Synthesis and Thermal Properties of Alternating Copolymers of N‐Methylmaleimide with Olefins Including Cyclic and Polar Groups

The radical alternating copolymerization of N‐methylmaleimide with various olefins was carried out to obtain thermally stable and transparent polymers. Cyclic olefins including an exo‐methylene group showed high polymerization reactivities during the copolymerization. The introduction of a polar substituent into the olefin monomers results in the formation of copolymers with a high yield. The polymerization reactivity of the olefins is discussed based on DFT calculations. The introduction of cyclic and polar substituents into the olefin repeating units increased the glass transition temperature of the obtained copolymers, similar to the previously reported results for the introduction of bulkier and polar substituents into the N‐substituents of the maleimide.

     

The Effect of Side Chain Length and Hydrogen Bonding on the Viscoelastic Property of Isobutene/Maleimide Copolymers

The viscoelastic properties of the alternating copolymers of N‐substituted maleimides with n‐alkyl and ω‐carboxy‐n‐alkyl groups as the N‐substituent with isobutene were investigated by dynamic mechanical analysis. The transition temperatures in the α‐relaxation region depended on the alkyl chain length and the presence or absence of a terminal carboxy group in the side chain. β‐Relaxation due to side chain dynamics was also observed in a lower temperature region without merging the α‐ and β‐relaxation processes for all the copolymers. The molecular motions of the semiflexible main chain and the flexible side alkyl groups were investigated as well as the intermolecular interaction by hydrogen bonding of the carboxyl groups.

     

Synthesis and Thermal Properties of Comb‐Like Maleimide Copolymers Containing Polymethylene and Poly(Ethylene Oxide) Side Chains as the N‐Substituents

The radical copolymerization of N‐substituted maleimides containing polymethylene and poly(ethylene oxide) side chains as the N‐substituent groups with isobutene, styrene, and α‐methylstyrene as the electron‐donating monomers is carried out in order to investigate the structure and thermal properties of the resulting comb‐like copolymers. The obtained copolymers show excellent thermal stability and their glass transition temperatures vary depending on the chain length of the introduced N‐substituents. The main‐ and side‐chain motions of the copolymers are investigated by dynamic mechanical analysis at various frequencies over the temperature range of ?150 to 100 °C.

     

Radical Copolymerization Reactivity of N‐Substituted Maleimides with α‐Substituted Styrenes with Various N‐ and α‐Substituents and the Thermal and Optical Properties of the Resulting Copolymers

The radical alternating copolymerization of N‐substituted maleimides (RMIs) with N‐methyl, n‐butyl, and 2‐ethylhexyl groups and styrene derivatives with various α‐substituents (RSs) is carried out. The yield and the molecular weight of the obtained copolymers significantly decrease with an increase in the size of the α‐substituent of RSs, but are independent of the N‐substituents. The glass‐transition temperature of the copolymers increases on the introduction of the large substituents into the RS repeating units. The high‐molecular‐weight poly(RMI‐alt‐RS)s are soluble in organic solvents and provide flexible and transparent films with excellent transparency by casting the solutions.

     

Thermosetting Maleimide/Isobutene Alternating Copolymer as a New Class of Transparent Materials

We synthesized an alternating copolymer of N‐allylmaleimide (AMI) and isobutene (IB) [poly(AMI‐alt‐IB)] as a new class of thermosetting polymers by the free radical copolymerization process. The reactivity of the maleimide group of the AMI monomer was evaluated to be 10³ times higher than that of the N‐allyl group based on the results for the ternary copolymerization system composed of N‐methylmaleimide (MMI), N‐allylphthalimide (AP), and IB. The maleimide moiety exclusively participated in the propagation during the copolymerization of AMI with IB, resulting in the formation of the soluble poly(AMI‐alt‐IB). The copolymer included an alternating repeating structure consisting of maleimide and IB units in the main chain and the unreacted allyl group in the side chain. The onset temperature of the decomposition for poly(AMI‐alt‐IB) was over 400 °C in a nitrogen stream. The transparent cast film of poly(AMI‐alt‐IB) was readily cured upon heating without any catalyst.

     

Synthesis and Ozone Degradation of Alternating Copolymers of N‐Substituted Maleimides with Diene Monomers

Radical copolymerization of N‐substituted maleimides (RMIs) and maleic anhydride (MAn) in combination with 2,4‐dimethyl‐1,3‐pentadiene (DMPD) and 1,3‐pentadiene (PD) provides alternating copolymers with excellent thermal stability. Onset temperatures of decomposition are 280–331 and 336–371 °C for the copolymers with DMPD and PD, respectively. Glass transition temperatures of RMI copolymers are in a wide range of 54–138 °C depending on the bulkiness of N‐substituents. MAn copolymers are transformed to the corresponding RMI copolymers by postpolymerization reactions, which consist of quantitative addition of an alkylamine to an anhydride moiety of MAn copolymers and the subsequent heating. The copolymers synthesized in this study include ozone‐degradable carbon‐to‐carbon double bonds in their main chain. Molecular weight of the copolymers rapidly decreases by ozone degradation. Surface modification of casted polymer films is also performed by exposure to ozone‐containing air.     

The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free‐Radical Polymerizations of Hydroxypropyl Methacrylate

The propagation rate coefficient k_p was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size‐exclusion chromatography. k_p data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO₂. With the exception of THF, no solvent influence on k_p was observed. For polymerizations in THF k_p values 40% below the corresponding bulk data were obtained. In addition, the activation energy of k_p for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1 703 cm^?1 and 1 720 cm^?1 is indicative of the vibrations of two different – associated vs. not associated – types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs.

