Synthesis and Photoinitiated Cationic Polymerization of Substituted 2‐Cyclopropyl‐4‐methylene‐1,3‐dioxolanes

The synthesis of substituted 2‐cyclopropyl‐4‐methylene‐1,3‐dioxolanes 6 a – c is described. Photoinitiated cationic polymerization at ambient temperatures in bulk and in solution was investigated using (η⁵‐2,4‐cyclopentadiene‐1‐yl)[1,2,3,4,5,6‐η (1‐(methylethyl) benzene)iron(II) hexafluorophosphate (Irgacure 261, I‐1 ) and ditolyliodonium hexafluoro‐phosphate ( I‐2 ). Upon irradiation a single ring‐opening polymerization occured within 4 min leading to polyether ketones 6 a – c with number average molecular weights M_w between 5 000 and 33 600 g/mol. No ring‐opening polymerization of the cyclopropane ring could be detected. A volume shrinkage of about 6.4% was found.     

Networks Based on Poly(α‐methylene‐δ‐valerolactone‐co‐δ‐valerolactone): Crosslinking Through Free‐Radical Vinyl Copolymerization

Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.

     

Synthesis of a Liquid Bisoxazolin‐5‐one by Radical Reaction of Bismercaptan onto 2‐Ethenyloxazolin‐ 5‐one

The synthesis of a liquid chain‐coupling agent obtained by the radical diaddition of bis(mercaptoethyl) ether on 2‐ethenyl‐4,4‐dimethyloxazolin‐5‐one is described. Different methods of synthesis have been studied and their products were characterized by IR, ¹H NMR spectroscopy, and by SEC. The classic thermal radical initiation leads to bisazlactone compounds, but a side reaction of azlactone ring opening occurs, which prevents this product from being employed as a chain‐extender. The low thermal initiation and the UV initiation lead to interesting products, but they are not suitable for being employed as chain‐coupling agent because of their functionality (less or more a difunctional compound). The most interesting method consists in synthesizing by low thermal initiation in a first step, and then in transforming residual 2‐ethenyl‐4,4‐dimethyloxazolin‐5‐one by UV initiation in a second step. The compound is composed by more than 95 per cent of difunctional azlactone compound and a few polyazlactone functional compound. The final compound is a stable liquid at room temperature under nitrogen atmosphere.     

Radical Polymerization Behavior of 4‐Monosubstituted and 2,4‐Disubstituted Enynes

The radical polymerization of 4‐mono‐ and 2,4‐disubstituted enyne monomers (CH₂=CH—C≡C—R and CH₂=C(CH₃)—C≡C—R, respectively; R = Ph, n‐Bu, t‐Bu, and (CH₃)₃Si—) was carried out to elucidate the polymerizability of the monomers and the effect of substituents on the structure of the resulting polymers. The polymerization of 4‐monosubstituted monomers proceeded in a specific 1,2‐fashion to give polymers having acetylene moieties as pendent groups. In contrast, that of 2,4‐disubstituted monomers accompanied ca. 10% of the 1,4‐polymerization to give allenic main chain structures. The monomer reactivity ratios of monosubstituted monomers were estimated from the copolymerization system with methyl methacrylate, from which the Q and e values were estimated as Q = 1.52–2.11 and e = –0.63 to –0.73, respectively. The Q and e values demonstrated that the resonance stabilizing character of the substituents on the 4‐position affects the reactivity of the monomers.     

Catalytic 1,3‐Cyclohexadiene Homopolymerization and Regioselective Copolymerization with Ethylene

Summary: 1,3‐Cyclohexadiene (CHD) was homo‐ and copolymerized by means of diimine nickel complexes and various substituted titanium based half‐sandwich complexes activated with methylaluminoxane (MAO). Soluble polycyclohexadienes were produced with the constrained geometry catalyst [Me₂Si(N^tBu)(Me₄Cp)]TiCl₂ (CBT) (Cp = cyclopentadienyl, Me = methyl). Only in the presence of CBT/MAO soluble high molecular weight CHD copolymers with ethylene were obtained. The CHD incorporation was varied between 0 and 12.3 mol‐%. According to NMR analysis the CHD/ethylene copolymerization is highly regioselective, accounting for exclusive formation of 1,4‐cyclohexene units randomly distributed in the polyethylene backbone.

