Chin-Ping Yang

Polymorphism, thermal behavior, and crystal stability in syndiotactic polystyrene vs. its miscible blends

Four crystal types (α, β, γ, δ) and some mesophases/sub-modifications have been identified and discussed in syndiotactic polystyrene (sPS). The α- and β-forms are the main crystal packing forms in thermally-processed sPS, while the γ- and δ-crystals are identified only in solvent-treated sPS. In addition, the δ- and γ-forms are of a monoclinic crystal cell (with helical chain conformation) and the cell dimensions depend on the types and amount of residual solvent trapped in the crystal. The δ- and γ-crystal in solvent-treated sPS are more like mesophases that transform readily to the α-, β″- or β′-crystal upon heating the solvent-treated sPS to high temperatures near melting. This review thus focuses on studies of the α, β-crystals in sPS, and provides comprehensive discussions on the thermal behavior, crystal structures, thermodynamics, kinetics, and stability of these two major crystal packings (α vs. β) in sPS upon melt crystallization in comparison with cold crystallization. Analyses of melting behavior, diffractograms, or IR spectra, etc. of sPS can be complicated by the presence of co-existing polymorphic crystals. In general, a total of four melting peaks (labeled as P-I, P-II, P-III, P-IV from low to high temperatures) have been identified in a melt-crystallized sPS that typically contains mixed fractions of both crystals. By refining the techniques of obtaining sPS with individually isolated α- or β-crystal, recent studies have been able to correct suspected inaccuracy of some thermodynamic and kinetic measurements in earlier studies and to interpret the relative stability of the various crystals in sPS. sPS samples could be prepared such that they contained purely isolated α- or β-crystal, and the individual crystal types are used for more precise characterization of analysis. The P-I and P-III melting peaks are attributed to the β′-crystal while the P-II and P-IV peaks are attributed to the α″-type. In addition, kinetic and thermodynamic characterization has been thoroughly performed on individually isolated crystal types. The α-crystal of sPS has a lower melting temperature than the β-crystal, with Tm,α0=281.7°C and Tm,β0=288.7°C. The crystallization kinetics of the α-crystal is a heterogeneous nucleation with higher rates while the β-crystal is a homogeneous nucleation with lower rates. The β′-type is more thermodynamically stable than the α″-type; but the α″-type is kinetically more favorable. In addition, although there is literature report concerning a transformation of δ or γ mesophase crystals to α- or β-crystal; there is no evidence showing a solid–solid transition from the α- to β-crystal or β- to α-crystal during normal thermal processes. It suggests that both α- to β-crystal are stable solid and transformation between them can only be achieved by melting and re-packing. This could be fully explained using a stability/metastability chart of free energy vs. temperature. Nevertheless, the individual melting/reorganization of these two crystals might undergo crystal transformation via solid–liquid–solid transition. The crystallization kinetics of β′-crystal is a homogeneous nucleation with lower rates. By comparison, crystallization kinetics of the α-crystal is a heterogeneous nucleation with higher rates. Microscopy characterization also revealed a highly nucleated crystallization of the α-crystal. The effect of blend miscibility on the polymorphism behavior in sPS is also discussed. The effects of miscibility on polymorphism was investigated by studying miscible blends of sPS with atactic polystyrene (aPS) or sPS with poly(1,4-dimethyl phenylene oxide) (PPO). Miscible blends containing sPS have been found to favor growth of β-crystal than neat sPS when subjected to the same melt crystallization conditions.

Organosoluble optically transparent poly(ether imide)s based on a tert‐butylhydroquinone bis(ether anhydride)

Full Paper: A novel bis(ether anhydride) monomer, 1,4-bis(3,4-dicarboxyphenoxy)-2-tert-butylbenzene dianhydride, was synthesized from the nitro displacement of 4-nitrophthalodinitrile by the phenoxide ion of tert-butylhydroquinone, followed by alkaline hydrolysis of the intermediate bis(ether dinitrile) and dehydration of the resulting bis(ether diacid). A series of colorless and organosoluble poly(ether imide)s (PEIs) bearing pendent tert-butyl groups were prepared from the bis(ether anhydride) with various aromatic diamines via a conventional two-stage process that included ring-opening polyaddition to form the poly(amic acid)s followed by chemical or thermal cyclodehydration to the PEIs. The inherent viscosities of these PEIs are in the range of 0.70-1.44 dL/g. Most PEIs show excellent solubilities in amide polar solvents, m-cresol and chlorohydrocarbons. The glass transition temperatures (T g ) of these PEIs were recorded between 217-278°C, and the decomposition temperatures at 10% weight loss are all above 460°C in air or nitrogen atmosphere. Solvent-cast films have high tensile moduli and strengths. The PEIs obtained from long chain diamines exhibit high extension to break.

