Thermal analysis and FT‐IR studies of adsorbed poly(ethylene‐stat‐vinyl acetate) on silica

Adsorbed poly(ethylene‐stat‐vinyl acetate) (PEVAc) on fumed silica was studied using temperature‐modulated differential scanning calorimetry (TMDSC) and FT‐IR spectroscopy. The properties of the copolymers were compared with poly(vinyl acetate) (PVAc) and low density polyethylene (LDPE) as references. TMDSC analysis of the copolymer‐silica samples in the glass transition region was complicated for the copolymers because of the ethylene crystallinity. Nevertheless, examination of the glass transition region for small adsorbed amounts of these copolymers indicated the presence of tightly‐ and loosely‐bound polymer segments, similar to other polymers which have an attraction to silica. Compared with bulk polymers with the same composition, the tightly‐bound polymers showed an increased glass transition temperature (T_g) and a loosely‐bound fraction with a lower T_g than bulk. FT‐IR spectra of the surface copolymers indicated that the fraction of bound carbonyls (p) increased as the fraction of vinyl acetate in the copolymers decreased, consistent with the notion that the carbonyls from vinyl acetate preferentially find their way to the silica surface. Spectra from samples with different adsorbed amounts of polymer were used to obtain the amount of bound polymer (M_b) and the ratio of molar absorption coefficients of bound carbonyls to free carbonyls (X). The copolymers had very large p values (up to 0.8) at small adsorbed amounts and dependent on the composition of the polymer. However, an analysis of the bound fractions, based on only the vinyl acetate groups, superimposed the data, suggesting that the ethylene units simply dilute the vinyl acetate groups in the surface polymer. The sample with the smallest fraction of vinyl acetate did not show this behavior and may be considered to be “carbonyl poor.” © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 727–736     

Facile synthesis of graft copolymers containing rigid poly(dialkyl fumarate) branches by macromonomer method

Graft copolymers show microphase separated structure as seen in block copolymers and have lower intrinsic viscosity than block copolymers because of a branching structure. Therefore, considering molding processability, especially for polymers containing rigid segments, graft copolymers are useful architectures. In this work, graft copolymers containing rigid poly(diisopropyl fumarate) (PDiPF) branches were synthesized by full free‐radical polymerization process. First, synthesis of PDiPF macromonomers by addition‐fragmentation chain transfer (AFCT) was investigated. 2,2‐Dimethyl‐4‐methylene‐pentanedioic acid dimethyl ester was found to be an efficient AFCT agent for diisopropyl fumarate (DiPF) polymerization because of the suppression of undesired primary radical termination, which significantly took place when common AFCT agent, methyl 2‐(bromomethyl)acrylate, was used. Copolymerization of PDiPF macromonomer with ethyl acrylate accomplished the generation of the graft copolymer having flexible poly(ethyl acrylate) backbone and rigid PDiPF branches. The graft copolymer showed a microphase separated structure, high transparency, and characteristic thermal properties to PDiPF and poly(ethyl acrylate). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2474–2480     

Amphiphilic Graft Copolymers of Hydroxypropyl Cellulose Backbone with Nonpolar Polyisobutylene Branches

The novel amphiphilic graft copolymers with hydrophilic hard polar hydroxypropyl cellulose(HPC) backbone and hydrophobic soft nonpolar polyisobutylene(PIB) branches have been successfully synthesized through nucleophilic substitution reaction of living PIB chains carrying oxonium ions with the-OH groups along HPC backbone. The PIB branch length in the graft copolymers could be designed by living cationic polymerization and the grafting density could be adjusted by PIB~+/-OH molar ratio. The living PIB chains carrying oxonium ion were prepared by transformation of allyl bromide end groups in the presence of AgClO_4 and silver nanoparticles(3.2±0.3 nm, 0.7 wt%-1.8 wt%)generated in situ from AgBr. The phase-separation morphology was formed in the graft copolymers due to their incompatibility between backbone and branches. The hydrophilicity on the surface of graft copolymer films could be turned to hydrophobicity by increasing grafting density or/and length of PIB branches. The soft PIB segments in graft copolymers provided an unique surface via self-assembly for anti-protein adsorption against bovine serum albumin. A small amount of Ag nanoparticles in the copolymers contributed to good antibacterial activities against Staphylococcus aureus or Escherichia coli.     