Temperature dependence of k_p for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22 . Open symbols refer to ν_rep = 10 Hz and filled symbols to ν_rep = 25 Hz.     

pH‐Sensitive Micelles Formed by Interchain Hydrogen Bonding of Poly(methacrylic acid)‐block‐Poly(ethylene oxide) Copolymers

pH‐sensitive micelles formed by interchain hydrogen bonding of poly(methacrylic acid)‐block‐poly(ethylene oxide) copolymers were prepared and investigated at pH < 5. Both and R_h of the micelles increase with decreasing pH of the solution, displaying an asymptotic tendency at low pH values. The observed micelles are well‐defined nanoparticles with narrow size distributions (polydispersity ΔR_h/R_h ≤ 0.05) comparable with regular diblock copolymer micelles. The CMCs occur slightly below c = 1 × 10^?4 g · mL^?1. The micelles are negatively charged and their time stability is lower than that of regular copolymer micelles based purely on hydrophobic interactions.

     

Evidence of Intramolecular Cyclization in Copolymerization of Ethylene with 1,3‐Butadiene: Thermal Properties of the Resulting Copolymers

Summary: Ethylene and butadiene were copolymerized with a silylene‐bridged bis(fluorenyl) complex {[Me₂Si(C₁₃H₈)₂]NdCl} ( 1 ) in combination with various alkylating agents (BuLi/AlH(iBu)₂, (Bu)MgCl, Mg(Bu)(Oct)). Copolymers have a unique microstructure since they contain 1,2‐cyclohexane rings and unsaturations along the polymer chain. An intramolecular mechanism was proposed for the formation of six‐membered rings. The influence of these cyclic structures on thermal properties of the copolymers has been investigated.

Proposed mechanism for formation of 1,2‐cyclohexane rings.     

The F···H Hydrogen Bonding Effect on the Dynamic Mechanical and Shape‐Memory Properties of a Fluorine‐Containing Polybenzoxazine

A fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based on o‐allylphenol and p‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular Ar F···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the Ar F···HO hydrogen bonding.

     

Chain Features and Their Influence on the Thermal Stability of Poly(propylene‐co‐1‐nonene) Copolymers

The thermal stability of several isotactic polypropylenes and propylene‐co‐1‐nonene copolymers is assessed under nitrogen by means of thermogravimetric analysis (TGA). The samples involve wide ranges of molecular weight, isotactic average length, and 1‐nonene content, in order to perform a comprehensive analysis of the effect that chain features exert on the apparent activation energy (E_a), in the initial stages of the molten state degradation. The degradation process correlates with chain mobility and, accordingly, with chain features that are linked to. Thus, microstructure and chain size are found to play a key role. In fact, isotactic average length of propylene sequences and molecular weight are driving factors in the E_a required for main chain thermal scission.     

Radical Copolymerization of Vinylidene Fluoride with 8‐Bromo‐1H,1H,2H‐perfluorooct‐1‐ene: Microstructure,Crosslinking and Thermal Properties

An original synthesis of 8‐bromo‐1H,1H,2H‐perfluorooct‐1‐ene (BDFO) and its radical copolymerization with vinylidene fluoride (VDF), initiated by 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane at 134 °C, are presented. The fluorinated bromoalkene was obtained by dehydrobromination of 1,8‐dibromo‐1H,1H,2H,2H‐perfluorooctane in a satisfactory yield. Although BDFO did not homopolymerize under radical initiation, it did copolymerize with VDF. The compositions of the resulting random type copolymers were calculated by means of ¹⁹F NMR spectroscopy and allowed the quantification of the respective amounts of both comonomers in the copolymers, showing good incorporation of the brominated monomer. Nevertheless, obtaining PVDF copolymers containing a high molar percentage of BDFO in good yields was difficult to achieve from initial molar ratios of BDFO higher than 9.2 mol‐%. Radical terpolymerization of VDF, BDFO and hexafluoropropene (HFP) was also successfully achieved. BDFO contents in these co‐ or terpolymers ranged from 3.6 to 12.2 mol‐%. The bromoalkene acted as a cure site monomer and the resulting poly(VDF‐co‐BDFO) copolymers were crosslinked via the bromine atom in the presence of a triallyl isocyanurate/peroxide system. The materials obtained led to more thermally stable copolymers than the uncured ones and their thermostabilities were compared to those of commercially available poly(VDF‐co‐HFP) copolymers crosslinked using diamines.

     

Control of Molecular Weight and Tacticity in Stereospecific Living Cationic Polymerization of α‐Methylstyrene at 0 °C Using FeCl3‐Based Initiators: Effect of Tacticity on Thermal Properties

The successful stereospecific living cationic polymerization of α‐methylstyrene (α‐MeSt) using FeCl₃‐based initiator systems at 0 °C is reported. Linear first‐order ln([M]₀/[M]) vs. time and linear molecular weight vs. conversion plots suggest that the polymerization is living in nature, which is further confirmed from successful chain‐extension experiments. Poly(α‐methylstyrene)s of varying syndiotacticities (59.1% to 79.2%) and controllable molecular weights (4300–32 100 g mol^?1) with moderately narrow polydispersity indices (PDIs ≈1.3) are synthesized simply by varying the monomer‐to‐initiator ratio ([M]₀/[I]₀). A possible mechanism for this stereospecific polymerization is proposed. The glass‐transition temperature and thermal‐decomposition temperature depend on the syndiotacticity of poly(α‐methylstyrene).