The nature of active sites and stereospecificity of their action in diene polymerization catalysed by chromium-containing systems

A study has been made of the nature of active sites, stereospecificity of their action and the regularities of diene polymerization catalysed by chromium-containing systems. All possible polymer structures with high stereospecificity can be produced for butadiene and isoprene with π-allyl chromium compounds. Tris-π-allyl chromium produces polybutadiene predominantly of 1,2-units. Cis-polybutadiene is formed when the electronegative group (Cl^?, CCl₃COO^?) is substituted for one or two π-allyl groups in Tris-allyl chromium or in the catalytic system (π-C₃H₅)₃CrAl₂O₃. A catalyst obtained through interaction of (π-C₃H₅)₃Cr with silica-alumina or silica gel produces 1,4-trans-polybutadiene and 1,4-trans-polyisoprene. The rate of butadiene polymerization in the presence of Tris-π-allyl chromium is given by k[Cr]², and in polymerization of isoprene with the catalytic system (π-C₃H₅)₃Cr-silica-alumina, by k[Cr].[M]². Polymerization of dienes catalysed by (π-C₃H₅)₃Cr-silica-alumina system or supported chromium oxide catalyst proceeds according to a type of living system. A study was made of copolymerization of butadiene and isoprene in the presence of supported chromium oxide catalyst and with that produced by the reaction of (π-C₃H₅)₃Cr with silica-alumina. The constants of copolymerization for the systems were equal. A conclusion has been drawn regarding the similar mechanisms for diene polymerization under the action of supported chromium oxide catalyst or of catalyst formed in the reaction of (π-C₃H₅)₃Cr with silica-alumina or silica gel.     

The Ionization Potentials of Butadiene,Hexatriene, and their Methyl Derivatives: Evidence for through space interaction between double bond π-orbitals and non-bonded pseudo-π orbitals of methyl groups?

It is shown that the correlation of the π-ionization potentials of ethylene ( 1 ), butadiene ( 2 ) and trans-1,3,5-hexatriene ( 4 ) favours the orbital sequence π, π, σ in butadiene and π, π, σ, π in the hexatriene in excellent agreement with the results of SPINDO calculations. Within the experimental error the π-ionization potentials of cis-1,3,5-hexatriene ( 3 ) and trans-1,3,5-hexatriene ( 4 ) are the same. Methyl-substitution of 2 lowers the π-ionization potentials I₁(π) and I₂(π). For 1 and/or 4 substitution the difference I₂(π)?I₁(π) remains constant (≈ 2.5 eV). On the other hand 2 and/or 3 substitution leads to a smaller gap of I₂(π)–I₁(π) ≈ 1.6 to 2.0 eV without changing the mean π-ionization potential I (π) relative to the corresponding 1,4 substituted derivatives. This result is rationalized in terms of a through space interaction between double bond π-orbitals and non-bonded pseudo-π-orbitals of the substituting methyl groups. The reduced split I₂(π)–I₁(π) in cyclopentadiene is attributed to hyperconjugation across the methylene group.     

The characteristics of lanthanide coordination catalysts and the cis-polydienes prepared therewith

The stereoregularity of polydienes is almost the same in regard to the individual elements of the lanthanide series, whereas the activity of the Ln catalysts in diene polymerization varies from one to the other within the series. The latter may be attributed to the difference in the number of electrons that occupy the 4f orbitals. It has been proved that the polymerization of dienes with Ln catalysts under certain conditions proceeds by a “living polymer” mechanism. With regard to the polymerization of butadiene, the most active catalyst is a Nd³⁺species a new binary system of NdCl₃-3ROH + AlR₃ has been discovered. The cis- 1,4 content in polybutadiene is about 97% and the 1,2 content, less than 1%. For the polymerization of isoprene with a Nd³⁺ catalyst system, the effects of ligand and alkyl groups in AIR₃ on cis-1,4 content (ca. 95%) in polyisoprene can be neglected. For the copolymerization of butadiene and isoprene, the cis-1,4 contents of these two monomeric units in the copolymer are greater than 95% the reactivity ratios r₁ and r₂ are determined. and the T_g's of the copolymers of various compositions deviate slightly from the calculated values for random copolymers. A linear relationship exists between the yield strength from the stress-strain curve of Ln-polvbutadiene and its [n] This relationship is verified by Ln-polyisoprene and natural rubber but different slopes are obtained     

