperature dependence, and isochronal plots of the storage shear moduls at 100 radians/see all show that the properties of poly(n-hexyl methacrylate) are very slightly affected by incorporation of 18% styrene and only moderately affected by 30% styrene. By contrast, comparison of styrene–butadiene rubber with 1,4-polybutadiene shows a very large effect of incorporation of 23.5% styrene. These differences may be associated with local packing relations of the comonomer residues and suggest that copolymer properties cannot be readily predicted from those of the component homopolymers.     

Temperature‐modulated differential scanning calorimetry studies on the origin of double melting peaks in isothermally melt‐crystallized poly(L‐lactic acid)

In this work, the melting behaviors of nonisothermally and isothermally melt‐crystallized poly(L ‐lactic acid) (PLLA) from the melt were investigated with differential scanning calorimetry (DSC) and temperature‐modulated differential scanning calorimetry (TMDSC). The isothermal melt crystallizations of PLLA at a temperature in the range of 100–110 °C for 120 min or at 110 °C for a time in the range of 10–180 min appeared to exhibit double melting peaks in the DSC heating curves of 10 °C/min. TMDSC analysis revealed that the melting–recrystallization mechanism dominated the formation of the double melting peaks in PLLA samples following melt crystallizations at 110 °C for a shorter time (≤30 min) or at a lower temperature (100, 103, or 105 °C) for 120 min, whereas the double lamellar thickness model dominated the formation of the double melting peaks in those PLLA samples crystallized at a higher temperature (108 or 110 °C) for 120 min or at 110 °C for a longer time (≥45 min). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 466–474, 2007     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008     

Crystallization,morphology, and thermal behavior of poly(p‐phenylene sulfide)

This article deals with the structure, crystallization, morphology, and thermal behavior of poly(p‐phenylene sulfide) (PPS) with low‐molecular mass, probed by DSC, optical, and electron microscopy. The growth rates of spherulites were measured over the temperature range 235–275°C. A regime II–III transition was found at T = 250°C. The regime transition was accompanied by a morphological change from sheaflike structure to classical spherulites. The Avrami equation poorly described the isothermal crystallization of PPS, for the occurrence of mixed growth mechanisms and secondary crystallization, in agreement with the morphology and the thermal behavior. Two melting peaks were detected on DSC curves and attributed to the melting of crystals formed isothermally at T_c by primary and secondary crystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 415–424, 2001     

Calorimetric investigation of polymerization reactions. IV. Curing reaction of polyester fumarate with styrene

The curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally. The change in rate of cure was followed over the whole range of conversion. The rate of cure is accelerated by the gel effect to about ten to fifty times the rate of model copolymerization of diethyl fumarate with styrene. This autoacceleration is much enhanced for systems with higher crosslinking densities and at lower temperatures. The results confirm that both termination and propagation steps of the curing reaction are controlled by diffusion of polymeric segments and monomer molecules over almost the whole range of conversion. The final extent of conversion is short of completion for isothermal cure and even for postcure of polyester fumarate with styrene because of crosslink formation. The final conversion of isothermal cure decreases with increasing crosslinking density and shows a maximum with increasing reaction temperature. This temperature dependency of the final conversion is caused by the difference in the activation energies for two propagation rate constants k_pf and k_ps, which were evaluated to be 7–10 and 5–8 kcal/mole, respectively, for the intermediate stage of the curing reaction.     

Styrene 4‐vinylbenzocyclobutene copolymer for microelectronic applications

Styrene and 4‐vinylbenzocyclobutene (vinyl‐BCB) random copolymers were prepared by free radical polymerization and studied for suitability as a dielectric material for microelectronic applications. The percentage of vinyl‐BCB in the copolymer was varied from 0 to 26 mol % to optimize the physical and mechanical properties of the cured copolymer as well as the cost. Copolymer in which 22 mol % of vinyl‐BCB was incorporated along with styrene produced a thermoset polymer which, after cure, did not show a T_g before decomposition at about 350 °C. The polymeric material has a very low dielectric constant, dissipation factor, and water uptake. The fracture toughness of the copolymer was improved with the addition of 20 wt % of a star‐shaped polystyrene‐block‐polybutadiene. Blends of the poly(styrene‐co‐vinyl‐BCB) with the thermoplastic elastomer provided material that maintained high T_g of the cured copolymer with only a slight decrease in thermal stability. The crosslinked styrenic polymer and toughened blends possess many properties that are desirable for high frequency‐high speed mobile communication applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2799–2806, 2008     

Thermally induced fixed diradical generation on solid supports for surface‐initiated polymerization