Syntheses and properties of polyimides based on bis(p-aminophenoxy)biphenyls

Three biphenyl unit-containing diamines,4,4′-bis(p-aminophenoxy)biphenyl (IIIa), 2,2′-bis(p-aminophenoxy)biphenyl (IIIb), and 3,3′,5,5′-tetramethyl-4,4′-bis(p-aminophenoxy)biphenyl (IIIc), were prepared by the chlorodisplacement ofp-chloronitrobenzene with 4,4′-biphenol (Ia), 2,2′-biphenol (Ib), and 3,3′,5,5′-tetramethyl-4,4′-biphenol (Ic), respectively, giving the corresponding bis(nitrophenoxy) compounds IIa-c, followed by catalytic reduction with palladium (Pd) and hydrazine. Three series of polyimidesp-PI,o-PI, and Me-PI were prepared from diamines IIIa-c and aromatic tetracarboxylic dianhydrides via a two-stage procedure that included ring-opening polyaddition to give poly(amic acid)s followed by thermal cyclodehydration to polyimides. The resultant three series of poly(amic acid)s had inherent viscosities of 1.09–2.83, 0.78–1.93, and 1.55–3.09 dL/g, respectively. Almost all the poly(amic acid)s could be solution-cast and thermally converted into transparent, flexible, and tough polyimide films. All the polyimides were characterized by solubility, tensile test, wide-angle X-ray scattering measurements, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Effects of the structures of aromatic diamines and dianhydrides on the properties of polyimides were investigated.

Syntheses and properties of aromatic polyamides and polyimides based on 3,3-bis[4-(4-aminophenoxy)phenyl]- phthalimidine

Abstract 3,3-Bis[4-(4-aminophenoxy)phenyl]phthalimidine ( 2 ) was used as the monomer with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to synthesize polyamides and polyimides, respectively. The diamine 2 was derived by a nucleophilic substitution of 3,3-bis(4-hydroxyphenyl)phthalimidine with p -chloronitrobenzene in the presence of K 2 CO 3 and then reduced by hydrazine and catalyst. Polyamides ( 4a–g ) having inherent viscosities of 0.94 – 2.08 dl g −1 were prepared by direct polycondensation of the diamine 2 with various aromatic diacids using triphenyl phosphite and pyridine as condensing agents. All the aromatic polyamides were amorphous and readily soluble in various polar solvents such as N,N - dimethylacetamide (DMAc), N,N -dimethylformamide, dimethylsulfoxide and N -methyl-2-pyrrolidone (NMP). Transparent and flexible films of these polymers could be cast from the DMAc solutions. These aromatic polyamides had glass transition temperatures in the range of 307–338°C and 10% weight loss occurred up to 460°C. The polyimides were synthesized from diamine 2 and various aromatic dianhydrides via a two-stage procedure that included ring-opening polyaddition in DMAc to give poly(amic acid)s, followed by thermal or chemical conversion to polyimides. Most of the aromatic polyimides obtained by chemical cyclization were found to be soluble in NMP, m -cresol and o -chlorophenol. These polyimides showed almost no weight loss up to 500°C in air or nitrogen atmosphere.

Synthesis and properties of ortho‐linked aromatic polyimides based on 1,2‐bis(4‐aminophenoxy)‐4‐tert‐butylbenzene

A bis(ether amine) containing the ortho-substituted phenylene unit and pendant tert-butyl group, 1,2-bis(4-aminophenoxy)-4-tert-butylbenzene, was synthesized and used as a monomer to prepare polyimides with six commercial dianhydrides via a conventional two-stage procedure. The intermediate poly(amic acid)s had inherent viscosities of 0.78–1.44 dL/g, and most of them could be thermally converted into transparent, flexible, and tough polyimide films. The inherent viscosities of the resulting polyimides were in the range of 0.46–0.87 dL/g. All polyimides were noncrystalline, and most of them showed excellent solubility in polar organic solvents. The glass-transition temperatures of these polyimides were in the range of 222–259 °C in differential scanning calorimetry and 212–282 °C in thermomechanicl analysis. These polyimides showed no appreciable decomposition up to 500 °C in thermogravimetric analysis in air or nitrogen. A comparative study of the properties with the corresponding polyimides without pendant tert-butyl groups derived from 1,2-bis(4-aminophenoxy)benzene is also presented.

Synthesis and properties of new organo‐soluble and strictly alternating aromatic poly(ester‐imide)s from 3,3‐bis[4‐(trimellitimidophenoxy)phenyl]phthalide and bisphenols

A series of new strictly alternating aromatic poly(ester-imide)s having inherent viscosities of 0.20 - 0.98 dL/g was synthesized by the diphenylchlorophosphate (DPCP) activated direct polycondensation of the preformed imide ring-containing di- acid, 3,3-bis(4-(trimellitimidophenoxy)phenyl)phthalide (I), with various bisphenols in a medium consisting of pyridine and lithium chloride. The diimide- diacid I was prepared from the condensation of 3,3-bis(4-(4-aminophenoxy)phenyl)phthalide and trimellitic anhydride. Most of the resulting polymers showed an amorphous nature and were readily soluble in a variety of organic solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Transparent and flexible films of these polymers could be cast from their DMAc solutions. The cast films had tensile strengths ranging 66 -105 MPa, elongations at break from 7-10%, and initial moduli from 1.9 -2.4 GPa. The glass-transition temperatures of these polymers were recorded between 208 -275 °C. All polymers showed no significant weight loss below 400 °C in the air or in nitrogen, and the decomposition temperatures at 10% weight loss all occurred above 460 °C.