Synthesis of transparent block copolymers consisting of poly(diisopropyl fumarate) and poly(2-ethylhexyl acrylate) segments by reversible addition-fragmentation chain transfer polymerization using trithiocarbonates as the chain transfer agents

The reversible addition-fragmentation chain transfer polymerization of diisopropyl fumarate (DiPF) was carried out using ethyl 2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate (T1) and 1,1′-(1,2-ethanediyl) bis[2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate] (T2) as the monofunctional and difunctional chain transfer agents (CTAs) to synthesize poly(diisopropyl fumarate) (PDiPF) with a rigid chain conformation. The obtained PDiPF had a well-controlled molecular weight, molecular weight distribution, and structure of the chain ends. Size exclusion chromatography and NMR measurements revealed an excellent introduction efficiency (84–98%) of the terminal trithiocarbonate group into the polymer chain end. They were available as the monofunctional and difunctional macro-CTAs to synthesize the AB and ABA block copolymers, respectively. While the well-controlled block copolymers were solely obtained by the polymerization of 2-ethylhexyl acrylate as the second monomer in the presence of PDiPF as the macro-CTA, the block copolymerization of DiPF using poly(2-ethylhexyl acrylate) as the macro-CTA failed. The trithiocarbonate group at the chain end was completely removed by the reaction with n-butylamine and it was valid for the improvement of the coloration and other optical properties of the transparent polymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2584–2594     

Getting to the bottom morphology of block copolymer thin films

We demonstrate a general approach for attaining the bottom morphology of block copolymer(BCP) thin films. In our former measurements on PS-b-PMMA films, surface morphology maps of the BCP films revealed distinct ordering regimes where the cylinders orient predominantly perpendicular or parallel to the interface and an ‘intermediate' regime where these morphologies coexist. However, this earlier work did not explore the bottom morphology of BCP thin films. In this study, we investigated the block copolymer morphology near the solid substrate in the cast block copolymer film having a perpendicular cylinder morphology on the surface.     

Improved self‐assembly of poly(dimethylsiloxane‐b‐ethylene oxide) using a hydrogen‐bonding additive

Block copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub‐10 nm nanopatterns in the growing field of directed self‐assembly for next generation lithographic applications. A library of PDMS‐b‐PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χ measured in our samples was 0.21 at 150 °C, which resulted in phase‐separated domains with periods as small as 7.9 nm, suggesting that PDMS‐b‐PEO is a prime candidate for sub‐10 nm nanopatterning. To suppress PEO crystallization, PDMS‐b‐PEO was blended with (l )‐tartaric acid (LTA) which allows for tuning of the self‐assembled morphologies. Additionally, it was observed that the order‐disorder transition temperature (T_ODT) of PDMS‐b‐PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self‐assembly. To understand the mechanism of this phenomenon, we present a novel field‐based supramolecular model, which describes the formation of copolymer‐additive complexes by reversible hydrogen bonding. The mean‐field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS‐b‐(PEO/LTA suprablock). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2200–2208     

Alternating copolymers of hexafluoroisobutylene with vinyl trifluoroacetate and vinyl pentafluorobenzoate

Copolymerizations of hexafluoroisobutylene (HFIB) with vinyl pentafluorobenzoate (VPFB) and vinyl trifluoroacetate (VTFA) were carried out in bulk using perfluorodibenzoyl peroxide as the radical initiator. The copolymers obtained were characterized by proton and fluorine NMR spectroscopy. The monomer reactivity ratios in the polymerization of HFIB with VPFB were r₁ (HFIB) = 0, r₂ (VPFB) = 0.373, and r₁r₂ = 0. The results indicated that these copolymers have alternating structures. Similarly, the copolymers of HFIB and VTFA also showed alternating structures. The films of HFIB‐co‐VPFB were prepared by casting THF solution of polymers. Films obtained were flexible and transparent. The refractive indices of copolymers were 1.4549, 1.4490, and 1.4438 at 532, 633, and 839 nm, respectively. The average T_gs of HFIB‐co‐VTFA and HFIB‐co‐VPFB were 52 and 71 °C, respectively. From these results, the T_g of the hypothetical HFIB homopolymer is postulated to be in between 70 and 90 °C, which may be useful in the assessment of T_gs of HFIB copolymers with other vinyl monomers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Controllable photopatterning and photochemical properties of novel copolymer containing dianthracene langmuir–blodgett films

A new series of copolymer poly(N‐hexadecylmeth acrylamide‐co‐bis(anthracen‐9‐ylmethyl) 2‐allylmalonate) [poly(HDMA‐co‐DAnMAMA)]s containing swallow‐tailed double anthracenyl groups and long alkyl group are designed and synthesized. The main route of the photochemical reaction of the p(HDMA‐DAnMAMA)copolymer Langmuir–Blodgett (LB) films is dimerization reaction between the anthracenyl groups under the irradiation of both 365 and 248 nm for limiting irradiation time, resulting to a fine negative‐tone pattern. On the other hand, the anthracenyl groups act just as photodecomposition group under 248 nm for longer irradiation time, resulting to a fine positive‐tone pattern. Consequently, positive‐tone and negative‐tone pattern are obtained by choosing not only a suitable irradiation light wavelength, but the irradiation time at 248 nm. Moreover, it is found that the exposed and unexposed regions of copolymer LB films irradiated at 248 nm have solubility differentiation in gold etchant (I₂/NH₄I/C₂H₅OH/H₂O), that is to say, the gold photopatterns with the maximal resolution of the used mask can be obtained easily without any development process. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 139–147, 2012