A method is presented for generation of all surface‐bound radicals on solid polymer surfaces. Thus, secondary amide group of newly synthesized crosslinking comonomer, methacryloyloxyethyl methacrylamide was determined as versatile precursor for generation fixed diradicals on solid microspheres, obtained by copolymerization with methyl methacrylate (MMA) in aqueous suspension. Nitrosoation of the secondary amide groups on the microbeads and followed thermolysis above 90 °C was demonstrated to give surface‐bound radicals, capable of initiating polymerization of vinyl monomers, such as; styrene, MMA, N‐vinyl formamide, and N‐vinyl, 2‐pyrrolidone, as evidenced by H NMR, Fourier transform infrared, thermogravimetric analysis, and differential scanning calorimeter techniques. Appreciable grafting yields (55.1%–286.1%) and low free‐homopolymer formation (7.2%–19.7%) were noted within 6 h of the grafting at 100 °C in each case. This strategy involving the use of amide functional crosslinker seemed to be generally applicable to generate surface‐bound radicals for surface‐initiated polymerization from various solid substrates. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and thermal dissociation of polymers having hemiacetal ester moieties

Polymers having hemiacetal ester moieties in the side chain were synthesized and their thermal dissociation was examined. 1‐Alkoxyethyl methacrylates (1) were synthesized from methacrylic acid with alkyl vinyl ethers and their radical copolymerizations with butyl methacrylate were carried out at 80°C for 6.5 h using AIBN as an initiator to afford the corresponding copolymers having the hemiacetal ester moieties in the side chain. The hemiacetal ester moieties in the copolymers thermally converted to carboxyl groups with elimination of the corresponding vinyl ethers. The thermal dissociation of the hemiacetal ester moieties in the side chain obeyed first‐order kinetics at 140°C, and their reactivities were in the following order: 1‐(tert‐butoxy)ethyl > 1‐isopropoxyethyl > 1‐ethoxyethyl > 1‐butoxyethyl ester. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 609–614, 1999     

Thermal dissociation behavior of copolymers bearing hemiacetal ester moieties and their reactions with epoxides

Copolymers from 1‐propoxyethyl methacrylate and various vinyl monomers such as n‐butyl methacrylate and styrene were synthesized, and the thermal dissociation reaction of the copolymers containing the hemiacetal ester structure was examined. The copolymers, having the ability of thermal dissociation, could control the thermal dissociation temperature because of the bulkiness and flexibility of the vinyl comonomers, the copolymer compositions, and so on. Furthermore, the possibility of control of the initiation in thermally latent addition with epoxides in the case of copolymers was also studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3966–3977, 2006     

Copolymerization of styrene with (Z)-1,3-pentadiene in the presence of a syndiotactic-specific catalyst

Copolymerization of styrene with (Z)-1,3-pentadiene affords copolymers mostly containing 1,2 pentadiene units. Both the styrene and the pentadiene units are in syndiotactic arrangement but the comonomer sequence distribution is far from bernoullian. Interestingly, the behavior of (Z)-1,3-pentadiene does not change much when polymerization temperature raises from −20 to +20°C, notwithstanding that (Z)-1,3-pentadiene affords a 1,2-syndiotactic homopolymer at −20°C but a prevailingly 1,4 cis homopolymer at +20°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2697–2702, 1997     

Isobaric cure shrinkage behaviors of epoxy molding compound in isothermal state

The warpage of plastic‐encapsulated IC packages after molding is believed to be induced by thermal and cure shrinkage of epoxy molding compound (EMC). To study the warpage behaviors of EMC, the amount of cure‐induced shrinkage needs to be understood. Volume shrinkage behaviors induced by cure reaction of EMC in isothermal and isobaric states were studied with a differential scanning calorimeter (DSC) and a pressure–temperature‐controlled dilatometer. The results show that higher pressure induce more volume shrinkage under fixed temperature but the difference of volume shrinkage under different pressure levels doesn't obey the principle of linearity. It is observed that the amount of chemical volume shrinkage at 145 °C is higher than those under three other temperatures: 160, 175, and 190 °C. The chemical volume shrinkage of EMC is found to be very process dependent. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2392–2398, 2005     

Cobalt‐mediated radical polymerization routes to poly(vinyl ester) block copolymers

Cobalt‐mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)₂, lauroyl peroxide, citric acid trisodium salt, and VPv at 30 °C results in controlled polymerizations that yield homopolymers with M_n = 2.5–27 kg/mol with M_w/M_n = 1.20–1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (M_n = 4–16 kg/mol; M_w/M_n = 1.34–1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small‐angle X‐ray scattering analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Novel active ester‐bridged copolynorbornene materials containing terminal functional hydroxyl,amino, methacryloyl,or ammonium groups via ring‐opening metathesis polymerization

Several random and block copolynorbornenes with side chains containing terminal hydroxyl, amino, methacryloyl or ammonium groups were derived from the functional alkyl ester‐containing norbornenes by ring‐opening metathesis polymerization (ROMP). The main chain of ROMP‐type polynorbornene had a more important role for glass‐transition temperature in comparison with vinyl addition polymerization. There is little effect on glass‐transition temperature (about ?39 °C) of polynorbornenes with different length of alkyl side chain. The organosoluble copolynorbornenes with active crosslinkable methylacryloyl side chains derived from functional hydroxyl group were prepared to improve the thermal stability of poly(methyl methacrylate) [decomposition temperature (T_d)^10% = 325 °C in nitrogen] by forming networked AB crosslinked polymer (T = 367 °C in nitrogen). The sizes of nanometer‐scale polymeric micelles of block copolymers having hydrophobic alkyl ester and hydrophilic ammonium groups were measured in the range of 11–25 nm by scanning electron microscopy. These polymeric materials with various functional groups or amphiphilic architectures are accessible by ROMP, whose topology makes them particularly attractive for application potential such as biomedical and photoelectric materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4233–4247, 2005     