Homo‐ and Copolymerization of Butadiene Catalyzed by an Bis(imino)pyridyl Vanadium Complex

Summary: The bis(imino)pyridyl vanadium(III ) complex [VCl₃{2,6‐bis[(2,6‐iPr₂C₆H₃)NC(Me)]₂(C₅H₃N)}] activated with different aluminium cocatalysts (AlEt₂Cl, Al₂Et₃Cl₃, MAO) promotes chemoselective 1,4‐polymerization of butadiene with activity values higher than classical vanadium‐chloride‐based catalysts. The polymer structure depends on the nature of the cocatalyst employed. The MAO‐activated complex was also found to be active in ethylene‐butadiene copolymerization, producing copolymers with up to 45 mol‐% of trans‐1,4‐butadiene. Crystalline polyethylene and trans‐1,4‐poly(butadiene) segments were detected in these copolymers by DSC and ¹³C NMR spectroscopy.

     

Equimolecular binary polydines. V. Equibinary poly(cis-1,4–trans-1,4)butadiene from bis(π-allyl nickel trifluoroacetate)

The preparation of equibinary poly(cis-1,4–trans-1,4)butadiene was investigated in the presence of bis(π-allyl nickel trifluoroacetate) modified with suitable additional ligands. The behavior of the catalytic species in the polymerization reaction as well as the specific basic properties of the equibinary polybutadiene produced support obviously a regular distribution of the cis and trans isomers in the polymer chains.     

Styrene/1,3‐butadiene copolymerization by C2‐symmetric group 4 metallocenes based catalysts

C₂‐symmetric group 4 metallocenes based catalysts (rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ (1) , rac‐[CH₂(1‐indenyl)₂]ZrCl₂ (2) and rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]TiCl₂ (3) ) are able to copolymerize styrene and 1,3‐butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by ¹³C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain‐end happens prevailingly with 1,4‐trans configuration. In the butadiene homosequences, using zirconocene‐based catalysts, the 1,4‐trans arrangement is favored over 1,4‐cis, but the latter is prevailing in the presence of titanocene (3) . Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r₁ × r₂ = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene–butadiene copolymers (r₁ × r₂ = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (n_s = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476–1487, 2008     

Homo- and copolymerization of butadiene and styrene with neodymium tricarboxylate catalysts

Homo- and copolymerizations of butadiene (BD) and styrene (St) with rare-earth metal catalysts, including the most active neodymium (Nd)-based catalysts, have been examined, and the cis-1,4 polymerization mechanism was investigated by the diad analysis of copolymers. Polymerization activity of BD was markedly affected not only by the ligands of the catalysts but also by the central rare-earth metals, whereas that of St was mainly affected by the ligands. In the series of Nd-based catalysts [Nd(OCOR)₃:R = CF₃, CCl₃, CHCl₂, CH₂Cl, CH₃], Nd(OCOCCl₃)₃ gave a maximum polymerization activity of BD, which decreased with increasing or decreasing the pKa value of the ligands. This tendency was different from that for Gd(OCOR)₃ catalysts, where the CF₃ derivative led to the highest polymerization activity of BD. For the polymerization of St and its copolymerization with BD, the maximum activities were attained at R = CCl₃ for both Nd- and Gd-based catalysts. The copolymerization of BD and St with Nd(OCOCCl₃)₃ catalyst was also carried out at various monomer feed ratios, to evaluate the monomer reactivity ratios as r_BD = 5.66 and r_St = 0.86. The cis-1,4 content in BD unit decreased with increasing St content in copolymers. From the diad analysis of copolymers, it was indicated that Nd(OCOCCl₃)₃ catalyst controls the cis-1,4 structure of the BD unit by a back-biting coordination of the penultimate BD unit. Furthermore, the long range coordination of polymer chain by the neodymium catalyst was suggested to assist the cis-1,4 polymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 241–247, 1998     

