Liquid crystal polymers

Nanophase separation on length scales of 1–5 nanometres has been reported previously for small-molecule liquids1, metallic glasses and also for several semicrystalline, liquid-crystalline2,3 and amorphous4 polymers. Here we show that nanophase separation of incompatible main and side-chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups. We conclude from X-ray scattering and relaxation spectroscopy data for higher poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) that alkyl groups of different monomeric units aggregate in the melt and form self-assembled alkyl nanodomains with a typical size of 0.5–2 nm. A comparison with data for other polymer series having alkyl groups reveals that important structural and dynamic aspects are main-chain independent. A polyethylene-like glass transition within the alkyl nanodomains is observed and discussed in the context of a hindered glass transition in self-assembled confinements. This is an interesting link between central questions in glass-transition research and structural aspects in nanophase-separated materials.

Nanophase separation and hindered glass transition in side-chain polymers

Shear data in the temperature range from −145 °C to the flow zone are presented for the poly(n-alkyl methacrylate)s from methyl (C = 1) to lauryl (C = 12). Three qualitatively different glass transitions are observed in the shear curves at 10 rad/s:  (i) the conventional α process in the C 5 members, and (iii) an additional polyethylene-like glass transition, αPE, in the C ≥ 3 members. All three processes depend systematically on side chain length. Two alternative empirical pictures for the coexistence of two glass transitions are discussed:  (a) a static nanophase separation between main chains and side chains and (b) a dynamic heterogeneity with two different time and length scales.

Multiple Glass Transition and Nanophase Separation in Poly(n-alkyl methacrylate) Homopolymers

Comb-like polymers with flexible side chains chemically pended onto a polymeric backbone afford some unusual properties due to their hierarchical structures, such as nanoscale confined crystallisation, phase transition and conformational variations, length scale effects, etc Considerable attention has been paid to these featured polymers, regarding their importance in understanding the correlation between hierarchical structure and the assembled morphologies In this review, we reviewed the recent research progress on the structure–property correlations of comb-like polymers This article brings together and highlights the fabrication, structure determination and morphology characterization for comb-like polymers, especially for nanostructured packing patterns and frustrated mobility of chain segments from the selected examples

Frustrated crystallisation and hierarchical self-assembly behaviour of comb-like polymers

New evidence for a nanophase separation of incompatible main and side chain parts in amorphous poly(n-alkyl methacrylates) with long alkyl groups are presented. Independent indications for the existence of alkyl nanodomains with a typical dimension in the 1 nm range from studies on dynamics and structure are reported. Results from nuclear magnetic resonance (NMR) experiments are compared with data from different relaxation spectroscopy methods on poly(n-decyl methacrylate). The NMR results in combination with relaxation spectroscopy data support the existence of an independent polyethylene-like glass transition, αPE, within the alkyl nanodomains in addition to the conventional glass transition a at higher temperatures. X-ray scattering data show that the situation in homopolymers is similar to that for random poly(n-alkyl methacrylate) copolymers with the same average length of the alkyl group in the side chains. Scattering data for a series of n-butyl methacrylate samples with polymerization degrees reaching from P=1 to 405 indicate that nanophase separation is chain-length independent above P=25, while the nanophase separation tends to disappear below P=6. Insensitivity of structural aspects in nanophase-separated poly(n-alkyl methacrylates) to changes in the molecular microstructure and consistency of NMR results with independent conclusions from relaxation spectroscopy underline the general importance of nanophase separation effects in a broad class of side chain polymers.

https://iopscience.iop.org/article/10.1088/1367-2630/6/1/010/pdf

Nanophase separation in side chain polymers: new evidence from structure and dynamics

Poly(alkyl itaconates): 8. Observations of dual glass transitions and crystallinity in the dialkyl ester series diheptyl to di-eicosyl

A series of poly(mono n-alkyl itaconic acid esters), with ester chain lengths varying from methyl to decyl, were prepared by emulsion polymerisation. The materials are all hard brittle glassy polymers at ambient temperatures and undergo a dehydration reaction in the range 430 K to 450 K. Dynamic mechanical measurements showed the presence of at least three other damping maxima: an Δ-transition at 90−95 K, a δ-transition at 190–200 K and a γ-transition at 240–260 K. The e is associated with motion in the hydrocarbon part of the side chain, while the δ and γ transitions are associated with relaxations involving the carboxyl and alkoxycarbonyl groups respectively. Glass transitions were only detectable in higher esters. The thermal stability of the polymers is also briefly discussed.

Poly(mono n-alkyl itaconic acid esters): Their preparation and some physical properties†

The thermal stability of members of several series of polyitaconates has been assessed using thermogravimetric and thermal volatilisation techniques. From these data general degradation patterns have been established. The poly (di-n-alkyl itaconates) are stable up to 570K before chain breakdown occurs. The poly(mono-n-alkyl itaconates) are less stable and undergo a dehydration/de-esterification reaction at 430K which results in the formation of anhydride structures. This reaction can be suppressed by the formation of the salts. In the copolymers, salt formation also leads to increased stability but the range of copolymers studied was too restricted to draw general conclusions about their thermal behaviour.

Zia Haq

Papers

Poly(alkyl itaconates): 8. Observations of dual glass transitions and crystallinity in the dialkyl ester series diheptyl to di-eicosyl

Poly(mono n-alkyl itaconic acid esters): Their preparation and some physical properties†

Some aspects of the thermal stability of poly(alkyl itaconic acid esters)

Poly(alkyl itaconates) part v copolymers of Selected mono- and di-alkyl esters

Poly(alkyl itaconates): 6. Ionomers based on butyl- and heptyl-itaconic acid esters