¹³C NMR spectra of 1,4‐poly(1,3‐cyclohexadiene‐co‐ethylene) with 6.8 mol‐% CHD content in the copolymer.     

Radical telomerization of 1,3‐butadiene with perfluoroalkyl iodides

The radical telomerization of 1,3‐butadiene in the presence of 1‐iodoperfluorohexane and 1‐iodoperfluorooctane (R_FI) is presented. Experimental parameters (such as the nature of the radical initiator, temperature, solvent and initial molar ratios of the reactants) were varied to increase both 1,3‐butadiene and R_FI conversions. Best conditions are reached at 140–150°C with di‐tert‐butyl peroxide as initiator and acetonitrile as solvent. According to different conditions, the monoadduct and higher order telomers were synthesized with average number molecular weights ranging from 250 to 4 000 as determined by ¹H NMR spectroscopy and elemental analysis. 80% of the 1,4‐adducts were noted to lack a terminal iodine atom. The transfer constant of R_FI towards 1,3‐butadiene was determined to be C_T = 2.59 at 145°C which induces the formation of nonfunctional oligomers when a high [butadiene]₀/[R_FI]₀ molar ratio was used.     

Syndiospecific Living Block Copolymerization of Styrenic Monomers Containing Functional Groups,and Preparation of Syndiotactic Poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]}

At –25°C, the sequential block copolymerizations of 4‐(tert‐butyldimethylsilyloxy)styrene (TBDMSS) and 4‐methylstyrene (4MS) were investigated by using a syndiospecific living polymerization catalyst system composed of (trimethyl)pentamethylcyclopentadienyltitanium (Cp*TiMe₃), trioctylaluminum (AlOct₃) and tris(pentafluorophenyl)borane (B(C₆F₅)₃). The number‐average molecular weight (M̄_n) of the poly(TBDMSS)s increased linearly with increasing the polymer yield up to almost 100 wt.‐% consumption of TBDMSS used as 1^st monomer. The M̄_n value of the polymer after the second monomer (4MS) addition continued to increase proportionally to the polymer yield. The molecular weight distributions (MWDs) of the polymers remained constant at around 1.05–1.18 over the entire course of block copolymerization. It was concluded that the block copolymerizations of TBDMSS and 4MS with the Cp*TiMe₃ /B(C₆F₅)₃ /AlOct₃ catalytic system proceeded with a high block efficiency. The ¹³C NMR analysis clarified that the block copolymers obtained in this work had highly syndiotactic structure. By the deprotection reaction of silyl group with conc. hydrochloric acid (HCl), syndiotactic poly{(4‐hydroxystyrene)‐block‐[(4‐methylstyrene)‐co‐(4‐hydroxystyrene)]} (poly[HOST‐b‐(4MS‐co‐HOST)]) was successfully prepared.     

“Living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane by atom transfer radical polymerization

The “living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane (MPDO) in the presence of ethyl α‐bromobutyrate/CuBr/2,2′‐bipyridine at various temperatures has been investigated. In comparison with the conventional ring‐opening polymerization of MPDO, a lower content of ring‐opened unit in the polymer was found. The results of ln[M]₀/[M]) against polymerization time, (M_n)_th and (M_n)_NMR vs conversion, and GPC of the polymers are strongly indicative of the “living” polymerization process. Initiator efficiency was measured. The mechanism of polymerization, and the effect of pyridine on the polymerization mechanism were discussed.     

Oxidative Coupling Copolymerization of 4‐Methyltriphenylamine with Arenes

A novel synthetic method for the preparation of high‐molecular‐weight conjugated polymers is presented. It consists of the oxidation copolymerization of different arenes with triphenylamine. The structure of the copolymers was characterized by ¹H and ¹³C NMR spectra. The copolymers have good solubility in common organic solvents and are thermally stable. Photoluminescence (PL) spectra (see Figure) showed that the color of emission depends on the type of arene units in the copolymer chain. Cyclic voltammetry (CV) measurements revealed electrochemical activity of the copolymers.

PL spectra of the copolymers.     

Novel Methylaluminoxane‐Activated Neodymium Isopropoxide Catalysts for 1,3‐Butadiene Polymerization and 1,3‐Butadiene/Isoprene Copolymerization

The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)₃] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)₃/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 10⁵ g mol^‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)₃/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).