Synthesis and characterization of new diphenylfluorene‐based aromatic polyamides derived from 9,9‐bis[4‐(4‐carboxy‐phenoxy)phenyl]fluorene

A new bis(ether-carboxylic acid), 9,9-bis[4-(4-carboxyphenoxy)phenyl]fluorene (3), was synthesized from the nucleophilic fluorodisplacement of p-fluorobenzonitrile with the dipotassium bisphenolate of 9,9-bis(4-hydroxyphenyl)fluorene, followed by alkaline hydrolysis of the intermediate bis(ether nitrile). A novel series of aromatic polyamides containing ether and bulky fluorenylidene groups were prepared by the direct polycondensation of the diacid 3 with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) solution containing dissolved CaCl 2 using triphenyl phosphite and pyridine as condensing agents. The obtained polyamides have inherent viscosities in the range of 0.50-1.75 dL/g. All the polymers are readily soluble in a variety of organic solvents, such as NMP, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and m-cresol, and afford transparent, flexible, and tough films by solvent casting. These polyamides have glass transition temperatures ranging from 200 to 303°C and show no significant weight loss up to 450°C, with 10% weight loss being recorded above 511°C in nitrogen or air.

Synthesis and properties of organosoluble poly(amide-imide)s with propeller-shaped 1,1,1-triphenylethane units in the main chain

A dicarboxylic acid {1,1-bis[4-(4-trimellitimidophenoxy)phenyl]-1-phenylethane (II)} bearing two performed imide rings was prepared from the condensation of 1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenylethane and trimellitic anhydride in a 1/2 molar ratio. A novel family of poly(amide-imide)s with inherent viscosities of 0.83–1.51 dL/g was prepared by triphenyl phosphite-activated polycondensation from the diimide-diacid II with various aromatic diamines in a medium consisting of N-methyl-2-pyrrolidinone (NMP), pyridine, and calcium chloride. Because the 1,1,1-triphenylethane group of II was unsymmetrical, most of the resulting polymers showed an amorphous nature and were readily soluble in polar solvents such as NMP and N,N-dimethylacetamide. All the soluble poly(amide-imide)s afforded tough, transparent, and flexible films, which had tensile strengths ranging from 88 to 102 MPa, elongations at break from 6 to 11%, and initial moduli from 2.23 to 2.71 GPa. The synthesized poly(amide-imide)s possessed glass-transition temperatures from 250 to 287 °C. The poly(amide-imide)s exhibited excellent thermal stabilities and had 10% weight losses from 501 to 534 °C under a nitrogen atmosphere. A comparative study of some corresponding poly(amide-imide)s is also presented.

Synthesis and characterization of aromatic polyamides based on a bis(ether-carboxylic acid) or a dietheramine derived from tert- butylhydroquinone

1,4-Bis(4-carboxyphenoxy)-2-tert-butylbenzene (2a) and 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (2b) were synthesized in two steps starting from the nucleophilic aromatic substitution reaction of p-fluorobenzonitrile and p-chloronitrobenzene, respectively, with tert-butylhydroquinone in the presence of potassium carbonate in N,N-dimethylformamide (DMF). Aromatic polyamides were synthesized by direct polycondensation from diacid 2a with various diamines or from diamine 2b with various diacids, by means of triphenyl phosphite and pyridine in N-methyl-2-pyrrolidone solution containing calcium chloride. Inherent viscosities of the polyamides ranged from 0.64 to 1.04 dL/g. Almost all the polyamides are readily soluble in various organic solvents and afford transparent and tough films by solvent casting. The polyamides display T g values of 209-267°C and 10% weight loss values above 460°C in nitrogen and 439°C in air. A comparative study of some polyamides with an isomeric repeating unit is also presented.

Preparation and characterization of organosoluble copolyimides based on a pair of commercial aromatic dianhydride and one aromatic diamine, 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene, series

A series of copolyimides (co-PIs) with high molecular weights, excellent mechanical properties, heat-resistant properties, and good solubilities in organic solvents were synthesized from six kinds of commercial dianhydrides (IIa–f) and 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (I). Monomers (IIa–d) for synthesizing insoluble PIs and monomers (IIe,f) for synthesizing soluble PIs were used to synthesize co-PIs with arbitrary solubilities. Nine kinds of soluble co-PIs (IIIa–e and IVa–d) were synthesized through chemical or thermal cyclodehydration. These co-PIs were found to be easily soluble as well as able to be processed by casting from their solutions such as NMP, DMAc, m-cresol, pyridine, THF, and CH2Cl2. The easily dissolved characteristics of this series of co-PIs stemmed from the t-butyl group and ether group within I. Besides, when the used dianhydride molecules contained the organosoluble groups, the solubilities in organic solvents could be greatly enhanced. The co-PIs could improve the processability of polymers, while increasing their flexible mechanical properties and maintaining their excellent heat-resistant properties.