Relationship between Architecture and Adhesive Properties of Macromolecular Materials, 1

This study deals with the preparation of polyurethane‐graft‐poly(n‐butyl acrylate)s copolymers by polymerization of diphenyl‐methane‐4,4‐di‐isocyanate (MDI) with α,α′‐di‐hydroxyl‐poly(n‐butyl acrylate)s of different sizes as macromonomers. The polyaddition has been studied on the basis of kinetic measurements, and the comb‐like structure of the resulting polymer has been well‐established. Such grafted copolymers display specific adhesive properties in connection with their comb‐like architecture.

     

Stable Free Radical Polymerization Kinetics of Alkyl Acrylate Monomers Using in situ FTIR Spectroscopy: Influence of Hydroxyl‐Containing Monomers and Additives

Summary: The homopolymerization and copolymerization of various alkyl acrylate monomers was studied under stable free radical polymerization (SFRP) conditions using in situ FTIR spectroscopy to monitor polymerization kinetics. The IR absorbance corresponding to the C? H deformation of the monomer (968 cm^?1) was measured to determine monomer conversion in real‐time fashion. The monomer disappearance profiles were subsequently converted to pseudo‐first order kinetic plots. Altering the alkyl ester chain length and configuration did not reveal a significant trend in the resulting polymerization kinetics. However, addition of 2‐hydroxyethyl acrylate (HEA) to a polymerization of n‐butyl acrylate (nBA) substantially accelerated the rate of total monomer conversion, increasing the observed rate constant almost two times. ¹H NMR spectroscopy also showed that the resulting HEA/nBA copolymers were enriched with the HEA monomer. Moreover, a similar but enhanced effect was also observed upon the addition of small amounts of dodecanol to an n‐butyl acrylate homopolymerization resulting in more than a doubling of the observed rate constant.

Resonance forms associated with the DEPN nitroxide and stabilization resulting from hydrogen bonding.     

Block Copolymers from Organomodified Siloxane‐Containing Macroinitiators by Atom Transfer Radical Polymerization

Alternating copolymers of 1,3‐diisopropenylbenzene and 1,1,3,3‐tetramethyldisiloxane were synthesized by hydrosilylation–polyaddition. These linear copolymers were functionalized at both ends with 2‐bromoisobutyryl or benzyl chloride moieties. Subsequently, the obtained organomodified siloxane‐containing macroinitiators were successfully used for the preparation of ABA‐type block copolymers by atom transfer radical polymerization (ATRP) of styrene and tert‐butyl acrylate. The high chain‐end functionality of the macroinitiators was confirmed by ¹H NMR analysis of the macroinitiators and GPC measurements of the obtained ABA‐type block copolymers. The macroinitiator peaks disappeared in GPC traces after ATRP, and the obtained block copolymers showed a significantly narrower molecular‐weight distribution than the macroinitiators.

Synthesis of ABA‐type block copolymers by means of ATRP using organomodified siloxane‐containing, benzyl chloride functionalized macroinitiators.     

Thermodynamic Differences Between Deuterated and Protonated Polystyrenes Evaluated Using Reversed Phase Liquid Chromatography

Summary: Deuterated compounds are generally considered to possess very similar properties to their protonated analogues. Reversed phase liquid chromatography (RPLC) was used to measure thermodynamic interactions between deuterated and protonated n‐butyl polystyrenes and a C18 stationary phase. Significant differences in enthalpies and entropies of interaction were observed for deuterated and protonated n‐butyl polystyrenes. This is very important because many techniques, such as small‐angle neutron scattering and neutron reflectivity, assume that the interaction of these molecules are identical.

Structure of n‐butyl polystyrenes.     

Structural Reasons for Restricted Backbone Motion in Poly(n‐alkyl methacrylates): Degree of Polymerization,Tacticity and Side‐Chain Length

Summary: The complex dynamics of poly(n‐alkyl methacrylates) is studied by advanced ¹³C NMR spectroscopy as well as mechanical and dielectric relaxation. Extended backbone conformations are identified as the molecular units involved in structural relaxation. From the variation in the degree of polymerization and a comparison with the presence of stereoregular sequences in the sample, the length of the extended units is determined to involve about five, at most ten monomeric units. Syndiotactic and isotactic sequences behave similarly. These findings are indicative of locally structured polymer melts.

     

Synthesis and Characterization of New Acrylate and Methacrylate Monomers with Pendant Pyridine Groups

To overcome some drawbacks of polyvinylpyridines, new monomers of acrylate and methacrylate type with pendant pyridine groups i.e., 4‐(3‐methacryloylpropyl)pyridine 1a and 4‐(3‐acryloylpropyl)pyridine 1b were successfully prepared, although it turned out to be challenging work to synthesize the acrylate monomer 1b . First polymerization studies showed that the new monomers could be polymerized easily by atom transfer radical polymerization (ATRP). The new polymers show excellent characteristics, such as very good solubility, low glass‐transition temperature, and easy quaternization.

Design and structure of new monomers 1a and 1b .     