Copolymerization of dienes with neodymium tricarboxylate-based catalysts and cis-polymerization mechanism of dienes

It was found that poly(butadiene), poly(isoprene), and poly(2,3-dimethylbutadiene) with high cis-1,4 content were obtained with Nd(OCOR)₃–(i-Bu)₃Al–Et₂AlCl catalysts (R = CF₃, CCl₃, CHCl₂, CH₂Cl, CH₃) in hexane at 50°C [cis-1,4 content: poly(BD), > 98%; poly(IP), ≥ 96%; poly(DMBD), ≥ 94%]. Copolymerization of IP and styrene (St) was carried out at various monomer feed ratios to evaluate the monomer reactivity ratio and cis-1,4 content of the diene unit and then to elucidate the cis-1,4 polymerization mechanism of IP. The cis-1,4 content of the IP unit in the copolymers decreased with increasing St content in the copolymers. The cis-1,4 polymerization was disturbed by incorporating St unit in the copolymers, since the penultimate St unit hardly coordinates to the neodymium metal, resulting in a decrease of the cis-1,4 content in the copolymers. That is, the cis-1,4 polymerization of IP is suggested to be controlled by a back-biting coordination of the penultimate diene unit. On the other hand, in the case of poly(BD-co-IP) and poly(BD-co-DMBD), the cis-1,4 content of the BD, IP, and DMBD units in the copolymers was almost constant (cis: 94–98%), irrespective of the monomer feed ratios and polymerization temperature. Consequently, the penultimate IP and DMBD units favorably control the terminal BD, IP, or DMBD unit to the cis-1,4 configuration through the back-biting coordination. For the monomer reactivity ratios, a clear difference was observed in each system: r_BD = 1.22, r_IP = 1.14; r_BD = 40.9, r_DMBD = 0.15. Low polymerizability of DMBD was mainly ascribed to the steric effect of the methyl substituents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1707–1716, 1998     

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride immobilized on MgCl2‐based supports as a highly effective precursor for ethylene polymerization

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride supported on MgCl₂(THF)₂ or on the same carrier modified by Et_nAlCl_3?n, where n = 1–3, was used in ethylene polymerization in the presence of MAO or a common alkylaluminium compounds as a cocatalyst. The support type alter vanadium loading and also change the characteristic of the catalytic active sites. Et₂AlCl is the best activator for a catalyst which has been immobilized on a nonmodified support, whereas the systems which contain a carrier which has been modified by an organoaluminium compound reveal the highest activity in conjunction with MAO. That difference, together with different temperature effects on polymerization efficiency (i.e., decrease and increase of catalytic activity for increasing temperatures, respectively) suggest the formation of different types of active sites in the catalytic systems supported on modified and nonmodified magnesium carrier. However, all supported precatalysts possess a long lifetime, still being active towards ethylene polymerization after 2 h. All the systems yield wide MWD polyethylene, while bimodal MWD is found for some part of analyzed samples. Polyethylene with bimodal particle size distribution is formed with the system which contain modified carriers at higher temperatures. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3480–3489, 2009     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. IV. Mechanism of syndiotactic polymerization of butadiene with cobalt compounds–organoaluminum–CS2

A mechanism is proposed for the polymerization of syndiotactic 1,2-polybutadiene (s-PB) with soluble cobalt-organoaluminum-CS₂. The proposed active species have structures which consist of side-on coordination of CS₂ to cobalt, anti-π-allyl growing end, cisoid bidentate coordination of butadiene, and activation by complex formation with organoaluminum at the nonbonded sulfur of the coordinated CS₂. This proposal is based on findings for the aluminum-free catalyst Co(C₄H₆)(C₈H₁₃)-CS₂. It is tentatively interpreted that syndiotactic 1,2 polymerization proceeds under the influence of the side-on coordinated CS₂, by which the reactivity between the terminal carbons of butadiene and the C3 of the π-allyl end is enhanced.     