     

Influence of β‐Cyclodextrin on the Free‐Radical Copolymerization of N‐(4‐Methylphenyl)maleimide with N‐Vinylpyrrolidone in Water

Randomly methylated β‐cyclodextrin (me‐β‐CD) is used to include the hydrophobic monomer N‐(4‐methylphenyl)maleimide (MPM) ( 1 ) yielding the corresponding water‐soluble host‐guest structure 1a . Free‐radical copolymerization of 1a with N‐vinylpyrrolidone (NVP) ( 2 ) is performed and the reactivity ratios r₁ and r₂ are determined: 0.24 ± 0.03 (r₂) and 1.10 ± 0.05 (r_1a). This indicates a preferred incorporation of complexed maleimide into the copolymer chain. In contrast to that, the copolymerization of the uncomplexed monomers 1 and 2 is carried out using organic solvent (DMF/H₂O) showing reactivity ratios corresponding to nearly alternating copolymerization (r₂ = 0.09 ± 0.02; r₁ = 0.34 ± 0.03).

     

Novel Hyperbranched Poly(aryl ether urethane)s Using AB2‐Type Blocked Isocyanate Monomers and Copolymerization with AB‐Type Monomers

A novel AB₂‐type blocked isocyanate monomer was synthesized which was de‐blocked to provide a hyperbranched poly(aryl ether urethane). Copolymerization of this monomer with a functionally similar AB monomer yielded polymers with molecular weights in the range 8.0–310 kDa with a DB of 41–59% that underwent two‐stage decomposition above 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.09 to 1.10 dL · g^?1. End‐group modification of hyperbranched poly(aryl ether urethane)s was carried out with PEG monomethyl ether and 1‐decanol and affected the thermal properties and solubilities of the polymers. T_g of the polymers was reduced significantly from 201 to 71 °C upon incorporation of AB monomer in the copolymerization.

     

Synthesis of Hyperbranched Polyisoprene by Isoprene/Dimethyl‐di‐2,4‐Pentadieneyl‐(E,E)‐Silane Copolymerization Catalyzed with Half‐Sandwich Scandium Complex

A series of hyperbranched polyisoprenes (HBPIps) are synthesized by copolymerization of isoprene and a novel dipentadiene‐containing branching agent dimethyl‐di‐2,4‐pentadieneyl‐(E,E)‐silane (DMDPS) catalyzed by the half‐sandwich scandium complex (C₅Me₄SiMe₃)Sc(CH₂C₆H₄NMe₂‐o)₂/[Ph₃C][B(C₆F₅)₄]. Due to the high activity of DMDPS in copolymerization, and the very similar reactivity of the two pentadieneyl groups in DMDPS, the gelation reaction is successfully avoided in the highly branched products. The structural parameter branching factor (g′) of the HBPIps is determined to evaluate the branching degree. It is proved that in the polymerization both the concentration of DMDPS and isoprene exhibits significant influence on branching degree of HBPIps. By using the DMDPS as branching agent and simply controlling the polymerization conditions, high branching degree of g′ = 0.35 is achieved.     

Radical Copolymerization of α‐Trifluoromethylacrylic Acid with Vinylidene Fluoride and Vinylidene Fluoride/Hexafluoropropene

Summary: The radical copolymerization of α‐trifluoromethylacrylic acid (TFMAA) with vinylidene fluoride (VDF), initiated by tert‐butyl 2,2‐dimethyl peroxypropanoate (or tert‐butyl peroxypivalate) is presented. The kinetics of copolymerization were investigated from a series of eight reactions for which the initial [VDF]₀/[TFMAA]₀ molar ratios ranged between 15.0/85.0 and 89.4/10.6. The compositions of the copolymers, i.e. the molar ratios of VDF and TFMAA monomeric units, were determined mainly by ¹⁹F and ¹H NMR spectroscopy. According to the Tidwell and Mortimer method, the reactivity ratios, r_i, were assessed to be: r_VDF = 0.33 ± 0.09 and r_TFMAA = 0 at 55 °C, leading to copolymers of mainly alternating structure. Then, the radical terpolymerization of TFMAA with VDF and hexafluoropropene (HFP), initiated by 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane is described and the thermal properties of the materials produced are discussed.