Living cationic polymerization of vinylnaphthalene derivatives

The living cationic polymerization of 6‐tert‐butoxy‐2‐vinylnaphthalene (tBOVN), a vinylnaphthalene derivative with an electron‐donating group, was achieved with a TiCl₄/SnCl₄ combined initiating system in the presence of ethyl acetate as an added base at –30 °C. The absence of side reactions at low temperature was confirmed by ¹H NMR analysis of the resulting polymer. In contrast to this controlled reaction at –30 °C, reactions performed at higher temperature, such as 0 °C, frequently involved unwanted intramolecular or intermolecular Friedel–Crafts reactions of naphthalene rings due to the high electron density of these rings. The cationic polymerization of 6‐acetoxy‐2‐vinylnaphthalene, a derivative with an acetoxy group, was also controlled under similar conditions, but chain transfer reactions were not completely suppressed during the polymerization of 2‐vinylnaphthalene. The glass transition temperature (T_g) of the obtained poly(tBOVN) was 157 °C, a value higher by 94 °C than that of the corresponding styrene derivative. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4828–4834     

Crystallization kinetics and melting behavior of syndiotactic 1,2‐polybutadiene

Differential scanning calorimetry was used to investigate the isothermal crystallization, subsequent melting behavior, and nonisothermal crystallization of syndiotactic 1,2‐polybutadiene (st‐1,2‐PB) produced with an iron‐based catalyst system. The isothermal crystallization of two fractions was analyzed according to the Avrami equation. The morphology of the crystallite was observed with polarized optical microscopy. Double melting peaks were observed for the samples isothermally crystallized at 125–155 °C. The low‐temperature melting peak, which appeared approximately 5 °C above the crystallization temperature, was attributed to the melting of imperfect crystals formed by the less stereoregular fraction. The high‐temperature melting peak was associated with the melting of perfect crystals formed by the stereoregular fraction. With the Hoffman–Weeks approach, the value of the equilibrium melting temperature was derived. During the nonisothermal crystallization, the Ozawa method was limited in obtaining the kinetic parameters of st‐1,2‐PB. A new method that combined the Ozawa method and the Avrami method was employed to analyze the nonisothermal crystallization of st‐1,2‐PB. The activation energies of crystallization under nonisothermal conditions were calculated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 553–561, 2005     

Crystallization behavior and morphology of poly(butylene succinate) modified with rosin maleopimaric acid anhydride

The melting behavior, crystallization behavior, and morphology of PBSR, which is Poly(butylene succinate) modified with rosin maleopimaric acid anhydride (RMA), were investigated with differential scanning calorimetry (DSC) and polarized optical microscope (POM). The multiple endotherms were ascribed to the recrystallization during DSC measurement and the equilibrium melting temperature determined by the Peak L, which was associated with the fusion of the crystals grown by normal primary crystallization, was 125.9 °C. After the kinetic parameters for isothermal crystallization of PBSR were determined by Avrami equation, to make a detailed regime transition analysis, the well‐established Lauritzen–Hoffman equation was employed. The results indicated that there were two regimes, regime II and regime III, in the range of higher and lower crystallization temperature, respectively. The regime transition temperature is about 81 °C. At last, the spherulitic morphologies of PBSR after being crystallized isothermally at different temperature were observed with the help of POM. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2694–2704, 2005     

Relevance of a prereaction for the in situ NMP of styrene using the C‐Phenyl‐N‐tert‐butylnitrone/2,2′‐azobis(isobutyronitrile) pair

In this article, we compare two routes for carrying out in situ nitroxide‐mediated polymerization of styrene using the C‐phenyl‐N‐tert‐butylnitrone (PBN)/2,2′‐azobis(isobutyronitrile) (AIBN) pair to identify the best one for an optimal control. One route consists in adding PBN to the radical polymerization of styrene, while the other approach deals with a prereaction between the nitrone and the free radical initiator prior to the addition of the monomer and the polymerization. The combination of ESR and kinetics studies allowed demonstrating that when the polymerization of styrene is initiated by AIBN in the presence of enough PBN at 110 °C, fast decomposition of AIBN is responsible for the accumulation of dead polymer chains at the early stages of the polymerization, in combination with controlled polystyrene chains. On the other hand, PBN acts as a terminating agent at 70 °C with the formation of a polystyrene end‐capped by an alkoxyamine, which is not labile at this temperature but that can be reactivated and chain‐extended by increasing the temperature. Finally, the radical polymerization of styrene is better controlled when the nitrone/initiator pair is prereacted at 85 °C for 4 h in toluene before styrene is added and polymerized at 110 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1085–1097, 2009