The polymerization of butadiene by bis(η3-allylnickeltrifluoroacetate)/tetrachloro-1,4-benzoquinone revisited

The catalytic system bis(n³-allylnickeltrifluoroacetate)/tetrachloro-1,4-benzoquinone, reported in the literature to initiate the living polymerization of butadiene, was re-examined in more detail. All experiments dealing with catalyst-cocatalyst preparation indicate that, although polymerization rates are comparable to those reported previously, the present system is far from perfectly living. The dependence of M̄_n on conversion suggests that chain-transfer, most probably by β-hydride elimination, plays an important role.     

Polymerization of butadiene sulfone

Polymerization of butadiene sulfone (BdSO₂) by various catalysts was studied. Azobisisobutyronitrile (AIBN), butyllithium, tri-n-butylborn (n-Bu)₃B, boron trifluoride etherate, Ziegler catalyst, and γ-radiation were used as catalysts. Butadiene sulfone did not polymerize with these catalysts at low temperatures (below 60°C.), but polymers were obtained at high temperature with AIBN or (n-Bu)₃B. The polymerization of BdSO₂ initiated by AIBN in benzene at 80–140°C. was studied in detail. The obtained polymers were white, rubberlike materials and insoluble in organic solvents. The polymer composition was independent of monomer and initiator concentrations and reaction time. The sulfur content in polymer decreased with increasing polymerization temperature. The polymers prepared at 80 and 140°C. have the compositions (C₄H₆)_1.55- (SO₂) and (C₄H₆)_3.14(SO₂), respectively, and have double bonds. These polymers were not alternating copolymers of butadiene with sulfur dioxide. The polymerization mechanism was discussed from polymerization rate, polymer composition, and decomposition rate of BdSO₂. From these results, the polymerization was thought to be “decomposition polymerization,” i.e., butadiene and sulfur dioxide, formed by the thermal decomposition of BdSO₂, copolymerized.     

Stereospecific and molecular weight‐controlled polymerization of 1,3‐butadiene with Co(acac)3‐MAO catalyst

The polymerization of butadiene (Bd) with Co(acac)₃ in combination with methylaluminoxane (MAO) was investigated. The polymerization of Bd with Co(acac)₃‐MAO catalysts proceeded to give cis‐1,4 polymers (94 – 97%) bearing high molecular weights (40 × 10⁴) with relatively narrow molecular weight distributions (M_w's/M_n's). The molecular weight of the polymers increased linearly with the polymer yield, and the line passed through an original point. The polydispersities of the polymers kept almost constant during reaction time. This indicates that the microstructure and molecular weight of the polymers can be controlled in the polymerization of Bd with the Co(acac)₃‐MAO catalyst. The effects of reaction temperature, Bd concentration, and the MAO/Co molar ratio on the cis‐1,4 microstructure and high molecular weight polymer in the polymerization of Bd with Co(acac)₃‐MAO catalyst were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2793–2798, 2001     

Synthesis of ladder polymers containing polydiacetylene backbones connected with methylene chains and their optical properties