A Poly(vinyl alcohol)‐graft‐Copolyester: Synthesis of a Novel Graft Copolymer Containing Adamantane Moieties as Guest for Cyclodextrin

A novel graft copolymer is synthesized from commercially available poly(vinyl alcohol) using ring‐opening polymerization. For the polymerization reaction of novel brush‐like poly(vinyl alcohol)‐graft‐poly(?‐caprolactone‐co‐(3‐/7‐(prop‐2‐ynyl)oxepan‐2‐one) 5 Sn(Oct)₂ is used as a catalyst. The formation of the graft copolymer is confirmed by ¹H NMR, ¹³C NMR, and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the modification of the novel synthesized graft copolymer via a “click” reaction to implement adamantane groups is described. The success of the “click” reaction is proven by ¹H NMR spectroscopy and visualized by decomplexation of cyclodextrin with included phenolphthalein.

     

Characterization of Carbon Monoxide Centered Triads in Poly[ethylene‐co‐(butyl acrylate)‐co‐(13C‐carbon monoxide)] by Isotopic Labeling and Two‐Dimensional NMR

Summary: Poly[ethylene‐co‐(butyl acrylate)‐co‐(carbon monoxide)] (polyEBC) samples, prepared from ¹³C‐labeled carbon monoxide, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex mixture of structures present in this terpolymer, 2D ¹H/¹³C‐heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced peaks resulting from ¹³C‐labeling. High resolution 2D NMR combined with ¹³C‐labeling of the polymer greatly simplifies the 2D NMR spectra, selectively enhances the weak peaks from low occurrence C‐centered triad structures and aids in their resonance assignments.

     

The evaluation of the size and the structure of the interphase in composite particles containing a macromonomer studied by solid‐state NMR

The degree of coverage and the structure and thickness of interphases in composite latex particles consisting of a poly(butyl acrylate) (PBA) core incorporated with poly(methyl methacrylate) (PMMA) macromonomer of different molecular weight and a PMMA shell was analyzed by using solid‐state NMR spin‐diffusion measurements. By changing the temperature at a given filter strength or by adjusting the filter strength at a given temperature, the spin‐diffusion experiment could be performed in such a way that the overall structure could be detected. At filter strengths softer than necessary for the detection of the overall structure, information regarding larger structures can be obtained, whereas for stronger filters detailed information about small structures in the interphase region can be extracted. The data obtained by NMR were related to previous TEM and dynamic mechanical studies on these particles.

     

Synthesis and Characterization of Block Copolymers of ε‐Caprolactone and DL‐Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

Biodegradable copolymers were prepared by ring‐opening polymerization of sequentially added ε‐caprolactone and DL ‐lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by ¹H NMR, SEC, IR, DSC, TGA, and X‐ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA‐containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering.

Block copolymerization of ε‐caprolactone and DL ‐lactide initiated by dihydroxyl PEG.     

Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

The average kinetic coefficient for chain transfer to monomer 〈k_tr,M〉 in the free‐radical polymerization of n‐butyl methacrylate (BMA) has been determined by the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain‐stopping event. Measurements between 40 and 70 °C gave data fitting an Arrhenius‐type relationship with exponential factor E_A = 30 900 ± 4 500 J · mol^?1 and pre‐exponential factor log A = 3.45 ± 0.15. The value for E_A is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n‐butyl acrylate (BA). The A value, however, is 1–3 orders of magnitude smaller, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.

     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Bulk and Solution Copolymerization of Butyl Acrylate/Methyl Methacrylate at Elevated Temperatures

A series of bulk and solution (in toluene) copolymerizations of butyl acrylate/methyl methacrylate were performed independently at two laboratories. The runs were at elevated temperatures ranging from 90 to 140 °C conducted to high conversion levels, and samples were characterized for conversion, cumulative copolymer composition and number‐ and weight‐average molecular weights and distribution. Variation of the comonomer feed composition, temperature, and the solvent, initiator and chain transfer agent concentrations was studied. Using a mechanistic model, conversion data were predicted to high conversions using terminal model kinetics at 90 and 115 °C. The copolymer composition data conformed to the terminal kinetic model over the entire temperature range. Solvent effects were reflected by changes in the butyl acrylate rate constants.

Composition vs. conversion. Effect of feed composition for runs at 140 °C.     

Grafting of Polystyrene onto Poly(butyl acrylate) and Polystyrene Backbones Using Functionalized Methacrylates

Summary: Grafting of terminal epoxide‐functionalized polystyrene onto poly[styrene‐co‐(2‐hydroxyethyl methacrylate)] or poly[(butyl acrylate)‐co‐(2‐hydroxyethyl methacrylate)] backbones was carried out by coupling reactions catalyzed by boron trifluoride. The functionalized backbones were prepared by free radical copolymerization of 2‐hydroxyethyl methacrylate (HEMA) with styrene or butyl acrylate. For the synthesis of terminal functionalized polymer chains a side reaction of the TEMPO‐mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO‐terminated polymers into terminal epoxide‐functionalized polymers by the use of glycidyl methacrylate. The number of epoxide units attached to the backbone was directly related to the TEMPO concentration during the disproportionation reaction. Taking P(S‐co‐HEMA) as well as P(BuA‐co‐HEMA) backbones in coupling reactions with different epoxy‐functionalized polystyrenes in the presence of boron trifluoride, graft polymers with up to 7 and 37 side chains per backbone were produced.