     

Termination Kinetics of 1‐Vinylpyrrolidin‐2‐one Radical Polymerization in Aqueous Solution

Termination kinetics of 1‐vinylpyrrolidin‐2‐one radical polymerization in aqueous solution has been studied at 40 °C between 20 and 100 wt.‐% VP. The <k_t>/k_p values from laser single‐pulse experiments with microsecond time‐resolved NIR detection of monomer conversion, in conjunction with k_p from literature, yield chain‐length‐averaged termination rate coefficients, <k_t>. Because of better signal‐to‐noise quality, experiments were carried out at 2 000 bar, but also at 1 500, 1 000, and 500 bar, thus allowing for estimates of <k_t> at ambient pressure. The dependence of <k_t> on monomer conversion indicates initial control by segmental diffusion followed by translational diffusion and finally reaction diffusion control. To assist the kinetic studies, viscosities of VP–water mixtures at ambient pressure have been determined.

     

Stable Free‐Radical Copolymerization of Styrene with Acrylates Using OH‐TEMPO

Summary: Stable free‐radical copolymerizations (SFRP) of styrene with N‐acryloyl morpholine (AMo), 2‐ethoxyethyl acrylate (EOEA) and isobornyl acrylate (iBoA), respectively, were carried out under control of the stable nitroxide radical 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐N‐oxyl (OH‐TEMPO). The polymerizations were initiated by a polystyrene macroinitiator (PS‐MI). No accelerating agents were used. In contrast to the experiences made with methacrylates there was no decrease in the polymerization rates up to 50 mol‐% of AMo or EOEA in the monomer mixture. This behavior was ascribed to a compensation of the lack of thermal initiation by the high propagation rate constants of the acrylates. The produced AB diblock polymers were successfully employed in block extension reactions in styrene yielding ABA triblock polymers. Copolymerization reactivity ratios (r‐values) and glass transition temperatures have been estimated.

Monomer structures.     

Atom Transfer Radical Copolymerization of α‐Olefins with Methyl Acrylate: Determination of Activation Rate Parameters

Summary: The activation rate parameters of three model compounds for an acrylate/α‐olefin atom transfer radical copolymerization were investigated. It appeared that the activation of the model compound for the dormant acrylate chain (methyl‐2‐bromopropionate) was quite fast (k_act = 0.018 (±0.001) L · mol^?1 · s^?1 at 0 °C). The activation of the model compound for the dormant α‐olefin chain end (2‐bromobutane) did not take place at any appreciable rate (0 and 35 °C). The introduction of a penultimate acrylate unit in the model compound for the dormant α‐olefin chain end (H‐MA‐hexene‐Br) did not result in any activation at 0 and 35 °C. Only at 70 °C some activation was visible after 18 h reaction time. By inference, these results confirm our earlier conclusion that the ATR copolymerization of acrylates and α‐olefins is possible due to the fast crosspropagation of an α‐olefin chain end radical with an acrylate.

¹H NMR spectra for the MBrP/Cu(I)Br/PMDETA/hydroxy TEMPO (1/10/10/10) mixture.     

Radical Polymerization and Copolymerization of 12‐[(N‐Methacryloyl)carbamoyloxy]octadecanoic Acid

Radical polymerization of 12‐[(N‐methacryloyl)carbamoyloxy] octadecanoic acid ( 1 ) was kinetically and ESR spectroscopically investigated in acetone, using dimethyl 2,2′‐azobisisobutyrate ( 2 ) as initiator. The polymerization rate (R_p) is given by R_p = k [2]^0.7[1]^1.4 at 50°C. Propagating poly( 1 ) radical was observed as a 13‐lines spectrum by ESR under the actual polymerization conditions. The ESR‐determined k_p values (1.8–7.9 L/mol·s) are much lower than those of usual methacrylate monomers. The rate constant (k_t) of termination was determined to be k_t = 1.0–2.7·10⁴ L/mol·s from decay curve of the propagating radical. The Arrhenius plots of k_p and k_t gave the activation energies of propagation (63 kJ/mol) and termination (24 kJ/mol). A significant solvent effect was observed on the radical polymerization of 1 . The copolymerizations of 1 with styrene(St) and acrylonitrile were examined at 50°C. Copolymerization parameters obtained for the 1  (M₁)/St (M₂) system are as follows; r₁ = 0.73, r₂ = 0.57, Q₁ = 0.83, and e₁ = 0.13.