The polymers consisting of polydiacetylene (PDA) backbones were obtained from the novel monomer derivatives, R CC CC R′ CC CC R [where R =  (CH₂)₄OCONHCH₂COOC₄H₉, R′ =  (CH₂)_n ; n = 2, 4, 8] [4BCMU4A(n)], in which linear methylene chain is sandwiched between two diacetylene moieties by solid-state 1,4-addition reaction. The polymerization process was investigated in detail by using spectroscopic techniques such as solid-state ¹³C-NMR, visible absorption, and IR absorption spectra. It was estimated that the polymerization of 4BCMU4A(8) and 4BCMU4A(4) takes place by two consecutive 1,4-addition reactions to form two PDA backbones, which constitute the two poles of the respective ladders. The bridging methylene chain length in the monomer was found to play a vital role as far as the polymerization process is concerned. Thus, the monomers with eight or four methylene units could form the ladder–PDAs by a two-step process, whereas the monomer containing two methylene units could only undergo one-step of 1,4-addition reaction. Further, it was found that the crystallinity of the polymers depends on the methylene chain length in the monomers, 4BCMU4A(8) being the most crystalline of all. These structural features strongly affect their absorption spectra. The third-order nonlinear optical susceptibilities (χ⁽³⁾) for these polymers were measured using third-harmonic generation method. The largest χ⁽³⁾ value obtained was 3.4 × 10⁻¹¹ esu for the poly[4BCMU4A(8)] thin film in resonant region. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3537–3548, 1999     

Copolymerization of 1,3‐butadiene and isoprene with cobalt dichloride/methylaluminoxane in the presence of triphenylphosphine

The homopolymerization and copolymerization of 1,3‐butadiene and isoprene were achieved at 0 °C with cobalt dichloride in combination with methylaluminoxane and triphenylphosphine (Ph₃P). For 1,3‐butadiene, highly cis‐specific and 1,2‐syndiospecific polymerization proceeded in the absence or presence of Ph₃P, respectively, although the activity with Ph₃P was much higher than that without Ph₃P. Only a trace of the polymer was, however, obtained in isoprene polymerization when Ph₃P had been added. For copolymerization, the polymer yield in the presence of Ph₃P was about three times higher than that in its absence. Copolymerization in the presence of Ph₃P was, therefore, investigated in more detail. Unimodal gel permeation chromatography elution curves with narrower polydispersity (weight‐average molecular weight/number‐average molecular weight ≈ 1.5) indicated that the propagation reaction proceeded by single‐site active species. Both the yield and molecular weight of the copolymer decreased with an increasing amount of isoprene in the feed, and this was followed by an increase in the isoprene content in the copolymer. The monomer reactivity ratios, r₁ (1,3‐butadiene) and r₂ (isoprene), were estimated to be 2.8 and 0.15, respectively. Although the 1,3‐butadiene content in the copolymer was strongly dependent on the comonomer composition in the feed, the ratio of 1,2‐inserted units to 1,4‐inserted units of 1,3‐butadiene was constant. Concerning the isoprene unit, the percentage of 1,2‐ and 3,4‐inserted units was increased at the expense of 1,4‐inserted units with an increasing isoprene content in the feed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3086–3092, 2002     

Polar,functionalized diene‐based material. III. Free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadienes

The bulk free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadiene with methyl, ethyl, and n‐propyl substituents was studied. The monomers were synthesized via substitution reactions of 2‐bromomethyl‐1,3‐butadiene with the corresponding dialkylamines. For each monomer the effects of the polymerization initiator, initiator concentration, and reaction temperature on the final polymer structure, molecular weight, and glass‐transition temperature (T_g) were examined. Using 2,2′‐azobisisobutyronitrile as the initiator at 75 °C, the resulting polymers displayed a majority of 1,4 microstructures. As the temperature was increased to 100 and 125 °C using t‐butylperacetate and t‐butylhydroperoxide, the percentage of the 3,4 microstructure increased. Differential scanning calorimetry indicated that all of the T_g values were lower than room temperature. The T_g values were higher when the majority of the polymer structure was 1,4 and decreased as the percentage of the 3,4 microstructure increased. The Diels–Alder side products found in the polymer samples were characterized using NMR and gas chromatography‐mass spectrometry methods. The polymerization temperature and initiator concentration were identified as the key factors that influenced the Diels–Alder dimer yield. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4070–4080, 2000     