Molecular weight distribution curves of a linking experiment between P(BuA‐co‐HEMA) backbones and epoxide‐functionalized polystyrene side chains.     

Atom Transfer Radical Polymerization of Solketal Acrylate Using Cyclohexanone as the Solvent

Summary: Solketal acrylate (SA) was homopolymerized by atom transfer radical polymerization (ATRP) using CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the catalyst and cyclohexanone as the solvent with controlled molecular weights and low polydispersities. The prepared bromine‐terminated homopolymers, PSA, were used as macroinitiators to initiate polymerization of tert‐butyl acrylate (tBA) under similar ATRP conditions to produce diblock copolymers, PSA‐b‐PtBA, with controlled molecular weights and low polydispersities. ATRP of SA using bromine‐terminated PtBA as the macroinitiator was also carried out and diblock copolymers, PtBA‐b‐PSA, were obtained. The PSA block was selectively hydrolyzed by stirring for 3 h in 6 N HCl/THF (1/9, v/v) at room temperature to form a poly(glycerol monoacrylate) block. Both blocks of PSA and PtBA were hydrolyzed by stirring in anhydrous trifluoroacetic acid (TFA)/dichloromethane for 4 h, then adding water to the system and stirring for another 3 h to form corresponding diblock copolymers of glycerol monoacrylate and acrylic acid.

Kinetic plot for the atom transfer radical polymerization of solketal acrylate at 90 °C.     

Nanoscale Blends between Immiscible Polymers via Simultaneous Non‐Interfering Polymerisation

Summary: An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non‐interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring‐opening polymerisation of caprolactone is assessed. The molecular weights range from 2 000 to 3 500 for polycaprolactone and up to 140 000 for polystyrene, with reasonable polydispersity indexes. From calorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer‐scale phase segregation.

AFM surface image of a nanoscale blend.     

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

The technique of SPPLP EPR, which is single‐pulse pulsed‐laser polymerization (SPPLP) in conjunction with electron paramagnetic resonance (EPR) spectroscopy, is used to carry out a detailed investigation of secondary (chain‐end) radical termination of acrylates. Measurements are performed on methyl acrylate, n‐butyl acrylate, and dodecyl acrylate in bulk and in toluene solution at ?40 °C. The reason for the low temperature is to avoid formation of mid‐chain radicals (MCRs), a complicating factor that has imparted ambiguity to the results of previous studies of this nature. Consistent with these previous studies, composite‐model behavior for chain‐length‐dependent termination (CLDT) rate coefficients, , is found in this work. However, lower and more reasonable values of α_s, the exponent for variation of at short chain lengths, are found in the present study. Most likely this is because of the absence of MCRs, thereby validating the methodology of this work. Family‐type termination behavior is observed, with the following average parameter values adequately describing all results, regardless of acrylate or the presence of toluene: α_s = 0.79, α_l = 0.21 (long chains) and i_c ≈ 30 (crossover chain length). All indications are that these values carry over to termination of acrylate chain‐end radicals at higher, more practical temperatures. Further, these values largely make sense in terms of what is understood about the physical meaning of the parameters. Variation of the rate coefficient for termination between monomeric radicals, , is found to be well described by the simple Smoluchowski and Stokes–Einstein equations. This allows easy prediction of for different alkyl acrylates, solvent, and temperature. Through all this the unrivalled power of SPPLP EPR for measuring and understanding (chain‐length‐dependent) termination rate coefficients shines through.

     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Are Electrografted Polymers Chemisorbed or Physisorbed onto their Substrate?

Summary: AFM‐based single‐molecule force spectroscopy was used to evaluate the mechanical strength of the link between a polymer and the substrate onto which the polymer is electrografted. Poly(N‐succinimidyl acrylate) was electrografted onto gold substrates and brought into contact with an aminothiol‐functionalized AFM tip. Bridging of single polymer chains resulting from the strong coupling between the activated esters on the polymer and amine groups on the tip was investigated. We found that the link between the polymer and the gold substrate can withstand a force far beyond the force characteristic for physisorption on gold.

     

Synthesis and Characterisation of Organogels from ABA Triblock Copolymers

Polystyrene‐block‐poly(2‐ethylhexanyl acrylate)‐block‐polystyrene triblock copolymers with different molar masses were synthesised by atom transfer radical polymerisation which led to the formation of elastic gels in paraffin oil. Copolymers with control over molecular weight and low polydispersity were first obtained with different midblock lengths (10 000, 20 000, 60 000 g · mol^?1). In paraffin oil, some triblock copolymers led to a gelation process due to appropriate chain length and concentration. We assumed that polystyrene endblocks aggregated into micelles whereas poly(2‐ethylhexanyl acrylate) midblocks formed loops or bridges between different micelles leading to the formation of a physical network of interconnected polymer chains. Rheological measurements proved that time and slow controlled cooling improved the elastic properties with the creation of new interactions in the network.