Synthesis of [?CH2C(CO2Et)2CH2Ar?]n polymers and their unique optical properties by through‐space interactions between Ar and CO groups

Polymers of type [? CH₂C(CO₂Et)₂CH₂Ar? ]_n (Ar = 1,4‐phenylene, 2,6‐naphthylene, 9,10‐anthrylene, or 1,4‐phenylene‐ethynylene‐1,4‐phenylene) were synthesized by alkylation of diethyl malonate with XCH₂ArCH₂X (X = Cl or Br). These polymers exhibited unexpectedly enhanced UV absorption and strong, broad, bathochromically shifted fluorescence spectra compared with the parent Ar compounds. The origin of these photophysical characteristics was postulated to be a configuration interaction between the π→π* excitation of the aromatic moiety and the n→π* excitation of the carbonyl moiety on the trimethylene tether via intramolecular charge transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

C2‐Symmetric Zirconocenes in the Polymerization of Conjugated Diolefins

C₂‐symmetric zirconocenes activated by methylaluminoxane were utilized as catalysts in the polymerization of 1,3‐diolefins. The results indicate that the most crowded catalytic precursor rac[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ ( 1 ) is also the most active one, giving 1,4‐polymerization of 1,3‐butadiene and (Z)‐1,3‐pentadiene and 1,2‐polymerization of (E)‐1,3‐pentadiene and 4‐methyl‐1,3‐pentadiene. Probably, the different behavior of 1 with respect to other C₂‐symmetric zirconocenes utilized is due to the different stability of the bond between the last inserted monomer unit and the metal, as well as to the coordination of incoming monomer.     

Interaction of LnCl3 · 6H2O crystal hydrates with the alkoxy derivatives of aluminum in organic solvents

The interaction of LnCl₃ · 6H₂O (Ln = Pr, Nd, and Tb) with the alkoxy derivatives of aluminum (RO)_nAlCl_3?n (where R = Et or iso-Bu; n = 1–3) in organic solvents was studied. It was found that the reaction of the crystal water of LnCl₃ · 6H₂O with (RO)_nAlCl_3?n resulted in the partial dehydration of the crystal hydrates with the formation of an alcohol (ROH) and the LnCl₃ · 3H₂O · 3(RO)_mAl(OH)Cl_2?m complex (m = 1, 2). The solid colloidal particles of this complex and a solvent form a lanthanide-containing gel. The physicochemical (including luminescence) and catalytic properties of the complex in butadiene polymerization and 1,1-gem-dibromo-2-phenylcyclopropane dehalogenation were studied.     

Anionic polymerization of N,N‐dialkyl‐2‐methylenebut‐3‐enamide: Effect of alkyl substituents on polymerization behavior

Anionic polymerizations of three 1,3‐butadiene derivatives containing different N,N‐dialkyl amide functions, N,N‐diisopropylamide (DiPA), piperidineamide (PiA), and cis‐2,6‐dimethylpiperidineamide (DMPA) were performed under various conditions, and their polymerization behavior was compared with that of N,N‐diethylamide analogue (DEA), which was previously reported. When polymerization of DiPA was performed at ?78 °C with potassium counter ion, only trace amounts of oligomers were formed, whereas polymers with a narrow molecular weight distribution were obtained in moderate yield when DiPA was polymerized at 0 °C in the presence of LiCl. Decrease in molecular weight and broadening of molecular weight distribution were observed when polymerization was performed at a higher temperature of 20 °C, presumably because of the effect of ceiling temperature. In the case of DMPA, no polymer was formed at 0 °C and polymers with relatively broad molecular weight distributions (M_w/M_n = 1.2) were obtained at 20 °C. The polymerization rate of PiA was much faster than that of the other monomers, and poly(PiA) was obtained in high yield even at ?78 °C in 24 h. The microstructure of the resulting polymers were exclusively 1,4‐ for poly(DMPA), whereas 20–30% of the 1,2‐structure was contained in poly(DiPA) and poly(PiA). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3714–3721, 2010